Editing Solar System (section)

===Evolution of the Solar System===
[[File:Lunar cataclysm.jpg|thumb|upright=1.1|Artist's impression of the [[Moon]] during the Late Heavy Bombardment (above) and today (below)]]
One of the most important steps in the Solar System's history was the clearing of the [[protoplanetary disk]]. This was the spinning cloud of gas and dust around the young Sun where planets were forming. As the [[Sun]] got older and became a full [[main-sequence star]], it started sending out strong [[solar wind]]s, streams of tiny, charged particles. It also gave off intense [[Ultraviolet|ultraviolet radiation]]. Together, these forces began to blow away the leftover gas and dust in the disk. This process is called [[photoevaporation]]. Photoevaporation was especially strong in the inner part of the Solar System, where the Sun's [[heat]] and [[light]] were most powerful.<ref>{{Cite journal|last1=Owen|first1=James E.|last2=Ercolano|first2=Barbara|last3=Clarke|first3=Cathie J.|date=2011-03-21|title=Protoplanetary disc evolution and dispersal: the implications of X-ray photoevaporation: Disc evolution and dispersal|journal=Monthly Notices of the Royal Astronomical Society|language=en|volume=412|issue=1|pages=13–25|doi=10.1111/j.1365-2966.2010.17818.x |doi-access=free }}</ref> Once the gas was gone, planets could not grow much more, especially [[gas giant]]s, because the materials they needed had disappeared. Scientists believe this clearing happened within about 10 million years after the Solar System began. We know this by looking at other young stars and their disks in space today. The clearing of the disk marked the end of major planet formation and shaped the Solar System as we know it.<ref>{{Cite journal|last=C. Lin|first=Douglas N.|date=2008|title=The Genesis of Planets|url=https://www.scientificamerican.com/article/the-genesis-of-planets-2008-05|journal=Scientific American|volume=298|issue=5|pages=50–59|doi=10.1038/scientificamerican0508-50|doi-broken-date=12 July 2025|pmid=18444325|issn=0036-8733}}{{Dead link|date=August 2025 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref>{{cite journal | author=B. G. Elmegreen| title=On the disruption of a protoplanetary disc nebula by a T Tauri like solar wind | journal=Astronomy & Astrophysics |year=1979 | volume=80 | issue=1 | pages=77 | bibcode=1979A&A....80...77E }}</ref><ref>{{cite web |date=24 November 2004 |author=Heng Hao |publisher=Harvard University |title=Disc-Protoplanet interactions |url=http://cfa-www.harvard.edu/~kstanek/astro200/disk-protoplanet.pdf |access-date=2006-11-19 |url-status=dead |archive-url=https://web.archive.org/web/20060907170907/http://cfa-www.harvard.edu/~kstanek/astro200/disk-protoplanet.pdf |archive-date=7 September 2006 }}</ref>

After the planets finished forming and started to settle into their [[orbit]]s, the Solar System went through a chaotic time called the [[Late Heavy Bombardment|Late Heavy Bombardment (LHB)]]. This happened about 4.1 to 3.8 billion years ago and was a period when the inner planets, like [[Earth]], [[Moon|the Moon]], [[Mars]], and [[Mercury (planet)|Mercury]], were hit by tons of [[asteroid]]s and [[comet]]s.<ref>{{Cite web|date=2024-12-19|title=What is the Late Heavy Bombardment? - NASA Science|url=https://science.nasa.gov/moon/lunar-craters/what-is-the-late-heavy-bombardment/|access-date=2025-07-05|language=en-US}}</ref> Scientists know this happened because of rock samples from the Moon that were brought back by the [[Apollo mission]]s. Scientists studied the [[Impact crater|crater]]s on the Moon and used special techniques to figure out how old the rocks were. They found that many of the Moon’s biggest craters, like the [[Mare Imbrium|Imbrium]] and [[Mare Orientale|Orientale basin]]s, were all made around the same time. This shows that there was a sudden increase in [[Impact event|space impact]]s, not just a slow decline over time. The same thing probably happened on Earth and other nearby planets. [[Meteorite]]s found on Earth and information from Mars also support the idea that this was a Solar System-wide event with a huge number of collisions happening in a short period.