Editing South Pole–Aitken basin

{{Short description|Large impact crater on the Moon}}
{{Infobox lunar crater or mare
| name        = South Pole–Aitken basin
| image       = Aitken Kagu big.jpg
| caption     = [[Topographic map]] of the South Pole–Aitken basin based on [[SELENE|Kaguya]] data. Red represents high elevation, purple represents low elevation. The purple and grey elliptical rings trace the inner and outer walls of the basin. (The black ring is an old artifact of the image.)
| coordinates = {{coord|53|S|169|W|globe:moon_type:landmark|display=inline,title}}
| diameter    = About {{convert|2500|km|mi|abbr=on}}
| depth       = Between {{convert|6.2 and(-) 8.2|km|mi|abbr=on}}
| eponym      = [[Lunar south pole]]<br />[[Aitken (crater)]]
}}

The '''South Pole–Aitken basin''' (SPA Basin, {{IPAc-en|'|eɪ|t|k|ᵻ|n}}) is an immense [[impact crater]] on the [[far side of the Moon]]. At roughly {{convert|2500|km|mi|abbr=on}} in diameter and between {{convert|6.2 and(-) 8.2|km|mi|abbr=on}} deep, it is one of the [[list of largest craters in the Solar System|largest known impact craters]] in the [[Solar System]]. It is the largest, oldest, and deepest [[Depression (geology)|basin]] recognized on the [[Moon]].<ref name=Petro>{{Citation
| last1 = Petro
| first1 = Noah E.
| last2 = Pieters
| first2 = Carle M.
| title = Surviving the heavy bombardment: Ancient material at the surface of South Pole-Aitken Basin
| journal = Journal of Geophysical Research
| volume = 109
| issue = E6
| pages = E06004
| date = 2004-05-05
| doi = 10.1029/2003je002182
| bibcode = 2004JGRE..109.6004P
| doi-access = free
}}</ref> It is estimated that it was formed approximately 4.2 to 4.3 billion years ago, during the [[Pre-Nectarian]] epoch<ref>{{Cite journal |last1=Ivanov |first1=M. A. |last2=Hiesinger |first2=H. |last3=van der Bogert |first3=C. H. |last4=Orgel |first4=C. |last5=Pasckert |first5=J. H. |last6=Head |first6=J. W. |date=October 2018 |title=Geologic History of the Northern Portion of the South Pole-Aitken Basin on the Moon |journal=Journal of Geophysical Research: Planets |language=en |volume=123 |issue=10 |pages=2585–2612 |bibcode=2018JGRE..123.2585I |doi=10.1029/2018JE005590 |s2cid=53334293 |doi-access=free}}</ref> (with radiometric dating of lunar [[Zircon|zircons]] proposed to originate from the basin suggesting a precise age of 4.338 billion years<ref>{{Cite journal |last1=Barboni |first1=M. |last2=Szymanowski |first2=D. |last3= Schoene |first3=B. |last4=Dauphas |first4=N. |last5=Zhang |first5=Z. J. |last6=Chen |first6=X. |last7=McKeegan |first7=K. D. |date=2024-07-24 |title= High-precision U–Pb zircon dating identifies a major magmatic event on the Moon at 4.338 Ga |journal=Science Advances |volume = 10 |issue=30 |pages=eadn9871 |language=en |doi=10.1126/sciadv.adn9871 |doi-access=free |pmid=39047092 |hdl=20.500.11850/685478 |hdl-access=free }}</ref><ref>{{Cite journal |last1=Joy |first1=K. H. |last2=Wang |first2=N. |last3=Snape |first3=J. F. |last4=Goodwin |first4=A. |last5=Pernet-Fisher |first5=J. F. |last6=Whitehouse |first6=M. J. |last7=Liu |first7=Y. |last8=Lin |first8=Y. T. |last9=Darling |first9=J. R. |last10=Tar |first10=P. |last11=Tartèse |first11=R. |date=2024-10-16 |title=Evidence of a 4.33 billion year age for the Moon's South Pole–Aitken basin |journal=Nature Astronomy |volume=9 |issue=1 |pages=55–65 |language=en |doi=10.1038/s41550-024-02380-y |issn=2397-3366|doi-access=free |pmid=39866548 |pmc=11757148 }}</ref>). It was named for two features on opposite sides of the basin: the [[lunar south pole|lunar South Pole]] at one end and the crater [[Aitken (crater)|Aitken]] on the northern end. The outer rim of this basin can be seen from Earth as a huge [[mountain chain]] located on the Moon's southern limb, sometimes informally called "Leibnitz mountains".

