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September 16th, 2023
Maps of the south and north polar region of the Moon with the age of permanently shadowed areas. PSR ages are indicated in the legend and the angles in parenthesis are the maximum elevation of the Sun above the south pole. The background grayscale map is maximum direct solar irradiance for the present day.
Image credit: Norbert Schorghofer/PSI.
New research points to how much water ice may be lurking in the Moon’s permanently shadowed areas. Given that back-to-the-Moon plans by various nations are being shaped, in part, by that resource being available to sustain operations there, new data can be welcomed, or viewed as bad news.
Permanently shadowed regions on the Moon, known as PSRs, are thought to have trapped ices and are a main focus of lunar exploration.
Planetary Science Institute senior scientist, Norbert Schorghofer, is lead author of “Past Extent of Lunar Permanently Shadowed Areas” that appears in Science Advances.
Ancient water ice reservoirs
“These findings change the prediction for where we would expect to find water ice on the Moon, and it dramatically changes estimates for how much water ice there is on the Moon. Ancient water ice reservoirs are no longer expected,” said Schorghofer, in a Planetary Science Institute (PSI) statement.
Permanently shadowed regions (PSRs) on the Moon are those sunlight-shy craters that are believed to contain precious water ice. Credit: Hongyu Cui
The crux of the new research paper is this: Early in the Moon’s 4.5 billion years old history, Earth’s celestial partner was bombarded by comets and volcanism-released water vapor from its interior.
Schorghofer notes that continuously shadowed areas on the Moon, however, started to appear only 3.4 billion years ago.
“By that time these processes had started to die down, so most of the water that was delivered to the Moon or outgassed from its interior could not have been trapped in the polar regions. Any ice in the polar regions today must have a more recent origin,” Schorghofer explains in the PSI statement.
LCROSS impact
“We have been able to quantify how young the lunar PSRs really are,” Schorghofer said. “The average age of PSRs is 1.8 billion years, at most. There are no ancient reservoirs of water ice on the Moon.”
But throwing cold water on gobs and gobs of available PSR water ice, well it’s not totally a slam dunk negative.
Artist’s rendering of the LCROSS spacecraft and Centaur separation.
Credit: NASA
Schorghofer points to the impact site of the Lunar Crater Observation and Sensing Satellite (LCROSS) project, a robotic pile-driving mission that in October 2009 purposely crashed within the Cabeus crater at the lunar south pole.
The resulting impact excavated roughly 350 (metric) tons of lunar material and created a crater estimated to be about 66 feet (20 meters) in diameter.
Plumbing the plume
Schorghofer said the plume of LCROSS-vacated volatiles — which include water and carbon dioxide – must be young, he said, and lies within a PSR that is less than 1 billion years old.
In a way this is very encouraging, Schorghofer said, because even the young PSRs contain ice. Older PSRs should contain even more ice.
Rendering of Artemis astronauts exploring a lunar south pole crater. A water ice-rich resource ready for processing?
Image credit: NASA
The bottom line of the new research by Schorghofer and colleague Raluca Rufu of the Southwest Research Institute in Boulder, Colorado: Overall estimates for the amount of cold-trapped ices have to be revised downward.
“Impacts and outgassing are potential sources of water but peaked early in lunar history, so the age of PSRs is a dominant factor for the amount of water ice trapped in the lunar polar regions, which is the prime target of upcoming crewed and uncrewed missions to the Moon,” Schorghofer notes in the research paper – “Past Extent of Lunar Permanently Shadowed Areas” that can be accessed at:
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