CINXE.COM

<!DOCTYPE html><html lang="en-US"><head><title>Just a moment...</title><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=Edge"><meta name="robots" content="noindex,nofollow"><meta name="viewport" content="width=device-width,initial-scale=1"><style>*{box-sizing:border-box;margin:0;padding:0}html{line-height:1.15;-webkit-text-size-adjust:100%;color:#313131;font-family:system-ui,-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Helvetica Neue,Arial,Noto Sans,sans-serif,Apple Color Emoji,Segoe UI Emoji,Segoe UI Symbol,Noto Color Emoji}body{display:flex;flex-direction:column;height:100vh;min-height:100vh}.main-content{margin:8rem auto;max-width:60rem;padding-left:1.5rem}@media (width <= 720px){.main-content{margin-top:4rem}}.h2{font-size:1.5rem;font-weight:500;line-height:2.25rem}@media (width <= 720px){.h2{font-size:1.25rem;line-height:1.5rem}}#challenge-error-text{background-image:url(data:image/svg+xml;base64,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);background-repeat:no-repeat;background-size:contain;padding-left:34px}@media (prefers-color-scheme:dark){body{background-color:#222;color:#d9d9d9}}</style><meta http-equiv="refresh" content="120"></head><body class="no-js"><div class="main-wrapper" role="main"><div class="main-content"><noscript><div class="h2"><span id="challenge-error-text">Enable JavaScript and cookies to continue</span></div></noscript></div></div><script>(function(){window._cf_chl_opt={cvId: '3',cZone: "www.annualreviews.org",cType: 'non-interactive',cRay: '91380f10edb0f8fb',cH: 'batSQyA7dxvOVM6k6N1BwhyjtT_K0w8Cv2GvpbU9rhM-1739819230-1.2.1.1-3qcPILjFMKlOAG7KIKY4nkOgTkT2YY8qCi8N2siLiLUVCQFHsnTFnCO97N9JQiIS',cUPMDTk: "\/doi\/10.1146\/annurev.astro.35.1.309?__cf_chl_tk=TDzJNRYgkaYnAPq5XNQbjC.uyi5HdSyMR9II4qGBTHA-1739819230-1.0.1.1-SlEDnwYnHQifAmS3j7ZSWXfUOSdy1QP9.H52vLBQT6E",cFPWv: 'g',cITimeS: '1739819230',cTTimeMs: '1000',cMTimeMs: '120000',cTplC: 0,cTplV: 5,cTplB: 'cf',cK: "",fa: "\/doi\/10.1146\/annurev.astro.35.1.309?