Editing South Pole–Aitken basin (section)

== 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>