Editing Moon (section)

==== Volcanic features ====
{{Main |Volcanism on the Moon}}
[[File:Moon names.svg|thumb|upright=1.35|The names of the main volcanic features, the [[lunar mare|maria]] (blue), and of some [[lunar craters|craters]] (brown) of the near side of the Moon]]
The main features visible from Earth by the naked eye are dark and relatively featureless lunar plains called ''[[lunar mare|maria]]'' (singular ''mare''; [[Latin]] for "seas", as they were once believed to be filled with water)<ref>{{cite book |author=Wlasuk, Peter |title=Observing the Moon |url=https://books.google.com/books?id=TWtLIOlPwS4C |date=2000 |publisher=[[Springer Science+Business Media|Springer]] |isbn=978-1-85233-193-1 |page=19}}</ref> are vast solidified pools of ancient [[basalt]]ic lava. Although similar to terrestrial basalts, lunar basalts have more iron and no minerals altered by water.<ref>{{cite web |url=http://www.psrd.hawaii.edu/April04/lunarAnorthosites.html |title=The Oldest Moon Rocks |last=Norman |first=M. |work=Planetary Science Research Discoveries |publisher=Hawai'i Institute of Geophysics and Planetology |date=April 21, 2004 |access-date=April 12, 2007 |url-status=live |archive-url=https://web.archive.org/web/20070418152325/http://www.psrd.hawaii.edu/April04/lunarAnorthosites.html |archive-date=April 18, 2007}}</ref> The majority of these lava deposits erupted or flowed into the depressions associated with [[impact basins]], though the Moon's largest expanse of basalt flooding, [[Oceanus Procellarum]], does not correspond to an obvious impact basin. Different episodes of lava flow in maria can often be recognized by variations in surface albedo and distinct flow margins.<ref>{{cite journal |last1=Friedman |first1=R.C. |last2=Blewett |first2=D. T. |last3=Taylor |first3=G.J. |last4=Lucey |first4=P. G. |year=1996 |title=FeO and TiO2 Variations in Mare Imbrium |journal=Lunar and Planetary Science |volume=27 |pages=383 |bibcode=1996LPI....27..383F |url=https://adsabs.harvard.edu/full/1996LPI....27..383F}}</ref>

As the maria formed, cooling and contraction of the basaltic lava created [[wrinkle ridge]]s in some areas. These low, sinuous ridges can extend for hundreds of kilometers and often outline buried structures within the mare. Another result of maria formation is the creation of concentric depressions along the edges, known as [[rille|arcuate rilles]]. These features occur as the mare basalts sink inward under their own weight, causing the edges to fracture and separate.

In addition to the visible maria, the Moon has mare deposits covered by ejecta from impacts. Called cryptomares, these hidden mares are likely older than the exposed ones.<ref>{{cite journal |last1=Izquierdo |first1=Kristel |last2=Sori |first2=M. M. |last3=Checketts |first3=B. |last4=Hampton |first4=I. |last5=Johnson |first5=B.C. |last6=Soderblom |first6=J.M. |year=2024 |title=Global Distribution and Volume of Cryptomare and Visible Mare on the Moon From Gravity and Dark Halo Craters |journal=Journal of Geophysical Research: Planets |volume=129 |issue=2 |doi=10.1029/2023JE007867 |bibcode=2024JGRE..12907867I |doi-access=free}}</ref> Conversely, mare lava has obscured many impact melt sheets and pools. Impact melts are formed when intense shock pressures from collisions vaporize and melt zones around the impact site. Where still exposed, impact melt can be distinguished from mare lava by its distribution, albedo, and texture.<ref>{{cite journal |last1=Spudis |first1=Paul |year=2016 |title=Mapping Melts on the Moon |journal=Smithsonian Air and Space Magazine |url=https://www.smithsonianmag.com/air-space-magazine/mapping-melted-moon-180958645/}}</ref>

[[Sinuous rilles]], found in and around maria, are likely extinct [[lava channels]] or collapsed [[lava tubes]]. They typically originate from volcanic [[Volcanism on the Moon|vents]], meandering and sometimes branching as they progress. The largest examples, such as [[Schroter's Valley]] and [[Hadley–Apennine|Rima Hadley]], are significantly longer, wider, and deeper than terrestrial lava channels, sometimes featuring bends and sharp turns that again, are uncommon on Earth.