<ref>{{Citation|last1=Claeys|first1=Philippe|title=Late Heavy Bombardment|date=2015|url=https://link.springer.com/rwe/10.1007/978-3-662-44185-5_869|encyclopedia=Encyclopedia of Astrobiology|pages=1365–1369|publisher=Springer, Berlin, Heidelberg|language=en|doi=10.1007/978-3-662-44185-5_869|isbn=978-3-662-44185-5|access-date=2025-07-05|last2=Morbidelli|first2=Alessandro}}</ref><ref name=":0">{{Cite journal|last1=Gomes|first1=R.|last2=Levison|first2=H. F.|last3=Tsiganis|first3=K.|last4=Morbidelli|first4=A.|date=2005|title=Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets|url=https://www.nature.com/articles/nature03676|journal=Nature|language=en|volume=435|issue=7041|pages=466–469|doi=10.1038/nature03676|pmid=15917802 |issn=1476-4687}}</ref>

Scientists are still trying to figure out exactly what caused the Late Heavy Bombardment (LHB), but one popular idea is called the [[Nice model]] (named after a city in France). This model suggests that the [[giant planet]]s, like [[Jupiter]] and [[Saturn]], did not always stay in the same [[orbit]]s. They might have moved. At some point in the early Solar System, Jupiter and Saturn may have crossed a special point in their orbits called a [[Orbital resonance|resonance]]. This happens when their orbits line up in a way that their gravitational pulls reinforce each other. In this case, it created a powerful gravitational effect that caused destabilized the orbits of many icy bodies in the [[Kuiper Belt]] and rocky objects in the asteroid belt. These objects were either flung out of the Solar System or sent crashing inward toward the inner planets, like [[Earth]], [[Mars]], and [[Venus]]. This sudden movement of so many objects led to the Late Heavy Bombardment, when the inner planets were hit by lots of [[asteroid]]s and [[comet]]s.<ref name=":0" /> These impacts helped shape the surfaces of the planets and may have even brought [[water]] and [[Organic compound|organic material]]s to Earth, ingredients that later made [[life]] possible.<ref>{{Cite web|last=bgray|date=2016-12-24|title=Late Heavy Bombardment may not have happened|url=https://geologyglasgow.org.uk/headlines/late-heavy-bombardment-may-not-have-happened/|access-date=2025-07-05|website=Geological Society of Glasgow|language=en-GB}}</ref>

One idea in [[planetary science]] is the [[Grand Tack hypothesis]]. This theory tries to explain some strange things about our Solar System by suggesting that Jupiter did not always stay where it is now. Instead, it says that Jupiter once moved inward, getting much closer to the [[Sun]], about 1.5 times the distance from Earth to the Sun, before turning around and moving back outward to where it is today. This big change in direction, or "tack" (like a [[sailboat]] changing course), may have happened because of [[Saturn]]. After Jupiter formed, Saturn also started forming, and the gravity between the two may have caused Jupiter to change direction.<ref>{{Cite web|title=Jupiter's Youthful Travels Redefined Solar System|url=https://www.nasa.gov/topics/solarsystem/features/young-jupiter.html|access-date=2025-07-05|website=www.nasa.gov|archive-date=2017-03-01|archive-url=https://web.archive.org/web/20170301170530/https://www.nasa.gov/topics/solarsystem/features/young-jupiter.html|url-status=dead}}</ref> As Jupiter moved inward, it would have pushed away or scattered a lot of [[dust]], [[rock]]s, and [[planetesimal]]s. This would have cleared out space in the Solar System and changed how the rocky planets, like Earth and Mars, formed. When Jupiter moved back outward, it may have pulled in a new mix of material, adding both rocky and icy objects into the [[asteroid belt]]. This helps explain why the asteroid belt today has a mix of different types of [[asteroid]]s, some rocky, some icy.<ref>{{Cite web|author1=Charles Q. Choi|date=2015-03-23|title=Jupiter's 'Smashing' Migration May Explain Our Oddball Solar System|url=https://www.space.com/28901-wandering-jupiter-oddball-solar-system.html|access-date=2025-07-05|website=Space|language=en}}</ref><ref>{{Cite web|title=How Did Jupiter Shape Our Solar System?|url=https://www.universetoday.com/articles/how-did-jupiter-shape-our-solar-system|access-date=2025-07-05|website=Universe Today|language=en}}</ref>

