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Image: NASA, STScI, JHU, UCO/Lick, the ACS Science Team and ESA)</p> </div><script type="text/javascript"></script></div> <div id="related"> <h3>Related Stories</h3> <ul> <li><a href="/science/articles/2004/10/20/1223881.htm">Planets form in a messy muddle</a>, Science Online, 20 Oct 2004</li> <li><a href="/science/articles/2005/03/21/1328218.htm">Cool answer to planet formation</a>, Science Online, 21 Mar 2005</li> </ul> </div> </div> <p class="first">Gaps in the dusty discs surrounding newborn stars seem the key to how planets form, scientists say.</p> <p>They've used a new 3D model, the first of its type to include information about both gas and dust in the proto-planetary disc, to predict what happens.</p> <p>The Australian, French and Swiss scientists will publish their findings in the journal <a href="http://www.aanda.org/" target="_blank"><I>Astronomy and Astrophysics</I></a>.</p> <p>Dr Sarah Maddison, from the <a href="http://astronomy.swinburne.edu.au/" target="_blank">Centre for Astrophysics and Supercomputing</a> at <a href="http://www.swinburne.edu.au/" target="_blank">Swinburne University</a>, and colleagues show that as dust grains stick together and grow into bigger chunks, they attract smaller nearby particles with their gravitational pull.</p> <p>This sweeps the surrounding area clean, forming a gap, in much the same way as gaps form in Saturn's rings.</p> <p>"That turns out to be very important to what happens next," Maddison says. </p> <p>This gap stops the migration of dust and gas into the centre of the disc.</p> <p>Gas cannot cross the gap and dust tends to build up at the edge, perhaps facilitating the growth of a second planet.</p> <p>"Our simulations show is that once we've formed one planet, what happens to the dust in the disc can retard or enhance the further growth of planets," says Maddison.</p> <p><b>It's a drag</b></p> <p>The simulations also show that, because of 'dust drag', the size of the dust grains can be a critical factor in the planet-building process.</p> <p>"With micron-sized dust grains, the drag is very high, so the whole disc is quickly brought into equilibrium and you end up with a large slow-moving disc and long evolutionary time scales: nothing happens for millions of years," says Maddison.</p> <p>With big boulder-sized grains, there's much less drag and the gas and the dust can completely decouple, she says.</p> <p>When that happens, the boulders can end up just bouncing up and down in the midplane of the gas disc and there may be no further evolution. </p> <p>"But somewhere in the middle we've got the Goldilocks 'just right' sized grains and the gas and dust start to become very interesting," she says.</p> <p><b>Let's talk about dust</b></p> <p>Maddison and colleagues from the <a href="http://www-obs.univ-lyon1.fr/" target="_blank">Centre for Astrophysics Research</a> in Lyon, the <a href="http://www.ethz.ch/index_EN" target="_blank">Swiss Federal Institute of Technology Zurich</a> and Swinburne, used a new computer code to give a 3D picture of both the gas and dust in proto-planetary discs.</p> <p>Previously, scientists have relied on 2D simulations of the gas component only and have had to make assumptions about what happens to the dust. </p> <p>"Being able to see what is happening edge-on in the vertical profile has made all the difference," Maddison says.</p> <p class="tags"><strong>Tags: </strong><a href="/science/tag/browse.htm?site=science&topic=latest&tag=science-and-technology">science-and-technology</a>, <a href="/science/tag/browse.htm?site=science&topic=latest&tag=astronomy-space">astronomy-space</a>, <a href="/science/tag/browse.htm?site=science&topic=latest&tag=computers-and-technology">computers-and-technology</a></p>  <div class="clear"></div> <div id="artShareLinks"> <p class="right"><a href="/science/contact/?contact=newsinscience" class="editor" title="Contact the News in Science editor"><span class="email i16"></span>Email the editor</a></p> <ul 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Scientists plug gap in how planets form › News in Science (ABC Science)