On 3 January 2019, the [[Chang'e 4]], a [[People's Republic of China|Chinese]] spacecraft, landed in the basin,<ref>{{cite news |last1=Lyons |first1=Kate |title=Chang'e 4 landing: China probe makes historic touchdown on far side of the moon |url=https://www.theguardian.com/science/2019/jan/03/china-probe-change-4-land-far-side-moon-basin-crater |access-date=3 January 2019 |newspaper=The Guardian |language=en}}</ref> specifically within a crater called [[Von Kármán (lunar crater)|Von Kármán]].<ref name='A&S'>[https://www.airspacemag.com/daily-planet/chinas-journey-lunar-far-side-missed-opportunity-180963703/ China's Journey to the Lunar Far Side: A Missed Opportunity?] Paul D. Spudis, ''Air & Space Smithsonian''. 14 June 2017.</ref> In May 2019, scientists announced that a [[Mass concentration (astronomy)|large mass]] of material had been identified deep within the crater.<ref>{{cite journal |last1=James |first1=Peter B. |last2=Smith |first2=David E. |last3=Byrne |first3=Paul K. |last4=Kendall |first4=Jordan D. |last5=Melosh |first5=H. Jay |last6=Zuber |first6=Maria T. |title=Deep Structure of the Lunar South Pole-Aitken Basin |journal=Geophysical Research Letters |volume= 46|issue=10 |pages=5100–5106 |doi=10.1029/2019GL082252 |language=en |issn=1944-8007|year=2019 |bibcode=2019GeoRL..46.5100J |s2cid=134219155 }}</ref><ref>{{cite news |last1=Griffin |first1=Andrew |title=Huge, unexplained 'mass' spotted under the Moon |url=https://www.independent.co.uk/life-style/gadgets-and-tech/news/nasa-moon-mass-crater-metal-mystery-south-pole-aitken-a8952786.html |archive-url=https://ghostarchive.org/archive/20220524/https://www.independent.co.uk/life-style/gadgets-and-tech/news/nasa-moon-mass-crater-metal-mystery-south-pole-aitken-a8952786.html |archive-date=2022-05-24 |url-access=subscription |url-status=live |access-date=11 June 2019 |work=The Independent |date=10 June 2019 |language=en}}</ref> [[Chang'e 6]] aims to collect sample from this crater, specifically within the [[Apollo (crater)|Apollo basin]].<ref>{{cite web |last=Jones |first=Andrew |url=https://spacenews.com/chinas-change-6-probe-arrives-at-spaceport-for-first-ever-lunar-far-side-sample-mission/ |title=China's Chang'e-6 probe arrives at spaceport for first-ever lunar far side sample mission |work=[[SpaceNews]] |date=10 January 2024 |access-date=10 January 2024}}</ref>
== Discovery ==
[[File:South Pole-Aitken basin rim As08-13-2319hr.jpg|thumb|left|[[Apollo 8]] photograph showing the mountains along the northern rim of the basin]]

