Editing Solar System (section)

=== Inner planets<span class="anchor" id="Terrestrial planets"></span> ===
{{Main|Terrestrial planet}}
[[File:Terrestrial planet sizes 3.jpg|right|thumb|alt=Venus and Earth about the same size, Mars is about 0.55 times as big and Mercury is about 0.4 times as big|The four terrestrial planets [[Mercury (planet)|Mercury]], [[Venus]], [[Earth]] and [[Mars]]]]
The four terrestrial or inner planets have dense, rocky compositions, few or no [[natural satellite|moons]], and no [[planetary ring|ring systems]]. They are composed largely of [[Refractory (planetary science)|refractory]] minerals such as [[silicates]]{{Mdash}}which form their [[crust (geology)|crusts]] and [[mantle (geology)|mantles]]{{Mdash}}and metals such as iron and nickel which form their [[planetary core|cores]]. Three of the four inner planets (Venus, Earth, and Mars) have [[atmosphere]]s substantial enough to generate weather; all have impact craters and [[tectonics|tectonic]] surface features, such as [[rift valley]]s and volcanoes.<ref name="Ryden">{{Cite journal |last=Ryden |first=Robert |date=December 1999 |title=Astronomical Math |url=https://pubs.nctm.org/view/journals/mt/92/9/article-p786.xml |url-status=live |journal=The Mathematics Teacher |volume=92 |issue=9 |pages=786–792 |doi=10.5951/MT.92.9.0786 |issn=0025-5769 |jstor=27971203 |archive-url=https://web.archive.org/web/20220412010049/https://pubs.nctm.org/view/journals/mt/92/9/article-p786.xml |archive-date=12 April 2022 |access-date=29 March 2022}}</ref>
* {{Visible anchor|Mercury|text=[[Mercury (planet)|Mercury]]}} (0.31–0.59&nbsp;AU from the Sun)<ref name="nasa-factsheet" group="D">{{Cite web |last=Williams |first=David |date=27 December 2021 |title=Planetary Fact Sheet - Metric |url=https://nssdc.gsfc.nasa.gov/planetary/factsheet |access-date=11 December 2022 |publisher=[[Goddard Space Flight Center]] |archive-date=18 August 2011 |archive-url=https://web.archive.org/web/20110818181734/http://nssdc.gsfc.nasa.gov/planetary/factsheet/ |url-status=live }}</ref> is the smallest planet in the Solar System. Its surface is grayish, with an expansive [[rupes]] (cliff) system generated from [[thrust fault]]s and bright [[ray system]]s formed by [[Ejecta|impact event remnants]].<ref>{{Cite journal |last1=Watters |first1=Thomas R. |last2=Solomon |first2=Sean C. |last3=Robinson |first3=Mark S. |last4=Head |first4=James W. |last5=André |first5=Sarah L. |last6=Hauck |first6=Steven A. |last7=Murchie |first7=Scott L. |date=August 2009 |title=The tectonics of Mercury: The view after MESSENGER's first flyby |journal=Earth and Planetary Science Letters |language=en |volume=285 |issue=3–4 |pages=283–296 |bibcode=2009E&PSL.285..283W |doi=10.1016/j.epsl.2009.01.025}}</ref> The surface has widely varying temperature, with the [[equator]]ial regions ranging from {{convert|-170|C|F|sigfig=2}} at night to {{convert|420|C|F|sigfig=2}} during sunlight. In the past, Mercury was volcanically active, producing smooth [[basalt]]ic plains similar to the Moon.<ref name=Head_et_al_1981>{{cite journal |last1=Head |first1=James W. |author-link1=James W. Head |last2=Solomon |first2=Sean C. |author-link2=Sean Solomon |year=1981 |title=Tectonic Evolution of the Terrestrial Planets |url=http://www.planetary.brown.edu/pdfs/323.pdf |url-status=dead |journal=Science |volume=213 |issue=4503 |pages=62–76 |bibcode=1981Sci...213...62H |citeseerx=10.1.1.715.4402 |doi=10.1126/science.213.4503.62 |pmid=17741171 |archive-url=https://web.archive.org/web/20180721153426/http://www.planetary.brown.edu/pdfs/323.pdf |archive-date=21 July 2018 |access-date=25 October 2017 |hdl=2060/20020090713}}</ref> It is likely that Mercury has a silicate crust and a large iron core.