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class="vector-toc-text"> <span class="vector-toc-numb">2.3</span> <span>Detectability</span> </div> </a> <ul id="toc-Detectability-sublist" class="vector-toc-list"> <li id="toc-False_positives" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#False_positives"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.3.1</span> <span>False positives</span> </div> </a> <ul id="toc-False_positives-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-False_negatives" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#False_negatives"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.3.2</span> <span>False negatives</span> </div> </a> <ul id="toc-False_negatives-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Human_limitations" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Human_limitations"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.3.3</span> <span>Human limitations</span> </div> </a> <ul id="toc-Human_limitations-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> </ul> </li> <li id="toc-General_examples" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#General_examples"> <div class="vector-toc-text"> <span class="vector-toc-numb">3</span> <span>General examples</span> </div> </a> <button aria-controls="toc-General_examples-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle General examples subsection</span> </button> <ul id="toc-General_examples-sublist" class="vector-toc-list"> <li id="toc-Geomicrobiology" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Geomicrobiology"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.1</span> <span>Geomicrobiology</span> </div> </a> <ul id="toc-Geomicrobiology-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Morphology" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Morphology"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.2</span> <span>Morphology</span> </div> </a> <ul id="toc-Morphology-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Chemistry" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Chemistry"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.3</span> <span>Chemistry</span> </div> </a> <ul id="toc-Chemistry-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Atmospheric" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Atmospheric"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.4</span> <span>Atmospheric</span> </div> </a> <ul id="toc-Atmospheric-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Atmospheric_disequilibrium" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Atmospheric_disequilibrium"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.5</span> <span>Atmospheric disequilibrium</span> </div> </a> <ul id="toc-Atmospheric_disequilibrium-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Agnostic_biosignatures" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Agnostic_biosignatures"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.6</span> <span>Agnostic biosignatures</span> </div> </a> <ul id="toc-Agnostic_biosignatures-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Antibiosignatures" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Antibiosignatures"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.7</span> <span>Antibiosignatures</span> </div> </a> <ul id="toc-Antibiosignatures-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Polyelectrolytes" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Polyelectrolytes"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.8</span> <span>Polyelectrolytes</span> </div> </a> <ul id="toc-Polyelectrolytes-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Specific_examples" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Specific_examples"> <div class="vector-toc-text"> <span class="vector-toc-numb">4</span> <span>Specific examples</span> </div> </a> <button aria-controls="toc-Specific_examples-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Specific examples subsection</span> </button> <ul id="toc-Specific_examples-sublist" class="vector-toc-list"> <li id="toc-Methane_on_Mars" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Methane_on_Mars"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.1</span> <span>Methane on Mars</span> </div> </a> <ul id="toc-Methane_on_Mars-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Martian_atmosphere" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Martian_atmosphere"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.2</span> <span>Martian atmosphere</span> </div> </a> <ul id="toc-Martian_atmosphere-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Missions_inside_the_Solar_System" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Missions_inside_the_Solar_System"> <div class="vector-toc-text"> <span class="vector-toc-numb">5</span> <span>Missions inside the Solar System</span> </div> </a> <button aria-controls="toc-Missions_inside_the_Solar_System-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Missions inside the Solar System subsection</span> </button> <ul id="toc-Missions_inside_the_Solar_System-sublist" class="vector-toc-list"> <li id="toc-The_Viking_missions_to_Mars" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#The_Viking_missions_to_Mars"> <div class="vector-toc-text"> <span class="vector-toc-numb">5.1</span> <span>The <i>Viking</i> missions to Mars</span> </div> </a> <ul id="toc-The_Viking_missions_to_Mars-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Mars_Science_Laboratory" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Mars_Science_Laboratory"> <div class="vector-toc-text"> <span class="vector-toc-numb">5.2</span> <span>Mars Science Laboratory</span> </div> </a> <ul id="toc-Mars_Science_Laboratory-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-ExoMars_Orbiter" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#ExoMars_Orbiter"> <div class="vector-toc-text"> <span class="vector-toc-numb">5.3</span> <span>ExoMars Orbiter</span> </div> </a> <ul id="toc-ExoMars_Orbiter-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Mars_2020_Rover" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Mars_2020_Rover"> <div class="vector-toc-text"> <span class="vector-toc-numb">5.4</span> <span>Mars 2020 Rover</span> </div> </a> <ul id="toc-Mars_2020_Rover-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Titan_Dragonfly" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Titan_Dragonfly"> <div class="vector-toc-text"> <span class="vector-toc-numb">5.5</span> <span>Titan <i>Dragonfly</i></span> </div> </a> <ul id="toc-Titan_Dragonfly-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Europa_Clipper" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Europa_Clipper"> <div class="vector-toc-text"> <span class="vector-toc-numb">5.6</span> <span><i>Europa Clipper</i></span> </div> </a> <ul id="toc-Europa_Clipper-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Enceladus" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Enceladus"> <div class="vector-toc-text"> <span class="vector-toc-numb">5.7</span> <span>Enceladus</span> </div> </a> <ul id="toc-Enceladus-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Searching_outside_of_the_Solar_System" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Searching_outside_of_the_Solar_System"> <div class="vector-toc-text"> <span class="vector-toc-numb">6</span> <span>Searching outside of the Solar System</span> </div> </a> <ul id="toc-Searching_outside_of_the_Solar_System-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> <span class="vector-toc-numb">7</span> <span>See also</span> </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> <span class="vector-toc-numb">8</span> <span>References</span> </div> </a> <ul id="toc-References-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <nav aria-label="Contents" class="vector-toc-landmark"> <div id="vector-page-titlebar-toc" class="vector-dropdown vector-page-titlebar-toc vector-button-flush-left" > <input type="checkbox" id="vector-page-titlebar-toc-checkbox" role="button" aria-haspopup="true" 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Available in 20 languages" > <label id="p-lang-btn-label" for="p-lang-btn-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive mw-portlet-lang-heading-20" aria-hidden="true" ><span class="vector-icon mw-ui-icon-language-progressive mw-ui-icon-wikimedia-language-progressive"></span> <span class="vector-dropdown-label-text">20 languages</span> </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-ar mw-list-item"><a href="https://ar.wikipedia.org/wiki/%D8%A8%D8%B5%D9%85%D8%A9_%D8%AD%D9%8A%D9%88%D9%8A%D8%A9" title="بصمة حيوية – Arabic" lang="ar" hreflang="ar" data-title="بصمة حيوية" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target"><span>العربية</span></a></li><li class="interlanguage-link interwiki-bn mw-list-item"><a href="https://bn.wikipedia.org/wiki/%E0%A6%9C%E0%A7%88%E0%A6%AC%E0%A6%B8%E0%A7%8D%E0%A6%AC%E0%A6%BE%E0%A6%95%E0%A7%8D%E0%A6%B7%E0%A6%B0" title="জৈবস্বাক্ষর – Bangla" lang="bn" hreflang="bn" data-title="জৈবস্বাক্ষর" data-language-autonym="বাংলা" data-language-local-name="Bangla" class="interlanguage-link-target"><span>বাংলা</span></a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Biosignatura" title="Biosignatura – Catalan" lang="ca" hreflang="ca" data-title="Biosignatura" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target"><span>Català</span></a></li><li class="interlanguage-link interwiki-da mw-list-item"><a href="https://da.wikipedia.org/wiki/Biosignatur" title="Biosignatur – Danish" lang="da" hreflang="da" data-title="Biosignatur" data-language-autonym="Dansk" data-language-local-name="Danish" class="interlanguage-link-target"><span>Dansk</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/Biosignatur" title="Biosignatur – German" lang="de" hreflang="de" data-title="Biosignatur" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Biofirma" title="Biofirma – Spanish" lang="es" hreflang="es" data-title="Biofirma" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D8%B1%D8%AF_%D9%BE%D8%A7%DB%8C_%D8%B2%DB%8C%D8%B3%D8%AA%DB%8C" title="رد پای زیستی – Persian" lang="fa" hreflang="fa" data-title="رد پای زیستی" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target"><span>فارسی</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Biosignature" title="Biosignature – French" lang="fr" hreflang="fr" data-title="Biosignature" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-id mw-list-item"><a href="https://id.wikipedia.org/wiki/Tanda_biologis" title="Tanda biologis – Indonesian" lang="id" hreflang="id" data-title="Tanda biologis" data-language-autonym="Bahasa Indonesia" data-language-local-name="Indonesian" class="interlanguage-link-target"><span>Bahasa Indonesia</span></a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/Biofirma" title="Biofirma – Italian" lang="it" hreflang="it" data-title="Biofirma" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target"><span>Italiano</span></a></li><li class="interlanguage-link interwiki-he mw-list-item"><a href="https://he.wikipedia.org/wiki/%D7%97%D7%AA%D7%99%D7%9E%D7%94_%D7%91%D7%99%D7%95%D7%9C%D7%95%D7%92%D7%99%D7%AA" title="חתימה ביולוגית – Hebrew" lang="he" hreflang="he" data-title="חתימה ביולוגית" data-language-autonym="עברית" data-language-local-name="Hebrew" class="interlanguage-link-target"><span>עברית</span></a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/Biosignatuur_(astrobiologie)" title="Biosignatuur (astrobiologie) – Dutch" lang="nl" hreflang="nl" data-title="Biosignatuur (astrobiologie)" data-language-autonym="Nederlands" data-language-local-name="Dutch" class="interlanguage-link-target"><span>Nederlands</span></a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/%E7%94%9F%E5%91%BD%E5%AD%98%E5%9C%A8%E6%8C%87%E6%A8%99" title="生命存在指標 – Japanese" lang="ja" hreflang="ja" data-title="生命存在指標" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target"><span>日本語</span></a></li><li class="interlanguage-link interwiki-no mw-list-item"><a href="https://no.wikipedia.org/wiki/Biosignatur" title="Biosignatur – Norwegian Bokmål" lang="nb" hreflang="nb" data-title="Biosignatur" data-language-autonym="Norsk bokmål" data-language-local-name="Norwegian Bokmål" class="interlanguage-link-target"><span>Norsk bokmål</span></a></li><li class="interlanguage-link interwiki-pt mw-list-item"><a href="https://pt.wikipedia.org/wiki/Bioassinatura" title="Bioassinatura – Portuguese" lang="pt" hreflang="pt" data-title="Bioassinatura" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-ru mw-list-item"><a href="https://ru.wikipedia.org/wiki/%D0%91%D0%B8%D0%BE%D1%81%D0%B8%D0%B3%D0%BD%D0%B0%D1%82%D1%83%D1%80%D0%B0" title="Биосигнатура – Russian" lang="ru" hreflang="ru" data-title="Биосигнатура" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target"><span>Русский</span></a></li><li class="interlanguage-link interwiki-simple mw-list-item"><a href="https://simple.wikipedia.org/wiki/Biosignature" title="Biosignature – Simple English" lang="en-simple" hreflang="en-simple" data-title="Biosignature" data-language-autonym="Simple English" data-language-local-name="Simple English" class="interlanguage-link-target"><span>Simple English</span></a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/%D0%91%D1%96%D0%BE%D1%81%D0%B8%D0%B3%D0%BD%D0%B0%D1%82%D1%83%D1%80%D0%B0" title="Біосигнатура – Ukrainian" lang="uk" hreflang="uk" data-title="Біосигнатура" data-language-autonym="Українська" data-language-local-name="Ukrainian" class="interlanguage-link-target"><span>Українська</span></a></li><li class="interlanguage-link interwiki-vi mw-list-item"><a href="https://vi.wikipedia.org/wiki/Ch%E1%BB%AF_k%C3%BD_sinh_h%E1%BB%8Dc" title="Chữ ký sinh học – Vietnamese" lang="vi" hreflang="vi" data-title="Chữ ký sinh học" data-language-autonym="Tiếng Việt" data-language-local-name="Vietnamese" class="interlanguage-link-target"><span>Tiếng Việt</span></a></li><li class="interlanguage-link interwiki-zh mw-list-item"><a href="https://zh.wikipedia.org/wiki/%E7%94%9F%E5%91%BD%E5%8D%B0%E8%BF%B9" title="生命印迹 – Chinese" lang="zh" hreflang="zh" data-title="生命印迹" data-language-autonym="中文" data-language-local-name="Chinese" class="interlanguage-link-target"><span>中文</span></a></li> </ul> <div class="after-portlet after-portlet-lang"><span class="wb-langlinks-edit wb-langlinks-link"><a href="https://www.wikidata.org/wiki/Special:EntityPage/Q2912794#sitelinks-wikipedia" title="Edit interlanguage links" class="wbc-editpage">Edit links</a></span></div> </div> </div> </div> </header> <div class="vector-page-toolbar"> <div 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print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">For other uses, see <a href="/wiki/Biomarker_(disambiguation)" class="mw-disambig" title="Biomarker (disambiguation)">Biomarker (disambiguation)</a>.</div> <p>A <b>biosignature</b> (sometimes called <b>chemical fossil</b> or <b>molecular fossil</b>) is any substance – such as an element, <a href="/wiki/Isotope" title="Isotope">isotope</a>, <a href="/wiki/Molecule" title="Molecule">molecule</a>, or <a href="/wiki/Phenomenon" title="Phenomenon">phenomenon</a> – that provides <a href="/wiki/Scientific_evidence" title="Scientific evidence">scientific evidence</a> of past or present <a href="/wiki/Life" title="Life">life</a> on a planet.<sup id="cite_ref-SSG_1-0" class="reference"><a href="#cite_note-SSG-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Biosignatures_2011_3-0" class="reference"><a href="#cite_note-Biosignatures_2011-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> Measurable attributes of life include its physical or chemical structures, its use of <a href="/wiki/Thermodynamic_free_energy" title="Thermodynamic free energy">free energy</a>, and the production of <a href="/wiki/Biomass" title="Biomass">biomass</a> and <a href="/wiki/Cellular_waste_product" title="Cellular waste product">wastes</a>. </p><p>The field of <a href="/wiki/Astrobiology" title="Astrobiology">astrobiology</a> uses biosignatures as evidence for the search for past or present extraterrestrial life. </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Types">Types</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=1" title="Edit section: Types"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Biosignatures can be grouped into ten broad categories:<sup id="cite_ref-NASA_strategy_2015_4-0" class="reference"><a href="#cite_note-NASA_strategy_2015-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> </p> <ol><li><a href="/wiki/Isotope" title="Isotope">Isotope</a> patterns: Isotopic evidence or patterns that require biological processes.</li> <li><a href="/wiki/Chemistry" title="Chemistry">Chemistry</a>: Chemical features that require biological activity.</li> <li><a href="/wiki/Organic_matter" title="Organic matter">Organic matter</a>: Organics formed by biological processes.</li> <li><a href="/wiki/Mineral" title="Mineral">Minerals</a>: Minerals or biomineral-phases whose composition and/or morphology indicate biological activity (e.g., <a href="/wiki/Magnetite" title="Magnetite">biomagnetite</a>).</li> <li>Microscopic structures and textures: Biologically-formed cements, microtextures, <a href="/wiki/Micropaleontology" title="Micropaleontology">microfossils</a>, and films.</li> <li>Macroscopic physical structures and textures: Structures that indicate microbial ecosystems, <a href="/wiki/Biofilm" title="Biofilm">biofilms</a> (e.g., <a href="/wiki/Stromatolite" title="Stromatolite">stromatolites</a>), or <a href="/wiki/Fossil" title="Fossil">fossils</a> of larger organisms.</li> <li>Temporal variability: Variations in time of atmospheric gases, <a href="/wiki/Reflectance" title="Reflectance">reflectivity</a>, or macroscopic appearance that indicates life's presence.</li> <li>Surface reflectance features: Large-scale reflectance features due to biological pigments.</li> <li>Atmospheric gases: Gases formed by <a href="/wiki/Metabolism" title="Metabolism">metabolic</a> processes, which may be present on a planet-wide scale.</li> <li><a href="/wiki/Technosignature" title="Technosignature">Technosignatures</a>: Signatures that indicate a technologically advanced civilization.<sup id="cite_ref-WP-20201231_5-0" class="reference"><a href="#cite_note-WP-20201231-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup></li></ol> <div class="mw-heading mw-heading2"><h2 id="Viability">Viability</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=2" title="Edit section: Viability"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div><p> Determining whether an observed feature is a true biosignature is complex. There are three criteria that a potential biosignature must meet to be considered viable for further research: Reliability, survivability, and detectability.<sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-8" class="reference"><a href="#cite_note-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-:3_9-0" class="reference"><a href="#cite_note-:3-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup></p><figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:O2_false_positives2.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/e/e4/O2_false_positives2.png/220px-O2_false_positives2.png" decoding="async" width="220" height="134" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/e4/O2_false_positives2.png/330px-O2_false_positives2.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/e/e4/O2_false_positives2.png/440px-O2_false_positives2.png 2x" data-file-width="1972" data-file-height="1204" /></a><figcaption>False positive mechanisms for oxygen on a variety of planet scenarios. The molecules in each large rectangle represent the main contributors to a spectrum of the planet's atmosphere. The molecules circled in yellow represent the molecules that would help confirm a false positive biosignature if they were detected. Furthermore, the molecules crossed out in red would help confirm a false positive biosignature if they were <i>not</i> detected. Cartoon adapted from <a href="/wiki/Victoria_Meadows" title="Victoria Meadows">Victoria Meadows</a>' 2018 oxygen as a biosignature study.