Editing Solar System (section)

=== Past ===
[[File:Soot-line1.jpg|thumb|upright=1.35|Diagram of the early Solar System's [[protoplanetary disk]], out of which Earth and other Solar System bodies formed]]
The Solar System formed at least 4.568&nbsp;billion years ago from the gravitational collapse of a region within a large [[molecular cloud]].{{Refn|name=AgeSolarSystem|group=lower-alpha|The date is based on the oldest [[inclusion (mineral)|inclusions]] found to date in [[meteorite]]s, {{Val|4568.2|+0.2|-0.4}} million years, and is thought to be the date of the formation of the first solid material in the collapsing nebula.<ref>{{Cite journal |last1=Bouvier |first1=A. |last2=Wadhwa |first2=M. |author-link2=Meenakshi Wadhwa |year=2010 |title=The age of the Solar System redefined by the oldest Pb–Pb age of a meteoritic inclusion |journal=Nature Geoscience |volume=3 |issue=9 |pages= 637–641 |bibcode=2010NatGe...3..637B |doi=10.1038/NGEO941 |s2cid=56092512}}</ref>}} This initial cloud was likely several light-years across and probably birthed several stars.<ref name="Arizona">{{Cite web |last=Zabludoff |first=Ann |title= Lecture 13: The Nebular Theory of the origin of the Solar System |url=http://atropos.as.arizona.edu/aiz/teaching/nats102/mario/solar_system.html |url-status=live |archive-url=https://archive.today/20120710135114/http://atropos.as.arizona.edu/aiz/teaching/nats102/mario/solar_system.html |archive-date=10 July 2012 |access-date=27 December 2006 |website=NATS 102: The Physical Universe |publisher=University of Arizona}}</ref> As is typical of molecular clouds, this one consisted mostly of hydrogen, with some helium, and small amounts of heavier elements [[Nuclear fusion|fused]] by previous generations of stars.<ref name=":3" />

As the [[Presolar nebula|pre-solar nebula]]<ref name=":3">{{Cite conference |last=Irvine |first=W. M. |date=1983 |title= The chemical composition of the pre-solar nebula |volume=1 |pages=3 |bibcode= 1983coex....1....3I |book-title=Cometary exploration; Proceedings of the International Conference}}</ref> collapsed, [[conservation of angular momentum]] caused it to rotate faster. The center, where most of the mass collected, became increasingly hotter than the surroundings.<ref name="Arizona" /> As the contracting nebula spun faster, it began to flatten into a [[protoplanetary disc]] with a diameter of roughly {{val|200|u=AU}}<ref name="Arizona" /><ref>{{cite journal | title=Embedded Protostellar Disks Around (Sub-)Solar Stars. II. Disk Masses, Sizes, Densities, Temperatures, and the Planet Formation Perspective | last=Vorobyov | first=Eduard I. | journal=The Astrophysical Journal | volume=729 | issue=2 | at=id. 146 | date=March 2011 | doi=10.1088/0004-637X/729/2/146 | arxiv=1101.3090 | bibcode=2011ApJ...729..146V | quote=estimates of disk radii in the Taurus and Ophiuchus star forming regions lie in a wide range between 50 AU and 1000 AU, with a median value of 200 AU.}}</ref> and a hot, dense [[protostar]] at the center.<ref>{{Cite journal |last=Greaves |first=Jane S. |date=7 January 2005 |title=Disks Around Stars and the Growth of Planetary Systems |journal=[[Science (journal)|Science]] |volume=307 |issue=5706 |pages=68–71 |bibcode=2005Sci...307...68G |doi=10.1126/science.1101979 |pmid=15637266 |s2cid=27720602}}</ref><ref>{{Cite book |publisher= Space Studies Board, Committee on Planetary and Lunar Exploration, National Research Council, Division on Engineering and Physical Sciences, National Academies Press |title=Strategy for the Detection and Study of Other Planetary Systems and Extrasolar Planetary Materials: 1990–2000 |date=1990 |isbn=978-0309041935 |publication-place=Washington D.C. |pages=21–33 |chapter=3. Present Understanding of the Origin of Planetary Systems |access-date=9 April 2022 |chapter-url=https://books.google.com/books?id=y56pS7SJs_8C&pg=PT29 |archive-url=https://web.archive.org/web/20220409211803/https://books.google.com/books?id=y56pS7SJs_8C&pg=PT29&lpg=PT29 |archive-date=9 April 2022 |url-status=live}}</ref> The planets formed by [[accretion (astrophysics)|accretion]] from this disc,<ref>{{Cite journal |last1=Boss |first1=A. P. |last2=Durisen |first2=R. H. |date=2005 |title=Chondrule-forming Shock Fronts in the Solar Nebula: A Possible Unified Scenario for Planet and Chondrite Formation |journal=[[The Astrophysical Journal]] |volume=621 |issue=2 |page=L137 |arxiv=astro-ph/0501592 |bibcode=2005ApJ...621L.137B |doi=10.1086/429160 |s2cid=15244154}}</ref> in which dust and gas gravitationally attracted each other, coalescing to form ever larger bodies. Hundreds of protoplanets may have existed in the early Solar System, but they either merged or were destroyed or ejected, leaving the planets, dwarf planets, and leftover [[small Solar System body|minor bodies]].<ref name="bennett_8.2" /><ref>{{Cite book |last1=Nagasawa |first1=M. |title=Protostars and Planets V |last2=Thommes |first2=E. W. |last3=Kenyon |first3=S. J. |last4=Bromley |first4=B. C. |last5=Lin |first5=D. N. C. |date=2007 | display-authors = 3 |publisher=University of Arizona Press |editor-last=Reipurth |editor-first=B. |publication-place=Tucson |pages=639–654 |chapter=The Diverse Origins of Terrestrial-Planet Systems |bibcode= 2007prpl.conf..639N |access-date=10 April 2022 |editor-last2=Jewitt |editor-first2=D. |editor-last3=Keil |editor-first3=K. |chapter-url=https://jila.colorado.edu/~pja/astr5820/nagasawa.pdf |archive-url=https://web.archive.org/web/20220412010025/https://jila.colorado.edu/~pja/astr5820/nagasawa.pdf |archive-date=12 April 2022 |url-status=live}}</ref>

