Lunar south pole

Geography

The lunar south pole lies at the center of the Antarctic Circle (80°S to 90°S). The Moon's rotational axis is tilted 88.5 degrees from the plane of the ecliptic.

Over billions of years, the pole has shifted 5.5 degrees, altering sunlight exposure but leaving some areas permanently shadowed and others constantly sunlit. The region contains the South Pole–Aitken basin and mountains such as Epsilon Peak, which at 9.050 km is taller than any mountain on Earth. The rotational axis lies within Shackleton Crater.

Discoveries

Crater rims near the lunar south pole receive near-constant sunlight while their interiors remain permanently shaded. High-resolution digital models from the Lunar Reconnaissance Orbiter were used to study this illumination. The lunar surface reflects solar wind as energetic neutral atoms; on average, 16% of these atoms are protons, varying by location, and they produce an integral flux of backscattered hydrogen atoms that reveal magnetic dynamics.

Cold traps in the region contain water ice and other volatiles from comets, meteorites, and solar wind-induced iron reduction. Experiments and sample readings confirmed ice in these traps, and hydroxyl was also found. These discoveries led to funding for missions using global-scale infrared detection. Ice persists due to thermal behavior controlled by scattered sunlight, thermal re-radiation, internal heat, and Earth's light.

Some areas of the Moon have magnetized crust, a magnetic anomaly possibly from metal iron emplaced by the impactor that formed the South Pole–Aitken basin, though the expected iron concentration was not detected in mappings, possibly because it lies too deep. The anomaly may have another cause; findings were inconsistent between maps and could not detect the magnitude of magnetic fluctuations at the surface.

Exploration

Orbiters from several countries have explored the lunar south pole region, including Lunar Orbiters, Clementine, Lunar Prospector, Lunar Reconnaissance Orbiter, Kaguya, and Chandrayaan-1, which discovered lunar water. NASA's LCROSS mission deliberately crashed into Cabeus crater and found nearly 5% water there. ISRO's Chandrayaan 3 became the first lander to land near the south pole region. The Lunar Reconnaissance Orbiter, launched by NASA, continues mapping the region to assess resources for a permanent crewed station; it carries the Diviner Lunar Radiometer Experiment to detect reflected solar radiation and internal infrared emissions and identify where water ice may be trapped.

The LCROSS mission, launched with LRO, confirmed water ice in Cabeus. India's Moon Impact Probe, released from Chandrayaan-1, crashed near the rim of Shackleton Crater, making India the first to hard land on the lunar South Pole.