Lunar south pole

The lunar south pole is the southernmost point on the Moon. It is of interest to scientists because of the occurrence of water ice in permanently shadowed areas around it. The lunar south pole region features craters that are unique in that the near-constant sunlight does not reach their interior. Such craters are cold traps that contain fossil records of hydrogen, water ice, and other volatiles dating from the early Solar System. In contrast, the lunar north pole region exhibits a much lower quantity of similarly sheltered craters.

The lunar south pole is located on the center of the polar Antarctic Circle (80°S to 90°S). (The axis spin is 88.5 degrees from the plane of the ecliptic.) The lunar south pole has shifted 5.5 degrees from its original position billions of years ago. This shift has changed the rotational axis of the Moon, allowing sunlight to reach previously shadowed areas, but the south pole still features some completely shadowed areas. Conversely, the pole also contains areas with permanent exposure to sunlight. The south pole region features many craters and basins such as the South Pole–Aitken basin, which appears to be one of the most fundamental features of the Moon, and mountains, such as Epsilon Peak at 9.050 km, taller than any mountain found on Earth. The south pole temperature averages approximately 260 K (−13 °C; 8 °F).

The pole defined by the rotational axis of the Moon lies within Shackleton Crater. Notable craters nearest to the lunar south pole include de Gerlache, Sverdrup, Shoemaker, Faustini, Haworth, Nobile, and Cabeus.^{[citation needed]}

The lunar south pole features a region with crater rims exposed to near-constant solar illumination, yet the interior of the craters are permanently shaded from sunlight. The area's illumination was studied using high-resolution digital models produced from data by the Lunar Reconnaissance Orbiter. The lunar surface can also reflect solar wind as energetic neutral atoms. On average, 16% of these atoms have been protons that vary based on location. These atoms have created an integral flux of backscattered hydrogen atoms due to the reflected amount of plasma that exists on the surface of the Moon. They also reveal the line boundary and the magnetic dynamics within the regions of these neutral atoms on the Moon' surface.

Cold traps are some of the important places on the lunar south pole region in terms of possible water ice and other volatile deposits. Cold traps can contain water and ice that were originally from comets, meteorites and solar wind-induced iron reduction. From experiments and sample readings, scientists were able to confirm that cold traps do contain ice. Hydroxyl has also been found in these cold traps. The discovery of these two compounds has led to the funding of missions focusing primarily on the lunar poles using global-scale infrared detection. The ice stays in these traps because of the thermal behavior of the Moon that are controlled by thermophysical properties such as scattered sunlight, thermal re-radiation, internal heat and light given off by the Earth.

There are areas of the Moon where the crust is magnetized. This is known as a magnetic anomaly due to the remnants of metal iron that was emplaced by the impactor that formed the South Pole–Aitken basin (SPA basin). However, the concentration of iron that is thought to be in the basin was not present in the mappings, as they could be too deep in the Moon's crust for the mappings to detect. Or the magnetic anomaly is caused by another factor that does not involve metallic properties. The findings were proven inadequate due to the inconsistencies between the maps that were used, and also, they were not able to detect the magnitude of the magnetic fluctuations at the Moon's surface.^{[needs update]}

Orbiters from several countries have explored the region around the lunar south pole. Extensive studies were conducted by the Lunar Orbiters, Clementine, Lunar Prospector, Lunar Reconnaissance Orbiter, Kaguya, and Chandrayaan-1, that discovered the presence of lunar water. NASA's LCROSS mission found a significant amount of water in Cabeus. The LCROSS mission deliberately crashed into the floor of Cabeus and from samples found that it contained nearly 5% water.

The Lunar Reconnaissance Orbiter (LRO) was launched by NASA on 18 June 2009 and is still mapping the lunar south pole region. This mission will help scientists see if the lunar south pole region has enough sustainable resources to sustain a permanent crewed station. The LRO carries the Diviner Lunar Radiometer Experiment, which investigates the radiation and thermophysical properties of the south pole surface. It can detect reflected solar radiation and internal infrared emissions. The LRO Diviner is able to detect where water ice could be trapped on the surface.