<ref>{{cite web |date=21 March 2012 |editor-last=Talbert |editor-first=Tricia |title=MESSENGER Provides New Look at Mercury's Surprising Core and Landscape Curiosities |url=https://www.nasa.gov/mission_pages/messenger/media/PressConf20120321.html |url-status=dead |archive-url=https://web.archive.org/web/20190112170032/https://www.nasa.gov/mission_pages/messenger/media/PressConf20120321.html |archive-date=12 January 2019 |access-date=20 April 2018 |publisher=NASA}}</ref><ref name="Margot2012">{{cite journal |last1=Margot |first1=Jean-Luc |last2=Peale |first2=Stanton J. |last3=Solomon |first3=Sean C. |last4=Hauck |first4=Steven A. |last5=Ghigo |first5=Frank D. |last6=Jurgens |first6=Raymond F. |last7=Yseboodt |first7=Marie |last8=Giorgini |first8=Jon D. |last9=Padovan |first9=Sebastiano |last10=Campbell |first10=Donald B. |year=2012 |title=Mercury's moment of inertia from spin and gravity data |journal=Journal of Geophysical Research: Planets |volume=117 |issue=E12 |pages=n/a |bibcode=2012JGRE..117.0L09M |citeseerx=10.1.1.676.5383 |doi=10.1029/2012JE004161 |issn=0148-0227 |s2cid=22408219}}</ref> Mercury has a very tenuous atmosphere, consisting of [[Solar wind|solar-wind]] particles and ejected atoms.<ref>{{Cite journal |last1=Domingue |first1=Deborah L. |last2=Koehn |first2=Patrick L. |last3=Killen |first3=Rosemary M. |last4=Sprague |first4=Ann L. |last5=Sarantos |first5=Menelaos |last6=Cheng |first6=Andrew F. |last7=Bradley |first7=Eric T. |last8=McClintock |first8=William E. |display-authors=2 |date=2009 |title=Mercury's Atmosphere: A Surface-Bounded Exosphere |journal=Space Science Reviews |volume=131 |issue=1–4 |pages=161–186 |bibcode=2007SSRv..131..161D |doi=10.1007/s11214-007-9260-9 |s2cid=121301247 |quote=The composition of Mercury's exosphere, with its abundant H and He, clearly indicates a strong solar wind source. Once solar wind plasma and particles gain access to the magnetosphere, they predominantly precipitate to the surface, where solar wind species are neutralized, thermalized, and released again into the exosphere. Moreover, bombardment of the surface by solar wind particles, especially energetic ions, contributes to ejection of neutral species from the surface into the exosphere (via "sputtering") as well as other chemical and physical surface modification processes.}}</ref> Mercury has no natural satellites.<ref name="spaceplace.nasa.gov">{{Cite web |title=How Many Moons Does Each Planet Have? {{!}} NASA Space Place – NASA Science for Kids |url=https://spaceplace.nasa.gov/how-many-moons/en/ |access-date=21 April 2024 |website=spaceplace.nasa.gov |archive-date=21 April 2024 |archive-url=https://web.archive.org/web/20240421061913/https://spaceplace.nasa.gov/how-many-moons/en/ |url-status=live }}</ref>
* {{Visible anchor|Venus|text=[[Venus]]}} (0.72–0.73&nbsp;AU)<ref name="nasa-factsheet" group="D" /> has a reflective, whitish atmosphere that is mainly composed of [[carbon dioxide]]. At the surface, the atmospheric pressure is ninety times as dense as on Earth's sea level.