Editing Planet (section)

==== Atmosphere ====
{{Main|Atmosphere|extraterrestrial atmospheres}}
{{see also|Extraterrestrial skies}}
[[File:Top of Atmosphere.jpg|thumb|left|Earth's atmosphere]]
All of the Solar System planets [[Atmosphere of Mercury|except Mercury]]<ref>{{cite journal |last1=Zurbuchen |first1=Thomas H. |last2=Raines |first2=Jim M. |last3=Gloeckler |first3=George |last4=Krimigis |first4=Stamatios M. |last5=Slavin |first5=James A. |last6=Koehn |first6=Patrick L. |last7=Killen |first7=Rosemary M. |last8=Sprague |first8=Ann L. |last9=McNutt Jr. |first9=Ralph L. |last10=Solomon |first10=Sean C. |display-authors=4 |name-list-style=vanc |year=2008 |title=MESSENGER Observations of the Composition of Mercury's Ionized Exosphere and Plasma Environment |journal=Science |volume=321 |issue=5885 |pages=90–92 |bibcode=2008Sci...321...90Z |doi=10.1126/science.1159314 |pmid=18599777 |s2cid=206513512}}</ref> have substantial [[atmosphere]]s because their gravity is strong enough to keep gases close to the surface. Saturn's largest moon [[Titan (moon)|Titan]] also has a substantial atmosphere thicker than that of Earth;<ref>{{cite book|title=Titan: Exploring an Earthlike World|author1=Coustenis, Athéna|author2=Taylor, F. W.|name-list-style=amp|publisher=World Scientific|year=2008|page=130|url=https://books.google.com/books?id=j3O47dxrDAQC&q=Titan|access-date=25 March 2010|isbn=978-981-270-501-3|archive-date=14 December 2023|archive-url=https://web.archive.org/web/20231214142630/https://books.google.com/books?id=j3O47dxrDAQC&q=Titan#v=snippet&q=Titan&f=false|url-status=live}}</ref> Neptune's largest moon [[Triton (moon)|Triton]]<ref name="Solar System">{{cite web |url=http://solarsystem.nasa.gov/planets/profile.cfm?Object=Nep_Triton |title=Neptune: Moons: Triton |work=Solar System Exploration |access-date=31 December 2007 |archive-url=https://web.archive.org/web/20080110095537/http://solarsystem.nasa.gov/planets/profile.cfm?Object=Nep_Triton |archive-date=10 January 2008 }}</ref> and the dwarf planet [[Pluto]] have more tenuous atmospheres.<ref name=Lellouch_2015>{{cite journal
 |author1=Lellouch, E. |author2=de Bergh, C. |author3=Sicardy, B. |author4=Forget, F. |author5=Vangvichith, M. |author6=Käufl, H.-U. |title  =Exploring the spatial, temporal, and vertical distribution of methane in Pluto's atmosphere
 |journal=Icarus
 |date   =January 2015
 |doi    =10.1016/j.icarus.2014.03.027
 |bibcode=2015Icar..246..268L
 |arxiv  =1403.3208
 |volume=246 |pages=268–278
|s2cid=119194193 }}</ref> The larger giant planets are massive enough to keep large amounts of the light gases hydrogen and helium, whereas the smaller planets lose these gases into [[Interplanetary medium|space]].<ref>{{Cite journal | last1 = Sheppard | first1 = S. S. | last2 = Jewitt | first2 = D. | last3 = Kleyna | first3 = J. | title = An Ultradeep Survey for Irregular Satellites of Uranus: Limits to Completeness | doi = 10.1086/426329 | journal = The Astronomical Journal | volume = 129 | issue = 1 | pages = 518–525 | year = 2005 |arxiv = astro-ph/0410059 |bibcode = 2005AJ....129..518S | s2cid = 18688556 }}</ref> Analysis of exoplanets suggests that the threshold for being able to hold on to these light gases occurs at about {{val|2.0|0.7|0.6}} ''M''<sub>🜨</sub>, so that Earth and Venus are near the maximum size for rocky planets.<ref name=ChenKipping/>