<sup id="cite_ref-:3_9-1" class="reference"><a href="#cite_note-:3-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup></figcaption></figure> <div class="mw-heading mw-heading3"><h3 id="Reliability">Reliability</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=3" title="Edit section: Reliability"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>A biosignature must be able to dominate over all other processes that may produce similar physical, spectral, and chemical features. When investigating a potential biosignature, scientists must carefully consider all other possible origins of the biosignature in question. Many forms of life are known to mimic geochemical reactions. One of the theories on the <a href="/wiki/Abiogenesis" title="Abiogenesis">origin of life</a> involves molecules developing the ability to catalyse geochemical reactions to exploit the energy being released by them. These are some of the earliest known metabolisms (see <a href="/wiki/Methanogenesis" title="Methanogenesis">methanogenesis</a>).<sup id="cite_ref-10" class="reference"><a href="#cite_note-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-:4_11-0" class="reference"><a href="#cite_note-:4-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> In such case, scientists might search for a disequilibrium in the geochemical cycle, which would point to a reaction happening more or less often than it should. A disequilibrium such as this could be interpreted as an indication of life.<sup id="cite_ref-:4_11-1" class="reference"><a href="#cite_note-:4-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Survivability">Survivability</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=4" title="Edit section: Survivability"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>A biosignature must be able to last for long enough so that a probe, telescope, or human can be able to detect it. A consequence of a biological organism's use of metabolic reactions for energy is the production of <a href="/wiki/Metabolic_waste" title="Metabolic waste">metabolic waste</a>. In addition, the structure of an organism can be preserved as a <a href="/wiki/Fossil" title="Fossil">fossil</a> and we know that some fossils on Earth are <a href="/wiki/Earliest_known_life_forms" title="Earliest known life forms">as old as 3.5 billion years</a>.<sup id="cite_ref-12" class="reference"><a href="#cite_note-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-13" class="reference"><a href="#cite_note-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup> These byproducts can make excellent biosignatures since they provide direct evidence for life. However, in order to be a viable biosignature, a byproduct must subsequently remain intact so that scientists may discover it. </p> <div class="mw-heading mw-heading3"><h3 id="Detectability">Detectability</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=5" title="Edit section: Detectability"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>A biosignature must be detectable with the most latest technology to be relevant in scientific investigation. This seems to be an obvious statement, however, there are many scenarios in which life may be present on a planet yet remain undetectable because of human-caused limitations. </p> <div class="mw-heading mw-heading4"><h4 id="False_positives">False positives</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=6" title="Edit section: False positives"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Every possible biosignature is associated with its own set of unique <a href="/wiki/False_positives_and_false_negatives" title="False positives and false negatives">false positive</a> mechanisms or non-biological processes that can mimic the detectable feature of a biosignature. An important example is using <a href="/wiki/Oxygen" title="Oxygen">oxygen</a> as a biosignature. On Earth, the majority of life is centred around oxygen. It is a byproduct of <a href="/wiki/Photosynthesis" title="Photosynthesis">photosynthesis</a> and is subsequently used by other life forms to breathe. Oxygen is also readily detectable in <a href="/wiki/Spectral_line" title="Spectral line">spectra</a>, with multiple bands across a relatively wide wavelength range, therefore, it makes a very good biosignature. However, finding oxygen alone in a planet's atmosphere is not enough to confirm a biosignature because of the false-positive mechanisms associated with it. One possibility is that oxygen can build up abiotically via <a href="/wiki/Photodissociation" title="Photodissociation">photolysis</a> if there is a low inventory of non-condensable gasses or if the planet loses a lot of water.<sup id="cite_ref-14" class="reference"><a href="#cite_note-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-15" class="reference"><a href="#cite_note-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Lisse_2020_16-0" class="reference"><a href="#cite_note-Lisse_2020-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> Finding and distinguishing a biosignature from its potential false-positive mechanisms is one of the most complicated parts of testing for viability because it relies on human ingenuity to break an abiotic-biological degeneracy, if nature allows. </p> <div class="mw-heading mw-heading4"><h4 id="False_negatives">False negatives</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=7" title="Edit section: False negatives"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Opposite to false positives, <a href="/wiki/False_positives_and_false_negatives" title="False positives and false negatives">false negative</a> biosignatures arise in a scenario where life may be present on another planet, but some processes on that planet make potential biosignatures undetectable.<sup id="cite_ref-17" class="reference"><a href="#cite_note-17"><span class="cite-bracket">[</span>17<span class="cite-bracket">]</span></a></sup> This is an ongoing problem and area of research in preparation for future telescopes that will be capable of observing exoplanetary atmospheres. </p> <div class="mw-heading mw-heading4"><h4 id="Human_limitations">Human limitations</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=8" title="Edit section: Human limitations"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>There are many ways in which humans may limit the viability of a potential biosignature. The resolution of a telescope becomes important when vetting certain false-positive mechanisms, and many current telescopes do not have the capabilities to observe at the resolution needed to investigate some of these. In addition, probes and telescopes are worked on by huge collaborations of scientists with varying interests. As a result, new probes and telescopes carry a variety of instruments that are a compromise to everyone's unique inputs. For a different type of scientist to detect something unrelated to biosignatures, a sacrifice may have to be made in the capability of an instrument to search for biosignatures.<sup id="cite_ref-18" class="reference"><a href="#cite_note-18"><span class="cite-bracket">[</span>18<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="General_examples">General examples</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=9" title="Edit section: General examples"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <div class="mw-heading mw-heading3"><h3 id="Geomicrobiology">Geomicrobiology</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=10" title="Edit section: Geomicrobiology"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <table id="Container" role="presentation" class="nomobile toccolours searchaux" style="text-align:left;padding:0 0.5em;border-style:solid;float:right;clear:right;margin:0.3em 0 0.8em 1.4em;overflow:hidden;min-width:29.95em"><tbody><tr><td colspan="3" id="Title" style="padding:1em 1em 0 1em"><div style="background-color:#77bb77;padding:0 0.2em 0 0.2em;font-weight:bold;text-align:center"><a href="/wiki/Timeline_of_the_evolutionary_history_of_life" title="Timeline of the evolutionary history of life"><span style="color:#ffffff;">Life timeline</span></a></div></td></tr><tr><td colspan="3" id="Navbox" style="padding:0;margin:0 1em 0 0;text-align:right"><style data-mw-deduplicate="TemplateStyles:r1129693374">.mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output .hlist dt,.mw-parser-output .hlist li{margin:0;display:inline}.mw-parser-output .hlist.inline,.mw-parser-output .hlist.inline dl,.mw-parser-output .hlist.inline ol,.mw-parser-output .hlist.inline ul,.mw-parser-output .hlist dl dl,.mw-parser-output .hlist dl ol,.mw-parser-output .hlist dl ul,.mw-parser-output .hlist ol dl,.mw-parser-output .hlist ol ol,.mw-parser-output .hlist ol ul,.mw-parser-output .hlist ul dl,.mw-parser-output .hlist ul ol,.mw-parser-output .hlist ul ul{display:inline}.mw-parser-output .hlist .mw-empty-li{display:none}.mw-parser-output .hlist dt::after{content:": "}.mw-parser-output .hlist dd::after,.mw-parser-output .hlist li::after{content:" · ";font-weight:bold}.mw-parser-output .hlist dd:last-child::after,.mw-parser-output .hlist dt:last-child::after,.mw-parser-output .hlist li:last-child::after{content:none}.mw-parser-output .hlist dd dd:first-child::before,.mw-parser-output .hlist dd dt:first-child::before,.mw-parser-output .hlist dd li:first-child::before,.mw-parser-output .hlist dt dd:first-child::before,.mw-parser-output .hlist dt dt:first-child::before,.mw-parser-output .hlist dt li:first-child::before,.mw-parser-output .hlist li dd:first-child::before,.mw-parser-output .hlist li dt:first-child::before,.mw-parser-output .hlist li li:first-child::before{content:" (";font-weight:normal}.mw-parser-output .hlist dd dd:last-child::after,.mw-parser-output .hlist dd dt:last-child::after,.mw-parser-output .hlist dd li:last-child::after,.mw-parser-output .hlist dt dd:last-child::after,.mw-parser-output .hlist dt dt:last-child::after,.mw-parser-output .hlist dt li:last-child::after,.mw-parser-output .hlist li dd:last-child::after,.mw-parser-output .hlist li dt:last-child::after,.mw-parser-output .hlist li li:last-child::after{content:")";font-weight:normal}.mw-parser-output .hlist ol{counter-reset:listitem}.mw-parser-output .hlist ol>li{counter-increment:listitem}.mw-parser-output .hlist ol>li::before{content:" "counter(listitem)"\a0 "}.mw-parser-output .hlist dd ol>li:first-child::before,.mw-parser-output .hlist dt ol>li:first-child::before,.mw-parser-output .hlist li ol>li:first-child::before{content:" ("counter(listitem)"\a0 "}</style><style data-mw-deduplicate="TemplateStyles:r1239400231">.mw-parser-output .navbar{display:inline;font-size:88%;font-weight:normal}.mw-parser-output .navbar-collapse{float:left;text-align:left}.mw-parser-output .navbar-boxtext{word-spacing:0}.mw-parser-output .navbar ul{display:inline-block;white-space:nowrap;line-height:inherit}.mw-parser-output .navbar-brackets::before{margin-right:-0.125em;content:"[ "}.mw-parser-output .navbar-brackets::after{margin-left:-0.125em;content:" ]"}.mw-parser-output .navbar li{word-spacing:-0.125em}.mw-parser-output .navbar a>span,.mw-parser-output .navbar a>abbr{text-decoration:inherit}.mw-parser-output .navbar-mini abbr{font-variant:small-caps;border-bottom:none;text-decoration:none;cursor:inherit}.mw-parser-output .navbar-ct-full{font-size:114%;margin:0 7em}.mw-parser-output .navbar-ct-mini{font-size:114%;margin:0 4em}html.skin-theme-clientpref-night .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}@media(prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}}@media print{.mw-parser-output .navbar{display:none!important}}</style><div class="navbar plainlinks hlist"><span>This box: </span><ul><li class="nv-view"><a href="/wiki/Template:Life_timeline" title="Template:Life timeline"><span title="View this template">view</span></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Life_timeline" title="Template talk:Life timeline"><span title="Discuss this template">talk</span></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Life_timeline" title="Special:EditPage/Template:Life timeline"><span title="Edit this template">edit</span></a></li></ul></div></td></tr><tr style="vertical-align:top"><td id="Scale" style="padding:0;margin:0.7em 0 0.7em 0;width:4.2em;position:relative;float:left;font-size:100%;height:50em;border-right:1px solid #242020"><div style="float:right;position:absolute;right:-1px;top:49.56em;transform:translateY(-50%)"><span style="font-size:90%">−4500 —</span></div><div style="float:right;position:absolute;right:-1px;top:48.18em;transform:translateY(-50%)"><span style="font-size:90%">–</span></div><div style="float:right;position:absolute;right:-1px;top:46.81em;transform:translateY(-50%)"><span style="font-size:90%">—</span></div><div style="float:right;position:absolute;right:-1px;top:45.43em;transform:translateY(-50%)"><span style="font-size:90%">–</span></div><div style="float:right;position:absolute;right:-1px;top:44.05em;transform:translateY(-50%)"><span style="font-size:90%">−4000 —</span></div><div style="float:right;position:absolute;right:-1px;top:42.68em;transform:translateY(-50%)"><span style="font-size:90%">–</span></div><div style="float:right;position:absolute;right:-1px;top:41.30em;transform:translateY(-50%)"><span style="font-size:90%">—</span></div><div style="float:right;position:absolute;right:-1px;top:39.92em;transform:translateY(-50%)"><span style="font-size:90%">–</span></div><div style="float:right;position:absolute;right:-1px;top:38.55em;transform:translateY(-50%)"><span style="font-size:90%">−3500 —</span></div><div style="float:right;position:absolute;right:-1px;top:37.17em;transform:translateY(-50%)"><span style="font-size:90%">–</span></div><div style="float:right;position:absolute;right:-1px;top:35.79em;transform:translateY(-50%)"><span style="font-size:90%">—</span></div><div style="float:right;position:absolute;right:-1px;top:34.42em;transform:translateY(-50%)"><span style="font-size:90%">–</span></div><div style="float:right;position:absolute;right:-1px;top:33.04em;transform:translateY(-50%)"><span style="font-size:90%">−3000 —</span></div><div style="float:right;position:absolute;right:-1px;top:31.66em;transform:translateY(-50%)"><span style="font-size:90%">–</span></div><div style="float:right;position:absolute;right:-1px;top:30.29em;transform:translateY(-50%)"><span style="font-size:90%">—</span></div><div style="float:right;position:absolute;right:-1px;top:28.91em;transform:translateY(-50%)"><span style="font-size:90%">–</span></div><div style="float:right;position:absolute;right:-1px;top:27.53em;transform:translateY(-50%)"><span style="font-size:90%">−2500 —</span></div><div style="float:right;position:absolute;right:-1px;top:26.16em;transform:translateY(-50%)"><span style="font-size:90%">–</span></div><div style="float:right;position:absolute;right:-1px;top:24.78em;transform:translateY(-50%)"><span style="font-size:90%">—</span></div><div style="float:right;position:absolute;right:-1px;top:23.40em;transform:translateY(-50%)"><span style="font-size:90%">–</span></div><div style="float:right;position:absolute;right:-1px;top:22.03em;transform:translateY(-50%)"><span style="font-size:90%">−2000 —</span></div><div style="float:right;position:absolute;right:-1px;top:20.65em;transform:translateY(-50%)"><span style="font-size:90%">–</span></div><div style="float:right;position:absolute;right:-1px;top:19.27em;transform:translateY(-50%)"><span style="font-size:90%">—</span></div><div style="float:right;position:absolute;right:-1px;top:17.90em;transform:translateY(-50%)"><span style="font-size:90%">–</span></div><div style="float:right;position:absolute;right:-1px;top:16.52em;transform:translateY(-50%)"><span style="font-size:90%">−1500 —</span></div><div style="float:right;position:absolute;right:-1px;top:15.14em;transform:translateY(-50%)"><span style="font-size:90%">–</span></div><div style="float:right;position:absolute;right:-1px;top:13.77em;transform:translateY(-50%)"><span style="font-size:90%">—</span></div><div style="float:right;position:absolute;right:-1px;top:12.39em;transform:translateY(-50%)"><span style="font-size:90%">–</span></div><div style="float:right;position:absolute;right:-1px;top:11.01em;transform:translateY(-50%)"><span style="font-size:90%">−1000 —</span></div><div style="float:right;position:absolute;right:-1px;top:9.64em;transform:translateY(-50%)"><span style="font-size:90%">–</span></div><div style="float:right;position:absolute;right:-1px;top:8.26em;transform:translateY(-50%)"><span style="font-size:90%">—</span></div><div style="float:right;position:absolute;right:-1px;top:6.88em;transform:translateY(-50%)"><span style="font-size:90%">–</span></div><div style="float:right;position:absolute;right:-1px;top:5.51em;transform:translateY(-50%)"><span style="font-size:90%">−500 —</span></div><div style="float:right;position:absolute;right:-1px;top:4.13em;transform:translateY(-50%)"><span style="font-size:90%">–</span></div><div style="float:right;position:absolute;right:-1px;top:2.75em;transform:translateY(-50%)"><span style="font-size:90%">—</span></div><div style="float:right;position:absolute;right:-1px;top:1.38em;transform:translateY(-50%)"><span style="font-size:90%">–</span></div><div style="float:right;position:absolute;right:-1px;top:0.00em;transform:translateY(-50%)"><span style="font-size:90%">0 —</span></div></td><td id="Timeline" class="toccolours notheme" style="padding:0px;margin:0.7em 0 0.7em 0;position:relative;font-size:100%;width:13em;height:50em;float:left;border:none"><div class="notheme" style="font-size:100%;background-color:#e5cc7f;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:0.000em;height:50.000em;left:0.910em;width:12.090em"><div style="font-size:100%;position:relative;top:0em;left:0em"><div class="notheme" style="position:relative;text-align:center;vertical-align:middle;display:block;bottom:-25.000em;transform:translateY(-50%);z-index:5"> </div></div></div><div class="notheme" style="font-size:100%;background-color:#aebfd1;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:44.053em;height:4.537em;left:1.040em;width:11.960em"><div style="font-size:100%;position:relative;top:0em;left:0em"><div class="notheme" style="position:relative;text-align:center;vertical-align:middle;display:block;bottom:-2.269em;transform:translateY(-50%);z-index:5"><a href="/wiki/Origin_of_water_on_Earth" title="Origin of water on Earth">Water</a></div></div></div><div class="notheme" style="font-size:100%;background-color:#aebfd1;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:0.000em;height:44.053em;left:1.040em;width:0.130em"><div style="font-size:100%;position:relative;top:0em;left:0em"><div class="notheme" style="position:relative;text-align:center;vertical-align:middle;display:block;bottom:-22.026em;transform:translateY(-50%);z-index:5"> </div></div></div><div class="notheme" style="font-size:100%;background-color:#b3d9ff;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:38.546em;height:5.507em;left:1.170em;width:11.830em"><div style="font-size:100%;position:relative;top:0em;left:0em"><div class="notheme" style="position:relative;text-align:center;vertical-align:middle;display:block;bottom:-2.753em;transform:translateY(-50%);z-index:5"><a href="/wiki/Unicellular_organism" title="Unicellular organism">Single-celled life</a></div></div></div><div class="notheme" style="font-size:100%;background-color:#b3d9ff;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:0.000em;height:38.546em;left:1.170em;width:0.260em"><div style="font-size:100%;position:relative;top:0em;left:0em"><div class="notheme" style="position:relative;text-align:center;vertical-align:middle;display:block;bottom:-19.273em;transform:translateY(-50%);z-index:5"> </div></div></div><div class="notheme" style="font-size:100%;background-color:#99ffff;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:23.128em;height:15.419em;left:1.430em;width:11.570em"><div style="font-size:100%;position:relative;top:0em;left:0em"><div class="notheme" style="position:relative;text-align:center;vertical-align:middle;display:block;bottom:-7.709em;transform:translateY(-50%);z-index:5"><a href="/wiki/Evolution_of_photosynthesis" title="Evolution of photosynthesis">Photosynthesis</a></div></div></div><div class="notheme" style="font-size:100%;background-color:#99ffff;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:0.000em;height:23.128em;left:1.430em;width:0.260em"><div style="font-size:100%;position:relative;top:0em;left:0em"><div class="notheme" style="position:relative;text-align:center;vertical-align:middle;display:block;bottom:-11.564em;transform:translateY(-50%);z-index:5"> </div></div></div><div class="notheme" style="font-size:100%;background-color:#b3ffea;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:17.621em;height:5.507em;left:1.690em;width:11.310em"><div style="font-size:100%;position:relative;top:0em;left:0em"><div class="notheme" style="position:relative;text-align:center;vertical-align:middle;display:block;bottom:-2.753em;transform:translateY(-50%);z-index:5"><a