<ref name="u3r1a">{{cite journal |last1=Lebonnois |first1=Sebastien |last2=Schubert |first2=Gerald |date=26 June 2017 |title=The deep atmosphere of Venus and the possible role of density-driven separation of CO2 and N2 |url=https://hal.archives-ouvertes.fr/hal-01635402/file/deepatm_persp_rev2.pdf |url-status=live |journal=Nature Geoscience |publisher=Springer Science and Business Media LLC |volume=10 |issue=7 |pages=473–477 |bibcode=2017NatGe..10..473L |doi=10.1038/ngeo2971 |issn=1752-0894 |s2cid=133864520 |archive-url=https://web.archive.org/web/20190504081028/https://hal.archives-ouvertes.fr/hal-01635402/file/deepatm_persp_rev2.pdf |archive-date=4 May 2019 |access-date=11 August 2023}}</ref> Venus has a surface temperatures over {{Cvt|400|C|F}}, mainly due to the amount of [[greenhouse gas]]es in the atmosphere.<ref>{{Cite thesis |last=Bullock |first=Mark Alan |title=The Stability of Climate on Venus |date=1997 |degree=PhD |publisher=Southwest Research Institute |url=http://www.boulder.swri.edu/~bullock/Homedocs/PhDThesis.pdf |access-date=26 December 2006 |url-status=dead |archive-url=https://web.archive.org/web/20070614202751/http://www.boulder.swri.edu/~bullock/Homedocs/PhDThesis.pdf |archive-date=14 June 2007}}</ref> The planet lacks a protective magnetic field to protect against [[Atmospheric stripping|stripping]] by the solar wind, which suggests that its atmosphere is sustained by volcanic activity.<ref>{{Cite web |last=Rincon |first=Paul |date=1999 |title=Climate Change as a Regulator of Tectonics on Venus |url=http://www.boulder.swri.edu/~bullock/Homedocs/Science2_1999.pdf |url-status=dead |archive-url=https://web.archive.org/web/20070614202807/http://www.boulder.swri.edu/~bullock/Homedocs/Science2_1999.pdf |archive-date=14 June 2007 |access-date=19 November 2006 |website=Johnson Space Center Houston, TX, Institute of Meteoritics, University of New Mexico, Albuquerque, NM}}</ref> Its surface displays extensive evidence of volcanic activity with stagnant [[lid tectonics]].<ref>{{Cite journal |last1=Elkins-Tanton |first1=L. T. |last2=Smrekar |first2=S. E. |last3=Hess |first3=P. C. |last4=Parmentier |first4=E. M. |date=March 2007 |title=Volcanism and volatile recycling on a one-plate planet: Applications to Venus |journal=Journal of Geophysical Research |volume=112 |issue=E4 |bibcode=2007JGRE..112.4S06E |doi=10.1029/2006JE002793 |id=E04S06 |doi-access=free}}</ref> Venus has no natural satellites.<ref name="spaceplace.nasa.gov"/>
* {{Visible anchor|Earth|text=[[Earth]]}} (0.98–1.02&nbsp;AU)<ref name="nasa-factsheet" group="D" /> is the only place in the universe where [[life]] and [[Water distribution on Earth|surface liquid water]] are known to exist.<ref name="life">{{Cite web |title=What are the characteristics of the Solar System that lead to the origins of life? |url=https://science.nasa.gov/planetary-science/big-questions/what-are-the-characteristics-of-the-solar-system-that-lead-to-the-origins-of-life-1 |url-status=dead |archive-url=https://web.archive.org/web/20100408055814/http://science.nasa.gov/planetary-science/big-questions/what-are-the-characteristics-of-the-solar-system-that-lead-to-the-origins-of-life-1 |archive-date=8 April 2010 |access-date=30 August 2011 |publisher=NASA Science (Big Questions)}}</ref> Earth's atmosphere contains 78% [[nitrogen]] and 21% [[oxygen]], which is the result of the presence of life.<ref name="handbook">{{Cite book |title=[[CRC Handbook of Chemistry and Physics]] |publisher=CRC Press |year=2016–2017 |isbn=978-1-4987-5428-6 |editor-last=Haynes |editor-first=H. M. |edition=97th |page=14{{Hyphen}}3<!