New research indicates that if even a moderate amount of the water delivered by asteroids to the Moon was sequestered, the lunar poles would contain gigaton deposits (1 billion metric tons) of ice in sheltered craters and beneath its surface.
By modeling over 4 billion years of the Moon’s impact history, researchers were able to track the origin and potential quantity of ice that might be obscured from view beneath the lunar surface.
“We looked at the entire time history of ice deposition on the Moon,” said Kevin Cannon, a planetary scientist at the Colorado School of Mines in Golden and lead author of the new study in the AGU journal Geophysical Research Letters.
Cannon and his team used conservative estimates for the amount of water that asteroids were likely to contain upon impact with the Moon and how much of it was likely to be retained once the dust had settled. Their results suggest the Moon might hold much more water in the subsurface than previously expected.
“If the very oldest regions have been stable and accumulating ice for billions of years, then some could have very substantial deposits, but they might be buried up to 10 meters deep or more,” Cannon said.
In spite of their depth, polar ice reserves are likely to be the most accessible for astronauts during future lunar missions. Ice in significant enough quantities could potentially be harvested for drinking water, oxygen, and rocket fuel.
Something Deeply Hidden
Scientists first speculated about the presence of water on the Moon years before Neil Armstrong and Edwin “Buzz” Aldrin stepped foot on its surface. The Moon is pockmarked with craters, some deep enough that their ridges cast permanent shadows under which ice—protected from the constant barrage of solar wind—has accumulated for potentially billions of years.
Despite evidence for its existence, however, scientists have only recently confirmed that our nearest stellar neighbor harbors water in abundant quantities. Recent research provided the first definitive evidence for the presence of ice in sunlit portions of the Moon, where it is likely locked up in glass created by high-intensity impacts or resides in small amounts between grains of lunar dust.
The majority of ice on the Moon, however, is trapped at the poles, where light is scarce and temperatures remain below –163°C.
Scientists have made a number of direct observations of ice at the lunar poles, but because of their extreme antiquity—most ice on the surface was deposited over 3 billion years ago during the nascent stages of the Moon’s development—much of it has been covered by debris from asteroid impacts or has been buried at depths beyond the ability of satellite ultraviolet and radar devices to detect.
Estimating the amount of ice on the Moon has consequently been a difficult task. Most studies over the past few decades infer that deposits on the Moon have only a shallow veneer of frost or ice, measuring a meter or so in thickness.
On the basis of the latest estimates, however, it is thought that even moderately sized craters at the poles could contain an amount of ice roughly equivalent to that of water in the Lake of the Ozarks in Missouri. (Geophysical Research Letters, https://doi.org/10.1029/2020GL088920, 2020)
—Jerald Pinson (@jerald_pinson), Science Writer