href="/wiki/Eukaryote" title="Eukaryote">Eukaryotes</a></div></div></div><div class="notheme" style="font-size:100%;background-color:#b3ffea;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:0.000em;height:17.621em;left:1.690em;width:0.260em"><div style="font-size:100%;position:relative;top:0em;left:0em"><div class="notheme" style="position:relative;text-align:center;vertical-align:middle;display:block;bottom:-8.811em;transform:translateY(-50%);z-index:5"> </div></div></div><div class="notheme" style="font-size:100%;background-color:#ccffe7;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:5.958em;height:11.663em;left:1.950em;width:11.050em"><div style="font-size:100%;position:relative;top:0em;left:0em"><div class="notheme" style="position:relative;text-align:center;vertical-align:middle;display:block;bottom:-5.831em;transform:translateY(-50%);z-index:5"><a href="/wiki/Multicellular_organism" title="Multicellular organism">Multicellular life</a></div></div></div><div class="notheme" style="font-size:100%;background-color:#ccffe7;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:0.000em;height:5.958em;left:1.950em;width:0.260em"><div style="font-size:100%;position:relative;top:0em;left:0em"><div class="notheme" style="position:relative;text-align:center;vertical-align:middle;display:block;bottom:-2.979em;transform:translateY(-50%);z-index:5"> </div></div></div><div class="notheme" style="font-size:100%;background-color:#77dd00;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:1.982em;height:7.379em;left:2.210em;width:1.170em"><div style="font-size:100%;position:relative;top:0em;left:0em"><div class="notheme" style="position:relative;text-align:center;font-size:90%;vertical-align:middle;display:block;bottom:-3.689em;transform:translateY(-50%);z-index:5"><a href="/wiki/Plant" title="Plant"><span style="display:block; text-align:center; line-height: 0.85em;">P<br />l<br />a<br />n<br />t<br />s</span></a></div></div></div><div class="notheme" style="font-size:100%;background-color:#77dd00;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:0.000em;height:1.982em;left:2.210em;width:0.260em"><div style="font-size:100%;position:relative;top:0em;left:0em"><div class="notheme" style="position:relative;text-align:center;vertical-align:middle;display:block;bottom:-0.991em;transform:translateY(-50%);z-index:5"> </div></div></div><div class="notheme" style="font-size:100%;background-color:#ccbbaa;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:2.203em;height:3.756em;left:3.380em;width:9.620em"><div style="font-size:100%;position:relative;top:0.5em;left:0em"><div class="notheme" style="position:relative;text-align:center;font-size:90%;vertical-align:middle;display:block;bottom:-1.878em;transform:translateY(-50%);z-index:5"><a href="/wiki/Arthropod" title="Arthropod">Arthropods</a> <a href="/wiki/Mollusca" title="Mollusca">Molluscs</a></div></div></div><div class="notheme" style="font-size:100%;background-color:#ffff00;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:0.000em;height:1.982em;left:2.470em;width:3.510em"><div style="font-size:100%;position:relative;top:-0.53em;left:0em"><div class="notheme" style="position:relative;text-align:center;font-size:90%;vertical-align:middle;display:block;bottom:-0.991em;transform:translateY(-50%);z-index:5"><a href="/wiki/Flowering_plant#Evolutionary_history" title="Flowering plant">Flowers</a></div></div></div><div class="notheme" style="font-size:100%;background-color:#e6b880;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:0.721em;height:2.583em;left:3.380em;width:5.070em"><div style="font-size:100%;position:relative;top:0.5em;left:0em"><div class="notheme" style="position:relative;text-align:center;font-size:90%;vertical-align:middle;display:block;bottom:-1.291em;transform:translateY(-50%);z-index:5"><a href="/wiki/Dinosaur" title="Dinosaur">Dinosaurs</a></div></div></div><div class="notheme" style="font-size:100%;background-color:#ffcc00;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:0.000em;height:2.203em;left:8.580em;width:4.420em"><div style="font-size:100%;position:relative;top:0em;left:0em"><div class="notheme" style="position:relative;text-align:center;vertical-align:middle;display:block;bottom:-1.101em;transform:translateY(-50%);z-index:5"> </div></div></div><div class="notheme" style="font-size:100%;background-color:#ffcc00;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:0.606em;height:1.597em;left:8.450em;width:4.290em"><div style="font-size:100%;position:relative;top:0.15em;left:0em"><div class="notheme" style="position:relative;text-align:center;font-size:90%;vertical-align:middle;display:block;bottom:-0.798em;transform:translateY(-50%);z-index:5"><a href="/wiki/Mammal" title="Mammal">Mammals</a></div></div></div><div class="notheme" style="font-size:100%;background-color:#e6b880;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:0.000em;height:1.333em;left:5.980em;width:2.600em"><div style="font-size:100%;position:relative;top:-0.225em;left:0em"><div class="notheme" style="position:relative;text-align:center;font-size:90%;vertical-align:middle;display:block;bottom:-0.666em;transform:translateY(-50%);z-index:5"><a href="/wiki/Bird" title="Bird">Birds</a></div></div></div><div class="notheme" style="font-size:100%;background-color:#ffbbbb;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:0.000em;height:0.606em;left:8.710em;width:4.030em"><div style="font-size:100%;position:relative;top:0.1em;left:0em"><div class="notheme" style="position:relative;text-align:center;font-size:90%;vertical-align:middle;display:block;bottom:-0.303em;transform:translateY(-50%);z-index:5"><a href="/wiki/Primate" title="Primate">Primates</a></div></div></div><div class="notheme" style="font-size:100%;background-color:#993c00;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:44.053em;height:5.947em;left:0.000em;width:0.910em"><div style="font-size:100%;position:relative;top:0em;left:-0.05em"><div class="notheme" style="position:relative;text-align:center;font-size:100%;vertical-align:middle;display:block;bottom:-2.974em;transform:translateY(-50%);z-index:5"><span style="display:block; text-align:center; line-height: 0.80em;"><a href="/wiki/Hadean" title="Hadean"><span style="color:#ffffff;">H<br />a<br />d<br />e<br />a<br />n</span></a></span></div></div></div><div class="notheme" style="font-size:100%;background-color:#936a00;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:27.533em;height:16.520em;left:0.000em;width:0.910em"><div style="font-size:100%;position:relative;top:-1.2em;left:-0.05em"><div class="notheme" style="position:relative;text-align:center;font-size:100%;vertical-align:middle;display:block;bottom:-8.260em;transform:translateY(-50%);z-index:5"><span style="display:block; text-align:center; line-height: 0.85em;"><a href="/wiki/Archean" title="Archean"><span style="color:#ffffff;"><br /><br /><br />A<br />r<br />c<br />h<br />e<br />a<br />n</span></a></span></div></div></div><div class="notheme" style="font-size:100%;background-color:#f1c309;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:5.958em;height:21.575em;left:0.000em;width:0.910em"><div style="font-size:100%;position:relative;top:0em;left:0em"><div class="notheme" style="position:relative;text-align:center;font-size:100%;vertical-align:middle;display:block;bottom:-10.787em;transform:translateY(-50%);z-index:5"><span style="display:block; text-align:center; line-height: 0.85em;"><a href="/wiki/Proterozoic" title="Proterozoic"><br /><br /><br /><br /><br /><br /><br />P<br />r<br />o<br />t<br />e<br />r<br />o<br />z<br />o<br />i<br />c</a></span></div></div></div><div class="notheme" style="font-size:100%;background-color:#c1e0c1;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:0.000em;height:5.958em;left:0.000em;width:0.910em"><div style="font-size:100%;position:relative;top:2em;left:0em"><div class="notheme" style="position:relative;text-align:center;font-size:100%;vertical-align:middle;display:block;bottom:-2.979em;transform:translateY(-50%);z-index:5"><span style="display:block; text-align:center; line-height: 0.85em;"><a href="/wiki/Phanerozoic" title="Phanerozoic">P<br />h<br />a<br />n<br />e<br />r<br />o<br />z<br />o<br />i<br />c</a></span></div></div></div><div class="notheme" style="font-size:100%;background-color:#ccbbaa;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:0.000em;height:8.260em;left:12.714em;width:0.286em"><div style="font-size:100%;position:relative;top:0em;left:0em"><div class="notheme" style="position:relative;text-align:center;vertical-align:middle;display:block;bottom:-4.130em;transform:translateY(-50%);z-index:5"> </div></div></div><div class="notheme" style="font-size:100%;background-color:#ccbbaa;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:0.000em;height:2.203em;left:12.714em;width:0.286em"><div style="font-size:100%;position:relative;top:0em;left:0em"><div class="notheme" style="position:relative;text-align:center;vertical-align:middle;display:block;bottom:-1.101em;transform:translateY(-50%);z-index:5"> </div></div></div></td><td id="Annotations" style="padding:0;margin:0.7em 0 0.7em 0;float:left;position:relative;width:11.05em;height:50em"><table role="presentation" style="position:absolute;z-index:15;top:50.000em;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle"><span style="color:var( --color-base, #000)">←</span></td><td style="padding:0;text-align:left;vertical-align:middle"><div class="annot-nudge" style="font-size:100%;float:left;position:relative;top:0em"><div style="z-index:10;font-size:90%;color:var( --color-base, #000);display:block;line-height:105%;bottom:0"><a href="/wiki/Age_of_Earth" title="Age of Earth">Earth formed</a></div></div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:48.568em;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle"><span style="color:var( --color-base, #000)">←</span></td><td style="padding:0;text-align:left;vertical-align:middle"><div class="annot-nudge" style="font-size:100%;float:left;position:relative;top:0.2em"><div style="z-index:10;font-size:90%;color:var( --color-base, #000);display:block;line-height:105%;bottom:0"><a href="/wiki/Origin_of_water_on_Earth" title="Origin of water on Earth">Earliest water</a></div></div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:47.907em;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle"><span style="color:var( --color-base, #000)">←</span></td><td style="padding:0;text-align:left;vertical-align:middle"><div class="annot-nudge" style="font-size:100%;float:left;position:relative;top:0em"><div style="z-index:10;font-size:90%;color:var( --color-base, #000);display:block;line-height:105%;bottom:0"><a href="/wiki/Last_universal_common_ancestor" title="Last universal common ancestor">LUCA</a></div></div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:44.053em;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle"><span style="color:var( --color-base, #000)">←</span></td><td style="padding:0;text-align:left;vertical-align:middle"><div class="annot-nudge" style="font-size:100%;float:left;position:relative;top:0em"><div style="z-index:10;font-size:90%;color:var( --color-base, #000);display:block;line-height:105%;bottom:0"><a href="/wiki/Earliest_known_life_forms" title="Earliest known life forms">Earliest fossils</a></div></div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:42.952em;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle"><span style="color:var( --color-base, #000)">←</span></td><td style="padding:0;text-align:left;vertical-align:middle"><div class="annot-nudge" style="font-size:100%;float:left;position:relative;top:0em"><div style="z-index:10;font-size:90%;color:var( --color-base, #000);display:block;line-height:105%;bottom:0"><a href="/wiki/Late_Heavy_Bombardment" title="Late Heavy Bombardment">LHB meteorites</a></div></div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:38.546em;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle"><span style="color:var( --color-base, #000)">←</span></td><td style="padding:0;text-align:left;vertical-align:middle"><div class="annot-nudge" style="font-size:100%;float:left;position:relative;top:0em"><div style="z-index:10;font-size:90%;color:var( --color-base, #000);display:block;line-height:105%;bottom:0"><a href="/wiki/Geological_history_of_oxygen" title="Geological history of oxygen">Earliest oxygen</a></div></div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:31.278em;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle"><span style="color:var( --color-base, #000)">←</span></td><td style="padding:0;text-align:left;vertical-align:middle"><div class="annot-nudge" style="font-size:100%;float:left;position:relative;top:0em"><div style="z-index:10;font-size:90%;color:var( --color-base, #000);display:block;line-height:105%;bottom:0"><a href="/wiki/Pongola_glaciation" title="Pongola glaciation">Pongola glaciation</a>*</div></div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:25.330em;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle"><span style="color:var( --color-base, #000)">←</span></td><td style="padding:0;text-align:left;vertical-align:middle"><div class="annot-nudge" style="font-size:100%;float:left;position:relative;top:0.2em"><div style="z-index:10;font-size:90%;color:var( --color-base, #000);display:block;line-height:105%;bottom:0"><a href="/wiki/Great_Oxidation_Event" title="Great Oxidation Event">Atmospheric oxygen</a></div></div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:24.780em;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle"><span style="color:var( --color-base, #000)">←</span></td><td style="padding:0;text-align:left;vertical-align:middle"><div class="annot-nudge" style="font-size:100%;float:left;position:relative;top:-0.2em"><div style="z-index:10;font-size:90%;color:var( --color-base, #000);display:block;line-height:105%;bottom:0"><a href="/wiki/Huronian_glaciation" title="Huronian glaciation">Huronian glaciation</a>*</div></div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:22.026em;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle"><span style="color:var( --color-base, #000)">←</span></td><td style="padding:0;text-align:left;vertical-align:middle"><div class="annot-nudge" style="font-size:100%;float:left;position:relative;top:0em"><div style="z-index:10;font-size:90%;color:var( --color-base, #000);display:block;line-height:105%;bottom:0"><a href="/wiki/Evolution_of_sexual_reproduction#Origin_of_sexual_reproduction" title="Evolution of sexual reproduction">Sexual reproduction</a></div></div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:17.621em;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle"><span style="color:var( --color-base, #000)">←</span></td><td style="padding:0;text-align:left;vertical-align:middle"><div class="annot-nudge" style="font-size:100%;float:left;position:relative;top:0em"><div style="z-index:10;font-size:90%;color:var( --color-base, #000);display:block;line-height:105%;bottom:0"><a href="/wiki/Francevillian_biota" title="Francevillian biota">Earliest multicellular life</a></div></div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:16.520em;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle"><span style="color:var( --color-base, #000)">←</span></td><td style="padding:0;text-align:left;vertical-align:middle"><div class="annot-nudge" style="font-size:100%;float:left;position:relative;top:0em"><div style="z-index:10;font-size:90%;color:var( --color-base, #000);display:block;line-height:105%;bottom:0"><a href="/wiki/Evolution_of_fungi" title="Evolution of fungi">Earliest fungi</a></div></div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:9.361em;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle"><span style="color:var( --color-base, #000)">←</span></td><td style="padding:0;text-align:left;vertical-align:middle"><div class="annot-nudge" style="font-size:100%;float:left;position:relative;top:0.25em"><div style="z-index:10;font-size:90%;color:var( --color-base, #000);display:block;line-height:105%;bottom:0"><a href="/wiki/Evolutionary_history_of_plants" title="Evolutionary history of plants">Earliest plants</a></div></div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:8.260em;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle"><span style="color:var( --color-base, #000)">←</span></td><td style="padding:0;text-align:left;vertical-align:middle"><div class="annot-nudge" style="font-size:100%;float:left;position:relative;top:0.4em"><div style="z-index:10;font-size:90%;color:var( --color-base, #000);display:block;line-height:105%;bottom:0"><a href="/wiki/Caveasphaera" title="Caveasphaera">Earliest animals</a></div></div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:7.489em;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle"><span style="color:var( --color-base, #000)">←</span></td><td style="padding:0;text-align:left;vertical-align:middle"><div class="annot-nudge" style="font-size:100%;float:left;position:relative;top:0.2em"><div style="z-index:10;font-size:90%;color:var( --color-base, #000);display:block;line-height:105%;bottom:0"><a href="/wiki/Cryogenian" title="Cryogenian">Cryogenian ice age</a>*</div></div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:6.993em;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle"><span style="color:var( --color-base, #000)">←</span></td><td style="padding:0;text-align:left;vertical-align:middle"><div class="annot-nudge" style="font-size:100%;float:left;position:relative;top:-0.2em"><div style="z-index:10;font-size:90%;color:var( --color-base, #000);display:block;line-height:105%;bottom:0"><a href="/wiki/Ediacaran_biota" title="Ediacaran biota">Ediacaran biota</a></div></div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:5.958em;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle"><span style="color:var( --color-base, #000)">←</span></td><td style="padding:0;text-align:left;vertical-align:middle"><div class="annot-nudge" style="font-size:100%;float:left;position:relative;top:-0.15em"><div style="z-index:10;font-size:90%;color:var( --color-base, #000);display:block;line-height:105%;bottom:0"><a href="/wiki/Cambrian_explosion" title="Cambrian explosion">Cambrian explosion</a></div></div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:4.956em;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle"><span style="color:var( --color-base, #000)">←</span></td><td style="padding:0;text-align:left;vertical-align:middle"><div class="annot-nudge" style="font-size:100%;float:left;position:relative;top:-0.1em"><div style="z-index:10;font-size:90%;color:var( --color-base, #000);display:block;line-height:105%;bottom:0"><a href="/wiki/Hirnantian_glaciation" title="Hirnantian glaciation">Hirnantian glaciation</a>*</div></div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:4.075em;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle"><span style="color:var( --color-base, #000)">←</span></td><td style="padding:0;text-align:left;vertical-align:middle"><div class="annot-nudge" style="font-size:100%;float:left;position:relative;top:-0.1em"><div style="z-index:10;font-size:90%;color:var( --color-base, #000);display:block;line-height:105%;bottom:0"><a href="/wiki/Tetrapod" title="Tetrapod">Earliest tetrapods</a></div></div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:3.304em;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle"><span style="color:var( --color-base, #000)">←</span></td><td style="padding:0;text-align:left;vertical-align:middle"><div class="annot-nudge" style="font-size:100%;float:left;position:relative;top:-0.2em"><div style="z-index:10;font-size:90%;color:var( --color-base, #000);display:block;line-height:105%;bottom:0"><a href="/wiki/Late_Paleozoic_icehouse" title="Late Paleozoic icehouse">Karoo ice age</a>*</div></div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:0.275em;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle"><span style="color:var( --color-base, #000)">←</span></td><td style="padding:0;text-align:left;vertical-align:middle"><div class="annot-nudge" style="font-size:100%;float:left;position:relative;top:0.3em"><div style="z-index:10;font-size:90%;color:var( --color-base, #000);display:block;line-height:105%;bottom:0"><a href="/wiki/Ape" title="Ape">Earliest apes</a> / <a href="/wiki/Human" title="Human">humans</a></div></div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:0.018em;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle"><span style="color:var( --color-base, #000)">←</span></td><td style="padding:0;text-align:left;vertical-align:middle"><div class="annot-nudge" style="font-size:100%;float:left;position:relative;top:-0.4em"><div style="z-index:10;font-size:90%;color:var( --color-base, #000);display:block;line-height:105%;bottom:0"><a href="/wiki/Quaternary_glaciation" title="Quaternary glaciation">Quaternary ice age</a>*</div></div></td></tr></tbody></table></td></tr><tr><td id="Caption" colspan="3" style="padding:0;margin:0 0.2em 0.7em 0.2em"><div id="Caption" class="toccolours" style="margin:0 0.5em;border-style:none;clear:both;text-align:center;width:26.8em"><div style="float:left;font-size:85%;">(<a href="/wiki/Myr" class="mw-redirect" title="Myr">million years ago</a>)</div><div style="float:right;font-size:95%;">*<i><a href="/wiki/Timeline_of_glaciation" title="Timeline of glaciation">Ice Ages</a></i></div></div></td></tr></tbody></table> <figure class="mw-halign-left" typeof="mw:File/Thumb"><a href="/wiki/File:Calcidiscus_leptoporus_05.