Moon's ice not as old as believed, study finds

A fresh perspective on Lunar water ice

Water ice on the Moon has long been considered a crucial element for sustaining human life during extended lunar stays and even as a fuel source for spacecraft. PSRs, the regions that are eternally masked from sunlight, were thought to have trapped ice over billions of years. These dark pockets were the primary focus of various exploratory missions, but Schorghofer's study suggests a need to adjust these trajectories.

One of the intriguing elements of the research is its alignment with a significant study released last year by a team of French researchers. The earlier work provided a comprehensive understanding of how the Earth-Moon distance has changed over time. Schorghofer noted that upon learning about this prior study, he instantly grasped its far-reaching impact on the quest for lunar ice and promptly started delving into the details.

Collaborating with co-author Raluca Rufu, Schorghofer computed the lunar spin axis orientation and mapped PSRs, taking into account the time-evolution models of the Earth-Moon distance.

Younger than we thought: Age of PSRs

Contrary to popular belief that the Moon was bombarded with water-carrying comets and volcanic activity releasing water vapor from its interior early in its 4.5-billion-year history, the study found that PSR only began to form around 3.4 billion years ago. "The water we find in the polar regions today cannot be from the early days of the Moon. Our data indicate an average age of PSRs to be at most 1.8 billion years. There are no ancient reservoirs of water ice on the Moon," Schorghofer emphasized.

Notably, the impact site where the Lunar Crater Observation and Sensing Satellite detected water in 2009 lies in a PSR younger than 1 billion years. Schorghofer points out that this is encouraging news; younger PSRs containing ice suggest that older ones should contain even more.

This study also raises questions about the polar regions of planet Mercury, which appear to have much more ice than the Moon. "Mercury's PSRs are considerably older and could have captured water at an earlier stage, which might explain the discrepancy," Schorghofer theorized.

Further research

Schorghofer's groundbreaking work has been funded through a grant from NASA, issued via the Lunar Data Analysis Program, and supported by the Solar System Exploration Research Virtual Institute (SSERVI) node GEODES.

The study was published in the journal Science Advances.

Study abstract:

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.