Due to their higher boiling points, only metals and silicates could exist in solid form in the warm inner Solar System close to the Sun (within the [[Frost line (astrophysics)|frost line]]). They eventually formed the rocky planets of Mercury, Venus, Earth, and Mars. Because these [[Refractory (planetary science)|refractory]] materials only comprised a small fraction of the solar nebula, the terrestrial planets could not grow very large.<ref name="bennett_8.2" />

The giant planets (Jupiter, Saturn, Uranus, and Neptune) formed further out, beyond the frost line, the point between the orbits of Mars and Jupiter where material is cool enough for [[Volatile (astrogeology)|volatile]] icy compounds to remain solid. The ices that formed these planets were more plentiful than the metals and silicates that formed the terrestrial inner planets, allowing them to grow massive enough to capture large atmospheres of hydrogen and helium, the lightest and most abundant elements.<ref name="bennett_8.2" /> Leftover debris that never became planets congregated in regions such as the asteroid belt, Kuiper belt, and Oort cloud.<ref name="bennett_8.2">{{Cite book |last=Bennett |first=Jeffrey O. |title=The cosmic perspective |date=2020 |publisher=Pearson |isbn= 978-0-134-87436-4 |edition=9th |location=Hoboken, New Jersey |chapter= Chapter 8.2}}</ref>

Within 50&nbsp;million years, the pressure and density of hydrogen in the center of the protostar became great enough for it to begin [[nuclear fusion|thermonuclear fusion]].<ref name="Yi2001">{{Cite journal |last1=Yi |first1=Sukyoung |last2=Demarque |first2=Pierre |last3=Kim |first3=Yong-Cheol |last4=Lee |first4=Young-Wook |last5=Ree |first5=Chang H. |last6=Lejeune |first6=Thibault |last7=Barnes |first7= Sydney | display-authors = 3| date=2001 |title=Toward Better Age Estimates for Stellar Populations: The ''Y''<sup>2</sup> Isochrones for Solar Mixture |journal= [[Astrophysical Journal Supplement]] |volume=136 |issue=2 |pages=417–437 |arxiv=astro-ph/0104292 |bibcode= 2001ApJS..136..417Y |doi=10.1086/321795 |s2cid=118940644}}</ref> As helium accumulates at its core, the Sun is growing brighter;<ref name=":4">{{Cite journal |last=Gough |first=D. O. |date=November 1981 |title=Solar Interior Structure and Luminosity Variations |journal=Solar Physics |volume=74 |issue=1 |pages=21–34 |bibcode=1981SoPh...74...21G |doi= 10.1007/BF00151270 |s2cid=120541081}}</ref> early in its main-sequence life its brightness was 70% that of what it is today.<ref>{{Cite journal |last=Shaviv |first=Nir J. |date=2003 |title=Towards a Solution to the Early Faint Sun Paradox: A Lower Cosmic Ray Flux from a Stronger Solar Wind |journal= [[Journal of Geophysical Research]] |volume=108 |issue=A12 |page=1437 |arxiv=astroph/0306477 |bibcode= 2003JGRA..108.1437S |doi= 10.1029/2003JA009997 |s2cid= 11148141}}</ref> The temperature, [[Nuclear reaction rate|reaction rate]], pressure, and density increased until [[hydrostatic equilibrium]] was achieved: the thermal pressure counterbalancing the force of gravity. At this point, the Sun became a [[main sequence|main-sequence]] star.<ref>{{Cite journal |last1= Chrysostomou |first1=A. |last2=Lucas |first2=P. W. |date=2005 |title=The Formation of Stars |journal= [[Contemporary Physics]] |volume=46 |issue=1 |pages=29–40 |bibcode= 2005ConPh..46...29C |doi= 10.1080/0010751042000275277 |s2cid= 120275197}}</ref> Solar wind from the Sun created the [[heliosphere]] and swept away the remaining gas and dust from the protoplanetary disc into interstellar space.<ref name=":4" />

Following the dissipation of the [[protoplanetary disk]], the [[Nice model]] proposes that [[Gravity assist|gravitational encounters]] between planetisimals and the gas giants caused each to [[Planetary migration|migrate]] into different orbits. This led to dynamical instability of the entire system, which scattered the planetisimals and ultimately placed the gas giants in their current positions. During this period, the [[grand tack hypothesis]] suggests that a final inward migration of Jupiter dispersed much of the asteroid belt, leading to the [[Late Heavy Bombardment]] of the inner planets.<ref>{{cite journal | title=Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets | last1=Gomes | first1=R. | last2=Levison | first2=H. F. | last3=Tsiganis | first3=K. | last4=Morbidelli | first4=A. | journal=Nature | year=2005 | volume=435 | pages=466–469 | doi=10.1038/nature03676 | pmid=15917802 | issue=7041 | bibcode=2005Natur.435..466G | doi-access=free }}</ref><ref>{{cite book | last=Crida | first=A. | chapter=Solar System Formation | date=2009 | title=Reviews in Modern Astronomy: Formation and Evolution of Cosmic Structures | volume=21 | pages=215–227 | arxiv=0903.3008 | bibcode= 2009RvMA...21..215C | doi=10.1002/9783527629190.ch12 | isbn=9783527629190 | s2cid=118414100 }}</ref>