The existence of a giant far side basin was suspected as early as 1962 based on early Soviet probe images (namely [[Luna 3]] and [[Zond 3]]), but it was not until wide-field photographs taken by the US [[Lunar Orbiter program]] became available in 1966-7 that geologists recognized its true size. Laser altimeter data obtained during the Apollo 15 and 16 missions showed that the northern portion of this basin was very deep,<ref>{{cite journal | display-authors = 4| author = W. M. Kaula| author2 = G. Schubert| author3 = R. E. Lingenfelter| author4 = W. L. Sjogren| author5 = W. R. Wollenhaupt | name-list-style = amp| title = Apollo laser altimetry and inferences as to lunar structure | journal= Proc. Lunar Planet. Sci. Conf. | volume = 5 | pages = 3049–3058 |date=1974}}</ref> but since these data were only available along the near-equatorial [[ground track]]s of the orbiting [[command and service module]]s, the topography of the rest of the basin remained unknown. The geologic map showing the northern half of this basin and with its edge depicted was published in 1978 by the [[United States Geological Survey]].<ref>{{cite journal|author = D. E. Stuart-Alexander | title= Geologic map of the central far side of the Moon | journal = U.S. Geological Survey|volume = I-1047|date=1978 | page= 1047 | bibcode= 1978USGS...IM.1047S |url=http://www.lpi.usra.edu/resources/mapcatalog/usgs/I1047}}</ref> Little was known about the basin until the 1990s, when the spacecraft ''[[Galileo (spacecraft)|Galileo]]'' and ''[[Clementine (spacecraft)|Clementine]]'' visited the Moon. Multispectral images obtained from these missions showed that this basin contains more [[FeO]] and [[Titanium dioxide|TiO<sub>2</sub>]] than typical lunar highlands,<ref>{{cite web|title=The Biggest Hole in the Solar System|first=G. Jeffrey |last=Taylor|date=July 1998
|url=http://www.psrd.hawaii.edu/July98/PSRD-spa.pdf|publisher=University of Hawaii|access-date=February 5, 2023}}</ref> and hence has a darker appearance. The topography of the basin was mapped in its entirety for the first time using altimeter data and the analysis of stereo image pairs taken during the Clementine mission. Most recently, the composition of this basin has been further constrained by the analysis of data obtained from a gamma-ray spectrometer that was on board the [[Lunar Prospector]] mission.{{citation needed|date=March 2024}}
{{clear|left}}

== Physical characteristics ==
[[File:Moon back-view (Clementine, cropped).png|thumb|200px|left|The South Pole–Aitken basin is the darker area at the bottom of this image of the [[far side of the Moon]].]]

The South Pole–Aitken basin is the largest, deepest and oldest basin recognized on the Moon.<ref name="Petro"/> The lowest elevations of the Moon (about −9,000&nbsp;m) are located within the South Pole–Aitken basin. The Moon's tallest mountains are found around the basin's rim – they have summit elevations of up to 8,500&nbsp;m and base-to-peak heights of up to 7,000&nbsp;m.<ref>[https://moonsummits.carrd.co The Moon's Highs and Lows]</ref> Because of this basin's great size, the crust at this locale is expected to be thinner than typical as a result of the large amount of material that was excavated due to an impact. Crustal thickness maps constructed using the Moon's topography and gravity field imply a thickness of about 30&nbsp;km beneath the floor of this basin, in comparison to 60–80&nbsp;km around it and the global average of about 50&nbsp;km.<ref name=Potter_2012/>