One big area scientists study is how the [[orbit]]s of [[planet]]s, [[Natural satellite|moon]]s, [[asteroid]]s, and [[comet]]s change over time. These changes happen slowly and are often caused by [[gravity]] pulling on objects in special ways. One important idea is called a [[Orbital resonance|resonance]]. This happens when two objects go around the Sun in a regular pattern, like one going around twice for every three times the other one goes around. These simple ratios (like 2:1 or 3:2) can keep orbits stable or sometimes make them unstable.<ref>{{Cite web|title=Orbital resonance|url=https://www.aanda.org/glossary/175-orbital-resonance|access-date=2025-07-05|website=www.aanda.org}}</ref><ref>{{Cite journal|last=Christopher|first=Lee|title=The effect of orbital resonance on the stability of a planetary system|url=https://www.the-iyrc.org/uploads/1/2/9/7/129787256/iyrc2021_14_final.pdf|journal=The International Young Researchers' Conference}}</ref> Resonances help explain why the asteroid belt looks the way it does, why certain moons are in just the right spots, and why icy objects beyond Neptune tend to cluster in certain areas.<ref>{{Cite web|title=Planetary orbits: Couplings and resonances {{!}} EBSCO Research Starters|url=https://www.ebsco.com/research-starters/history/planetary-orbits-couplings-and-resonances|access-date=2025-07-05|website=www.ebsco.com|language=en}}</ref><ref>{{Cite journal|last=Malhotra|first=Renu|date=2019-11-09|title=Resonant Kuiper belt objects: a review|journal=Geoscience Letters|volume=6|issue=1|article-number=12|doi=10.1186/s40562-019-0142-2|doi-access=free |issn=2196-4092|pmc=7067275|pmid=32215241}}</ref> Another idea is called [[secular variation]], which means slow, long-term changes in things like a planet’s orbit shape, tilt, or direction. These changes happen because planets gently pull on each other over millions of years.<ref>{{Cite web|title=Secular evolution of planetary orbits|url=https://farside.ph.utexas.edu/teaching/celestial/Celestial/node91.html#:~:text=78)-,for%20.,to%20the%20ecliptic%20plane,%20is|access-date=2025-07-05|website=farside.ph.utexas.edu}}</ref><ref>{{Citation|last=Rimrott|first=Fred P. J.|title=Secular Variations of the Orbital Elements|date=1989|url=https://doi.org/10.1007/978-3-322-90338-9_7|work=Introductory Orbit Dynamics|pages=101–106|editor-last=Rimrott|editor-first=Fred P. J.|place=Wiesbaden|publisher=Vieweg+Teubner Verlag|language=en|doi=10.1007/978-3-322-90338-9_7|isbn=978-3-322-90338-9|access-date=2025-07-05}}</ref> For example, Earth’s orbit and tilt slowly shift because of the gravity from Jupiter and Saturn. These changes affect Earth’s climate over a long time, in something called [[Milankovitch cycles]].<ref>{{Cite web|date=2020-02-27|title=Milankovitch (Orbital) Cycles and Their Role in Earth's Climate - NASA Science|url=https://science.nasa.gov/science-research/earth-science/milankovitch-orbital-cycles-and-their-role-in-earths-climate/|access-date=2025-07-05|language=en-US}}</ref> Sometimes, gravity can even throw objects off course or capture them. This is called [[gravitational scattering]].<ref>{{Cite web|title=Gravitational Dynamics {{!}} Center for Astrophysics {{!}} Harvard & Smithsonian|url=https://www.cfa.harvard.edu/research/topic/gravitational-dynamics|access-date=2025-07-05|website=www.cfa.harvard.edu}}</ref> For example, Neptune’s moon [[Triton (moon)|Triton]] orbits backward, which suggests it did not form around Neptune but was a Kuiper Belt object that got caught by Neptune’s gravity.<ref>{{Cite journal|last1=Farinella|first1=P.|last2=Milani|first2=A.|last3=Nobili|first3=A.M.|last4=Valsecchi|first4=G.B.|date=1980|title=Some remarks on the capture of Triton and the origin of Pluto|url=https://linkinghub.elsevier.com/retrieve/pii/0019103580901487|journal=Icarus|language=en|volume=44|issue=3|pages=810–812|doi=10.1016/0019-1035(80)90148-7}}</ref><ref>{{Cite web|date=2017-11-21|title=Triton - NASA Science|url=https://science.nasa.gov/neptune/moons/triton/|access-date=2025-07-05|language=en-US}}</ref> Mars’s tiny moons, [[Phobos]] and [[Deimos]], may also be captured asteroids because of their strange shapes and materials.<ref>{{Cite web|date=2017-11-11|title=Mars Moons - NASA Science|url=https://science.nasa.gov/mars/moons/|access-date=2025-07-05|language=en-US}}</ref>