__cf_chl_f_tk=TDzJNRYgkaYnAPq5XNQbjC.uyi5HdSyMR9II4qGBTHA-1739819230-1.0.1.1-SlEDnwYnHQifAmS3j7ZSWXfUOSdy1QP9.H52vLBQT6E",md: "_BriugE2IuN2l.2WfGxT1D7tFd3iNSqmDKPdtf45Kqs-1739819230-1.2.1.1-adZhjiW4wUtOcB5TYv0kQ7kO.2NOxBrHVfQWIfJ8kANxF9C8t_JkOZUulga4xr_a4enY8F5oUckHf0UIdI0jcVdWZGU29bcvHlVz_3HlmlcrgOerp_XbIp56a82JjU2tFT5Xv_U7rjMKpMXVgS9tsNvd2AG2F2tKwvAvUbaIIvOmoBn1RKR2a4MLR3BaMpl0.0lox52zTMpde_hN31CC_Xrni98XQTEtQq6Hm.NyeR5R6sfa99t_uNwDloWGT3nAOKcEgQ1ucy0K2i3jkXVEheLOdziYQPZUeROg.Tj4kIIT7CuNo6lLP9Y2nzkrDmDyXtzqBD7mrRDG9SY1rQFnyaSDaPr_ikbHnUtVugYm4M0EiS9QV9a5E4AMfOnmoSpvgckcfiN6wm3YRhUqVajYRg4RFQewuLtSW1ddOIIX4jw0IKAt127YZb3wnrc6DMuGlKRK.E5Nr5BT7HTSnD6vNswiv6JDsnFg.2G9OVnYXoSrxIUoFPXaCc8O1EgqEt66wABj.Eq2D0lmvggrhqOE90UBvdBAZlNXJGMv7bE0Eq2AOsOqR53hQRfjR0HQ0tQdVpQ97hbub0lWIyZJ0fuC8hlaSnhGbJM8NTm3hW052DotKlncrTfftz.rjf1GQb19H4UNemVi5vx22RIGwcOFzBprLIMFnVkC3VLBtS0SswRgeTbMwQsccNAUqdV1MwvycXo2ST_HQ8RiHtKft7BtcOkLE7WJ_ZxVBBJxcbx97_9JGDE_lRyLJBpay7nie7lZ_.fsZ7tRioPh3IU_.U7f0ePFioH0cpNaVzlcaB7bbSz2KuP4YMO64heaL5EU5xLvq3ow5f5l40wH7_Xb25dporSei15.p0idyzddFMiX.Kh5Uw0ZF1fXd_G0pcqttRWo1x.h5C1u2dATZpTswvr7T1okJyF8Nqlu0K68bJKnnPrmbUJg65i35_zNDBnn3vxLRXDXdaMCkeqzcz7mxDl7UZkTXc_YtNMXReO6VnyYguuvwekKNls1m3lw91_Kw_B0aFY3v82enb73Q_Yjf_Vnhta9j8UxNdF4RKTx.LZK9AXng1G3By.szDjMIAH4f4rcI0DUvzIyH._qaG26kYWBoHl8KSpXQ.MhYkSVAtzJEjpbT6_vZ_E5ncZWN5N52yZWLI2iY1RlPh.PAuZZrBiV9zBKXB0d_o.Suv6QAmk96zyOjt2wTNWdO.dkf481tob1OF18ZpRoAzmR9RkfCn9BPJAlK1aBbkki7MnKs_3uh9uaSAFaBsWTJXXCOuQTLNJKS0ujHPnoihkcZr0M.jJHfcIeEqhjxG1ji5npvEpri8P9YR8AGP0xOR97sv_LR7ahdhscGc98F2xRhAWl14yJm8BeY5cihNBBvrGjjexmPOurwEsBQguoLN4c5IMk0eMSMgM9dfxnP0htODTRKGmogdVkmN0LhJPXto3Z.0UkUKAGIfppGx7AzR2T8KQU43fBcmnulwXHj57hQP_Ru_OK2rRUusWY7xBQMN.u_vSgfZNzBasl1QPUnkUMmzch2oqnUwoXAk1tWTsJAUO1L_PU0pvwfODK4mKivibAMmk1S0QrPfOMYk.Ruk0ypH0rYfeQE0xpLXEhHmaRHiIN4qPSrmINAObluKS3wRD.3vZxVYzrDGeYNqxmojcugI0C3ejRmhvLvm2GWM5xTYmSoIuNKyPFHG_zNyh30Wugh0VdcFnSJFo2wgTWVkWOWb9tBhwvk440NHJ_Fzx.Of.M3tcI2Wz7uXQLdfEVJY65UgUVza16NsOO0tfdPs0Ypdo_2LeEKC_6HGm2YwWzi223B8DPfGzzWgCg0Zm4aD5lkL3pVzw",mdrd: "6lO60amxC.rkw00oGGTcVx.rEnDzcGBa1P.FtBry1Kc-1739819230-1.2.1.1-7ZDqrzgvB5VLGKwv0WYuoEOxuYjcE09cLF.oUuxgCJT2CgYXbaJ6OW2RXK5ecECcU.Z7qALcfQUgicSFBivymuV7gr4rupmUjzf3RuW6RyeUHUD2QXHCaeQ9RFQYaeBUIzzx_wLkkv0MxAZ13vHMTxEVQPwQ__omxYmGvz02yMeZBaBUOWzEJJ1VC9Vs4mumNyxNaoo.ekVtxT_yc0zlTVob2yd9PU7YKf_I3PqYSmhCaSZkAfKfnkx1y4oG0rzNDDmxignopxWgaUX67TytBOUnX9ZOiUdBHXlMhLqdB4XncVBDO1_OdiQ7gt7oBg9iyAjWBxNytHWYVP30Jh8JiM9UroEC5EevAKFj4QlPm5lrVLH5u7oMc1s5r9XqMlIkKUDqxAyHjXPrqAewFRS9dNug9Kom5BHSVborMxKf7GcN8v4wQzUhNKgDz2WjLDgLGYRp00wT4jnXXp6rErsr0yzey4m7n9jYP_xWc.BUtuE0TBlAq0wqB8GApqqzvRNM9Yy9Te5T2H_tHF5nmfxWuMW35WXb5XBa3IAmONKJG24VhM9pPHeU4S6SPWMie2Smpe8l4AfBJ8_UXjpeVkVupzwPtAmLqUqmJRdPchpzK5ioZhoV_CSjPI9jBl7HGQV5PMXE3_6AUHWy0W4i9.igFrFj3nfoRo3V59Fi8jNQoYifv9A.orHuD0bf.4O1bbAWhGDHmaI7k1oIXfRB.3mOiOm1S8sWCfhcLc3_wNsmy5qzH4fym4Wks5yGM_YGAY9Van1dWh5pxCjJ06Kx_vGLlqSy2FbgIrowGpzX.XGG0pfe3dQMKB6Vl9glnleThdgUmjearYGr82eHdOI0S8YFJnbfnNnNCkYmZQCUpA1A1bIdD0zIXqT.jWFEZC2FC9nLZQWD5_67rhLdUkjD8SLm6ecxGjEFj63muBWtNxaGLMmbs1o.j9L2AYdLhMpfz2AOLbG33YJWdd46dRzYYBsTuJ31eAK8qcP8w7jM1WIkPly4Qv2b1i2c83x3usJxHO5xRq.DT4GO8gdIsMBBE3ZDGBLBG5c.3W9FeYgYH67enCwhWCsrTJToYnlWuOCZndrTjOZUBrCkO1yEY9a0z2cCF3VuOSwY1Xw96aCOOEHaOLv2BN5r9FH0_Z.UFtC64f3mNlqYX8xmde._g0KkX.2z_nhR6dvYjc9lVKBJ1EqQ_XfZYGzOFy65S.SCZEk4.2tXrkYyhtW.y83eqPLU2oAhIki6oERIhvt1NyPm_JbCWJQGZhfnLfMoLT573dyMRDMl23rB.GJRnGMMOsUKcYkSW0Y_UlMqYFFjwvpqcWO40jo_v.D4pxu8J.tjNOHKH2UZeKKSOE0n7awHF4K8bCkg6wzRGojRquo5jJ6y0C5IOxiGnAXi1PFban1pmT_ewNuVwSHp2kIcTd56TNK9kgmgFVO1E.0Fd0M9E7MPQBR2gxVymuscopE.fTVNZoBMMc5sOaLBjtB1xRVdO6Y2DOaBzhR3LJZvTRCTIGdLPrbUt5PYMkN4sKyNqFYcwasT1ijBs6Mnuch_wuZaOJd.FMHYiGA.E_Kc3VpOjWhlhgEZN4GRIN0pHWMIkB_BXDFh2BQrTigWPvHkfBonL1hVEfnTEMA3fMGAGigUflVtZN6XRymyrbFzyFus6G4s0V3MrXPI1bVmiy2KdJqs.m9ccFWWn1atVoR3ecdzAOANPTxXtBQ3_K8DXkAfwj83Sr142nKSwUd9xEwtVzVSn4IutwBT2_r4S5PGm1BVq_H7X7R3smrXt.Ga9TG5R7aZm1d7aEH87yiHhzD0Qc.4pg1.FxgkUXPKQaZDPjmJhP0UuqLx0XS7e1ohQGHVosMP25kpF9lMMdXgVvHT9Ev30D8f8o.xwH5Bm599Dps3XEW_wteoE0n39f9LkE2WbjOazicN7KXi17bRFEBlTY7mVbVsXXsjGRtDewydFKr7ZRwm0DgvcI6NtLcpkAGBi_d58BcRXkIcNUnXLj0A0F9LOqcKTb1EsA"};var cpo = document.createElement('script');cpo.src = '/cdn-cgi/challenge-platform/h/g/orchestrate/chl_page/v1?ray=91380f10edb0f8fb';window._cf_chl_opt.cOgUHash = location.hash === '' && location.href.indexOf('#') !== -1 ? '#' : location.hash;window._cf_chl_opt.cOgUQuery = location.search === '' && location.href.slice(0, location.href.length - window._cf_chl_opt.cOgUHash.length).indexOf('?') !== -1 ? '?' : location.search;if (window.history && window.history.replaceState) {var ogU = location.pathname + window._cf_chl_opt.cOgUQuery + window._cf_chl_opt.cOgUHash;history.replaceState(null, null, "\/doi\/10.1146\/annurev.astro.35.1.309?__cf_chl_rt_tk=TDzJNRYgkaYnAPq5XNQbjC.uyi5HdSyMR9II4qGBTHA-1739819230-1.0.1.1-SlEDnwYnHQifAmS3j7ZSWXfUOSdy1QP9.H52vLBQT6E" + window._cf_chl_opt.cOgUHash);cpo.onload = function() {history.replaceState(null, null, ogU);}}document.getElementsByTagName('head')[0].appendChild(cpo);}());</script></body></html>