After decades of disagreements among the scientific community, an international research team has determined that the water on the Moon likely accumulated over billions of years, rather than during a single, violent event, such as a cometary collision.
Although the study did not confirm the actual origin of lunar ice deposits believed to reside in deep surface craters, the research team behind the findings said their study could also inform future lunar researchers’ and colonists‘ efforts to locate and exploit water ice that remains in several protected locations deep within the Moon’s surface.
A Decades-Long ‘Water on the Moon’ Mystery
According to a statement from the team led by Paul Hayne, a planetary scientist at the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado Boulder, decades of studies, including NASA missions, have provided “tantalizing hints” that Earth’s lone natural satellite might contain a significant amount of water in the form of frozen ice. Further research indicated that this water ice accumulates in the deep, dark craters of the Moon’s southern pole region, where it is sheltered from direct exposure to the sun.
For example, observations from the Lyman Alpha Mapping Project (LAMP) instrument on NASA’s Lunar Reconnaissance Orbiter(LRO) found possible evidence of ice in some of these craters. Still, the research team notes, there is some debate about the water’s origin. Hayne said that the discussion has been further complicated by studies suggesting that this “patchy” distribution of hidden water ice exists in some deep craters but not others.
“It’s not concentrated in the same quantities in every crater,” explained the researcher, who is also an associate professor in the Department of Astrophysics and Planetary Sciences. “And there was no great explanation for that.”
Scientists have proposed several models to explain its water-ice distribution, including ancient volcanoes that transported water from deep within the moon to its surface. Others have suggested that water reached the moon aboard asteroids and comets, or even arrived from space via the solar wind.
“Through the solar wind, a constant stream of hydrogen bombards the moon, and some of that hydrogen can be converted to water on the lunar surface,” Hayne explained.
Cold Traps Identified by Simulations Match NASA Observations
To identify the most likely explanation, Professor Hayne and study co-author Norbert Schörghofer constructed lunar simulations using LRO-collected surface-temperature data to estimate how water ice accumulated in the Moon’s deepest, oldest craters. This included correcting for the moon’s changing orientation over its multi-billion-year existence, which may have exposed currently shadowed craters to sunlight.
According to the team’s statement, this process revealed several “cold traps” on the lunar surface that have remained in permanent shadow the longest. The scientists were even more encouraged to see that their newly identified cold traps correlated with locations identified by LAMP as the most likely to contain frozen water ice deposits.
The researchers also found evidence suggesting that the moon’s oldest craters contain the most ice, while newer ones are less likely to contain significant amounts of frozen water. Hayne said that this “implies the moon has been accumulating water more or less continuously for as much as 3 or 3.5 billion years.”
“One of the Most Important Challenges in Astronomy”
When discussing the implications of their findings, lead author Oded Aharonson, a planetary scientist at the Weizmann Institute of Science in Israel, said the results could help future colonists and astronauts locate and exploit this extremely rare resource in a mostly arid lunar environment.
“The moon’s Haworth Crater, which sits near the South Pole, for example, has likely been in shadow for more than 3 billion years,” Haynes said. “It’s a top candidate for storing a lot of ice.”
For example, lunar scientists could extract the water to search for signs of life, while colonists could melt the ice deposits for drinking and watering crops. They could even split the water’s atoms to extract breathable oxygen and to form a hydrogen-based rocket fuel.
“Finding water beyond Earth in liquid and usable form is one of the most important challenges in astronomy,” Aharonson said.
To refine the study’s results, Hayne said his team will need to conduct more detailed observations of the craters deemed most likely to harbor water ice. This need has motivated the researcher’s efforts to develop the bespoke Lunar Compact Infrared Imaging System (L-CIRiS), which NASA plans to deploy near the moon’s South Pole in late 2027.
“Ultimately, the question of the source of the moon’s water will only be solved by sample analysis,” Haynes explained. “We will need to go to the moon to analyze those samples there or find ways to bring them from the moon back to Earth.”
The study was published in Nature Astronomy.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.