The composition of Earth's atmosphere is different from the other planets because the various life processes that have transpired on the planet have introduced free molecular [[oxygen]].<ref name="zeilik">{{cite book | last1=Zeilik |first1=Michael A. |author2=Gregory, Stephan A. |title=Introductory Astronomy & Astrophysics |edition=4th |date=1998 |publisher=Saunders College Publishing |isbn=978-0-03-006228-5 |page=67}}</ref> The atmospheres of Mars and Venus are both dominated by [[carbon dioxide]], but differ drastically in density: the average surface pressure of [[Atmosphere of Mars|Mars's atmosphere]] is less than 1% that of Earth's (too low to allow liquid water to exist),<ref>{{Citation|last=Haberle|first=R. M.|title=Solar System/Sun, Atmospheres, Evolution of Atmospheres {{!}} Planetary Atmospheres: Mars|date=2015|encyclopedia=Encyclopedia of Atmospheric Sciences |edition=2nd|pages=168–177|editor-last=North|editor-first=Gerald R.|publisher=Academic Press|doi=10.1016/b978-0-12-382225-3.00312-1|isbn=978-0123822253|editor2-last=Pyle|editor2-first=John|editor3-last=Zhang|editor3-first=Fuqing}}</ref> while the average surface pressure of [[Atmosphere of Venus|Venus's atmosphere]] is about 92 times that of Earth's.<ref name=Basilevsky2003>{{cite journal |last=Basilevsky|first=Alexandr T.|author2=Head, James W.|title=The surface of Venus|journal=Rep. Prog. Phys.|date=2003|volume=66|issue=10|pages=1699–1734|doi=10.1088/0034-4885/66/10/R04 |bibcode= 2003RPPh...66.1699B|s2cid=250815558 }}</ref> It is likely that Venus's atmosphere was the result of a [[runaway greenhouse effect]] in its history, which today makes it the hottest planet by surface temperature, hotter even than Mercury.<ref>{{cite journal |author=S. I. Rasoonl|author2=C. de Bergh|name-list-style=amp |title=The Runaway Greenhouse Effect and the Accumulation of CO<sub>2</sub> in the Atmosphere of Venus |journal=Nature |volume=226 |pages=1037–1039 |date=1970 |pmid=16057644 |issue=5250 |doi=10.1038/2261037a0 |bibcode=1970Natur.226.1037R|s2cid=4201521}}</ref> Despite hostile surface conditions, temperature, and pressure at about 50–55&nbsp;km altitude in Venus's atmosphere are close to Earthlike conditions (the only place in the Solar System beyond Earth where this is so), and this region has been suggested as a plausible base for future [[Space exploration#Human spaceflight and habitation|human exploration]].<ref name="Badescu">{{cite book |author=Badescu, Viorel |editor=Zacny, Kris |title=Inner Solar System: Prospective Energy and Material Resources |url=https://www.springer.com/us/book/9783319195681 |location=Heidelberg |publisher=Springer-Verlag GmbH |page=492 |date=2015 |isbn=978-3319195681 |access-date=4 May 2023 |archive-date=21 August 2018 |archive-url=https://web.archive.org/web/20180821093729/https://www.springer.com/us/book/9783319195681 |url-status=live }}.<!--Based on ''Technica Molodezhi TM - 9 1971''--></ref> Titan has the only [[nitrogen]]-rich planetary atmosphere in the Solar System other than Earth's. Just as Earth's conditions are close to the [[triple point]] of water, allowing it to exist in all three states on the planet's surface, so Titan's are to the triple point of [[methane]].<ref>{{Cite journal|last=Horst|first=Sarah|date=2017|title=Titan's Atmosphere and Climate|journal=J. Geophys. Res. Planets|volume=122|issue=3|pages=432–482|doi=10.1002/2016JE005240|arxiv=1702.08611|bibcode=2017JGRE..122..432H|s2cid=119482985}}</ref>