-- the page ref itself is hyphenated -->}}</ref><ref name="NYT-20131003">{{Cite news |last=Zimmer |first=Carl |author-link=Carl Zimmer |date=3 October 2013 |title=Earth's Oxygen: A Mystery Easy to Take for Granted |work=[[The New York Times]] |url=https://www.nytimes.com/2013/10/03/science/earths-oxygen-a-mystery-easy-to-take-for-granted.html |url-access=limited |access-date=3 October 2013 |archive-url=https://web.archive.org/web/20131003121909/http://www.nytimes.com/2013/10/03/science/earths-oxygen-a-mystery-easy-to-take-for-granted.html |archive-date=3 October 2013}}</ref> The planet has a complex [[climate]] and [[weather]] system, with conditions differing drastically between [[climate region]]s.<ref name="climate_zones">{{cite web |author=Staff |title=Climate Zones |url=http://www.ace.mmu.ac.uk/eae/climate/older/Climate_Zones.html |archive-url=https://web.archive.org/web/20100808131632/http://www.ace.mmu.ac.uk/eae/climate/older/Climate_Zones.html |archive-date=8 August 2010 |access-date=24 March 2007 |publisher=UK Department for Environment, Food and Rural Affairs}}</ref> The solid surface of Earth is dominated by green [[vegetation]], [[Hot deserts|deserts]] and white [[ice sheet]]s.<ref name="Carlowicz Simmon 2019">{{cite web |last1=Carlowicz |first1=Michael |last2=Simmon |first2=Robert |date=15 July 2019 |title=Seeing Forests for the Trees and the Carbon: Mapping the World's Forests in Three Dimensions |url=https://earthobservatory.nasa.gov/features/ForestCarbon#:~:text=They%20cover%20about%2030%20percent,percent%20of%20the%20Earth's%20land. |access-date=31 December 2022 |website=NASA Earth Observatory |archive-date=31 December 2022 |archive-url=https://web.archive.org/web/20221231005400/https://earthobservatory.nasa.gov/features/ForestCarbon#:~:text=They%20cover%20about%2030%20percent,percent%20of%20the%20Earth's%20land. |url-status=live }}</ref><ref name="Cain 2010">{{cite web |last=Cain |first=Fraser |date=1 June 2010 |title=What Percentage of the Earth's Land Surface is Desert? |url=https://www.universetoday.com/65639/what-percentage-of-the-earths-land-surface-is-desert/ |access-date=3 January 2023 |website=Universe Today |archive-date=3 January 2023 |archive-url=https://web.archive.org/web/20230103153344/https://www.universetoday.com/65639/what-percentage-of-the-earths-land-surface-is-desert/ |url-status=live }}</ref><ref name="National Geographic Society 2006">{{cite web |date=6 August 2006 |title=Ice Sheet |url=https://education.nationalgeographic.org/resource/ice-sheet/ |access-date=3 January 2023 |website=National Geographic Society |archive-date=27 November 2023 |archive-url=https://web.archive.org/web/20231127174259/https://education.nationalgeographic.org/resource/ice-sheet/ |url-status=live }}</ref> Earth's surface is shaped by [[plate tectonics]] that formed the continental masses.<ref name=Head_et_al_1981/> Earth's planetary [[magnetosphere]] shields the surface from radiation, limiting [[atmospheric stripping]] and maintaining life habitability.<ref>{{Cite book |last=Pentreath |first=R. J. |url=https://books.google.com/books?id=avRVEAAAQBAJ&pg=PA94 |title=Radioecology: Sources and Consequences of Ionising Radiation in the Environment |date=2021 |publisher=Cambridge University Press |isbn=978-1009040334 |pages=94–97 |access-date=12 April 2022 |archive-url=https://web.archive.org/web/20220420161217/https://www.google.com/books/edition/Radioecology/avRVEAAAQBAJ?hl=en&gbpv=1&pg=PA94 |archive-date=20 April 2022 |url-status=live}}</ref>