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/b/b9/Calcidiscus_leptoporus_05.jpg/200px-Calcidiscus_leptoporus_05.jpg" decoding="async" width="200" height="162" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/b/b9/Calcidiscus_leptoporus_05.jpg/300px-Calcidiscus_leptoporus_05.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/b/b9/Calcidiscus_leptoporus_05.jpg/400px-Calcidiscus_leptoporus_05.jpg 2x" data-file-width="3430" data-file-height="2770" /></a><figcaption>Electron micrograph of microfossils from a sediment core obtained by the <a href="/wiki/Deep_Sea_Drilling_Program" class="mw-redirect" title="Deep Sea Drilling Program">Deep Sea Drilling Program</a> </figcaption></figure><p>The ancient record on Earth provides an opportunity to see what geochemical signatures are produced by microbial life and how these signatures are preserved over geologic time. Some related disciplines such as <a href="/wiki/Geochemistry" title="Geochemistry">geochemistry</a>, <a href="/wiki/Geobiology" title="Geobiology">geobiology</a>, and <a href="/wiki/Geomicrobiology" title="Geomicrobiology">geomicrobiology</a> often use biosignatures to determine if living <a href="/wiki/Organism" title="Organism">organisms</a> are or were present in a sample. These possible biosignatures include: (a) <a href="/wiki/Microfossils" class="mw-redirect" title="Microfossils">microfossils</a> and <a href="/wiki/Stromatolites" class="mw-redirect" title="Stromatolites">stromatolites</a>; (b) molecular structures (<a href="/wiki/Biomarkers" class="mw-redirect" title="Biomarkers">biomarkers</a>) and <a href="/wiki/Isotope" title="Isotope">isotopic compositions</a> of carbon, nitrogen and hydrogen in <a href="/wiki/Organic_matter" title="Organic matter">organic matter</a>; (c) multiple sulfur and oxygen isotope ratios of minerals; and (d) abundance relationships and isotopic compositions of redox-sensitive metals (e.g., Fe, Mo, Cr, and rare earth elements).<sup id="cite_ref-PSARC_19-0" class="reference"><a href="#cite_note-PSARC-19"><span class="cite-bracket">[</span>19<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-20" class="reference"><a href="#cite_note-20"><span class="cite-bracket">[</span>20<span class="cite-bracket">]</span></a></sup> </p><p>For example, the particular <a href="/wiki/Fatty_acids" class="mw-redirect" title="Fatty acids">fatty acids</a> measured in a sample can indicate which types of <a href="/wiki/Bacterium" class="mw-redirect" title="Bacterium">bacteria</a> and <a href="/wiki/Archaea" title="Archaea">archaea</a> live in that environment. Another example is the long-chain <a href="/wiki/Fatty_alcohol" title="Fatty alcohol">fatty alcohols</a> with more than 23 atoms that are produced by <a href="/wiki/Plankton" title="Plankton">planktonic</a> <a href="/wiki/Bacteria" title="Bacteria">bacteria</a>.<sup id="cite_ref-21" class="reference"><a href="#cite_note-21"><span class="cite-bracket">[</span>21<span class="cite-bracket">]</span></a></sup> When used in this sense, geochemists often prefer the term <a href="/wiki/Biomarker" title="Biomarker">biomarker</a>. Another example is the presence of straight-chain <a href="/wiki/Lipids" class="mw-redirect" title="Lipids">lipids</a> in the form of <a href="/wiki/Alkanes" class="mw-redirect" title="Alkanes">alkanes</a>, <a href="/wiki/Alcohols" class="mw-redirect" title="Alcohols">alcohols</a>, and <a href="/wiki/Fatty_acids" class="mw-redirect" title="Fatty acids">fatty acids</a> with 20–36 <a href="/wiki/Carbon" title="Carbon">carbon</a> atoms in soils or sediments. <a href="/wiki/Peat" title="Peat">Peat</a> deposits are an indication of originating from the <a href="/wiki/Epicuticular_wax" title="Epicuticular wax">epicuticular wax</a> of higher <a href="/wiki/Plant" title="Plant">plants</a>. </p><p>Life processes may produce a range of biosignatures such as <a href="/wiki/Nucleic_acids" class="mw-redirect" title="Nucleic acids">nucleic acids</a>, <a href="/wiki/Lipid" title="Lipid">lipids</a>, <a href="/wiki/Protein" title="Protein">proteins</a>, <a href="/wiki/Amino_acid" title="Amino acid">amino acids</a>, <a href="/wiki/Kerogen" title="Kerogen">kerogen</a>-like material and various morphological features that are detectable in rocks and sediments.<sup id="cite_ref-Beegle_22-0" class="reference"><a href="#cite_note-Beegle-22"><span class="cite-bracket">[</span>22<span class="cite-bracket">]</span></a></sup> <a href="/wiki/Microbes" class="mw-redirect" title="Microbes">Microbes</a> often interact with geochemical processes, leaving features in the rock record indicative of biosignatures. For example, bacterial micrometer-sized pores in <a href="/wiki/Carbonate_rock" title="Carbonate rock">carbonate rocks</a> resemble inclusions under transmitted light, but have distinct sizes, shapes, and patterns (swirling or dendritic) and are distributed differently from common fluid inclusions.<sup id="cite_ref-23" class="reference"><a href="#cite_note-23"><span class="cite-bracket">[</span>23<span class="cite-bracket">]</span></a></sup> A potential biosignature is a phenomenon that <i>may</i> have been produced by life, but for which alternate <a href="/wiki/Abiotic_component" title="Abiotic component">abiotic</a> origins may also be possible. </p> <div class="mw-heading mw-heading3"><h3 id="Morphology">Morphology</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=11" title="Edit section: Morphology"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-halign-left" typeof="mw:File/Thumb"><a href="/wiki/File:ALH84001_structures.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/a/a8/ALH84001_structures.jpg/200px-ALH84001_structures.jpg" decoding="async" width="200" height="136" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/a/a8/ALH84001_structures.jpg/300px-ALH84001_structures.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/a/a8/ALH84001_structures.jpg/400px-ALH84001_structures.jpg 2x" data-file-width="1983" data-file-height="1351" /></a><figcaption>Some researchers suggested that these microscopic structures on the Martian <a href="/wiki/ALH84001" class="mw-redirect" title="ALH84001">ALH84001</a> meteorite could be fossilized bacteria.<sup id="cite_ref-disbelief_24-0" class="reference"><a href="#cite_note-disbelief-24"><span class="cite-bracket">[</span>24<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-life_25-0" class="reference"><a href="#cite_note-life-25"><span class="cite-bracket">[</span>25<span class="cite-bracket">]</span></a></sup></figcaption></figure><p>Another possible biosignature might be <a href="/wiki/Morphology_(biology)" title="Morphology (biology)">morphology</a> since the shape and size of certain objects may potentially indicate the presence of past or present life. For example, microscopic <a href="/wiki/Magnetite" title="Magnetite">magnetite</a> crystals in the Martian <a href="/wiki/Meteorite" title="Meteorite">meteorite</a> <a href="/wiki/ALH84001" class="mw-redirect" title="ALH84001">ALH84001</a><sup id="cite_ref-life_25-1" class="reference"><a href="#cite_note-life-25"><span class="cite-bracket">[</span>25<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-26" class="reference"><a href="#cite_note-26"><span class="cite-bracket">[</span>26<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-27" class="reference"><a href="#cite_note-27"><span class="cite-bracket">[</span>27<span class="cite-bracket">]</span></a></sup> are one of the longest-debated of several potential biosignatures in that specimen.<sup id="cite_ref-28" class="reference"><a href="#cite_note-28"><span class="cite-bracket">[</span>28<span class="cite-bracket">]</span></a></sup> The possible <a href="/wiki/Biomineralisation" class="mw-redirect" title="Biomineralisation">biomineral</a> studied in the Martian <a href="/wiki/ALH84001" class="mw-redirect" title="ALH84001">ALH84001 meteorite</a> includes putative microbial <a href="/wiki/Fossils" class="mw-redirect" title="Fossils">fossils</a>, tiny rock-like structures whose shape was a potential biosignature because it resembled known bacteria. Most scientists ultimately concluded that these were far too small to be fossilized <a href="/wiki/Cell_(biology)" title="Cell (biology)">cells</a>.<sup id="cite_ref-29" class="reference"><a href="#cite_note-29"><span class="cite-bracket">[</span>29<span class="cite-bracket">]</span></a></sup> A consensus that has emerged from these discussions, and is now seen as a critical requirement, is the demand for further lines of evidence in addition to any morphological data that supports such extraordinary claims.<sup id="cite_ref-SSG_1-1" class="reference"><a href="#cite_note-SSG-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> Currently, the scientific consensus is that "morphology alone cannot be used unambiguously as a tool for primitive life detection".<sup id="cite_ref-morphology_30-0" class="reference"><a href="#cite_note-morphology-30"><span class="cite-bracket">[</span>30<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-31" class="reference"><a href="#cite_note-31"><span class="cite-bracket">[</span>31<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-32" class="reference"><a href="#cite_note-32"><span class="cite-bracket">[</span>32<span class="cite-bracket">]</span></a></sup> Interpretation of morphology is notoriously subjective, and its use alone has led to numerous errors of interpretation.<sup id="cite_ref-morphology_30-1" class="reference"><a href="#cite_note-morphology-30"><span class="cite-bracket">[</span>30<span class="cite-bracket">]</span></a></sup> </p><div class="mw-heading mw-heading3"><h3 id="Chemistry">Chemistry</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=12" title="Edit section: Chemistry"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>No single compound will prove life once existed. Rather, it will be distinctive patterns present in any organic compounds showing a process of selection.<sup id="cite_ref-PhysOrg_Cousins_2018_33-0" class="reference"><a href="#cite_note-PhysOrg_Cousins_2018-33"><span class="cite-bracket">[</span>33<span class="cite-bracket">]</span></a></sup> For example, <a href="/wiki/Membrane_lipid" title="Membrane lipid">membrane lipids</a> left behind by degraded cells will be concentrated, have a limited size range, and comprise an even number of carbons. Similarly, life only uses left-handed amino acids.<sup id="cite_ref-PhysOrg_Cousins_2018_33-1" class="reference"><a href="#cite_note-PhysOrg_Cousins_2018-33"><span class="cite-bracket">[</span>33<span class="cite-bracket">]</span></a></sup> Biosignatures need not be chemical, however, and can also be suggested by a distinctive <a href="/wiki/Magnetic" class="mw-redirect" title="Magnetic">magnetic</a> biosignature.<sup id="cite_ref-Wall-20111213_34-0" class="reference"><a href="#cite_note-Wall-20111213-34"><span class="cite-bracket">[</span>34<span class="cite-bracket">]</span></a></sup> </p> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Biomarkers_(petroleum).png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/7/70/Biomarkers_%28petroleum%29.png/170px-Biomarkers_%28petroleum%29.png" decoding="async" width="170" height="374" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/7/70/Biomarkers_%28petroleum%29.png/255px-Biomarkers_%28petroleum%29.png 1.5x, //upload.wikimedia.org/wikipedia/commons/7/70/Biomarkers_%28petroleum%29.png 2x" data-file-width="277" data-file-height="609" /></a><figcaption>Structures of prime examples of biomarkers (petroleum), from top to bottom: Pristane, Triterpane, Sterane, Phytane and Porphyrin</figcaption></figure> <p>Chemical biosignatures include any suite of complex <a href="/wiki/Organic_compounds" class="mw-redirect" title="Organic compounds">organic compounds</a> composed of carbon, hydrogen, and other elements or heteroatoms such as oxygen, nitrogen, and sulfur, which are found in <a href="/wiki/Petroleum" title="Petroleum">crude oils</a>, <a href="/wiki/Bitumen" title="Bitumen">bitumen</a>, <a href="/wiki/Petroleum" title="Petroleum">petroleum</a> <a href="/wiki/Source_rock" title="Source rock">source rock</a> and eventually show simplification in molecular structure from the parent organic molecules found in all living organisms. They are complex carbon-based molecules derived from formerly <a href="/wiki/Living_organisms" class="mw-redirect" title="Living organisms">living organisms</a>.<sup id="cite_ref-biomarker_35-0" class="reference"><a href="#cite_note-biomarker-35"><span class="cite-bracket">[</span>35<span class="cite-bracket">]</span></a></sup> Each biomarker is quite distinctive when compared to its counterparts, as the time required for <a href="/wiki/Organic_matter" title="Organic matter">organic matter</a> to convert to crude oil is characteristic.<sup id="cite_ref-36" class="reference"><a href="#cite_note-36"><span class="cite-bracket">[</span>36<span class="cite-bracket">]</span></a></sup> Most biomarkers also usually have high <a href="/wiki/Molecular_mass" title="Molecular mass">molecular mass</a>.<sup id="cite_ref-37" class="reference"><a href="#cite_note-37"><span class="cite-bracket">[</span>37<span class="cite-bracket">]</span></a></sup> </p><p>Some examples of biomarkers found in petroleum are <a href="/wiki/Pristane" title="Pristane">pristane</a>, <a href="/wiki/Oleanane" title="Oleanane">triterpanes</a>, <a href="/wiki/Sterane" title="Sterane">steranes</a>, <a href="/wiki/Phytane" title="Phytane">phytane</a> and <a href="/wiki/Porphyrin" title="Porphyrin">porphyrin</a>. Such petroleum biomarkers are produced via <a href="/wiki/Chemical_synthesis" title="Chemical synthesis">chemical synthesis</a> using biochemical compounds as their main constituents. For instance, triterpenes are derived from biochemical compounds found on land <a href="/wiki/Angiosperm" class="mw-redirect" title="Angiosperm">angiosperm</a> plants.<sup id="cite_ref-38" class="reference"><a href="#cite_note-38"><span class="cite-bracket">[</span>38<span class="cite-bracket">]</span></a></sup> The abundance of petroleum biomarkers in small amounts in its reservoir or source rock make it necessary to use sensitive and differential approaches to analyze the presence of those compounds. The techniques typically used include <a href="/wiki/Gas_chromatography" title="Gas chromatography">gas chromatography</a> and <a href="/wiki/Mass_spectrometry" title="Mass spectrometry">mass spectrometry</a>.<sup id="cite_ref-39" class="reference"><a href="#cite_note-39"><span class="cite-bracket">[</span>39<span class="cite-bracket">]</span></a></sup> </p><p>Petroleum biomarkers are highly important in petroleum inspection as they help indicate the depositional territories and determine the geological properties of oils. For instance, they provide more details concerning their maturity and the source material.<sup id="cite_ref-40" class="reference"><a href="#cite_note-40"><span class="cite-bracket">[</span>40<span class="cite-bracket">]</span></a></sup> In addition to that they can also be good parameters of age, hence they are technically referred to as "chemical fossils".<sup id="cite_ref-41" class="reference"><a href="#cite_note-41"><span class="cite-bracket">[</span>41<span class="cite-bracket">]</span></a></sup> The ratio of pristane to phytane (pr:ph) is the geochemical factor that allows petroleum biomarkers to be successful indicators of their depositional environments.<sup id="cite_ref-42" class="reference"><a href="#cite_note-42"><span class="cite-bracket">[</span>42<span class="cite-bracket">]</span></a></sup> </p><p><a href="/wiki/Geologists" class="mw-redirect" title="Geologists">Geologists</a> and <a href="/wiki/Geochemist" class="mw-redirect" title="Geochemist">geochemists</a> use biomarker traces found in crude oils and their related <a href="/wiki/Source_rock" title="Source rock">source rock</a> to unravel the stratigraphic origin and migration patterns of presently existing <a href="/wiki/Petroleum" title="Petroleum">petroleum</a> deposits.<sup id="cite_ref-43" class="reference"><a href="#cite_note-43"><span class="cite-bracket">[</span>43<span class="cite-bracket">]</span></a></sup> The dispersion of biomarker molecules is also quite distinctive for each type of oil and its source; hence, they display unique fingerprints. Another factor that makes petroleum biomarkers more preferable than their counterparts is that they have a high tolerance to environmental weathering and corrosion.<sup id="cite_ref-44" class="reference"><a href="#cite_note-44"><span class="cite-bracket">[</span>44<span class="cite-bracket">]</span></a></sup> Such biomarkers are very advantageous and often used in the detection of <a href="/wiki/Oil_spill" title="Oil spill">oil spillage</a> in the major waterways.<sup id="cite_ref-biomarker_35-1" class="reference"><a href="#cite_note-biomarker-35"><span class="cite-bracket">[</span>35<span class="cite-bracket">]</span></a></sup> The same biomarkers can also be used to identify contamination in <a href="/wiki/Lubricant" title="Lubricant">lubricant</a> oils.<sup id="cite_ref-45" class="reference"><a href="#cite_note-45"><span class="cite-bracket">[</span>45<span class="cite-bracket">]</span></a></sup> However, biomarker analysis of untreated rock cuttings can be expected to produce misleading results. This is due to potential hydrocarbon contamination and <a href="/wiki/Biodegradation" title="Biodegradation">biodegradation</a> in the rock samples.<sup id="cite_ref-46" class="reference"><a href="#cite_note-46"><span class="cite-bracket">[</span>46<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Atmospheric">Atmospheric</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=13" title="Edit section: Atmospheric"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The atmospheric properties of exoplanets are of particular importance, as atmospheres provide the most likely observables for the near future, including habitability indicators and biosignatures.<sup id="cite_ref-NYT-20220915_47-0" class="reference"><a href="#cite_note-NYT-20220915-47"><span class="cite-bracket">[</span>47<span class="cite-bracket">]</span></a></sup> Over billions of years, the processes of life on a planet would result in a mixture of chemicals unlike anything that could form in an ordinary chemical equilibrium.<sup id="cite_ref-Lisse_2020_16-1" class="reference"><a href="#cite_note-Lisse_2020-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-48" class="reference"><a href="#cite_note-48"><span class="cite-bracket">[</span>48<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Seager_2017_49-0" class="reference"><a href="#cite_note-Seager_2017-49"><span class="cite-bracket">[</span>49<span class="cite-bracket">]</span></a></sup> For example, large amounts of <a href="/wiki/Oxygen" title="Oxygen">oxygen</a> and small amounts of <a href="/wiki/Methane" title="Methane">methane</a> are generated by life on Earth. </p><p>An exoplanet's color—or reflectance spectrum—can also be used as a biosignature due to the effect of pigments that are uniquely biologic in origin such as the pigments of <a href="/wiki/Phototroph" title="Phototroph">phototrophic</a> and photosynthetic life forms.