Mare volcanism has altered impact craters in various ways, including filling them to varying degrees, and raising and fracturing their floors from uplift of mare material beneath their interiors. Examples of such craters include [[Taruntius (crater)|Taruntius]] and [[Gassendi (crater)|Gassendi]]. Some craters, such as [[Hyginus (crater)|Hyginus]], are of wholly volcanic origin, forming as [[caldera]]s or [[pit crater|collapse pits]]. Such craters are relatively rare and tend to be smaller (typically a few kilometers wide), shallower, and more irregularly shaped than impact craters. They also lack the upturned rims characteristic of impact craters.

Several [[geologic province]]s containing [[shield volcano]]es and volcanic [[lunar dome|domes]] are found within the near side maria.<ref>{{cite journal |last1=Wilson |first1=Lionel |last2=Head |first2=James W. |title=Lunar Gruithuisen and Mairan domes: Rheology and mode of emplacement |journal=[[Journal of Geophysical Research]] |date=2003 |volume=108 |url=http://www.agu.org/pubs/crossref/2003/2002JE001909.shtml |access-date=April 12, 2007 |issue=E2 |doi=10.1029/2002JE001909 |page=5012 |bibcode=2003JGRE..108.5012W |citeseerx=10.1.1.654.9619 |s2cid=14917901 |url-status=live |archive-url=https://web.archive.org/web/20070312071105/http://www.agu.org/pubs/crossref/2003/2002JE001909.shtml |archive-date=March 12, 2007}}</ref> There are also some regions of [[pyroclastic rock|pyroclastic deposits]], [[scoria cones]] and [[volcanism on the Moon|non-basaltic domes]] made of particularly high viscosity lava.

Almost all maria are on the near side of the Moon, and cover 31% of the surface of the near side<ref name="worldbook" /> compared with 2% of the far side.<ref>{{cite journal |last1=Gillis |first1=J. J. |last2=Spudis |first2=P. D. |title=The Composition and Geologic Setting of Lunar Far Side Maria |journal=[[Lunar and Planetary Science]] |date=1996 |volume=27 |page=413 |bibcode=1996LPI....27..413G}}</ref> This is likely due to a [[KREEP|concentration of heat-producing elements]] under the crust on the near side, which would have caused the underlying mantle to heat up, partially melt, rise to the surface and erupt.<ref name="S06" /><ref>{{cite journal |title=Global Elemental Maps of the Moon: The Lunar Prospector Gamma-Ray Spectrometer |last1=Lawrence |first1=D. J. |last2=Feldman |first2=W. C. |last3=Barraclough |first3=B. L. |last4=Binder |first4=A. B. |last5=Elphic |first5=R. C. |last6=Maurice |first6=S. |last7=Thomsen |first7=D. R. |journal=[[Science (journal)|Science]] |volume=281 |issue=5382 |pages=1484–1489 |doi=10.1126/science.281.5382.1484 |date=August 11, 1998 |pmid=9727970 |bibcode=1998Sci...281.1484L |doi-access=free}}</ref><ref>{{cite journal |url=http://www.psrd.hawaii.edu/Aug00/newMoon.html |title=A New Moon for the Twenty-First Century |page=41 |last=Taylor |first=G. J. |journal=Planetary Science Research Discoveries |date=August 31, 2000 |access-date=April 12, 2007 |url-status=live |archive-url=https://web.archive.org/web/20120301074958/http://www.psrd.hawaii.edu/Aug00/newMoon.html |archive-date=March 1, 2012 |bibcode=2000psrd.reptE..41T}}</ref> Most of the Moon's [[lunar mare|mare basalts]] erupted during the [[Imbrian|Imbrian period]], 3.3–3.7&nbsp;billion years ago, though some being as young as 1.2&nbsp;billion years<ref name="Hiesinger" /> and as old as 4.2&nbsp;billion years.<ref name="Papike" />