The composition of the basin, as estimated from the ''[[Galileo (spacecraft)|Galileo]]'', ''[[Clementine (spacecraft)|Clementine]]'', and ''[[Lunar Prospector]]'' missions, appears to be different from typical highland regions. Most importantly, none of the samples obtained from the American [[Apollo program|Apollo]] and Russian [[Luna programme|Luna]] missions, nor the handful of identified [[lunar meteorites]], have comparable compositions. The orbital data indicate that the floor of the basin has slightly elevated abundances of iron, titanium, and thorium. In terms of mineralogy, the basin floor is much richer in [[clinopyroxene]] and [[orthopyroxene]] than the surrounding highlands, which are largely [[Anorthosite|anorthositic]].<ref name="L06">{{cite journal | author =P. Lucey| display-authors =etal |title = Understanding the lunar surface and space-Moon interactions |  journal = Reviews in Mineralogy and Geochemistry | volume = 60| issue =1 |pages = 83–219|date = 2006 |doi = 10.2138/rmg.2006.60.2|bibcode = 2006RvMG...60...83L }}</ref> Several possibilities exist for this distinctive chemical signature: one is that it might simply represent lower crustal materials that are somewhat richer in iron, titanium and thorium than the upper crust; another is that the composition reflects the widespread distribution of ponds of iron-rich [[basalt]]s, similar to those that make up the [[lunar mare|lunar maria]]; alternatively, the rocks in the basin could contain a component from the lunar mantle if the basin excavated all the way through the crust; and, finally, it is possible that a large portion of the lunar surface surrounding the basin was melted during the impact event, and differentiation of this impact melt sheet could have given rise to additional geochemical anomalies. Complicating the matter is the possibility that several processes have contributed to the basin's anomalous geochemical signature. Ultimately, the origin of the anomalous composition of the basin is not known with certainty and will likely require a sample return mission to determine.{{citation needed|date=March 2024}}

In 1994, the Clementine Mission detected several regions of water ice within the basin. These areas were mapped in greater detail by the [[Lunar Prospector]] mission in 1998 and several missions since then. <ref name="lunarice">{{cite web | url=
https://nssdc.gsfc.nasa.gov/planetary/ice/ice_moon.html |title=Ice on the Moon A Summary of Clementine and Lunar Prospector Results}}</ref>

==Exploration==
China sent [[Chang'e 6]] on 3 May 2024, which conducted the first lunar sample return from [[Apollo (crater)|Apollo Basin]] on the [[far side of the Moon]].<ref name="AJ_FI-20230425">{{cite tweet |author=Andrew Jones |user= AJ_FI |number=1650832520978526208 |title=China's Chang'e-6 sample return mission (a first ever lunar far side sample-return) is scheduled to launch in May 2024, and expected to take 53 days from launch to return module touchdown. Targeting southern area of Apollo basin (~43º S, 154º W) |date=25 April 2023}}</ref> This is China's second lunar sample return mission, the first was achieved by [[Chang'e 5]] from the lunar near side four years earlier.<ref>{{cite web |last=Jones |first=Andrew |url=https://spacenews.com/chinas-change-6-probe-arrives-at-spaceport-for-first-ever-lunar-far-side-sample-mission/ |title=China's Chang'e-6 probe arrives at spaceport for first-ever lunar far side sample mission |work=[[SpaceNews]] |date=10 January 2024 |access-date=10 January 2024}}</ref> It also carried a Chinese rover called ''Jinchan'' to conduct [[Absorption spectroscopy|infrared spectroscopy]] of lunar surface and imaged Chang'e 6 lander on lunar surface.<ref>{{cite web |last1=Jones |first1=Andrew |title=China's Chang'e-6 is carrying a surprise rover to the moon |url=https://spacenews.com/chinas-change-6-is-carrying-a-surprise-rover-to-the-moon/ |website=SpaceNews |access-date=8 May 2024 |date=6 May 2024 |archive-date=8 May 2024 |archive-url=https://web.archive.org/web/20240508193233/https://spacenews.com/chinas-change-6-is-carrying-a-surprise-rover-to-the-moon/ |url-status=live }}</ref> The lander-ascender-rover combination was separated with the orbiter and returner before landing on 1 June 2024 at 22:23 UTC. It landed on the Moon's surface on 1 June 2024.<ref name="AJ_FI-20240601">{{cite web |last=Jones |first=Andrew |url=https://spacenews.com/change-6-lands-on-far-side-of-the-moon-to-collect-unique-lunar-samples/ |title=Chang'e-6 lands on far side of the moon to collect unique lunar samples |work=[[SpaceNews]] |date=1 June 2024 |access-date=1 June 2024}}</ref><ref name="segeryu240602">{{cite tweet | author= Seger Yu | user= SegerYu | number= 1797042217804337307 | title= 落月时刻 2024-06-02 06:23:15.861 | language= zh }}</ref> The ascender was launched back to lunar orbit on 3 June 2024 at 23:38 UTC, carrying samples collected by the lander, and later completed another robotic rendezvous and docking in lunar orbit. The sample container was then transferred to the returner, which landed on [[Inner Mongolia]] on 25 June 2024, completing China's far side extraterrestrial sample return mission.