<sup id="cite_ref-50" class="reference"><a href="#cite_note-50"><span class="cite-bracket">[</span>50<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Berdyugina_2016_51-0" class="reference"><a href="#cite_note-Berdyugina_2016-51"><span class="cite-bracket">[</span>51<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-52" class="reference"><a href="#cite_note-52"><span class="cite-bracket">[</span>52<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-ColorCatalog_53-0" class="reference"><a href="#cite_note-ColorCatalog-53"><span class="cite-bracket">[</span>53<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-54" class="reference"><a href="#cite_note-54"><span class="cite-bracket">[</span>54<span class="cite-bracket">]</span></a></sup> Scientists use the Earth as an example of this when looked at from far away (see <a href="/wiki/Pale_Blue_Dot" title="Pale Blue Dot">Pale Blue Dot</a>) as a comparison to worlds observed outside of our solar system.<sup id="cite_ref-55" class="reference"><a href="#cite_note-55"><span class="cite-bracket">[</span>55<span class="cite-bracket">]</span></a></sup> Ultraviolet radiation on life forms could also induce <a href="/wiki/Biofluorescence" title="Biofluorescence">biofluorescence</a> in visible wavelengths that may be detected by the new generation of space observatories under development.<sup id="cite_ref-EA-20190813_56-0" class="reference"><a href="#cite_note-EA-20190813-56"><span class="cite-bracket">[</span>56<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-57" class="reference"><a href="#cite_note-57"><span class="cite-bracket">[</span>57<span class="cite-bracket">]</span></a></sup> </p><p>Some scientists have reported methods of detecting hydrogen and methane in <a href="/wiki/Extraterrestrial_atmospheres" class="mw-redirect" title="Extraterrestrial atmospheres">extraterrestrial atmospheres</a>.<sup id="cite_ref-Nature-20120627_58-0" class="reference"><a href="#cite_note-Nature-20120627-58"><span class="cite-bracket">[</span>58<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Wired-20120627_59-0" class="reference"><a href="#cite_note-Wired-20120627-59"><span class="cite-bracket">[</span>59<span class="cite-bracket">]</span></a></sup> Habitability indicators and biosignatures must be interpreted within a planetary and environmental context.<sup id="cite_ref-NASA_strategy_2015_4-1" class="reference"><a href="#cite_note-NASA_strategy_2015-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> For example, the presence of oxygen and methane together could indicate the kind of extreme thermochemical disequilibrium generated by life.<sup id="cite_ref-60" class="reference"><a href="#cite_note-60"><span class="cite-bracket">[</span>60<span class="cite-bracket">]</span></a></sup> Two of the top 14,000 proposed atmospheric biosignatures are <a href="/wiki/Dimethyl_sulfide" title="Dimethyl sulfide">dimethyl sulfide</a> and <a href="/wiki/Chloromethane" title="Chloromethane">chloromethane</a> (<span class="chemf nowrap">CH<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:-0.4em;line-height:1em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline">3</sub></span></span>Cl</span>).<sup id="cite_ref-Seager_2017_49-1" class="reference"><a href="#cite_note-Seager_2017-49"><span class="cite-bracket">[</span>49<span class="cite-bracket">]</span></a></sup> An alternative biosignature is the combination of methane and carbon dioxide.<sup id="cite_ref-SPC-20180124_61-0" class="reference"><a href="#cite_note-SPC-20180124-61"><span class="cite-bracket">[</span>61<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-SA-20180124_62-0" class="reference"><a href="#cite_note-SA-20180124-62"><span class="cite-bracket">[</span>62<span class="cite-bracket">]</span></a></sup> </p><p>The detection of <a href="/wiki/Phosphine" title="Phosphine">phosphine</a> in the atmosphere of <a href="/wiki/Venus" title="Venus">Venus</a> is <a href="/wiki/Life_on_Venus#Potential_biomarkers" title="Life on Venus">being investigated</a> as a possible biosignature. </p> <div class="mw-heading mw-heading3"><h3 id="Atmospheric_disequilibrium">Atmospheric disequilibrium</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=14" title="Edit section: Atmospheric disequilibrium"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:CH4_disequilibrium.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/8/8f/CH4_disequilibrium.png/220px-CH4_disequilibrium.png" decoding="async" width="220" height="150" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/8/8f/CH4_disequilibrium.png/330px-CH4_disequilibrium.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/8/8f/CH4_disequilibrium.png/440px-CH4_disequilibrium.png 2x" data-file-width="2030" data-file-height="1388" /></a><figcaption>Biogenic methane production is the main contributor to the methane flux coming from the surface of Earth. Methane has a photochemical sink in the atmosphere but will build up if the flux is high enough. If there is detectable methane in the atmosphere of another planet, especially with a host star of G or K type, this may be interpreted as a viable biosignature.<sup id="cite_ref-63" class="reference"><a href="#cite_note-63"><span class="cite-bracket">[</span>63<span class="cite-bracket">]</span></a></sup></figcaption></figure> <p>A disequilibrium in the abundance of gas species in an atmosphere can be interpreted as a biosignature. Life has greatly altered the atmosphere on Earth in a way that would be unlikely for any other processes to replicate. Therefore, a departure from equilibrium is evidence for a biosignature.<sup id="cite_ref-:0_64-0" class="reference"><a href="#cite_note-:0-64"><span class="cite-bracket">[</span>64<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-:1_65-0" class="reference"><a href="#cite_note-:1-65"><span class="cite-bracket">[</span>65<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-:2_66-0" class="reference"><a href="#cite_note-:2-66"><span class="cite-bracket">[</span>66<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-67" class="reference"><a href="#cite_note-67"><span class="cite-bracket">[</span>67<span class="cite-bracket">]</span></a></sup> For example, the abundance of methane in the Earth's atmosphere is orders of magnitude above the equilibrium value due to the constant methane flux that life on the surface emits.<sup id="cite_ref-:2_66-1" class="reference"><a href="#cite_note-:2-66"><span class="cite-bracket">[</span>66<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-68" class="reference"><a href="#cite_note-68"><span class="cite-bracket">[</span>68<span class="cite-bracket">]</span></a></sup> Depending on the host star, a disequilibrium in the methane abundance on another planet may indicate a biosignature.<sup id="cite_ref-69" class="reference"><a href="#cite_note-69"><span class="cite-bracket">[</span>69<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Agnostic_biosignatures">Agnostic biosignatures</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=15" title="Edit section: Agnostic biosignatures"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Because the only form of known life is that on Earth, the search for biosignatures is heavily influenced by the products that life produces on Earth. However, life that is different from life on Earth may still produce biosignatures that are detectable by humans, even though nothing is known about their specific biology. This form of biosignature is called an "agnostic biosignature" because it is independent of the form of life that produces it. It is widely agreed that all life–no matter how different it is from life on Earth–needs a source of energy to thrive.<sup id="cite_ref-70" class="reference"><a href="#cite_note-70"><span class="cite-bracket">[</span>70<span class="cite-bracket">]</span></a></sup> This must involve some sort of chemical disequilibrium, which can be exploited for metabolism.<sup id="cite_ref-71" class="reference"><a href="#cite_note-71"><span class="cite-bracket">[</span>71<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-:0_64-1" class="reference"><a href="#cite_note-:0-64"><span class="cite-bracket">[</span>64<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-:1_65-1" class="reference"><a href="#cite_note-:1-65"><span class="cite-bracket">[</span>65<span class="cite-bracket">]</span></a></sup> Geological processes are independent of life, and if scientists can constrain the geology well enough on another planet, then they know what the particular geologic equilibrium for that planet should be. A deviation from geological equilibrium can be interpreted as an atmospheric disequilibrium and agnostic biosignature. </p> <div class="mw-heading mw-heading3"><h3 id="Antibiosignatures">Antibiosignatures</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=16" title="Edit section: Antibiosignatures"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>In the same way that detecting a biosignature would be a significant discovery about a planet, finding evidence that life is <i>not</i> present can also be an important discovery about a planet. Life relies on <a href="/wiki/Redox" title="Redox">redox</a> imbalances to metabolize the resources available into energy. The evidence that nothing on an earth is taking advantage of the "free lunch" available due to an observed redox imbalance is called antibiosignatures.<sup id="cite_ref-Zahnle_2011_72-0" class="reference"><a href="#cite_note-Zahnle_2011-72"><span class="cite-bracket">[</span>72<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Polyelectrolytes">Polyelectrolytes</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=17" title="Edit section: Polyelectrolytes"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Polyelectrolyte_theory_of_the_gene" title="Polyelectrolyte theory of the gene">Polyelectrolyte theory of the gene</a></div> <p>The <a href="/wiki/Polyelectrolyte_theory_of_the_gene" title="Polyelectrolyte theory of the gene">Polyelectrolyte theory of the gene</a> is a proposed generic biosignature. In 2002, Steven A. Benner and Daniel Hutter proposed that for a linear genetic <a href="/wiki/Biopolymer" title="Biopolymer">biopolymer</a> dissolved in water, such as <a href="/wiki/DNA" title="DNA">DNA</a>, to undergo <a href="/wiki/Evolution" title="Evolution">Darwinian evolution</a> anywhere in the universe, it must be a <a href="/wiki/Polyelectrolyte" title="Polyelectrolyte">polyelectrolyte</a>, a <a href="/wiki/Polymer" title="Polymer">polymer</a> containing repeating <a href="/wiki/Ionic_charge" class="mw-redirect" title="Ionic charge">ionic</a> charges.<sup id="cite_ref-73" class="reference"><a href="#cite_note-73"><span class="cite-bracket">[</span>73<span class="cite-bracket">]</span></a></sup> Benner and others proposed methods for concentrating and analyzing these polyelectrolyte genetic biopolymers on Mars,<sup id="cite_ref-74" class="reference"><a href="#cite_note-74"><span class="cite-bracket">[</span>74<span class="cite-bracket">]</span></a></sup> Enceladus,<sup id="cite_ref-75" class="reference"><a href="#cite_note-75"><span class="cite-bracket">[</span>75<span class="cite-bracket">]</span></a></sup> and Europa.<sup id="cite_ref-76" class="reference"><a href="#cite_note-76"><span class="cite-bracket">[</span>76<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Specific_examples">Specific examples</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=18" title="Edit section: Specific examples"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Life_on_Mars#Possible_biosignatures" title="Life on Mars">Life on Mars § Possible biosignatures</a></div> <div class="mw-heading mw-heading3"><h3 id="Methane_on_Mars">Methane on Mars</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=19" title="Edit section: Methane on Mars"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Methane_on_Mars" class="mw-redirect" title="Methane on Mars">Methane on Mars</a></div> <figure typeof="mw:File/Thumb"><a href="/wiki/File:PIA19088-MarsCuriosityRover-MethaneSource-20141216.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/6/69/PIA19088-MarsCuriosityRover-MethaneSource-20141216.png/250px-PIA19088-MarsCuriosityRover-MethaneSource-20141216.png" decoding="async" width="250" height="188" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/69/PIA19088-MarsCuriosityRover-MethaneSource-20141216.png/375px-PIA19088-MarsCuriosityRover-MethaneSource-20141216.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/69/PIA19088-MarsCuriosityRover-MethaneSource-20141216.png/500px-PIA19088-MarsCuriosityRover-MethaneSource-20141216.png 2x" data-file-width="1440" data-file-height="1080" /></a><figcaption><a href="/wiki/Atmosphere_of_Mars#Methane" title="Atmosphere of Mars">Methane</a> (CH<sub>4</sub>) on Mars - potential sources and sinks.</figcaption></figure><p>The presence of methane in the <a href="/wiki/Atmosphere_of_Mars" title="Atmosphere of Mars">atmosphere of Mars</a> is an area of ongoing research and a highly contentious subject. Because of its tendency to be destroyed in the atmosphere by <a href="/wiki/Photochemistry" title="Photochemistry">photochemistry</a>, the presence of excess methane on a planet can indicate that there must be an active source. With life being the strongest source of methane on Earth, observing a disequilibrium in the methane abundance on another planet could be a viable biosignature.<sup id="cite_ref-:0_64-2" class="reference"><a href="#cite_note-:0-64"><span class="cite-bracket">[</span>64<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-:1_65-2" class="reference"><a href="#cite_note-:1-65"><span class="cite-bracket">[</span>65<span class="cite-bracket">]</span></a></sup> </p><p>Since 2004, there have been several detections of methane in the Mars atmosphere by a variety of instruments onboard orbiters and ground-based landers on the Martian surface as well as Earth-based telescopes.<sup id="cite_ref-77" class="reference"><a href="#cite_note-77"><span class="cite-bracket">[</span>77<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-78" class="reference"><a href="#cite_note-78"><span class="cite-bracket">[</span>78<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-auto_79-0" class="reference"><a href="#cite_note-auto-79"><span class="cite-bracket">[</span>79<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-80" class="reference"><a href="#cite_note-80"><span class="cite-bracket">[</span>80<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-81" class="reference"><a href="#cite_note-81"><span class="cite-bracket">[</span>81<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-82" class="reference"><a href="#cite_note-82"><span class="cite-bracket">[</span>82<span class="cite-bracket">]</span></a></sup> These missions reported values anywhere between a 'background level' ranging between 0.24 and 0.65 parts per billion by volume (p.p.b.v.)<sup id="cite_ref-83" class="reference"><a href="#cite_note-83"><span class="cite-bracket">[</span>83<span class="cite-bracket">]</span></a></sup> to as much as 45 ± 10 p.p.b.v.<sup id="cite_ref-auto_79-1" class="reference"><a href="#cite_note-auto-79"><span class="cite-bracket">[</span>79<span class="cite-bracket">]</span></a></sup> </p><p>However, recent measurements using the ACS and NOMAD instruments on board the ESA-Roscosmos ExoMars Trace Gas Orbiter have failed to detect any methane over a range of latitudes and longitudes on both Martian hemispheres. These highly sensitive instruments were able to put an upper bound on the overall methane abundance at 0.05 p.p.b.v.<sup id="cite_ref-84" class="reference"><a href="#cite_note-84"><span class="cite-bracket">[</span>84<span class="cite-bracket">]</span></a></sup> This nondetection is a major contradiction to what was previously observed with less sensitive instruments and will remain a strong argument in the ongoing debate over the presence of methane in the Martian atmosphere. </p><p>Furthermore, current photochemical models cannot explain the presence of methane in the atmosphere of Mars and its reported rapid variations in space and time.<sup id="cite_ref-Zahnle_2011_72-1" class="reference"><a href="#cite_note-Zahnle_2011-72"><span class="cite-bracket">[</span>72<span class="cite-bracket">]</span></a></sup> Neither its fast appearance nor disappearance can be explained yet.<sup id="cite_ref-85" class="reference"><a href="#cite_note-85"><span class="cite-bracket">[</span>85<span class="cite-bracket">]</span></a></sup> To rule out a biogenic origin for the methane, a future probe or lander hosting a <a href="/wiki/Mass_spectrometer" class="mw-redirect" title="Mass spectrometer">mass spectrometer</a> will be needed, as the isotopic proportions of <a href="/wiki/Carbon-12" title="Carbon-12">carbon-12</a> to <a href="/wiki/Carbon-14" title="Carbon-14">carbon-14</a> in methane could distinguish between a biogenic and non-biogenic origin, similarly to the use of the <a href="/wiki/%CE%9413C" title="Δ13C">δ13C</a> standard for recognizing biogenic methane on Earth.<sup id="cite_ref-nasa_86-0" class="reference"><a href="#cite_note-nasa-86"><span class="cite-bracket">[</span>86<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Martian_atmosphere">Martian atmosphere</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=20" title="Edit section: Martian atmosphere"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The Martian atmosphere contains high abundances of <a href="/wiki/Photochemistry" title="Photochemistry">photochemically</a> produced CO and H<sub>2</sub>, which are reducing molecules. Mars' atmosphere is otherwise mostly oxidizing, leading to a source of untapped energy that life could exploit if it used by a metabolism compatible with one or both of these reducing molecules. Because these molecules can be observed, scientists use this as evidence for an antibiosignature.<sup id="cite_ref-87" class="reference"><a href="#cite_note-87"><span class="cite-bracket">[</span>87<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-88" class="reference"><a href="#cite_note-88"><span class="cite-bracket">[</span>88<span class="cite-bracket">]</span></a></sup> Scientists have used this concept as an argument against life on Mars.<sup id="cite_ref-89" class="reference"><a href="#cite_note-89"><span class="cite-bracket">[</span>89<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Missions_inside_the_Solar_System">Missions inside the Solar System</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=21" title="Edit section: Missions inside the Solar System"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p><a href="/wiki/Astrobiology" title="Astrobiology">Astrobiological exploration</a> is founded upon the premise that biosignatures encountered in space will be recognizable as <a href="/wiki/Extraterrestrial_life" title="Extraterrestrial life">extraterrestrial life</a>. The usefulness of a biosignature is determined not only by the probability of life creating it but also by the improbability of non-biological (abiotic) processes producing it.<sup id="cite_ref-astrobiology_90-0" class="reference"><a href="#cite_note-astrobiology-90"><span class="cite-bracket">[</span>90<span class="cite-bracket">]</span></a></sup> Concluding that evidence of an extraterrestrial life form (past or present) has been discovered requires proving that a possible biosignature was produced by the activities or remains of life.<sup id="cite_ref-SSG_1-2" class="reference"><a href="#cite_note-SSG-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> As with most scientific discoveries, discovery of a biosignature will require evidence building up until no other explanation exists. </p><p>Possible examples of a biosignature include complex <a href="/wiki/Organic_compound" title="Organic compound">organic molecules</a> or structures whose formation is virtually unachievable in the absence of life:<sup id="cite_ref-astrobiology_90-1" class="reference"><a href="#cite_note-astrobiology-90"><span class="cite-bracket">[</span>90<span class="cite-bracket">]</span></a></sup> </p> <ol><li>Cellular and extracellular morphologies</li> <li><a href="/wiki/Biomolecule" title="Biomolecule">Biomolecules</a> in rocks</li> <li>Bio-organic molecular structures</li> <li><a href="/wiki/Chirality" title="Chirality">Chirality</a></li> <li><a href="/wiki/Biogenic_silica" title="Biogenic silica">Biogenic minerals</a></li> <li>Biogenic isotope patterns in minerals and organic compounds</li> <li>Atmospheric gases</li> <li><a href="/wiki/Photosynthetic_pigment" title="Photosynthetic pigment">Photosynthetic pigments</a></li></ol> <div class="mw-heading mw-heading3"><h3 id="The_Viking_missions_to_Mars">The <i>Viking</i> missions to Mars</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=22" title="Edit section: The Viking missions to Mars"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Viking_biological_experiments" class="mw-redirect" title="Viking biological experiments">Viking biological experiments</a></div> <p>The <a href="/wiki/Viking_Lander" class="mw-redirect" title="Viking Lander"><i>Viking</i> missions</a> to Mars in the 1970s conducted the first experiments which were explicitly designed to look for biosignatures on another planet. Each of the two <a href="/wiki/Viking_program" title="Viking program"><i>Viking</i> landers</a> carried three <a href="/wiki/Viking_Biological_Experiments" class="mw-redirect" title="Viking Biological Experiments">life-detection experiments</a> which looked for signs of <a href="/wiki/Metabolism" title="Metabolism">metabolism</a>; however, the results were declared inconclusive.