## 2 The Lunar South Pole
### Physical Analysis
Following this general introduction, we start exploring in detail our region of interest, the lunar south pole, investigating its main characteristics. The lunar south pole is situated inside the South Pole Aitken (SPA) basin, which is the largest and oldest discovered impact structure of the Solar System [7] with its 2600 km diameter and belonging to the pre-Nectarian period (ref. [8] offers a unified geological map of the lunar south pole region with a brief description of all the different geological areas); this massive impacts' history has largely shaped the surface, making it extremely jagged. The Lunar Orbiter Laser Altimeter (LOLA) instruments on board the Lunar Reconnaissance Orbiter (LRO) highlight how the elevation ranges from about \(-7000\) to \(+7000\) m with slopes that can reach \(80^{\circ}\) (Figure 1a); this uneven topography extremely affects local illumination. Sunlight reaches the polar surface for less than \(50\%\) of the time even if a limited area near the rims of the Shackleton, De Gerlache and Nobile craters and the crest of the Malapert Massif can reach \(80\%\) illumination on average (Figure 1b); these results come from a simulation carried out by [9] over several years. Figure 1: Maps of the lunar south pole (\(80^{\circ}\) to pole) derived from the Lunar Reconnaissance Orbiter (LRO) Lunar Orbiter Laser Altimeter (LOLA). (**a**) Topographic and slope maps adapted from [10], (**b**) Earth visibility and solar illumination maps of the lunar south pole adapted from [9]. Certain areas located in unfavorable regions and with particularly deep depressions reside in constant darkness; these zones are called permanently shadowed regions (PSRs). Temperatures lower than 110 K are generally reached in these PSRs (Figure 2). Some of them have no direct line of sight to any non-permanently shadowed zones and so they can be shielded from the direct solar illumination but also from scattered light and thermal emission; in this case, they take the name of double permanently shadowed regions (DPSRs). Clearly, the reachable temperatures are lower, about 25 K. South pole PSRs are located beyond 80\({}^{\circ}\) latitude and occupy about 7.25% of the total surface area in this region while the total doubly shadowed area poleward of 85\({}^{\circ}\) latitude constitutes only 0.07% of the PSRs' area in the region. These areas are of particular significance and make lunar poles different from any other region; due to their temperature, PSRs can harbor water ice while DPSRs could also potentially accommodate CO\({}_{2}\), CO, N\({}_{2}\), Ar and organic compounds delivered by the impacts of comets and meteorites [11]. Improving knowledge of these dark areas is essential to plan future missions to the PSRs like the NASA VIPER mission; the first results from the ShadowCam on board the KPLO seem to be encouraging, as transversal simulations of secondary illumination and topography imaging have revealed features of the surface of Shackleton and other PSR craters for the first time [12]. As well as the sunlight visibility, even the Earth visibility is strongly influenced by the surface morphology. An integrated remote sensing analysis of the lunar south pole between different missions is necessary to create the best overview of the lunar south pole mineralogy and to enrich the interpretation of the spectroscopic data. The Moon Mineralogy Mapper data reveal the south polar region to be enriched in mafic minerals with respect to the highland crust, which represents an anomaly compared to the predominantly aortic character of the South Pole Aitken basin; this mafic anomaly is backed up by elemental abundance (for example, Fe, Th or K) data from the Lunar Prospector [13], suggesting the presence of a lower crust/upper mantle ejecta (Figure 3).