Editing Extraterrestrial life (section)

==Planetary habitability in the Solar System==
{{main|Planetary habitability in the Solar System}}
[[File:Habitable Worlds 2.jpg|thumb|Besides Earth, [[Mars]], [[Europa (moon)|Europa]] and [[Enceladus]] are the most likely places in the Solar System to find life.]] 
The Solar System has a wide variety of planets, dwarf planets, and moons, and each one is studied for its potential to host life. Each one has its own specific conditions that may benefit or harm life. So far, the only lifeforms found are those from Earth. No [[extraterrestrial intelligence]] other than [[human]]s exists or has ever existed within the Solar System.<ref>Bennett, pp. 3-4</ref> Astrobiologist Mary Voytek points out that it would be unlikely to find large ecosystems, as they would have already been detected by now.<ref name="Neighbors">{{cite web |url= https://exoplanets.nasa.gov/news/1665/life-in-our-solar-system-meet-the-neighbors/|title= Life in Our Solar System? Meet the Neighbors|author= Pat Brennan|date= November 10, 2020|publisher= NASA|accessdate=March 30, 2023}}</ref>

The inner Solar System is likely devoid of life. However, [[Venus]] is still of interest to astrobiologists, as it is a [[terrestrial planet]] that was likely similar to Earth in its early stages and developed in a different way. There is a [[greenhouse effect]], the surface is the hottest in the Solar System, sulfuric acid clouds, all surface liquid water is lost, and it has a thick carbon-dioxide atmosphere with huge pressure.<ref>{{Cite journal |last1=Marcq |first1=Emmanuel |last2=Mills |first2=Franklin P. |last3=Parkinson |first3=Christopher D. |last4=Vandaele |first4=Ann Carine |date=2017-11-30 |title=Composition and Chemistry of the Neutral Atmosphere of Venus |url=https://hal-insu.archives-ouvertes.fr/insu-01656562/file/EMFMCP.pdf |journal=Space Science Reviews |language=en |volume=214 |issue=1 |pages=10 |doi=10.1007/s11214-017-0438-5 |s2cid=255067610 |issn=1572-9672}}</ref> Comparing both helps to understand the precise differences that lead to beneficial or harmful conditions for life. And despite the conditions against [[life on Venus]], there are suspicions that microbial life-forms may still survive in high-altitude clouds.<ref name="Neighbors"/>

[[Mars]] is a cold and almost airless desert, inhospitable to life. However, recent studies revealed that [[water on Mars]] used to be quite abundant, forming rivers, lakes, and perhaps even oceans. Mars may have been habitable back then, and [[life on Mars]] may have been possible. But when the planetary core ceased to generate a magnetic field, solar winds removed the atmosphere and the planet became vulnerable to solar radiation. Ancient life-forms may still have left fossilised remains, and microbes may still survive deep underground.<ref name="Neighbors"/>

As mentioned, the gas giants and [[ice giants]] are unlikely to contain life. The most distant solar system bodies, found in the [[Kuiper Belt]] and outwards, are locked in permanent deep-freeze, but cannot be ruled out completely.<ref name="Neighbors"/>

Although the giant planets themselves are highly unlikely to have life, there is much hope to find it on moons orbiting these planets. [[Europa (moon)|Europa]], from the Jovian system, has a subsurface ocean below a thick layer of ice. [[Ganymede (moon)|Ganymede]] and [[Callisto (moon)|Callisto]] also have subsurface oceans, but life is less likely in them because water is sandwiched between layers of solid ice. Europa would have contact between the ocean and the rocky surface, which helps the chemical reactions. It may be difficult to dig so deep in order to study those oceans, though. [[Enceladus]], a tiny moon of [[Saturn]] with another subsurface ocean, may not need to be dug, as it releases water to space in [[eruption column]]s. The space probe ''[[Cassini–Huygens|Cassini]]'' flew inside one of these, but could not make a full study because NASA did not expect this phenomenon and did not equip the probe to study ocean water. Still, ''Cassini'' detected complex organic molecules, salts, evidence of hydrothermal activity, hydrogen, and methane.<ref name="Neighbors"/>

[[Titan (moon)|Titan]] is the only celestial body in the Solar System besides Earth that has liquid bodies on the surface. It has rivers, lakes, and rain of hydrocarbons, methane, and ethane, and even a cycle similar to Earth's [[water cycle]]. This special context encourages speculations about [[Life on Titan|lifeforms]] with different biochemistry, but the cold temperatures would make such chemistry take place at a very slow pace. Water is rock-solid on the surface, but Titan does have a subsurface water ocean like several other moons. However, it is of such a great depth that it would be very difficult to access it for study.<ref name="Neighbors"/>