Editing Moon (section)

===Surface features===
{{Main|Selenography|Lunar terrane|List of lunar features|List of quadrangles on the Moon}}
[[File:Apollo 17 AS17-140-21497.jpg|thumb|[[Apollo 17]] astronaut [[Harrison H. Schmitt]] next to the large Moon boulder nicknamed "[[Tracy's Rock]]"]]
The [[topography of the Moon]] has been measured with [[laser altimetry]] and [[stereoscopy|stereo image analysis]].<ref>{{cite journal |title=Topography of the South Polar Region from Clementine Stereo Imaging |last1=Spudis |first1=Paul D. |last2=Cook |first2=A. |last3=Robinson |first3=M. |last4=Bussey |first4=B. |last5=Fessler |first5=B. |bibcode=1998nvmi.conf...69S |journal=Workshop on New Views of the Moon: Integrated Remotely Sensed, Geophysical, and Sample Datasets |page=69 |date=January 1998}}</ref> Its most extensive [[List of features on the Moon|topographic feature]] is the giant far-side [[South Pole–Aitken basin]], some {{Convert|2240 |km |abbr=on}} in diameter, the largest crater on the Moon and the second-largest confirmed impact [[List of largest craters in the Solar System|crater in the Solar System]].<ref name="Spudis1994" /><ref>{{cite journal |doi=10.1029/97GL01718 |first1=C. M. |last1=Pieters |first2=S. |last2=Tompkins |first3=J. W. |last3=Head |first4=P. C. |last4=Hess |title=Mineralogy of the Mafic Anomaly in the South Pole-Aitken Basin: Implications for excavation of the lunar mantle |journal=[[Geophysical Research Letters]] |volume=24 |issue=15 |pages=1903–1906 |date=1997 |bibcode=1997GeoRL..24.1903P |hdl=2060/19980018038 |s2cid=128767066 |hdl-access=free}}</ref> At {{Convert |13 |km |abbr=on}} deep, its floor is the lowest point on the surface of the Moon,<ref name="Spudis1994" /><ref>{{cite journal |url=http://www.psrd.hawaii.edu/July98/spa.html |title=The Biggest Hole in the Solar System |page=20 |last=Taylor |first=G. J. |date=July 17, 1998 |journal=Planetary Science Research Discoveries |access-date=April 12, 2007 |url-status=live |archive-url=https://web.archive.org/web/20070820042129/http://www.psrd.hawaii.edu/July98/spa.html |archive-date=August 20, 2007 |bibcode=1998psrd.reptE..20T}}</ref> reaching {{convert|-9.178|km}} at {{coord|70.368|S|172.413|W|globe:moon_type:landmark|display=inline}} in a crater within [[Antoniadi (lunar crater)|Antoniadi crater]].<ref name="n402">{{cite journal | last1=Li | first1=ChunLai | last2=Ren | first2=Xin | last3=Liu | first3=JianJun | last4=Zou | first4=XiaoDuan | last5=Mu | first5=LingLi | last6=Wang | first6=JianYu | last7=Shu | first7=Rong | last8=Zou | first8=YongLiao | last9=Zhang | first9=HongBo | last10=Lü | first10=Chang | last11=Liu | first11=JianZhong | last12=Zuo | first12=Wei | last13=Su | first13=Yan | last14=Wen | first14=WeiBin | last15=Bian | first15=Wei | last16=Wang | first16=Min | last17=Xu | first17=Chun | last18=Kong | first18=DeQing | last19=Wang | first19=XiaoQian | last20=Wang | first20=Fang | last21=Geng | first21=Liang | last22=Zhang | first22=ZhouBin | last23=Zheng | first23=Lei | last24=Zhu | first24=XinYing | last25=Li | first25=JunDuo | last26=Ouyang | first26=ZiYuan | title=Laser altimetry data of Chang'E-1 and the global lunar DEM model | journal=Science China Earth Sciences | volume=53 | issue=11 | date=2010 | issn=1674-7313 | doi=10.1007/s11430-010-4020-1 | pages=1582–1593| bibcode=2010ScChD..53.1582L }}</ref> The [[List of tallest mountains in the Solar System|highest elevations]] of the Moon's surface, with the so-called [[Selenean summit]] at {{convert|10.629|km}} , are located directly to the northeast ({{coord|5.441|N|158.656|W|globe:moon_type:landmark|display=inline}}),<ref name="n402"/> which might have been thickened by the oblique formation impact of the South Pole–Aitken basin.<ref>{{cite journal |last=Schultz |first=P.H. |date=March 1997 |page=1259 |volume=28 |title=Forming the south-pole Aitken basin – The extreme games |journal=Conference Paper, 28th Annual Lunar and Planetary Science Conference |bibcode=1997LPI....28.1259S}}</ref> Other large impact basins such as [[Mare Imbrium|Imbrium]], [[Mare Serenitatis|Serenitatis]], [[Mare Crisium|Crisium]], [[Mare Smythii|Smythii]], and [[Mare Orientale|Orientale]] possess regionally low elevations and elevated rims.<ref name="Spudis1994" /> The far side of the lunar surface is on average about {{Convert |1.9 |km |abbr=on}} higher than that of the near side.<ref name="W06" />