Planetary atmospheres are affected by the varying [[insolation]] or internal energy, leading to the formation of dynamic [[weather system]]s such as [[hurricane]]s (on Earth), planet-wide [[dust storm]]s (on Mars), a greater-than-Earth-sized [[Anticyclonic storm|anticyclone]] on Jupiter (called the [[Great Red Spot]]), and [[Great Dark Spot|holes in the atmosphere]] (on Neptune).<ref name="Weather" /> Weather patterns detected on exoplanets include a hot region on [[HD 189733 b]] twice the size of the Great Red Spot,<ref name="knutson">{{cite journal | last1=Knutson |first1=Heather A. | last2=Charbonneau | first2=David | last3=Allen | first3=Lori E. |author3-link=Lori Allen (astronomer)| last4=Fortney | first4=Jonathan J. |title=A map of the day-night contrast of the extrasolar planet HD 189733 b |journal=Nature |date=2007 |volume=447 |doi=10.1038/nature05782 |pmid=17495920 |issue=7141 |bibcode=2007Natur.447..183K | pages=183–186|arxiv = 0705.0993|s2cid=4402268}}
* {{cite press release |date=9 May 2007 |title=First Map of an Extrasolar Planet |website=Center for Astrophysics |url=https://pweb.cfa.harvard.edu/news/first-map-extrasolar-planet |access-date=10 July 2022 |archive-date=5 December 2022 |archive-url=https://web.archive.org/web/20221205045421/https://pweb.cfa.harvard.edu/news/first-map-extrasolar-planet |url-status=live }}</ref> as well as [[cloud]]s on the hot Jupiter [[Kepler-7b]],<ref name="ArXiv-20130930">{{cite journal |last1=Demory |first1= Brice-Olivier |first2= Julien |last2= de Wit |first3= Nikole |last3= Lewis |first4= Jonathan |last4= Fortney |first5= Andras |last5= Zsom |first6= Sara |last6= Seager |display-authors=4 |year=2013 |title=Inference of Inhomogeneous Clouds in an Exoplanet Atmosphere |journal=The Astrophysical Journal Letters |volume=776 |issue=2 |page=L25 |arxiv=1309.7894 |bibcode=2013ApJ...776L..25D |doi=10.1088/2041-8205/776/2/L25 |s2cid=701011}}</ref> the super-Earth [[Gliese 1214 b]], and others.<ref name="NAT-20140101a">{{cite journal |last=Moses |first=Julianne |date=1 January 2014 |title=Extrasolar planets: Cloudy with a chance of dustballs |journal=[[Nature (journal)|Nature]] |volume=505 |issue=7481 |pages=31–32 |bibcode=2014Natur.505...31M |doi=10.1038/505031a |pmid=24380949|s2cid=4408861 }}</ref><ref>{{Cite journal |last1=Benneke |first1=Björn |last2=Wong |first2=Ian |last3=Piaulet |first3=Caroline |last4=Knutson |first4=Heather A. |last5=Lothringer |first5=Joshua |last6=Morley |first6=Caroline V. |last7=Crossfield |first7=Ian J. M. |last8=Gao |first8=Peter |last9=Greene |first9=Thomas P. |last10=Dressing |first10=Courtney |last11=Dragomir |first11=Diana |display-authors= 4 |date=10 December 2019 |title=Water Vapor and Clouds on the Habitable-zone Sub-Neptune Exoplanet K2-18b |journal=The Astrophysical Journal Letters |volume=887 |issue=1 |pages=L14 |doi=10.3847/2041-8213/ab59dc |arxiv=1909.04642 |bibcode=2019ApJ...887L..14B |s2cid=209324670 |issn=2041-8205 |doi-access=free }}</ref>

Hot Jupiters, due to their extreme proximities to their host stars, have been shown to be losing their atmospheres into space due to stellar radiation, much like the tails of comets.<ref>{{cite journal |journal=Nature |last1=Ballester |first1=Gilda E. |last2=Sing |first2=David K. |last3=Herbert |first3=Floyd |title=The signature of hot hydrogen in the atmosphere of the extrasolar planet HD 209458b |volume=445 |date=2007 |doi=10.1038/nature05525 |pmid=17268463 |issue=7127 |bibcode=2007Natur.445..511B |pages=511–514 |hdl=10871/16060 |s2cid=4391861 |url=https://ore.exeter.ac.uk/repository/bitstream/10871/16060/2/HD209458.nature.rev105.pdf |hdl-access=free |access-date=24 September 2019 |archive-date=28 July 2020 |archive-url=https://web.archive.org/web/20200728035216/https://repository/bitstream/handle/10871/16060/HD209458.nature.rev105.pdf;jsessionid=35C3149FC9764FBF9D4ADEA8F1DA25E4?sequence=2 |url-status=live }}