== Origin ==
[[File:Chang'e-5 mockup at ZHAL 01.jpg|thumb|Chang'e-5/6 spacecraft full-stack full-scale mockup.]]
Simulations of near vertical impacts show that the bolide ought to have excavated vast amounts of mantle materials from depths as great as 200&nbsp;km below the surface. However, observations thus far do not favor a mantle composition for this basin and crustal thickness maps seem to indicate the presence of about 10 kilometers of crustal materials beneath this basin's floor. This has suggested to some that the basin was not formed by a typical high-velocity impact, but may instead have been formed by a low-velocity projectile around 200&nbsp;km in diameter (compare to the 10&nbsp;km diameter [[Chicxulub crater|Chicxulub impactor]]) that hit at a low angle (about 30 degrees or less), and hence did not dig very deeply into the Moon. Putative evidence for this comes from the high elevations north-east of the rim of the South Pole–Aitken basin that might represent ejecta from such an oblique impact. The impact theory would also account for magnetic anomalies on the Moon.<ref>{{cite journal | author=Wieczorek MA| author2= Weiss BP| author3=Stewart ST | title=An impactor origin for lunar magnetic anomalies | journal=[[Science (journal)|Science]]  | volume=335 | issue=6073 | date=2012 | pages=1212–1215  | doi= 10.1126/science.1214773 | pmid=22403388|bibcode = 2012Sci...335.1212W | s2cid= 28619676}}</ref>

== See also ==
{{Portal|Solar System}}

* [[Geology of the Moon]]
* [[Lunar craters]]
* [[Lunar water]]

== References ==
{{Reflist|refs=
<ref name=Potter_2012>{{cite journal |author=Potter, R. W. K. |author2=Collins, G. S. |author3=Kiefer, W. S. |author4=McGovern, P. J. |author5=Kring, D. A. |title=Constraining the size of the South Pole-Aitken basin impact |date=2012 |journal=Icarus |volume=220 |issue=2 |pages=730–743 |bibcode=2012Icar..220..730P |doi=10.1016/j.icarus.2012.05.032 |url=http://www.lpi.usra.edu/lpi/potter/publications/Potteretal2012.pdf |url-status=dead |archive-url=https://web.archive.org/web/20141221162807/http://www.lpi.usra.edu/lpi/potter/publications/Potteretal2012.pdf |archive-date=December 21, 2014 }}</ref>
}}

==Further reading==
* {{cite web|url = http://www.psrd.hawaii.edu/July98/spa.html | title = The biggest hole in the Solar System | author = G. Jeffrey Taylor | publisher = Planetary Science Research Discoveries | date = 1998}}

== External links ==
{{Commons category}}

* [http://www.lpi.usra.edu/publications/slidesets/clem2nd/slide_26.html Albedo, Topography, and Mineral Concentrations]
* [http://teams.kipr.org/2006/06-0001/research/AikenBasin.html Searching for water in the Aitken Basin]
* [https://web.archive.org/web/20061209095723/http://www.cmf.nrl.navy.mil/clementine/ The Clementine Mission found ice in the Aitken Basin while mapping southern lunar region]

{{The Moon}}

{{DEFAULTSORT:South Pole-Aitken Basin}}
[[Category:Surface features of the Moon]]
[[Category:Impact craters on the Moon]]
[[Category:Pre-Nectarian]]