The discovery of [[fault scarp]] cliffs suggest that the Moon has shrunk by about 90 metres (300&nbsp;ft) within the past billion years.<ref>{{cite web |publisher=NASA |title=NASA's LRO Reveals 'Incredible Shrinking Moon' |date=August 19, 2010 |url=http://www.nasa.gov/mission_pages/LRO/news/shrinking-moon.html |url-status=live |archive-url=https://web.archive.org/web/20100821124252/http://www.nasa.gov/mission_pages/LRO/news/shrinking-moon.html |archive-date=August 21, 2010}}</ref> Similar shrinkage features exist on [[Geology of Mercury|Mercury]]. Mare Frigoris, a basin near the north pole long assumed to be geologically dead, has cracked and shifted. Since the Moon does not have tectonic plates, its tectonic activity is slow, and cracks develop as it loses heat.<ref>{{Cite journal |last1=Watters |first1=Thomas R. |last2=Weber |first2=Renee C. |last3=Collins |first3=Geoffrey C. |last4=Howley |first4=Ian J. |last5=Schmerr |first5=Nicholas C. |last6=Johnson |first6=Catherine L. |date=June 2019 |title=Shallow seismic activity and young thrust faults on the Moon |journal=Nature Geoscience |publication-date=May 13, 2019 |volume=12 |issue=6 |pages=411–417 |doi=10.1038/s41561-019-0362-2 |bibcode=2019NatGe..12..411W |s2cid=182137223 |issn=1752-0894}}</ref>

Scientists have confirmed the presence of a cave on the Moon near the [[Sea of Tranquillity]], not far from the 1969 [[Apollo 11]] landing site. The cave, identified as an entry point to a collapsed lava tube, is roughly 45 meters wide and up to 80 m long. This discovery marks the first confirmed entry point to a lunar cave. The analysis was based on photos taken in 2010 by NASA's [[Lunar Reconnaissance Orbiter]]. The cave's stable temperature of around {{val|17|u=°C}} could provide a hospitable environment for future astronauts, protecting them from extreme temperatures, solar radiation, and micrometeorites. However, challenges include accessibility and risks of avalanches and cave-ins. This discovery offers potential for future lunar bases or emergency shelters.<ref>{{Cite web |date=July 18, 2024 |title=Cave on the Moon: What this discovery means for space exploration |url=https://indianexpress.com/article/explained/everyday-explainers/cave-on-the-moon-explained-9459805/ |access-date=July 19, 2024 |website=The Indian Express |language=en}}</ref>

