Clavius (crater)

Clavius' location toward the southern limb of the Moon causes it to appear oblong due to foreshortening. Its great size makes it visible to the unaided eye as a prominent notch in the terminator about one to two days after the Moon reaches first quarter. This formation dates to the Nectarian period of the lunar geologic timescale.^[3][4] Its creation would have excavated the lunar crust to a depth of 20–25 km, shifting a material volume of 6.8×10⁴ km³.^[10]

Clavius has a low outer wall in comparison to its size and is heavily worn and pock-marked by craterlets. The rim does not significantly overlook the surrounding terrain making it a "walled depression". The inner surface of the rim is hilly, notched and varies in width with the steepest portion to the south. The rim has been observed to have a somewhat polygonal outline overall.^[11]: 126 The northeast rim is broken by Porter crater.^[5]

The floor of Clavius forms a convex plain that is marked by some interesting crater impacts. The most notable of these is a curving chain of craters that begins with Rutherfurd in the south then arcs across the floor in a counterclockwise direction forming a sequence of ever diminishing diameters. From largest to smallest, these craters are designated Clavius D, C, N, J, and JA.^[7] This sequence of diminishing craters has proved a useful tool for amateur astronomers who want to test the resolution of their small telescopes.

This formation is sufficiently large that is could have developed a peak ring formation, but no such feature has survived, if it existed.^[10] The crater floor retains a remnant of a central massif, which lies between Clavius C and N. The spectra of the central peak fits an anorthositic gabbro mineralogy, which originated from a depth of 24.5 to 42.4 km.^[12] The relative smoothness of the floor and the low size of the central peaks may indicate that the crater surface was formed some time after the original impact.

In October 2020, NASA confirmed the existence of molecular water near Clavius, at concentrations of up to 412 parts per million. The water could be trapped into tiny beadlike structures in the soil that form out of the high heat created by micrometeorite impacts.^[13] The water might also be sheltered between lunar soil grains. Another possibility is from very small asteroid strikes, such as a rubble pile from a much more massive "parent" asteroid collision. Pulled apart in its descent to the lunar surface similar to Comet Shoemaker–Levy 9, and hitting the surface in a modest dispersal area with a small mass at low, oblique impact angle and bouncing could allow some water to remain in the lithic matrix. The carbonaceous chondrite class is often water-rich, and the CI sub group are as much as 22% water.

By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Clavius.^[14]

• Clavius Base, the site of an American lunar administrative facility in the movie 2001: A Space Odyssey^{[citation needed]}
• Time-travel facility located under Clavius in the 2015 Madeira Desouza novel entitled Baja Clavius: Moon Men Deep Inside^[15]
• The location of the fictional Tranquility Base Hotel & Casino in the Arctic Monkeys song "Four Out of Five"^{[citation needed]}