** The [[Moon]] is Earth's only natural satellite.<ref>{{Cite web |title=Facts About Earth - NASA Science |url=https://science.nasa.gov/earth/facts/ |access-date=11 January 2024 |website=NASA Science |date=30 May 2023 |language=en}}</ref> Its diameter is one-quarter the size of Earth's.<ref name="Metzger2021">{{Citation |last1=Metzger |first1=Philip |title=Moons are planets: Scientific usefulness versus cultural teleology in the taxonomy of planetary science |date=2021 |journal=[[Icarus (journal)|Icarus]] |volume=374 |page=114768 |arxiv=2110.15285 |bibcode=2022Icar..37414768M |doi=10.1016/j.icarus.2021.114768 |s2cid=240071005 |last2=Grundy |first2=Will |last3=Sykes |first3=Mark |last4=Stern |first4=Alan |last5=Bell |first5=James |last6=Detelich |first6=Charlene |last7=Runyon |first7=Kirby |last8=Summers |first8=Michael |author-link1=Philip T. Metzger}}</ref> Its surface is covered in [[Lunar soil|very fine regolith]] and dominated by [[impact crater]]s.<ref>{{cite web |date=30 January 2006 |title=The Smell of Moondust |url=https://science.nasa.gov/headlines/y2006/30jan_smellofmoondust.htm |url-status=dead |archive-url=https://web.archive.org/web/20100308112332/http://science.nasa.gov/headlines/y2006/30jan_smellofmoondust.htm |archive-date=8 March 2010 |access-date=15 March 2010 |publisher=NASA}}</ref><ref>{{cite book |last=Melosh |first=H. J. |title=Impact cratering: A geologic process |date=1989 |publisher=[[Oxford University Press]] |isbn=978-0-19-504284-9}}</ref> Large dark patches on the Moon, [[Lunar mare|maria]], are formed from past volcanic activity.<ref>{{cite web |last=Norman |first=M. |date=21 April 2004 |title=The Oldest Moon Rocks |url=http://www.psrd.hawaii.edu/April04/lunarAnorthosites.html |url-status=live |archive-url=https://web.archive.org/web/20070418152325/http://www.psrd.hawaii.edu/April04/lunarAnorthosites.html |archive-date=18 April 2007 |access-date=12 April 2007 |work=Planetary Science Research Discoveries |publisher=Hawai'i Institute of Geophysics and Planetology}}</ref> The Moon's atmosphere is extremely thin, consisting of a [[partial vacuum]] with particle densities of under 10<sup>7</sup> per cm<sup>−3</sup>.<ref>{{cite book |last=Globus |first=Ruth |title=Space Settlements: A Design Study |date=1977 |publisher=NASA |editor=Richard D. Johnson & Charles Holbrow |chapter=Chapter 5, Appendix J: Impact Upon Lunar Atmosphere |access-date=17 March 2010 |chapter-url=http://settlement.arc.nasa.gov/75SummerStudy/5appendJ.html |archive-url=https://web.archive.org/web/20100531205037/http://settlement.arc.nasa.gov/75SummerStudy/5appendJ.html |archive-date=31 May 2010 |url-status=dead}}</ref>
* {{Visible anchor|Mars|text=[[Mars]]}} (1.38–1.67&nbsp;AU)<ref name="nasa-factsheet" group="D" /> has a radius about half of that of Earth.<ref name="Seidelmann2007">{{cite journal |last1=Seidelmann |first1=P. Kenneth |last2=Archinal |first2=Brent A. |last3=A'Hearn<!-- written A'hearn here, mostly A'Hearn elsewhere --> |first3=Michael F. |last4=Conrad |first4=Albert R. |last5=Consolmagno |first5=Guy J. |last6=Hestroffer |first6=Daniel |last7=Hilton |first7=James L. |last8=Krasinsky |first8=Georgij A. |last9=Neumann |first9=Gregory A. |last10=Oberst |first10=Jürgen |last11=Stooke |first11=Philip J. |last12=Tedesco |first12=Edward F. |last13=Tholen |first13=David J. |last14=Thomas |first14=Peter C. |last15=Williams |first15=Iwan P. |year=2007 |title=Report of the IAU/IAG Working Group on cartographic coordinates and rotational elements: 2006 |journal=Celestial Mechanics and Dynamical Astronomy |volume=98 |issue=3 |pages=155–180 |bibcode=2007CeMDA..98..155S |doi=10.1007/s10569-007-9072-y |ref={{sfnRef|Seidelmann Archinal A'hearn et al.