Geological Chronicle
Shackleton crater spans 21 kilometers across and 4.2 kilometers deep at the lunar South Pole, positioned where the Moon's rotational axis intersects its southern rim. Because the Moon's spin axis is tilted only 1.54 degrees from the ecliptic, sunlight strikes the polar terrain at grazing angles. Elevated massifs along Shackleton's rim receive sunlight for 80 to 90 percent of the lunar year, while the deep interior has remained shielded from direct solar radiation for billions of years.
The floor of the crater functions as a cryogenic cold trap where temperatures drop to 40 Kelvin (-233°C). At this temperature, volatile molecules delivered by comet and asteroid bombardments cannot easily sublimate into space. Measurements from orbital instruments, including the Lunar Prospector neutron spectrometer and the Lunar Reconnaissance Orbiter, recorded hydrogen enhancements and extreme thermal lows consistent with subsurface water ice and trapped volatiles.
Topographic data from laser altimetry shows that Shackleton is a well-preserved simple crater formed approximately 3.69 billion years ago during the Imbrian period. The impactor, estimated at 1.5 kilometers in diameter, struck the mountainous rim of the ancient South Pole-Aitken basin at roughly 15 kilometers per second. This event excavated deep crustal materials, exposing ancient norite and deposits of nearly pure anorthosite along the crater walls.
Because the rim offers near-continuous solar illumination for power generation alongside direct access to cryogenic volatile deposits below, Shackleton is a primary operational target for NASA's Artemis program and future international lunar surface outposts.