<sup id="cite_ref-Beegle_22-1" class="reference"><a href="#cite_note-Beegle-22"><span class="cite-bracket">[</span>22<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-91" class="reference"><a href="#cite_note-91"><span class="cite-bracket">[</span>91<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Chambers_92-0" class="reference"><a href="#cite_note-Chambers-92"><span class="cite-bracket">[</span>92<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-93" class="reference"><a href="#cite_note-93"><span class="cite-bracket">[</span>93<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-ExoMars_94-0" class="reference"><a href="#cite_note-ExoMars-94"><span class="cite-bracket">[</span>94<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Mars_Science_Laboratory">Mars Science Laboratory</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=23" title="Edit section: Mars Science Laboratory"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Timeline_of_Mars_Science_Laboratory" title="Timeline of Mars Science Laboratory">Timeline of Mars Science Laboratory</a></div> <p>The <i>Curiosity</i> rover from the <a href="/wiki/Mars_Science_Laboratory" title="Mars Science Laboratory">Mars Science Laboratory</a> mission, with its <a href="/wiki/Curiosity_rover" class="mw-redirect" title="Curiosity rover"><i>Curiosity</i> rover</a> is currently assessing the potential past and present <a href="/wiki/Planetary_habitability" title="Planetary habitability">habitability</a> of the Martian environment and is attempting to detect biosignatures on the surface of Mars.<sup id="cite_ref-Biosignatures_2011_3-1" class="reference"><a href="#cite_note-Biosignatures_2011-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> Considering the MSL instrument payload package, the following classes of biosignatures are within the MSL detection window: organism morphologies (cells, body fossils, casts), biofabrics (including microbial mats), diagnostic organic molecules, isotopic signatures, evidence of biomineralization and bioalteration, spatial patterns in chemistry, and biogenic gases.<sup id="cite_ref-Biosignatures_2011_3-2" class="reference"><a href="#cite_note-Biosignatures_2011-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> The <i>Curiosity</i> rover targets <a href="/wiki/Outcrop" title="Outcrop">outcrops</a> to maximize the probability of detecting 'fossilized' <a href="/wiki/Organic_matter" title="Organic matter">organic matter</a> preserved in sedimentary deposits. </p> <div class="mw-heading mw-heading3"><h3 id="ExoMars_Orbiter">ExoMars Orbiter</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=24" title="Edit section: ExoMars Orbiter"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The 2016 ExoMars <a href="/wiki/Trace_Gas_Orbiter" title="Trace Gas Orbiter">Trace Gas Orbiter</a> (TGO) is a Mars telecommunications orbiter and atmospheric gas analyzer mission. It delivered the <a href="/wiki/Schiaparelli_EDM_lander" class="mw-redirect" title="Schiaparelli EDM lander"><i>Schiaparelli</i> EDM lander</a> and then began to settle into its science orbit to map the sources of <a href="/wiki/Atmosphere_of_Mars#Methane" title="Atmosphere of Mars">methane on Mars</a> and other gases, and in doing so, will help select the landing site for the <a href="/wiki/Rosalind_Franklin_(rover)" title="Rosalind Franklin (rover)"><i>Rosalind Franklin</i> rover</a> to be launched in 2022.<sup id="cite_ref-95" class="reference"><a href="#cite_note-95"><span class="cite-bracket">[</span>95<span class="cite-bracket">]</span></a></sup> The primary objective of the <i>Rosalind Franklin</i> rover mission is the search for biosignatures on the surface and subsurface by using a drill able to collect samples down to a depth of 2 metres (6.6 ft), away from the destructive radiation that bathes the surface.<sup id="cite_ref-ExoMars_94-1" class="reference"><a href="#cite_note-ExoMars-94"><span class="cite-bracket">[</span>94<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-MSL-main_page_96-0" class="reference"><a href="#cite_note-MSL-main_page-96"><span class="cite-bracket">[</span>96<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Mars_2020_Rover">Mars 2020 Rover</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=25" title="Edit section: Mars 2020 Rover"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The <a href="/wiki/Mars_2020" title="Mars 2020">Mars 2020</a> rover, which launched in 2020, is intended to investigate an <a href="/wiki/Astrobiology" title="Astrobiology">astrobiologically</a> relevant ancient environment on Mars, investigate its surface <a href="/wiki/Geology_of_Mars" title="Geology of Mars">geological processes</a> and history, including the assessment of its past <a href="/wiki/Planetary_habitability" title="Planetary habitability">habitability</a>, the possibility of past <a href="/wiki/Life_on_Mars" title="Life on Mars">life on Mars</a>, and potential for preservation of biosignatures within accessible geological materials.<sup id="cite_ref-AP-20130709_97-0" class="reference"><a href="#cite_note-AP-20130709-97"><span class="cite-bracket">[</span>97<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-nasa-letapp20121220_98-0" class="reference"><a href="#cite_note-nasa-letapp20121220-98"><span class="cite-bracket">[</span>98<span class="cite-bracket">]</span></a></sup> In addition, it will cache the most interesting samples for possible future transport to Earth. </p> <div class="mw-heading mw-heading3"><h3 id="Titan_Dragonfly">Titan <i>Dragonfly</i></h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=26" title="Edit section: Titan Dragonfly"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>NASA's <i><a href="/wiki/Dragonfly_(Titan_space_probe)" title="Dragonfly (Titan space probe)">Dragonfly</a></i><sup id="cite_ref-99" class="reference"><a href="#cite_note-99"><span class="cite-bracket">[</span>99<span class="cite-bracket">]</span></a></sup> lander/aircraft concept is proposed to launch in 2025 and would seek evidence of biosignatures on the organic-rich surface and atmosphere of <a href="/wiki/Titan_(moon)" title="Titan (moon)">Titan</a>, as well as study its possible prebiotic <a href="/wiki/Primordial_soup" title="Primordial soup">primordial soup</a>.<sup id="cite_ref-100" class="reference"><a href="#cite_note-100"><span class="cite-bracket">[</span>100<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-LPSC_2017_101-0" class="reference"><a href="#cite_note-LPSC_2017-101"><span class="cite-bracket">[</span>101<span class="cite-bracket">]</span></a></sup> Titan is the largest moon of <a href="/wiki/Saturn" title="Saturn">Saturn</a> and is widely believed to have a large subsurface ocean consisting of a salty brine.<sup id="cite_ref-102" class="reference"><a href="#cite_note-102"><span class="cite-bracket">[</span>102<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-103" class="reference"><a href="#cite_note-103"><span class="cite-bracket">[</span>103<span class="cite-bracket">]</span></a></sup> In addition, scientists believe that Titan may have the conditions necessary to promote <a href="/wiki/Prebiotic_(chemistry)" class="mw-redirect" title="Prebiotic (chemistry)">prebiotic</a> chemistry, making it a prime candidate for biosignature discovery.<sup id="cite_ref-104" class="reference"><a href="#cite_note-104"><span class="cite-bracket">[</span>104<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-105" class="reference"><a href="#cite_note-105"><span class="cite-bracket">[</span>105<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-106" class="reference"><a href="#cite_note-106"><span class="cite-bracket">[</span>106<span class="cite-bracket">]</span></a></sup> </p> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Life_on_Titan" title="Life on Titan">Life on Titan</a></div> <div class="mw-heading mw-heading3"><h3 id="Europa_Clipper"><i>Europa Clipper</i></h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=27" title="Edit section: Europa Clipper"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Europa_Clipper_spacecraft_model.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/5/59/Europa_Clipper_spacecraft_model.png/220px-Europa_Clipper_spacecraft_model.png" decoding="async" width="220" height="183" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/5/59/Europa_Clipper_spacecraft_model.png/330px-Europa_Clipper_spacecraft_model.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/5/59/Europa_Clipper_spacecraft_model.png/440px-Europa_Clipper_spacecraft_model.png 2x" data-file-width="5423" data-file-height="4500" /></a><figcaption><i>Europa Clipper</i></figcaption></figure> <p>NASA's <i><a href="/wiki/Europa_Clipper" title="Europa Clipper">Europa Clipper</a></i> probe is designed as a flyby mission to Jupiter's smallest <a href="/wiki/Galilean_moons" title="Galilean moons">Galilean moon</a>, <a href="/wiki/Europa_(moon)" title="Europa (moon)">Europa</a>.<sup id="cite_ref-107" class="reference"><a href="#cite_note-107"><span class="cite-bracket">[</span>107<span class="cite-bracket">]</span></a></sup> The mission launched in October 2024 and is set to reach Europa in April 2030, where it will investigate the potential for habitability on Europa. Europa is one of the best candidates for biosignature discovery in the <a href="/wiki/Solar_System" title="Solar System">Solar System</a> because of the scientific consensus that it retains a subsurface ocean, with two to three times the volume of water on Earth. Evidence for this subsurface ocean includes: </p> <ul><li><i><a href="/wiki/Voyager_1" title="Voyager 1">Voyager 1</a></i> (1979): The first close-up photos of Europa are taken. Scientists propose that a subsurface ocean could cause the tectonic-like marks on the surface.<sup id="cite_ref-108" class="reference"><a href="#cite_note-108"><span class="cite-bracket">[</span>108<span class="cite-bracket">]</span></a></sup></li> <li><i><a href="/wiki/Galileo_(spacecraft)" title="Galileo (spacecraft)">Galileo</a></i> (1997): The <a href="/wiki/Magnetometer" title="Magnetometer">magnetometer</a> aboard this probe detected a subtle change in the magnetic field near Europa. This was later interpreted as a disruption in the expected magnetic field due to the current induction in a conducting layer on Europa. The composition of this conducting layer is consistent with a salty subsurface ocean.<sup id="cite_ref-109" class="reference"><a href="#cite_note-109"><span class="cite-bracket">[</span>109<span class="cite-bracket">]</span></a></sup></li> <li><a href="/wiki/Hubble_Space_Telescope" title="Hubble Space Telescope">Hubble Space Telescope</a> (2012): An image was taken of Europa which showed evidence for a plume of water vapor coming off the surface.<sup id="cite_ref-110" class="reference"><a href="#cite_note-110"><span class="cite-bracket">[</span>110<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-111" class="reference"><a href="#cite_note-111"><span class="cite-bracket">[</span>111<span class="cite-bracket">]</span></a></sup></li></ul> <p>The <i>Europa Clipper</i> probe includes instruments to help confirm the existence and composition of a subsurface ocean and thick icy layer. In addition, the instruments will be used to map and study surface features that may indicate tectonic activity due to a subsurface ocean.<sup id="cite_ref-112" class="reference"><a href="#cite_note-112"><span class="cite-bracket">[</span>112<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Enceladus">Enceladus</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=28" title="Edit section: Enceladus"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Enceladus_geysers_June_2009.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/e/e6/Enceladus_geysers_June_2009.jpg/220px-Enceladus_geysers_June_2009.jpg" decoding="async" width="220" height="136" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/e6/Enceladus_geysers_June_2009.jpg/330px-Enceladus_geysers_June_2009.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/e/e6/Enceladus_geysers_June_2009.jpg/440px-Enceladus_geysers_June_2009.jpg 2x" data-file-width="1580" data-file-height="977" /></a><figcaption>An image of the plumes of water and ice coming from the surface of Enceladus. Future missions will investigate these geysers to determine the composition and look for signs of life.</figcaption></figure> <p>Although there are no set plans to search for biosignatures on <a href="/wiki/Saturn" title="Saturn">Saturn</a>'s sixth-largest moon, <a href="/wiki/Enceladus" title="Enceladus">Enceladus</a>, the prospects of biosignature discovery there are exciting enough to warrant several mission concepts that may be funded in the future. Similar to Jupiter's moon Europa, there is much evidence for a subsurface ocean to also exist on Enceladus. Plumes of water vapor were first observed in 2005 by the <a href="/wiki/Cassini%E2%80%93Huygens" title="Cassini–Huygens">Cassini</a> mission<sup id="cite_ref-113" class="reference"><a href="#cite_note-113"><span class="cite-bracket">[</span>113<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-114" class="reference"><a href="#cite_note-114"><span class="cite-bracket">[</span>114<span class="cite-bracket">]</span></a></sup> and were later determined to contain salt as well as organic compounds.<sup id="cite_ref-115" class="reference"><a href="#cite_note-115"><span class="cite-bracket">[</span>115<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-116" class="reference"><a href="#cite_note-116"><span class="cite-bracket">[</span>116<span class="cite-bracket">]</span></a></sup> In 2014, more evidence was presented using gravimetric measurements on Enceladus to conclude that there is in fact a large reservoir of water underneath an icy surface.<sup id="cite_ref-117" class="reference"><a href="#cite_note-117"><span class="cite-bracket">[</span>117<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-118" class="reference"><a href="#cite_note-118"><span class="cite-bracket">[</span>118<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-119" class="reference"><a href="#cite_note-119"><span class="cite-bracket">[</span>119<span class="cite-bracket">]</span></a></sup> Mission design concepts include: </p> <ul><li><a href="/wiki/Enceladus_Life_Finder" title="Enceladus Life Finder">Enceladus Life Finder</a> (ELF)<sup id="cite_ref-120" class="reference"><a href="#cite_note-120"><span class="cite-bracket">[</span>120<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-121" class="reference"><a href="#cite_note-121"><span class="cite-bracket">[</span>121<span class="cite-bracket">]</span></a></sup></li> <li><a href="/wiki/Enceladus_Life_Signatures_and_Habitability" title="Enceladus Life Signatures and Habitability">Enceladus Life Signatures and Habitability</a><sup id="cite_ref-122" class="reference"><a href="#cite_note-122"><span class="cite-bracket">[</span>122<span class="cite-bracket">]</span></a></sup></li> <li>Enceladus Organic Analyzer<sup id="cite_ref-123" class="reference"><a href="#cite_note-123"><span class="cite-bracket">[</span>123<span class="cite-bracket">]</span></a></sup></li> <li><a href="/wiki/Enceladus_Explorer" title="Enceladus Explorer">Enceladus Explorer</a> (En-Ex)<sup id="cite_ref-124" class="reference"><a href="#cite_note-124"><span class="cite-bracket">[</span>124<span class="cite-bracket">]</span></a></sup></li> <li><a href="/wiki/Explorer_of_Enceladus_and_Titan" title="Explorer of Enceladus and Titan">Explorer of Enceladus and Titan</a> (E<sup>2</sup>T)<sup id="cite_ref-125" class="reference"><a href="#cite_note-125"><span class="cite-bracket">[</span>125<span class="cite-bracket">]</span></a></sup></li> <li><a href="/wiki/Journey_to_Enceladus_and_Titan" title="Journey to Enceladus and Titan">Journey to Enceladus and Titan</a> (JET)<sup id="cite_ref-126" class="reference"><a href="#cite_note-126"><span class="cite-bracket">[</span>126<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-127" class="reference"><a href="#cite_note-127"><span class="cite-bracket">[</span>127<span class="cite-bracket">]</span></a></sup></li> <li><a href="/wiki/Life_Investigation_For_Enceladus" title="Life Investigation For Enceladus">Life Investigation For Enceladus</a> (LIFE)<sup id="cite_ref-128" class="reference"><a href="#cite_note-128"><span class="cite-bracket">[</span>128<span class="cite-bracket">]</span></a></sup></li> <li>Testing the Habitability of Enceladus's Ocean (<a href="/wiki/Testing_the_Habitability_of_Enceladus%27s_Ocean" class="mw-redirect" title="Testing the Habitability of Enceladus's Ocean">THEO</a>)<sup id="cite_ref-129" class="reference"><a href="#cite_note-129"><span class="cite-bracket">[</span>129<span class="cite-bracket">]</span></a></sup></li></ul> <p>All of these concept missions have similar science goals: To assess the habitability of Enceladus and search for biosignatures, in line with the strategic map for exploring the ocean-world Enceladus.<sup id="cite_ref-130" class="reference"><a href="#cite_note-130"><span class="cite-bracket">[</span>130<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Searching_outside_of_the_Solar_System">Searching outside of the Solar System</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=29" title="Edit section: Searching outside of the Solar System"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>At 4.2 <a href="/wiki/Light-year" title="Light-year">light-years</a> (1.3 <a href="/wiki/Parsec" title="Parsec">parsecs</a>, 40 trillion <a href="/wiki/Km" class="mw-redirect" title="Km">km</a>, or 25 trillion miles) away from Earth, the closest potentially habitable <a href="/wiki/Exoplanet" title="Exoplanet">exoplanet</a> is <a href="/wiki/Proxima_Centauri_b" title="Proxima Centauri b">Proxima Centauri b</a>, which was discovered in 2016.<sup id="cite_ref-proxima_b_discovery_paper_131-0" class="reference"><a href="#cite_note-proxima_b_discovery_paper-131"><span class="cite-bracket">[</span>131<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-132" class="reference"><a href="#cite_note-132"><span class="cite-bracket">[</span>132<span class="cite-bracket">]</span></a></sup> This means it would take more than 18,100 years to get there if a vessel could consistently travel as fast as the <i><a href="/wiki/Juno_(spacecraft)" title="Juno (spacecraft)">Juno</a></i> spacecraft (250,000 kilometers per hour or 150,000 miles per hour).<sup id="cite_ref-133" class="reference"><a href="#cite_note-133"><span class="cite-bracket">[</span>133<span class="cite-bracket">]</span></a></sup> It is currently not feasible to send humans or even probes to search for biosignatures outside of the Solar System. The only way to search for biosignatures outside of the <a href="/wiki/Solar_System" title="Solar System">Solar System</a> is by observing exoplanets with telescopes. </p><p>There have been no plausible or confirmed biosignature detections outside of the Solar System. Despite this, it is a rapidly growing field of research due to the prospects of the next generation of telescopes. The <a href="/wiki/James_Webb_Space_Telescope" title="James Webb Space Telescope">James Webb Space Telescope</a>, which launched in December 2021, will be a promising next step in the search for biosignatures. Although its wavelength range and resolution will not be compatible with some of the more important atmospheric biosignature gas bands like oxygen, it will still be able to detect some evidence for oxygen false positive mechanisms.<sup id="cite_ref-134" class="reference"><a href="#cite_note-134"><span class="cite-bracket">[</span>134<span class="cite-bracket">]</span></a></sup> </p><p>The new generation of ground-based 30-meter class telescopes (<a href="/wiki/Thirty_Meter_Telescope" title="Thirty Meter Telescope">Thirty Meter Telescope</a> and <a href="/wiki/Extremely_Large_Telescope" title="Extremely Large Telescope">Extremely Large Telescope</a>) will have the ability to take high-resolution spectra of exoplanet atmospheres at a variety of wavelengths.