[[File:Lava flows in Mare Imbrium (AS15-M-1558).png|thumb|Old [[basalt|hardened]] lava flows of [[Mare Imbrium]] forming [[wrinkle ridge]]s]]

In 2006, a study of [[Ina (crater)|Ina]], a tiny depression in [[Lacus Felicitatis]], found jagged, relatively dust-free features that, because of the lack of erosion by infalling debris, appeared to be only 2 million years old.<ref name=Berardelli>{{cite journal |url=https://www.science.org/content/article/long-live-moon |title=Long Live the Moon! |journal=[[Science (journal)|Science]] |date=November 9, 2006 |author=Phil Berardelli |url-status=live |archive-url=https://web.archive.org/web/20141018153016/http://news.sciencemag.org/2006/11/long-live-moon |archive-date=October 18, 2014 |access-date=October 14, 2014}}</ref> [[Moonquake]]s and releases of gas indicate continued lunar activity.<ref name="Berardelli"/> Evidence of recent lunar volcanism has been identified at 70 [[irregular mare patch]]es, some less than 50 million years old. This raises the possibility of a much warmer lunar mantle than previously believed, at least on the near side where the deep crust is substantially warmer because of the greater concentration of radioactive elements.<ref>{{cite web |url=http://news.discovery.com/space/imps-reveal-volcanoes-erupted-recently-on-the-moon-141014.htm |title=Volcanoes Erupted 'Recently' on the Moon |publisher=[[Discovery News]] |date=October 14, 2014 |author=Jason Major |url-status=live |archive-url=https://web.archive.org/web/20141016190653/http://news.discovery.com/space/imps-reveal-volcanoes-erupted-recently-on-the-moon-141014.htm |archive-date=October 16, 2014}}</ref><ref>{{cite web |url=http://www.nasa.gov/press/2014/october/nasa-mission-finds-widespread-evidence-of-young-lunar-volcanism/#.VDxNw0t3uxo |title=NASA Mission Finds Widespread Evidence of Young Lunar Volcanism |publisher=NASA |date=October 12, 2014 |url-status=live |archive-url=https://web.archive.org/web/20150103095208/http://www.nasa.gov/press/2014/october/nasa-mission-finds-widespread-evidence-of-young-lunar-volcanism/#.VDxNw0t3uxo |archive-date=January 3, 2015}}</ref><ref>{{cite journal |url=https://www.science.org/content/article/recent-volcanic-eruptions-moon |title=Recent volcanic eruptions on the moon |journal=[[Science (journal)|Science]] |date=October 12, 2014 |author=Eric Hand |url-status=live |archive-url=https://web.archive.org/web/20141014092239/http://news.sciencemag.org/space/2014/10/recent-volcanic-eruptions-moon |archive-date=October 14, 2014}}</ref><ref>{{cite journal |title=Evidence for basaltic volcanism on the Moon within the past 100 million years |journal=[[Nature Geoscience]] |last1=Braden |first1=S.E. |last2=Stopar |first2=J.D. |last3=Robinson |first3=M.S. |last4=Lawrence |first4=S.J. |last5=van der Bogert |first5=C.H. |last6=Hiesinger |first6=H. |volume=7 |issue=11 |pages=787–791 |bibcode=2014NatGe...7..787B |doi=10.1038/ngeo2252 |year=2014}}</ref> Evidence has been found for 2–10 million years old basaltic volcanism within the crater Lowell,<ref>{{cite journal |last1=Srivastava |first1=N. |last2=Gupta |first2=R.P. |year=2013 |title=Young viscous flows in the Lowell crater of Orientale basin, Moon: Impact melts or volcanic eruptions? |journal=[[Planetary and Space Science]] |volume=87 |pages=37–45 |doi=10.1016/j.pss.2013.09.001 |bibcode=2013P&SS...87...37S}}</ref><ref>{{cite journal |last1=Gupta |first1=R.P. |last2=Srivastava |first2=N. |last3=Tiwari |first3=R.K. |year=2014 |title=Evidences of relatively new volcanic flows on the Moon |journal=[[Current Science]] |volume=107 |issue=3 |pages=454–460 |jstor=24103498}}</ref> inside the Orientale basin. Some combination of an initially hotter mantle and local enrichment of heat-producing elements in the mantle could be responsible for prolonged activities on the far side in the Orientale basin.<ref>{{cite journal |last1=Whitten |first1=Jennifer |last2=Head |first2=James W. |last3=Staid |first3=Matthew |last4=Pieters |first4=Carle M. |last5=Mustard |first5=John |last6=Clark |first6=Roger |last7=Nettles |first7=Jeff |last8=Klima |first8=Rachel L. |last9=Taylor |first9=Larry |year=2011 |title=Lunar mare deposits associated with the Orientale impact basin: New insights into mineralogy, history, mode of emplacement, and relation to Orientale Basin evolution from Moon Mineralogy Mapper (M3) data from Chandrayaan-1 |journal=[[Journal of Geophysical Research]] |volume=116 |page=E00G09 |doi=10.1029/2010JE003736 |bibcode=2011JGRE..116.0G09W |s2cid=7234547 |doi-access=free}}</ref><ref>{{cite journal |last1=Cho |first1=Y. |display-authors=etal |year=2012 |title=Young mare volcanism in the Orientale region contemporary with the Procellarum KREEP Terrane (PKT) volcanism peak period 2 b.y. ago |journal=[[Geophysical Research Letters]] |volume=39 |issue=11 |page=L11203 |bibcode=2012GeoRL..3911203C |doi=10.1029/2012GL051838 |s2cid=134074700}}</ref>