==== 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>

====Impact craters====
{{Further |List of craters on the Moon}}
[[File:Daedalus crater AS11-41-6151.jpg|alt=A gray, many-ridged surface from high above. The largest feature is a circular ringed structure with high walled sides and a lower central peak: the entire surface out to the horizon is filled with similar structures that are smaller and overlapping.|thumb|A view of a three-kilometer-deep larger crater [[Daedalus (crater)|Daedalus]] on the [[Far side of the Moon|Moon's far side]]]]
A major geologic process that has affected the Moon's surface is [[impact crater]]ing,<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> with craters formed when asteroids and comets collide with the lunar surface. There are estimated to be roughly 300,000 craters wider than {{Convert |1 |km |4=1 |abbr=on}} on the Moon's near side.<ref>{{cite web |title=Moon Facts |url=http://planck.esa.int/science-e/www/object/index.cfm?fobjectid=31412 |work=SMART-1 |publisher=[[European Space Agency]] |date=2010 |access-date=May 12, 2010 |archive-date=March 17, 2012 |archive-url=https://web.archive.org/web/20120317004513/http://planck.esa.int/science-e/www/object/index.cfm?fobjectid=31412 |url-status=dead}}</ref> Lunar craters exhibit a variety of forms, depending on their size. In order of increasing diameter, the basic types are simple craters with smooth bowl shaped interiors and upturned rims, [[complex crater]]s with flat floors, terraced walls and central peaks, [[peak ring]] basins, and [[multi-ring basin]]s with two or more concentric rings of peaks.<ref>[https://www.lpi.usra.edu/exploration/education/hsResearch/moon_101/ImpactCratering.pdf Impact Cratering Notes (LPI)]</ref> The vast majority of impact craters are circular, but some, like [[Cantor (crater)|Cantor]] and [[Janssen (lunar crater)|Janssen]], have more polygonal outlines, possibly guided by underlying faults and joints. Others, such as the [[Messier (crater)|Messier]] pair, [[Schiller (crater)|Schiller]], and [[Daniell (crater)|Daniell]], are elongated. Such elongation can result from highly oblique impacts, [[binary asteroid]] impacts, fragmentation of impactors before surface strike, or closely spaced [[secondary crater|secondary]] impacts.<ref>{{cite journal |last1=Herrick |first1=R.R. |last2=Forsberg-Taylor |first2=N. K. |year=2003 |title=The shape and appearance of craters formed by oblique impact on the Moon and Venus |journal=Meteoritics & Planetary Science |volume=38 |issue=11 |pages=1551–1578 |doi=10.1111/j.1945-5100.2003.tb00001.x |bibcode=2003M&PS...38.1551H |url=https://onlinelibrary.wiley.com/doi/pdfdirect/10.1111/j.1945-5100.2003.tb00001.x}}</ref>

The [[lunar geologic timescale]] is based on the most prominent impact events, such as multi-ring formations like [[Nectarian|Nectaris]], [[Lower Imbrian|Imbrium]], and [[Mare Orientale|Orientale]] that are between hundreds and thousands of kilometers in diameter and associated with a broad apron of ejecta deposits that form a regional [[stratigraphy|stratigraphic horizon]].<ref name="geologic" /> The lack of an atmosphere, weather, and recent geological processes mean that many of these craters are well-preserved. Although only a few [[multi-ring basins]] have been definitively dated, they are useful for assigning relative ages. Because impact craters accumulate at a nearly constant rate, counting the number of craters per unit area can be used to estimate the age of the surface.<ref name="geologic" />
However care needs to be exercised with the [[crater counting]] technique due to the potential presence of [[secondary crater]]s. Ejecta from impacts can create secondary craters that often appear in clusters or chains but can also occur as isolated formations at a considerable distance from the impact. These can resemble primary craters, and may even dominate small crater populations, so their unidentified presence can distort age estimates.<ref>{{cite journal |last1=Xiao |first1=Z. |last2=Strom |first2=R.G. |year=2012 |title=Problems determining relative and absolute ages using the small crater population |journal=Icarus |volume=220 |issue=1 |pages=254–267 |doi=10.1016/j.icarus.2012.05.012 |bibcode=2012Icar..220..254X |url=https://www.uni-muenster.de/imperia/md/content/planetology/lectures/ss2015/143897-hottopics/xiao_and_strom_2012.pdf}}</ref>