|2007}} |doi-access=free}}</ref> Most of the planet is red due to [[iron(III) oxide|iron oxide]] in Martian soil,<ref>{{Cite journal |last=Peplow |first=Mark |date=6 May 2004 |title=How Mars got its rust |url=http://www.nature.com/articles/news040503-6 |url-status=live |journal=Nature |language=en |pages=news040503–6 |doi=10.1038/news040503-6 |issn=0028-0836 |archive-url=https://web.archive.org/web/20220407105832/https://www.nature.com/articles/news040503-6 |archive-date=7 April 2022 |access-date=9 April 2022}}</ref> and the polar regions are covered in [[Martian polar ice caps|white ice caps]] made of water and [[carbon dioxide]].<ref>{{Cite web |title=Polar Caps |url=https://marsed.asu.edu/mep/ice/polar-caps |access-date=6 January 2022 |website=Mars Education at Arizona State University |archive-date=28 May 2021 |archive-url=https://web.archive.org/web/20210528133135/https://marsed.asu.edu/mep/ice/polar-caps |url-status=live }}</ref> Mars has an atmosphere composed mostly of carbon dioxide, with surface pressure 0.6% of that of Earth, which is sufficient to support some weather phenomena.<ref>{{Cite book |last1=Gatling |first1=David C. |title=Encyclopaedia of the Solar System |last2=Leovy |first2=Conway |date=2007 |editor-last=Lucy-Ann McFadden |pages=301–314 |chapter=Mars Atmosphere: History and Surface Interactions |display-editors=etal}}</ref> During the Mars year (687 Earth days), there are large surface temperature swings on the surface between {{Cvt|-78.5|C|F}} to {{Cvt|5.7|C|F}}. The surface is peppered with volcanoes and [[rift valley]]s, and has a rich collection of [[mineral]]s.<ref>{{Cite web |last=Noever |first=David |date=2004 |title=Modern Martian Marvels: Volcanoes? |url=https://www.astrobio.net/mars/modern-martian-marvels-volcanoes |url-status=dead |archive-url=https://web.archive.org/web/20200314112555/https://www.astrobio.net/mars/modern-martian-marvels-volcanoes |archive-date=14 March 2020 |access-date=23 July 2006 |website=NASA Astrobiology Magazine}}</ref><ref name="ismars">[http://mars.jpl.nasa.gov/msl/multimedia/videos/index.cfm?v=29&a=2 NASA – ''Mars in a Minute: Is Mars Really Red?''] {{Webarchive|url=https://web.archive.org/web/20140720135450/http://mars.jpl.nasa.gov/msl/multimedia/videos/index.cfm?v=29&a=2|date=20 July 2014}} ([http://mars.jpl.nasa.gov/multimedia/videos/movies/miam20111110/miam20111110.pdf Transcript] {{Webarchive|url=https://web.archive.org/web/20151106174558/http://mars.jpl.nasa.gov/multimedia/videos/movies/miam20111110/miam20111110.pdf|date=6 November 2015}}) {{PD-notice}}</ref> Mars has a highly [[Planetary differentiation|differentiated]] internal structure, and lost its magnetosphere 4&nbsp;billion years ago.<ref name="Nimmo 2005">{{cite journal |last1=Nimmo |first1=Francis |last2=Tanaka |first2=Ken |year=2005 |title=Early Crustal Evolution of Mars |journal=Annual Review of Earth and Planetary Sciences |volume=33 |issue=1 |pages=133–161 |bibcode=2005AREPS..33..133N |doi=10.1146/annurev.earth.33.092203.122637 |s2cid=45843366}}</ref><ref name="swind">{{cite web |last=Philips |first=Tony |date=31 January 2001 |title=The Solar Wind at Mars |url=https://science.nasa.gov/science-news/science-at-nasa/2001/ast31jan_1/ |url-status=dead |archive-url=https://web.archive.org/web/20110818180040/https://science.nasa.gov/science-news/science-at-nasa/2001/ast31jan_1/ |archive-date=18 August 2011 |access-date=22 April 2022 |website=Science@NASA}} {{PD-notice}}</ref> [[Moons of Mars|Mars has two tiny moons]]:<ref name="NYT-20200725">{{cite news |last=Andrews |first=Robin George |date=25 July 2020 |title=Why the 'Super Weird' Moons of Mars Fascinate Scientists - What's the big deal about little Phobos and tinier Deimos? |url=https://www.nytimes.com/2020/07/25/science/mars-moons-phobos-deimos.html |url-status=live |archive-url=https://web.archive.org/web/20200725094039/https://www.nytimes.com/2020/07/25/science/mars-moons-phobos-deimos.html |archive-date=25 July 2020 |access-date=25 July 2020 |work=[[The New York Times]]}}</ref>