<sup id="cite_ref-135" class="reference"><a href="#cite_note-135"><span class="cite-bracket">[</span>135<span class="cite-bracket">]</span></a></sup> These telescopes will be capable of distinguishing some of the more difficult false positive mechanisms such as the abiotic buildup of oxygen via photolysis. In addition, their large collecting area will enable high angular resolution, making <a href="/wiki/Direct_imaging" class="mw-redirect" title="Direct imaging">direct imaging</a> studies more feasible. </p> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=30" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Bioindicator" title="Bioindicator">Bioindicator</a></li> <li><a href="/wiki/MERMOZ" title="MERMOZ">MERMOZ</a> (remote detection of lifeforms)</li> <li><a href="/wiki/Taphonomy" title="Taphonomy">Taphonomy</a></li> <li><a href="/wiki/Technosignature" title="Technosignature">Technosignature</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Biosignature&action=edit&section=31" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist"> <div class="mw-references-wrap mw-references-columns"><ol class="references"> <li id="cite_note-SSG-1"><span class="mw-cite-backlink">^ <a href="#cite_ref-SSG_1-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-SSG_1-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-SSG_1-2"><sup><i><b>c</b></i></sup></a></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite id="CITEREFSteeleBeaty2006" class="citation book cs1">Steele; Beaty; et al. 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"Micrometer-scale porosity as a biosignature in carbonate crusts". <i>Geology</i>. <b>32</b> (9): 781. <a href="/wiki/Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2004Geo....32..781B">2004Geo....32..781B</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1130%2FG20681.1">10.1130/G20681.1</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Geology&rft.atitle=Micrometer-scale+porosity+as+a+biosignature+in+carbonate+crusts&rft.volume=32&rft.issue=9&rft.pages=781&rft.date=2004&rft_id=info%3Adoi%2F10.1130%2FG20681.1&rft_id=info%3Abibcode%2F2004Geo....32..781B&rft.aulast=Bosak&rft.aufirst=Tanja&rft.au=Souza-Egipsy%2C+Virginia&rft.au=Corsetti%2C+Frank+A.&rft.au=Newman%2C+Dianne+K.&rfr_id=info%3Asid%2Fen.wikipedia.org%3ABiosignature" class="Z3988"></span></span> </li> <li id="cite_note-disbelief-24"><span class="mw-cite-backlink"><b><a href="#cite_ref-disbelief_24-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFCrenson2006" class="citation web cs1">Crenson M (2006-08-06). <a rel="nofollow" class="external text" href="https://www.usatoday.com/tech/science/space/2006-08-06-mars-life_x.htm">"After 10 years, few believe life on Mars"</a>. <a href="/wiki/Associated_Press" title="Associated Press">Associated Press</a> (on usatoday.com)<span class="reference-accessdate">. Retrieved <span class="nowrap">2009-12-06</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=After+10+years%2C+few+believe+life+on+Mars&rft.pub=Associated+Press+%28on+usatoday.com%29&rft.date=2006-08-06&rft.aulast=Crenson&rft.aufirst=Matt&rft_id=https%3A%2F%2Fwww.usatoday.com%2Ftech%2Fscience%2Fspace%2F2006-08-06-mars-life_x.htm&rfr_id=info%3Asid%2Fen.wikipedia.org%3ABiosignature" class="Z3988"></span></span> </li> <li id="cite_note-life-25"><span class="mw-cite-backlink">^ <a href="#cite_ref-life_25-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-life_25-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFMcKayGibsonThomas-KeprtaVali1996" class="citation journal cs1">McKay DS, Gibson EK, Thomas-Keprta KL, Vali H, Romanek CS, Clemett SJ, et al. (August 1996). "Search for past life on Mars: possible relic biogenic activity in martian meteorite ALH84001". <i>Science</i>. <b>273</b> (5277): 924–30. <a href="/wiki/Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/1996Sci...273..924M">1996Sci...273..924M</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1126%2Fscience.273.5277.924">10.1126/science.273.5277.924</a>. <a href="/wiki/PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/8688069">8688069</a>. <a href="/wiki/S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:40690489">40690489</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Science&rft.atitle=Search+for+past+life+on+Mars%3A+possible+relic+biogenic+activity+in+martian+meteorite+ALH84001&rft.volume=273&rft.issue=5277&rft.pages=924-30&rft.date=1996-08&rft_id=info%3Adoi%2F10.1126%2Fscience.273.5277.924&rft_id=https%3A%2F%2Fapi.semanticscholar.org%2FCorpusID%3A40690489%23id-name%3DS2CID&rft_id=info%3Apmid%2F8688069&rft_id=info%3Abibcode%2F1996Sci...273..924M&rft.aulast=McKay&rft.aufirst=DS&rft.au=Gibson%2C+EK&rft.au=Thomas-Keprta%2C+KL&rft.au=Vali%2C+H&rft.au=Romanek%2C+CS&rft.au=Clemett%2C+SJ&rft.au=Chillier%2C+XD&rft.au=Maechling%2C+CR&rft.au=Zare%2C+RN&rfr_id=info%3Asid%2Fen.wikipedia.org%3ABiosignature" class="Z3988"></span></span> </li> <li id="cite_note-26"><span class="mw-cite-backlink"><b><a href="#cite_ref-26">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFFriedmannWierzchosAscasoWinklhofer2001" class="citation journal cs1">Friedmann EI, Wierzchos J, Ascaso C, Winklhofer M (February 2001). <a rel="nofollow" class="external text" href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC30112">"Chains of magnetite crystals in the meteorite ALH84001: evidence of biological origin"</a>. <i>Proceedings of the National Academy of Sciences of the United States of America</i>. <b>98</b> (5): 2176–81. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://doi.org/10.1073%2Fpnas.051514698">10.1073/pnas.051514698</a></span>. <a href="/wiki/PMC_(identifier)" class="mw-redirect" title="PMC (identifier)">PMC</a> <span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC30112">30112</a></span>. <a href="/wiki/PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/11226212">11226212</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Proceedings+of+the+National+Academy+of+Sciences+of+the+United+States+of+America&rft.atitle=Chains+of+magnetite+crystals+in+the+meteorite+ALH84001%3A+evidence+of+biological+origin&rft.volume=98&rft.issue=5&rft.pages=2176-81&rft.date=2001-02&rft_id=https%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC30112%23id-name%3DPMC&rft_id=info%3Apmid%2F11226212&rft_id=info%3Adoi%2F10.1073%2Fpnas.051514698&rft.aulast=Friedmann&rft.aufirst=EI&rft.au=Wierzchos%2C+J&rft.au=Ascaso%2C+C&rft.au=Winklhofer%2C+M&rft_id=https%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC30112&rfr_id=info%3Asid%2Fen.wikipedia.org%3ABiosignature" class="Z3988"></span></span> </li> <li id="cite_note-27"><span class="mw-cite-backlink"><b><a href="#cite_ref-27">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFThomas-KeprtaClemettBazylinskiKirschvink2001" class="citation journal cs1">Thomas-Keprta KL, Clemett SJ, Bazylinski DA, Kirschvink JL, McKay DS, Wentworth SJ, et al. (February 2001). <a rel="nofollow" class="external text" href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC30110">"Truncated hexa-octahedral magnetite crystals in ALH84001: presumptive biosignatures"</a>. <i>Proceedings of the National Academy of Sciences of the United States of America</i>. <b>98</b> (5): 2164–9. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://doi.org/10.1073%2Fpnas.051500898">10.1073/pnas.051500898</a></span>. <a href="/wiki/PMC_(identifier)" class="mw-redirect" title="PMC (identifier)">PMC</a> <span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC30110">30110</a></span>. <a href="/wiki/PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/11226210">11226210</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Proceedings+of+the+National+Academy+of+Sciences+of+the+United+States+of+America&rft.atitle=Truncated+hexa-octahedral+magnetite+crystals+in+ALH84001%3A+presumptive+biosignatures&rft.volume=98&rft.issue=5&rft.pages=2164-9&rft.date=2001-02&rft_id=https%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC30110%23id-name%3DPMC&rft_id=info%3Apmid%2F11226210&rft_id=info%3Adoi%2F10.1073%2Fpnas.051500898&rft.aulast=Thomas-Keprta&rft.aufirst=KL&rft.au=Clemett%2C+SJ&rft.au=Bazylinski%2C+DA&rft.au=Kirschvink%2C+JL&rft.au=McKay%2C+DS&rft.au=Wentworth%2C+SJ&rft.au=Vali%2C+H&rft.au=Gibson%2C+EK&rft.au=McKay%2C+MF&rft.au=Romanek%2C+CS&rft_id=https%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC30110&rfr_id=info%3Asid%2Fen.wikipedia.org%3ABiosignature" class="Z3988"></span></span> </li> <li id="cite_note-28"><span class="mw-cite-backlink"><b><a href="#cite_ref-28">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFChoi2016" class="citation web cs1">Choi CQ (August 2016). <a rel="nofollow" class="external text" href="https://www.space.com/33690-allen-hills-mars-meteorite-alien-life-20-years.html">"Mars Life? 20 Years Later, Debate Over Meteorite Continues"</a>. <i>Space.com</i><span class="reference-accessdate">. Retrieved <span class="nowrap">2019-06-07</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Space.com&rft.atitle=Mars+Life%3F+20+Years+Later%2C+Debate+Over+Meteorite+Continues&rft.date=2016-08&rft.aulast=Choi&rft.aufirst=Charles+Q.&rft_id=https%3A%2F%2Fwww.space.com%2F33690-allen-hills-mars-meteorite-alien-life-20-years.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3ABiosignature" class="Z3988"></span></span> </li> <li id="cite_note-29"><span class="mw-cite-backlink"><b><a href="#cite_ref-29">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFMcSween2019" class="citation cs2">McSween HY (2019), "The Search for Biosignatures in Martian Meteorite Allan Hills 84001", in Cavalazzi B, Westall F (eds.), <i>Biosignatures for Astrobiology</i>, Advances in Astrobiology and Biogeophysics, Springer International Publishing, pp. 167–182, <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1007%2F978-3-319-96175-0_8">10.1007/978-3-319-96175-0_8</a>, <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-3-319-96175-0" title="Special:BookSources/978-3-319-96175-0"><bdi>978-3-319-96175-0</bdi></a>, <a href="/wiki/S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:186696892">186696892</a></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=bookitem&rft.atitle=The+Search+for+Biosignatures+in+Martian+Meteorite+Allan+Hills+84001&rft.btitle=Biosignatures+for+Astrobiology&rft.series=Advances+in+Astrobiology+and+Biogeophysics&rft.pages=167-182&rft.pub=Springer+International+Publishing&rft.date=2019&rft_id=https%3A%2F%2Fapi.semanticscholar.org%2FCorpusID%3A186696892%23id-name%3DS2CID&rft_id=info%3Adoi%2F10.1007%2F978-3-319-96175-0_8&rft.isbn=978-3-319-96175-0&rft.aulast=McSween&rft.aufirst=Harry+Y.&rfr_id=info%3Asid%2Fen.wikipedia.org%3ABiosignature" class="Z3988"></span></span> </li> <li id="cite_note-morphology-30"><span class="mw-cite-backlink">^ <a href="#cite_ref-morphology_30-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-morphology_30-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFGarcia-Ruiz1999" class="citation book cs1 cs1-prop-long-vol">Garcia-Ruiz JM (December 30, 1999). "Morphological behavior of inorganic precipitation systems". In Hoover RB (ed.). <i>Instruments, Methods, and Missions for Astrobiology II</i>. 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NASA. Archived from <a rel="nofollow" class="external text" href="http://astrobiology.ucla.edu/pages/res3e.html">the original</a> on 23 January 2013<span class="reference-accessdate">. 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"Exoplanet Atmospheres and Giant Ground-Based Telescopes". <a href="/wiki/ArXiv_(identifier)" class="mw-redirect" title="ArXiv (identifier)">arXiv</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://arxiv.org/abs/1604.06458v1">1604.06458v1</a></span> [<a rel="nofollow" class="external text" href="https://arxiv.org/archive/astro-ph.IM">astro-ph.IM</a>].</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=preprint&rft.jtitle=arXiv&rft.atitle=Exoplanet+Atmospheres+and+Giant+Ground-Based+Telescopes&rft.date=2016-04-21&rft_id=info%3Aarxiv%2F1604.06458v1&rft.aulast=Crossfield&rft.aufirst=IJ&rfr_id=info%3Asid%2Fen.wikipedia.org%3ABiosignature" class="Z3988"></span></span> </li> </ol></div></div> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><style data-mw-deduplicate="TemplateStyles:r1236075235">.mw-parser-output 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planet">Ocean planet</a></li> <li><a href="/wiki/Panspermia" title="Panspermia">Panspermia</a></li> <li><a href="/wiki/Planetary_protection" title="Planetary protection">Planetary protection</a></li> <li><a href="/wiki/Search_for_extraterrestrial_intelligence" title="Search for extraterrestrial intelligence">Search for extraterrestrial intelligence (SETI)</a></li> <li><a href="/wiki/Yamato_000593" title="Yamato 000593">Yamato meteorite</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="text-align: center;;width:1%"><a href="/wiki/Planetary_habitability" title="Planetary habitability">Planetary<br />habitability</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Circumstellar_habitable_zone" class="mw-redirect" title="Circumstellar habitable zone">Circumstellar habitable zone</a></li> <li><a href="/wiki/Earth_analog" title="Earth analog">Earth analog</a></li> <li><a href="/wiki/Extraterrestrial_liquid_water" title="Extraterrestrial liquid water">Extraterrestrial liquid water</a></li> <li><a href="/wiki/Galactic_habitable_zone" title="Galactic habitable zone">Galactic habitable zone</a></li> <li><a href="/wiki/Habitability_of_binary_star_systems" title="Habitability of binary star systems">Habitability of binary star systems</a></li> <li><a href="/wiki/Habitability_of_natural_satellites" title="Habitability of natural satellites">Habitability of natural satellites</a></li> <li><a href="/wiki/Habitability_of_neutron_star_systems" title="Habitability of neutron star systems">Habitability of neutron star systems</a></li> <li><a href="/wiki/Habitability_of_red_dwarf_systems" title="Habitability of red dwarf systems">Habitability of red dwarf systems</a></li> <li><a href="/wiki/Habitability_of_K-type_main-sequence_star_systems" title="Habitability of K-type main-sequence star systems">Habitability of K-type main-sequence star systems</a></li> <li><a href="/wiki/Habitability_of_yellow_dwarf_systems" title="Habitability of yellow dwarf systems">Habitability of yellow dwarf systems</a></li> <li><a href="/wiki/Habitability_of_F-type_main-sequence_star_systems" title="Habitability of F-type main-sequence star systems">Habitability of F-type main-sequence star systems</a></li> <li><a href="/wiki/Habitable_zone_for_complex_life" title="Habitable zone for complex life">Habitable zone for complex life</a></li> <li><a href="/wiki/List_of_potentially_habitable_exoplanets" title="List of potentially habitable exoplanets">List of potentially habitable exoplanets</a></li> <li><a href="/wiki/Tholin" title="Tholin">Tholin</a></li> <li><a href="/wiki/Superhabitable_planet" class="mw-redirect" title="Superhabitable planet">Superhabitable planet</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="text-align: center;;width:1%">Space<br /> missions</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%;text-align: center;">Earth orbit</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Space_Flyer_Unit#Experimentation_data" title="Space Flyer Unit">BIO</a></li> <li><a href="/wiki/Apollo_17#Biological_cosmic_ray_experiment" title="Apollo 17">BIOCORE</a></li> <li><a href="/wiki/Biolab" title="Biolab">Biolab</a></li> <li><a href="/wiki/Bion_(satellite)" title="Bion (satellite)">Bion</a></li> <li><a href="/wiki/BIOPAN" title="BIOPAN">BIOPAN</a></li> <li><a href="/wiki/Biosatellite_program" title="Biosatellite program">Biosatellite program</a></li> <li><a href="/wiki/Exposing_Microorganisms_in_the_Stratosphere" title="Exposing Microorganisms in the Stratosphere">E-MIST</a></li> <li><a href="/wiki/Exobiology_Radiation_Assembly" title="Exobiology Radiation Assembly">ERA</a></li> <li><a href="/wiki/EuCROPIS" title="EuCROPIS">Eu:CROPIS</a></li> <li><a href="/wiki/Long_Duration_Exposure_Facility#EXOSTACK" title="Long Duration Exposure Facility">EXOSTACK</a></li> <li><a href="/wiki/EXPOSE" title="EXPOSE">EXPOSE</a></li> <li><a href="/wiki/Chang%27e_4#Lunar_lander" title="Chang'e 4">Lunar Micro Ecosystem</a></li> <li><a href="/wiki/O/OREOS" title="O/OREOS">O/OREOS</a></li> <li><a href="/wiki/OREOcube" title="OREOcube">OREOcube</a></li> <li><a href="/wiki/Tanpopo_(mission)" class="mw-redirect" title="Tanpopo (mission)">Tanpopo</a></li> <li><a href="/wiki/Vegetable_Production_System" title="Vegetable Production System">VEGGIE</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align: center;">Mars</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Beagle_2" title="Beagle 2">Beagle 2</a></li> <li><a href="/wiki/Fobos-Grunt" title="Fobos-Grunt">Fobos-Grunt</a></li> <li><a href="/wiki/Mars_Science_Laboratory" title="Mars Science Laboratory">Mars Science Laboratory</a> <ul><li><a href="/wiki/Curiosity_(rover)" title="Curiosity (rover)"><i>Curiosity</i> rover</a></li></ul></li> <li><a href="/wiki/Mars_2020" title="Mars 2020">Mars 2020</a> <ul><li><a href="/wiki/Perseverance_(rover)" title="Perseverance (rover)"><i>Perseverance</i> rover</a></li></ul></li> <li><i><a href="/wiki/Phoenix_(spacecraft)" title="Phoenix (spacecraft)">Phoenix</a></i></li> <li><a href="/wiki/Tianwen-1" title="Tianwen-1">Tianwen-1</a> <ul><li><a href="/wiki/Zhurong_(rover)" title="Zhurong (rover)"><i>Zhurong</i> rover</a></li></ul></li> <li><a href="/wiki/Trace_Gas_Orbiter" title="Trace Gas Orbiter">Trace Gas Orbiter</a></li> <li><a href="/wiki/Viking_lander_biological_experiments" title="Viking lander biological experiments">Viking</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align: center;">Comets and<br />asteroids</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><i><a href="/wiki/Hayabusa2" title="Hayabusa2">Hayabusa2</a></i></li> <li><a href="/wiki/OSIRIS-REx" title="OSIRIS-REx">OSIRIS-REx</a></li> <li><i><a href="/wiki/Rosetta_(spacecraft)" title="Rosetta (spacecraft)">Rosetta</a></i></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align: center;">Heliocentric</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/BioSentinel" title="BioSentinel">BioSentinel</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align: center;">Planned</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><i><a href="/wiki/Dragonfly_(Titan_space_probe)" title="Dragonfly (Titan space probe)">Dragonfly</a></i></li> <li><a href="/wiki/Europa_Clipper" title="Europa Clipper">Europa Clipper</a></li> <li><a href="/wiki/ExoMars" title="ExoMars">ExoMars</a> <ul><li><a href="/wiki/Rosalind_Franklin_(rover)" title="Rosalind Franklin (rover)"><i>Rosalind Franklin</i> rover</a></li></ul></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align: center;">Proposed</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Breakthrough_Enceladus_mission" title="Breakthrough Enceladus mission">Breakthrough Enceladus</a></li> <li><a href="/wiki/BRUIE" title="BRUIE">BRUIE</a></li> <li><a href="/wiki/CAESAR_(spacecraft)" title="CAESAR (spacecraft)">CAESAR</a></li> <li><a href="/wiki/Enceladus_Explorer" title="Enceladus Explorer">Enceladus Explorer</a></li> <li><a href="/wiki/Enceladus_Life_Finder" title="Enceladus Life Finder">Enceladus Life Finder‎</a></li> <li><a href="/wiki/Enceladus_Life_Signatures_and_Habitability" title="Enceladus Life Signatures and Habitability">Enceladus Life Signatures and Habitability</a></li> <li><a href="/wiki/Enceladus_Orbilander" title="Enceladus Orbilander">Enceladus Orbilander</a></li> <li><a href="/wiki/Europa_Lander_(NASA)" class="mw-redirect" title="Europa Lander (NASA)">Europa Lander</a></li> <li><a href="/wiki/ExoLance" title="ExoLance">ExoLance</a></li> <li><a href="/wiki/Explorer_of_Enceladus_and_Titan" title="Explorer of Enceladus and Titan">Explorer of Enceladus and Titan</a></li> <li><a href="/wiki/Icebreaker_Life" title="Icebreaker Life">Icebreaker Life</a></li> <li><a href="/wiki/Journey_to_Enceladus_and_Titan" title="Journey to Enceladus and Titan">Journey to Enceladus and Titan</a></li> <li><a href="/wiki/Laplace-P" title="Laplace-P">Laplace-P</a></li> <li><a href="/wiki/Life_Investigation_For_Enceladus" title="Life Investigation For Enceladus">Life Investigation For Enceladus</a></li> <li><a href="/wiki/Mars_sample_return_mission" class="mw-redirect" title="Mars sample return mission">Mars sample return mission</a></li> <li><a href="/wiki/Oceanus_(Titan_orbiter)" title="Oceanus (Titan orbiter)">Oceanus</a></li> <li><a href="/wiki/THEO" title="THEO">THEO</a></li> <li><a