Past extent of lunar permanently shadowed areas

As the Moon migrated away from Earth, it experienced a major spin axis reorientation. Permanently shadowed regions (PSRs), which are thought to have trapped ices and are a main focus of lunar exploration, appeared and grew after this (Cassini state) transition and are often younger than their host craters. Here, we calculate the lunar spin axis orientation and the extent of PSRs based on recent advances for the time evolution of the Earth-Moon distance. The solar declination reached twice its current value 2.1 billion years (Ga) ago, when the PSR area was about half as large. The PSR area becomes negligible beyond 3.4 Ga ago. The site of an artificial impact in Cabeus Crater, where various volatiles have been detected, became continuously shadowed only about 0.9 Ga ago, and hence, cold-trapping has continued into this relatively recent time period. Overall estimates for the amount of cold-trapped ices have to be revised downward.

Automated summary

As the Moon moved away from Earth, its spin axis underwent a significant reorientation, resulting in the formation and expansion of permanently shadowed regions (PSRs). Using recent advancements in the understanding of Earth-Moon distance evolution, we calculated the orientation of the lunar spin axis and the extent of PSRs. The PSR area reached its maximum size 2.1 billion years ago and became negligible beyond 3.4 billion years ago. Cold-trapping of volatiles has continued into a relatively recent time period.