The lighter-colored regions of the Moon are called ''terrae'', or more commonly ''highlands'', because they are higher than most maria. They have been radiometrically dated to having formed 4.4&nbsp;billion years ago and may represent [[plagioclase]] [[cumulates]] of the lunar magma ocean.<ref name="Hiesinger" /><ref name="Papike" /> In contrast to Earth, no major lunar mountains are believed to have formed as a result of tectonic events.<ref>{{cite web |last=Munsell |first=K. |publisher=NASA |work=Solar System Exploration |title=Majestic Mountains |url=http://sse.jpl.nasa.gov/educ/themes/display.cfm?Item=mountains |date=December 4, 2006 |access-date=April 12, 2007 |url-status=dead |archive-url=https://web.archive.org/web/20080917055643/http://sse.jpl.nasa.gov/educ/themes/display.cfm?Item=mountains |archive-date=September 17, 2008}}</ref>

The concentration of maria on the near side likely reflects the substantially thicker crust of the highlands of the Far Side, which may have formed in a slow-velocity impact of a second moon of Earth a few tens of millions of years after the Moon's formation.<ref>{{cite journal |author=Richard Lovett |url=http://www.nature.com/news/2011/110803/full/news.2011.456.html#B1 |title=Early Earth may have had two moons : Nature News |journal=Nature |access-date=November 1, 2012 |url-status=live |archive-url=https://web.archive.org/web/20121103145236/http://www.nature.com/news/2011/110803/full/news.2011.456.html#B1 |archive-date=November 3, 2012 |doi=10.1038/news.2011.456 |year=2011 |doi-access=free}}</ref><ref>{{cite web |url=http://theconversation.edu.au/was-our-two-faced-moon-in-a-small-collision-2659 |title=Was our two-faced moon in a small collision? |publisher=Theconversation.edu.au |access-date=November 1, 2012 |url-status=dead |archive-url=https://web.archive.org/web/20130130004522/http://theconversation.edu.au/was-our-two-faced-moon-in-a-small-collision-2659 |archive-date=January 30, 2013}}</ref> Alternatively, it may be a consequence of asymmetrical [[tidal heating]] when the Moon was much closer to the Earth.<ref>{{cite journal |title=Near/far side asymmetry in the tidally heated Moon |last1=Quillen |first1=Alice C. |last2=Martini |first2=Larkin |last3=Nakajima |first3=Miki |journal=Icarus |volume=329 |pages=182–196 |date=September 2019 |doi=10.1016/j.icarus.2019.04.010 |pmid=32934397 |pmc=7489467 |arxiv=1810.10676 |bibcode=2019Icar..329..182Q}}</ref>