href="/wiki/Trident_(spacecraft)" title="Trident (spacecraft)">Trident</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align: center;">Cancelled and <br />undeveloped</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Astrobiology_Field_Laboratory" title="Astrobiology Field Laboratory">Astrobiology Field Laboratory</a></li> <li><a href="/wiki/Beagle_3" title="Beagle 3">Beagle 3</a></li> <li><a href="/wiki/Biological_Oxidant_and_Life_Detection" title="Biological Oxidant and Life Detection">Biological Oxidant and Life Detection</a></li> <li><a href="/wiki/Kazachok" title="Kazachok">Kazachok</a></li> <li><a href="/wiki/Living_Interplanetary_Flight_Experiment" title="Living Interplanetary Flight Experiment">Living Interplanetary Flight Experiment</a></li> <li><a href="/wiki/Mars_Astrobiology_Explorer-Cacher" title="Mars Astrobiology Explorer-Cacher">Mars Astrobiology Explorer-Cacher</a></li> <li><a href="/wiki/MELOS" title="MELOS">MELOS</a></li> <li><a href="/wiki/Northern_Light_(spacecraft)" title="Northern Light (spacecraft)">Northern Light</a></li> <li><a href="/wiki/SpaceX_Red_Dragon" title="SpaceX Red Dragon">Red Dragon</a></li> <li><a href="/wiki/Terrestrial_Planet_Finder" title="Terrestrial Planet Finder">Terrestrial Planet Finder</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="text-align: center;;width:1%">Institutions<br />and programs</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Astrobiology_Society_of_Britain" title="Astrobiology Society of Britain">Astrobiology Society of Britain</a></li> <li><a href="/wiki/Astrobiology_Science_and_Technology_for_Exploring_Planets" title="Astrobiology Science and Technology for Exploring Planets">Astrobiology Science and Technology for Exploring Planets</a></li> <li><a href="/wiki/Breakthrough_Initiatives" title="Breakthrough Initiatives">Breakthrough Initiatives</a> <ul><li><a href="/wiki/Breakthrough_Listen" title="Breakthrough Listen">Breakthrough Listen</a></li> <li><a href="/wiki/Breakthrough_Message" class="mw-redirect" title="Breakthrough Message">Breakthrough Message</a></li> <li><a href="/wiki/Breakthrough_Starshot" title="Breakthrough Starshot">Breakthrough Starshot</a></li></ul></li> <li><a href="/wiki/Carl_Sagan_Institute" title="Carl Sagan Institute">Carl Sagan Institute</a></li> <li><a href="/wiki/Center_for_Life_Detection_Science" class="mw-redirect" title="Center for Life Detection Science">Center for Life Detection Science</a></li> <li><a href="/wiki/European_Astrobiology_Network_Association" title="European Astrobiology Network Association">European Astrobiology Network Association</a></li> <li><a href="/wiki/MERMOZ" title="MERMOZ">MERMOZ</a></li> <li><a href="/wiki/NASA_Astrobiology_Institute" title="NASA Astrobiology Institute">NASA Astrobiology Institute</a></li> <li><a href="/wiki/Nexus_for_Exoplanet_System_Science" title="Nexus for Exoplanet System Science">Nexus for Exoplanet System Science</a></li> <li><a href="/wiki/Ocean_Worlds_Exploration_Program" title="Ocean Worlds Exploration Program">Ocean Worlds Exploration Program</a></li> <li><a href="/wiki/Spanish_Astrobiology_Center" title="Spanish Astrobiology Center">Spanish Astrobiology Center‎</a></li></ul> </div></td></tr><tr><td class="navbox-abovebelow" colspan="2" style="text-align: center;"><div> <ul><li><span class="noviewer" typeof="mw:File"><span title="Category"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/16px-Symbol_category_class.svg.png" decoding="async" width="16" height="16" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/23px-Symbol_category_class.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/31px-Symbol_category_class.svg.png 2x" data-file-width="180" data-file-height="185" /></span></span> <b><a href="/wiki/Category:Astrobiology" title="Category:Astrobiology">Category</a></b></li> <li><span class="noviewer" typeof="mw:File"><span title="Commons page"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/12px-Commons-logo.svg.png" decoding="async" width="12" height="16" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/18px-Commons-logo.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/24px-Commons-logo.svg.png 2x" data-file-width="1024" data-file-height="1376" /></span></span> <b><a href="https://commons.wikimedia.org/wiki/Category:Astrobiology" class="extiw" title="commons:Category:Astrobiology">Commons</a></b></li></ul> </div></td></tr></tbody></table></div> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236075235"></div><div role="navigation" class="navbox" aria-labelledby="Extraterrestrial_life" style="padding:3px"><table class="nowraplinks mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2" style="text-align: center;"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239400231"><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Extraterrestrial_life" title="Template:Extraterrestrial life"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Extraterrestrial_life" title="Template talk:Extraterrestrial life"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Extraterrestrial_life" title="Special:EditPage/Template:Extraterrestrial life"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Extraterrestrial_life" style="font-size:114%;margin:0 4em"><a href="/wiki/Extraterrestrial_life" title="Extraterrestrial life">Extraterrestrial life</a></div></th></tr><tr><th scope="row" class="navbox-group" style="text-align: center;;width:1%">Events and objects</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Shergotty_meteorite" title="Shergotty meteorite">Shergotty meteorite</a> (1865)</li> <li><a href="/wiki/Nakhla_meteorite" title="Nakhla meteorite">Nakhla meteorite</a> (1911)</li> <li><a href="/wiki/Murchison_meteorite" title="Murchison meteorite">Murchison meteorite</a> (1969)</li> <li><a href="/wiki/Viking_lander_biological_experiments" title="Viking lander biological experiments">Viking lander biological experiments</a> (1976)</li> <li><a href="/wiki/Allan_Hills_77005" title="Allan Hills 77005">Allan Hills 77005</a> (1977)</li> <li><a href="/wiki/Allan_Hills_84001" title="Allan Hills 84001">Allan Hills 84001</a> (1984)</li> <li><a href="/wiki/Yamato_000593" title="Yamato 000593">Yamato 000593</a> (2000)</li> <li><a href="/wiki/CI1_fossils" title="CI1 fossils">CI1 fossils</a> (2011)</li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="text-align: center;;width:1%">Signals of interest</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%;text-align: center;">Misidentified</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/PSR_B1919%2B21" title="PSR B1919+21">CP 1919</a> <span style="font-size:85%;">(misidentified pulsar)</span></li> <li><a href="/wiki/CTA-102" title="CTA-102">CTA-102</a> <span style="font-size:85%;">(misidentified quasar)</span></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align: center;">Stars</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Tabby%27s_Star" title="Tabby's Star">KIC 8462852</a> <span style="font-size:85%;">(unusual light fluctuations)</span></li> <li><a href="/wiki/EPIC_204278916" title="EPIC 204278916">EPIC 204278916</a> <span style="font-size:85%;">(unusual light fluctuations)</span></li> <li><a href="/wiki/VVV-WIT-07" title="VVV-WIT-07">VVV-WIT-07</a> <span style="font-size:85%;">(unusual light fluctuations)</span></li> <li><a href="/wiki/HD_164595" title="HD 164595">HD 164595 signal</a> <span style="font-size:85%;">(unknown origin)</span></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align: center;">Other</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/SHGb02%2B14a" title="SHGb02+14a">SHGb02+14a</a> <span style="font-size:85%;">(radio source)</span></li> <li><a href="/wiki/Wow!_signal" title="Wow! signal">Wow! signal</a> <span style="font-size:85%;">(inconclusive)</span></li> <li><a href="/wiki/Fast_radio_burst" title="Fast radio burst">Fast radio burst</a> <span style="font-size:85%;">(unknown origin)</span></li> <li><a href="/wiki/BLC1" title="BLC1">BLC1</a> <span style="font-size:85%;">(radio signal)</span></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="text-align: center;;width:1%">Life in the Universe</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Earliest_known_life_forms" title="Earliest known life forms">Earliest known life forms</a></li> <li><a href="/wiki/Planetary_habitability_in_the_Solar_System" title="Planetary habitability in the Solar System">Planetary habitability in the Solar System</a></li> <li><a href="/wiki/Life_on_Venus" title="Life on Venus">Life on Venus</a></li> <li><a href="/wiki/Life_on_Mars" title="Life on Mars">Life on Mars</a></li> <li><a href="/wiki/Life_on_Titan" title="Life on Titan">Life on Titan</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="text-align: center;;width:1%"><a href="/wiki/Planetary_habitability" title="Planetary habitability">Planetary<br />habitability</a></th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Catalog_of_Nearby_Habitable_Systems" title="Catalog of Nearby Habitable Systems">Catalog of Nearby Habitable Systems</a></li> <li><a href="/wiki/Circumstellar_habitable_zone" class="mw-redirect" title="Circumstellar habitable zone">Circumstellar habitable zone</a></li> <li><a href="/wiki/Earth_analog" title="Earth analog">Earth analog</a></li> <li><a href="/wiki/Extraterrestrial_liquid_water" title="Extraterrestrial liquid water">Extraterrestrial liquid water</a></li> <li><a href="/wiki/Galactic_habitable_zone" title="Galactic habitable zone">Galactic habitable zone</a></li> <li><a href="/wiki/Habitability_of_binary_star_systems" title="Habitability of binary star systems">Habitability of binary star systems</a></li> <li><a href="/wiki/Habitability_of_natural_satellites" title="Habitability of natural satellites">Habitability of natural satellites</a></li> <li><a href="/wiki/Habitability_of_neutron_star_systems" title="Habitability of neutron star systems">Habitability of neutron star systems</a></li> <li><a href="/wiki/Habitability_of_red_dwarf_systems" title="Habitability of red dwarf systems">Habitability of red dwarf systems</a></li> <li><a href="/wiki/Habitability_of_K-type_main-sequence_star_systems" title="Habitability of K-type main-sequence star systems">Habitability of K-type main-sequence star systems</a></li> <li><a href="/wiki/Habitability_of_yellow_dwarf_systems" title="Habitability of yellow dwarf systems">Habitability of yellow dwarf systems</a></li> <li><a href="/wiki/Habitability_of_F-type_main-sequence_star_systems" title="Habitability of F-type main-sequence star systems">Habitability of F-type main-sequence star systems</a></li> <li><a href="/wiki/List_of_potentially_habitable_exoplanets" title="List of potentially habitable exoplanets">List of potentially habitable exoplanets</a></li> <li><a href="/wiki/Planetary_habitability" title="Planetary habitability">Planetary habitability</a></li> <li><a href="/wiki/Superhabitable_planet" class="mw-redirect" title="Superhabitable planet">Superhabitable planet</a></li> <li><a href="/wiki/Tholin" title="Tholin">Tholin</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="text-align: center;;width:1%"><a href="/wiki/Astrobiology#Missions" title="Astrobiology">Space missions</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Beagle_2" title="Beagle 2">Beagle 2</a></li> <li><a href="/wiki/Biological_Oxidant_and_Life_Detection" title="Biological Oxidant and Life Detection">Biological Oxidant and Life Detection</a></li> <li><a href="/wiki/BioSentinel" title="BioSentinel">BioSentinel</a></li> <li><a href="/wiki/Curiosity_(rover)" title="Curiosity (rover)"><i>Curiosity</i> rover</a></li> <li><i><a href="/wiki/Darwin_(spacecraft)" title="Darwin (spacecraft)">Darwin</a></i></li> <li><i><a href="/wiki/Dragonfly_(Titan_space_probe)" title="Dragonfly (Titan space probe)">Dragonfly</a></i></li> <li><a href="/wiki/Enceladus_Explorer" title="Enceladus Explorer">Enceladus Explorer</a></li> <li><a href="/wiki/Enceladus_Life_Finder" title="Enceladus Life Finder">Enceladus Life Finder</a></li> <li><i><a href="/wiki/Europa_Clipper" title="Europa Clipper">Europa Clipper</a></i></li> <li><a href="/wiki/ExoMars" title="ExoMars">ExoMars</a> <ul><li><a href="/wiki/Rosalind_Franklin_(rover)" title="Rosalind Franklin (rover)"><i>Rosalind Franklin</i> rover</a></li></ul></li> <li><a href="/wiki/ExoLance" title="ExoLance">ExoLance</a></li> <li><a href="/wiki/EXPOSE" title="EXPOSE">EXPOSE</a></li> <li><a href="/wiki/Foton-M" class="mw-redirect" title="Foton-M">Foton-M3</a></li> <li><a href="/wiki/Icebreaker_Life" title="Icebreaker Life">Icebreaker Life</a></li> <li><a href="/wiki/Journey_to_Enceladus_and_Titan" title="Journey to Enceladus and Titan">Journey to Enceladus and Titan</a></li> <li><a href="/wiki/Laplace-P" title="Laplace-P">Laplace-P</a></li> <li><a href="/wiki/Life_Investigation_For_Enceladus" title="Life Investigation For Enceladus">Life Investigation For Enceladus</a></li> <li><a href="/wiki/Living_Interplanetary_Flight_Experiment" title="Living Interplanetary Flight Experiment">Living Interplanetary Flight Experiment</a></li> <li><a href="/wiki/Mars_Geyser_Hopper" title="Mars Geyser Hopper">Mars Geyser Hopper</a></li> <li><a href="/wiki/Mars_sample-return_mission" title="Mars sample-return mission">Mars sample-return mission</a></li> <li><a href="/wiki/Mars_2020" title="Mars 2020">Mars 2020</a></li> <li><a href="/wiki/Northern_Light_(spacecraft)" title="Northern Light (spacecraft)">Northern Light</a></li> <li><a href="/wiki/Opportunity_(rover)" title="Opportunity (rover)"><i>Opportunity</i> rover</a></li> <li><a href="/wiki/Perseverance_(rover)" title="Perseverance (rover)"><i>Perseverance</i> rover</a></li> <li><a href="/wiki/SpaceX_Red_Dragon" title="SpaceX Red Dragon">SpaceX Red Dragon</a></li> <li><a href="/wiki/Spirit_(rover)" title="Spirit (rover)"><i>Spirit</i> rover</a></li> <li><a href="/wiki/Tanpopo_mission" title="Tanpopo mission">Tanpopo</a></li> <li><a href="/wiki/Titan_Mare_Explorer" title="Titan Mare Explorer">Titan Mare Explorer</a></li> <li><a href="/wiki/Venus_In_Situ_Explorer" title="Venus In Situ Explorer">Venus In Situ Explorer</a></li> <li><i><a href="/wiki/Viking_1" title="Viking 1">Viking 1</a></i></li> <li><i><a href="/wiki/Viking_2" title="Viking 2">Viking 2</a></i></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="text-align: center;;width:1%"><a href="/wiki/Interstellar_communication" title="Interstellar communication">Interstellar<br />communication</a></th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Active_SETI" title="Active SETI">Active SETI</a></li> <li><a href="/wiki/Allen_Telescope_Array" title="Allen Telescope Array">Allen Telescope Array</a></li> <li><a href="/wiki/Arecibo_message" title="Arecibo message">Arecibo message</a></li> <li><a href="/wiki/Arecibo_Observatory" title="Arecibo Observatory">Arecibo Observatory</a></li> <li><a href="/wiki/Berkeley_SETI_Research_Center" title="Berkeley SETI Research Center">Berkeley SETI Research Center</a></li> <li><a href="/wiki/Bracewell_probe" title="Bracewell probe">Bracewell probe</a></li> <li><a href="/wiki/Breakthrough_Initiatives" title="Breakthrough Initiatives">Breakthrough Initiatives</a> <ul><li><a href="/wiki/Breakthrough_Listen" title="Breakthrough Listen">Breakthrough Listen</a></li> <li><a href="/wiki/Breakthrough_Message" class="mw-redirect" title="Breakthrough Message">Breakthrough Message</a></li></ul></li> <li><a href="/wiki/Communication_with_extraterrestrial_intelligence" title="Communication with extraterrestrial intelligence">Communication with extraterrestrial intelligence</a></li> <li><a href="/wiki/Gauss%27s_Pythagorean_right_triangle_proposal" title="Gauss's Pythagorean right triangle proposal">Gauss's Pythagorean right triangle proposal</a></li> <li><a href="/wiki/Astrolinguistics" title="Astrolinguistics">Astrolinguistics</a></li> <li><a href="/wiki/Lincos_language" title="Lincos language">Lincos language</a></li> <li><a href="/wiki/NIROSETI" title="NIROSETI">NIROSETI</a></li> <li><a href="/wiki/Pioneer_plaque" title="Pioneer plaque">Pioneer plaque</a></li> <li><a href="/wiki/Project_Cyclops" title="Project Cyclops">Project Cyclops</a></li> <li><a href="/wiki/Project_Ozma" title="Project Ozma">Project Ozma</a></li> <li><a href="/wiki/Project_Phoenix_(SETI)" title="Project Phoenix (SETI)">Project Phoenix</a></li> <li><a href="/wiki/SERENDIP" title="SERENDIP">SERENDIP</a></li> <li><a href="/wiki/Search_for_extraterrestrial_intelligence" title="Search for extraterrestrial intelligence">Search for extraterrestrial intelligence</a></li> <li><a href="/wiki/SETI@home" title="SETI@home">SETI@home</a></li> <li><a href="/wiki/SetiQuest" title="SetiQuest">setiQuest</a></li> <li><a href="/wiki/Voyager_Golden_Record" title="Voyager Golden Record">Voyager Golden Record</a></li> <li><a href="/wiki/Water_hole_(radio)" title="Water hole (radio)">Water hole</a></li> <li><a href="/wiki/Alien_language" title="Alien language">Xenolinguistics</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="text-align: center;;width:1%"><a href="/wiki/List_of_alleged_extraterrestrial_beings" title="List of alleged extraterrestrial beings">Types of alleged<br /> extraterrestrial beings</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Energy_being" title="Energy being">Energy beings</a></li> <li><a href="/wiki/Grey_alien" title="Grey alien">Grey aliens</a></li> <li><a href="/wiki/Insectoids_in_science_fiction" class="mw-redirect" title="Insectoids in science fiction">Insectoids</a></li> <li><a href="/wiki/Little_green_men" title="Little green men">Little green men</a></li> <li><a href="/wiki/Nordic_aliens" title="Nordic aliens">Nordic aliens</a></li> <li><a href="/wiki/Reptilian_humanoid" title="Reptilian humanoid">Reptilian humanoids</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="text-align: center;;width:1%">Hypotheses</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Cosmic_pluralism" title="Cosmic pluralism">Cosmic pluralism</a></li> <li><a href="/wiki/Directed_panspermia" title="Directed panspermia">Directed panspermia</a></li> <li><a href="/wiki/Drake_equation" title="Drake equation">Drake equation</a></li> <li><a href="/wiki/Extraterrestrial_hypothesis" class="mw-redirect" title="Extraterrestrial hypothesis">Extraterrestrial hypothesis</a></li> <li><a href="/wiki/Fermi_paradox" title="Fermi paradox">Fermi paradox</a></li> <li><a href="/wiki/Hypothetical_types_of_biochemistry" title="Hypothetical types of biochemistry">Hypothetical types of biochemistry</a></li> <li><a href="/wiki/Interplanetary_contamination" title="Interplanetary contamination">Interplanetary contamination</a></li> <li><a href="/wiki/Kardashev_scale" title="Kardashev scale">Kardashev scale</a></li> <li><a href="/wiki/Mediocrity_principle" title="Mediocrity principle">Mediocrity principle</a></li> <li><a href="/wiki/Panspermia" title="Panspermia">Panspermia</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="text-align: center;;width:1%"><a href="/wiki/Fermi_paradox" title="Fermi paradox">Fermi paradox</a> solutions</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Aestivation_hypothesis" title="Aestivation hypothesis">Aestivation hypothesis</a></li> <li><a href="/wiki/Berserker_hypothesis" title="Berserker hypothesis">Berserker hypothesis</a></li> <li><a href="/wiki/Dark_forest_hypothesis" title="Dark forest hypothesis">Dark forest hypothesis</a></li> <li><a href="/wiki/Firstborn_hypothesis" title="Firstborn hypothesis">Firstborn hypothesis</a></li> <li><a href="/wiki/Great_Filter" title="Great Filter">Great Filter</a></li> <li><a href="/wiki/Hart%E2%80%93Tipler_conjecture" title="Hart–Tipler conjecture">Hart–Tipler conjecture</a></li> <li><a href="/wiki/Neocatastrophism" title="Neocatastrophism">Neocatastrophism</a></li> <li><a href="/wiki/Planetarium_hypothesis" title="Planetarium hypothesis">Planetarium hypothesis</a></li> <li><a href="/wiki/Rare_Earth_hypothesis" title="Rare Earth hypothesis">Rare Earth hypothesis</a></li> <li><a href="/wiki/Zoo_hypothesis" title="Zoo hypothesis">Zoo hypothesis</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="text-align: center;;width:1%"><a href="/wiki/Outline_of_extraterrestrial_life" title="Outline of extraterrestrial life">Related topics</a></th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Ancient_astronauts" title="Ancient astronauts">Ancient astronauts</a></li> <li><a href="/wiki/Astrobiology" title="Astrobiology">Astrobiology</a></li> <li><a href="/wiki/Astroecology" title="Astroecology">Astroecology</a></li> <li><a class="mw-selflink selflink">Biosignature</a></li> <li><a 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