Another important force that helps shape the Solar System is tidal interaction, especially between planets and their moons. [[Tidal force]]s happen because of gravity. Planets pull on their moons, and moons pull back on their planets. This tugging creates bulges, which causes [[energy]] to be lost and leads to slow changes in [[orbit]]s and [[rotation]].<ref>{{Cite web|last=Plait|first=Phil|title=Tides Move Heaven and Earth More Than You Know|url=https://www.scientificamerican.com/article/how-do-tides-shape-earth-and-the-solar-system/|access-date=2025-07-05|website=Scientific American|language=en}}</ref><ref>{{Cite web|date=2016-10-18|title=13.7: Tidal Forces|url=https://phys.libretexts.org/Bookshelves/University_Physics/University_Physics_(OpenStax)/Book%3A_University_Physics_I_-_Mechanics_Sound_Oscillations_and_Waves_(OpenStax)/13%3A_Gravitation/13.07%3A_Tidal_Forces|access-date=2025-07-05|website=Physics LibreTexts|language=en}}</ref> One famous example is the [[Earth]] and [[Moon]]. Because of tidal forces, the Moon always shows the same side to Earth. This is called being [[tidally locked]].<ref>{{Cite web|date=2023-06-06|title=Tidal Locking - NASA Science|url=https://science.nasa.gov/moon/tidal-locking/|access-date=2025-07-05|language=en-US}}</ref> Also, Earth’s rotation is slowly slowing down, and the Moon is very slowly moving farther away from us.<ref>{{Cite book|title=Time: from earth rotation to atomic physics|last1=McCarthy|first1=Dennis D.|last2=Seidelmann|first2=P. Kenneth|date=2009|publisher=Wiley-VCH|isbn=978-3-527-62795-0|location=Weinheim}}</ref><ref>{{Cite web|date=2017-11-15|title=Moon Facts - NASA Science|url=https://science.nasa.gov/moon/facts/|access-date=2025-07-05|language=en-US}}</ref> Tidal forces can also create heat inside moons, especially those that orbit big planets like Jupiter and Saturn. For example, [[Europa (moon)|Europa]] (a moon of Jupiter) and [[Enceladus (moon)|Enceladus]] (a moon of Saturn) are squeezed and stretched as they move around their planets.<ref>{{Cite web|title=Europa Tidal Heating|url=http://astronomy.nmsu.edu/candaceg/Europa/Tidal_Heating.html|access-date=2025-07-05|website=astronomy.nmsu.edu}}</ref><ref>{{Cite journal|last1=Meyer|first1=Jennifer|last2=Wisdom|first2=Jack|date=2007|title=Tidal heating in Enceladus|url=https://linkinghub.elsevier.com/retrieve/pii/S0019103507001054|journal=Icarus|language=en|volume=188|issue=2|pages=535–539|doi=10.1016/j.icarus.2007.03.001}}</ref> This squeezing, called [[Tidal heating|tidal flexing]], creates heat inside them.<ref>{{Citation|last=Lunine|first=Jonathan I.|title=Tidal heating|date=1997|url=https://link.springer.com/rwe/10.1007/1-4020-4520-4_408|encyclopedia=Encyclopedia of Planetary Science|series=Encyclopedia of Earth Science |pages=828|publisher=Springer, Dordrecht|language=en|doi=10.1007/1-4020-4520-4_408|isbn=978-1-4020-4520-2|access-date=2025-07-05}}</ref><ref>{{Cite web|title=tidal heating|url=https://evolution.berkeley.edu/glossary/tidal-heating/|access-date=2025-07-05|website=evolution.berkeley.edu}}</ref> That heat might keep liquid [[ocean]]s under their icy surfaces.<ref>{{Cite web|last=Owen|first=Rebecca|date=2024-01-10|title=Scientists Investigate How Heat Rises Through Europa's Ocean|url=https://eos.org/research-spotlights/scientists-investigate-how-heat-rises-through-europas-ocean|access-date=2025-07-05|website=Eos|language=en-US}}</ref> These hidden oceans could have [[geyser]]s or even [[cryovolcanoe]]s (volcanoes that erupt [[ice]] instead of [[lava]]).<ref>{{Cite web|date=2020-08-04|title=Cryovolcanism in the Solar System|url=https://www.skyatnightmagazine.com/space-science/cryovolcanism-in-the-solar-system|access-date=2025-07-05|website=BBC Sky at Night Magazine|language=en}}</ref> Because of this, Europa and Enceladus are interesting places to look for life beyond Earth.<ref>{{Cite web|last=Velasco|first=Rebecca Boyle, Juan|date=2023-05-01|title=The Six Moons Most Likely to Host Life in Our Solar System|url=https://www.scientificamerican.com/article/the-six-moons-most-likely-to-host-life-in-our-solar-system/|access-date=2025-07-05|website=Scientific American|language=en}}</ref>