The radiometric ages of impact-melted rocks collected during the [[Apollo missions]] cluster between 3.8 and 4.1&nbsp;billion years old: this has been used to propose a [[Late Heavy Bombardment]] period of increased impacts.<ref>{{cite journal |last1=Hartmann |first1=William K. |last2=Quantin |first2=Cathy |last3=Mangold |first3=Nicolas |date=2007 |volume=186 |issue=1 |pages=11–23 |journal=[[Icarus (journal)|Icarus]] |title=Possible long-term decline in impact rates: 2. Lunar impact-melt data regarding impact history |doi=10.1016/j.icarus.2006.09.009 |bibcode=2007Icar..186...11H}}</ref>

High-resolution images from the Lunar Reconnaissance Orbiter in the 2010s show a contemporary crater-production rate significantly higher than was previously estimated. A secondary cratering process caused by [[distal ejecta]] is thought to churn the top two centimeters of regolith on a timescale of 81,000 years.<ref>{{cite web |url=https://www.newscientist.com/article/2108929-the-moon-has-hundreds-more-craters-than-we-thought/ |title=The moon has hundreds more craters than we thought |first=Rebecca |last=Boyle |url-status=live |archive-url=https://web.archive.org/web/20161013143743/https://www.newscientist.com/article/2108929-the-moon-has-hundreds-more-craters-than-we-thought/ |archive-date=October 13, 2016}}</ref><ref>{{cite journal |title=Quantifying crater production and regolith overturn on the Moon with temporal imaging |first1=Emerson J. |last1=Speyerer |first2=Reinhold Z. |last2=Povilaitis |first3=Mark S. |last3=Robinson |first4=Peter C. |last4=Thomas |first5=Robert V. |last5=Wagner |date=October 13, 2016 |journal=[[Nature (journal)|Nature]] |volume=538 |issue=7624 |pages=215–218 |doi=10.1038/nature19829 |pmid=27734864 |bibcode=2016Natur.538..215S |s2cid=4443574}}</ref> This rate is 100 times faster than the rate computed from models based solely on direct micrometeorite impacts.<ref>{{cite web |title=Earth's Moon Hit by Surprising Number of Meteoroids |date=October 13, 2016 |publisher=NASA |url=https://www.nasa.gov/press-release/goddard/2016/lro-lunar-cratering |access-date=May 21, 2021 |archive-date=July 2, 2022 |archive-url=https://web.archive.org/web/20220702225136/https://www.nasa.gov/press-release/goddard/2016/lro-lunar-cratering/ |url-status=live}}</ref>

====Lunar swirls====
{{Main|Lunar swirls}}
[[File:Reiner-gamma-clem1.jpg|thumb|Wide-angle image of a lunar swirl, the 70-kilometer-long [[Reiner Gamma]]]]
Lunar swirls are enigmatic features found across the Moon's surface. They are characterized by a high albedo, appear optically immature (i.e. the optical characteristics of a relatively young [[regolith]]), and often have a sinuous shape. Their shape is often accentuated by low [[albedo]] regions that wind between the bright swirls. They are located in places with enhanced surface [[magnetic field]]s and many are located at the [[antipodal point]] of major impacts. Well known swirls include the [[Reiner Gamma]] feature and [[Mare Ingenii]]. They are hypothesized to be areas that have been partially shielded from the [[solar wind]], resulting in slower [[space weathering]].<ref>{{cite journal |title=Reflectance spectra of seven lunar swirls examined by statistical methods: A space weathering study |last1=Chrbolková |first1=Kateřina |last2=Kohout |first2=Tomáš |last3=Ďurech |first3=Josef |journal=Icarus |volume=333 |pages=516–527 |date=November 2019 |doi=10.1016/j.icarus.2019.05.024 |bibcode=2019Icar..333..516C |doi-access=free}}</ref>