** [[Phobos (moon)|Phobos]] is Mars's inner moon. It is a small, irregularly shaped object with a mean radius of {{convert|11|km|abbr=on|sigfig=1}}. Its surface is very unreflective and dominated by impact craters.<ref name="jplssd" group="D">{{cite web |date=13 July 2006 |title=Planetary Satellite Physical Parameters |url=http://ssd.jpl.nasa.gov/?sat_phys_par |access-date=29 January 2008 |publisher=[[JPL]] (Solar System Dynamics) |archive-date=1 November 2013 |archive-url=https://web.archive.org/web/20131101144111/http://ssd.jpl.nasa.gov/?sat_phys_par |url-status=live }}</ref><ref>{{cite web |date=12 January 2004 |title=Phobos |url=http://www.bbc.co.uk/science/space/solarsystem/mars/phobos.shtml |url-status=dead |archive-url=https://web.archive.org/web/20090422160500/http://www.bbc.co.uk/science/space/solarsystem/mars/phobos.shtml |archive-date=22 April 2009 |access-date=19 July 2021 |work=[[BBC Online]]}}</ref> In particular, Phobos's surface has a very large [[Stickney (crater)|Stickney impact crater]] that is roughly {{convert|4.5|km|mi|abbr=on}} in radius.<ref>{{cite web |title=Stickney Crater-Phobos |url=http://www.solarviews.com/cap/mars/phobos2.htm |quote=One of the most striking features of Phobos, aside from its irregular shape, is its giant crater Stickney. Because Phobos is only {{Convert|28|by|20|km||sp=us}}, it must have been nearly shattered from the force of the impact that caused the giant crater. Grooves that extend across the surface from Stickney appear to be surface fractures caused by the impact. |access-date=21 April 2024 |archive-date=3 November 2011 |archive-url=https://web.archive.org/web/20111103010644/http://www.solarviews.com/cap/mars/phobos2.htm |url-status=live }}</ref>
** [[Deimos (moon)|Deimos]] is Mars's outer moon. Like Phobos, it is irregularly shaped, with a mean radius of {{convert|6|km|mi|abbr=on|sigfig=1}} and its surface reflects little light.<ref name="Horizons-Deimos" group="D">{{cite web |date=21 September 2013 |title=HORIZONS Web-Interface |url=http://ssd.jpl.nasa.gov/?horizons |access-date=4 December 2013 |publisher=NASA |archive-date=28 March 2007 |archive-url=https://web.archive.org/web/20070328180634/http://ssd.jpl.nasa.gov/?horizons |url-status=live }}</ref><ref name="JPLSSD" group="D">{{cite web |date=13 July 2006 |title=Planetary Satellite Physical Parameters |url=http://ssd.jpl.nasa.gov/?sat_phys_par |access-date=29 January 2008 |publisher=[[Jet Propulsion Laboratory]] (Solar System Dynamics) |archive-date=1 November 2013 |archive-url=https://web.archive.org/web/20131101144111/http://ssd.jpl.nasa.gov/?sat_phys_par |url-status=live }}</ref> However, the surface of Deimos is noticeably smoother than Phobos because the regolith partially covers the impact craters.<ref>{{Cite web |date=6 June 2023 |title=Deimos |url=https://www.britannica.com/place/Deimos-moon-of-Mars |access-date=21 April 2024 |website=Britannica |language=en |quote=It thus appears smoother than Phobos because its craters lie partially buried under this loose material. |archive-date=12 November 2018 |archive-url=https://web.archive.org/web/20181112023547/https://www.britannica.com/place/Deimos-moon-of-Mars |url-status=live }}</ref>