* {{cite press release |first1=Donna |last1=Weaver |first2=Ray |last2=Villard |url=https://hubblesite.org/contents/news-releases/2007/news-2007-07.html |title=Hubble Probes Layer-cake Structure of Alien World's Atmosphere |publisher=Space Telescope Science Institute |date=31 January 2007 |access-date=23 October 2011 |archive-date=9 July 2016 |archive-url=https://web.archive.org/web/20160709121743/http://hubblesite.org/newscenter/archive/releases/2007/07/full/ |url-status=live }}</ref><ref>{{Cite journal |last1=Villarreal D'Angelo |first1=Carolina |last2=Esquivel |first2=Alejandro |last3=Schneiter |first3=Matías |last4=Sgró |first4=Mario Agustín |date=21 September 2018 |title=Magnetized winds and their influence in the escaping upper atmosphere of HD 209458b |url=https://academic.oup.com/mnras/article/479/3/3115/5035846 |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=479 |issue=3 |pages=3115–3125 |doi=10.1093/mnras/sty1544 |doi-access=free |issn=0035-8711 |hdl=11336/86936 |hdl-access=free |access-date=10 July 2022 |archive-date=10 July 2022 |archive-url=https://web.archive.org/web/20220710233411/https://academic.oup.com/mnras/article/479/3/3115/5035846 |url-status=live }}</ref> These planets may have vast differences in temperature between their day and night sides that produce supersonic winds,<ref>{{cite journal | last1=Harrington |first1=Jason | last2=Hansen | first2=Brad M. | last3=Luszcz | first3=Statia H. | last4=Seager | first4=Sara |title=The phase-dependent infrared brightness of the extrasolar planet Andromeda b |journal=Science |volume=314 |date=2006 |doi=10.1126/science.1133904 |pmid=17038587 |issue=5799 |bibcode=2006Sci...314..623H | pages=623–626|arxiv = astro-ph/0610491 |s2cid=20549014}}
* {{cite press release |date=12 October 2006 |title=NASA's Spitzer Sees Day and Night on Exotic World |website=NASA |url=http://www.nasa.gov/vision/universe/starsgalaxies/spitzer-20061012.html |access-date=16 August 2007 |archive-date=13 July 2017 |archive-url=https://web.archive.org/web/20170713035307/https://www.nasa.gov/vision/universe/starsgalaxies/spitzer-20061012.html |url-status=dead }}</ref> although multiple factors are involved and the details of the atmospheric dynamics that affect the day-night temperature difference are complex.<ref>{{Cite journal |last1=Showman |first1=Adam P. |last2=Tan |first2=Xianyu |last3=Parmentier |first3=Vivien |date=December 2020 |title=Atmospheric Dynamics of Hot Giant Planets and Brown Dwarfs |url=http://link.springer.com/10.1007/s11214-020-00758-8 |journal=Space Science Reviews |language=en |volume=216 |issue=8 |page=139 |doi=10.1007/s11214-020-00758-8 |arxiv=2007.15363 |bibcode=2020SSRv..216..139S |s2cid=220870881 |issn=0038-6308 |access-date=10 July 2022 |archive-date=14 December 2023 |archive-url=https://web.archive.org/web/20231214142633/https://link.springer.com/article/10.1007/s11214-020-00758-8 |url-status=live }}</ref><ref>{{Cite journal |last1=Fortney |first1=Jonathan J. |last2=Dawson |first2=Rebekah I. |last3=Komacek |first3=Thaddeus D. |date=March 2021 |title=Hot Jupiters: Origins, Structure, Atmospheres |url=https://onlinelibrary.wiley.com/doi/10.1029/2020JE006629 |journal=Journal of Geophysical Research: Planets |language=en |volume=126 |issue=3 |doi=10.1029/2020JE006629 |arxiv=2102.05064 |bibcode=2021JGRE..12606629F |s2cid=231861632 |issn=2169-9097 |access-date=10 July 2022 |archive-date=14 December 2023 |archive-url=https://web.archive.org/web/20231214142634/https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020JE006629 |url-status=live }}</ref>