Ancient cold traps at lunar south pole identified as prime targets for Artemis ice sampling

by Sophie Jenkins
London (SPX) May 01, 2026
Researchers from the Weizmann Institute of Science and US collaborators have found evidence that ice has been accumulating at the Moon's poles for at least 1.5 billion years, and have identified the oldest permanently shadowed cold traps near the lunar south pole as the most promising targets for future missions seeking to sample that ice.

The study, published in Nature Astronomy, was led by Prof. Oded Aharonson of Weizmann's Earth and Planetary Sciences Department, together with Prof. Paul Hayne of the University of Colorado Boulder and Dr. Norbert Schorghofer of the Planetary Science Institute in Honolulu. The findings carry direct relevance for NASA's crewed Artemis missions, which are scheduled to land astronauts at the Moon's south pole.

The Moon's near-zero axial tilt means sunlight stays close to the horizon at the poles throughout the monthly cycle, leaving the floors of deep, steep craters in permanent shadow. These permanently shadowed regions can cool to around minus 160 degrees Celsius and act as cold traps where water ice, once deposited, can persist for geological timescales without evaporating. The Moon's tilt was larger in the distant past, and as it decreased over billions of years, progressively more polar craters fell into permanent shadow and acquired cold-trap status.

The team analyzed ultraviolet data from NASA's Lunar Reconnaissance Orbiter, which has been mapping the Moon since 2009. Ice reflects ultraviolet light at different wavelengths than bare rock, and because ultraviolet light from distant stars can reach even permanently shadowed areas, the instrument provides a means of mapping ice distribution without direct sunlight. By comparing the inferred ice coverage of each permanently shadowed region with the calculated age at which that region became a cold trap, the researchers found a clear relationship: the older the cold trap, the greater the fraction of its area covered by ice.

"We found that the earlier a region became shadowed, the larger the area that was able to accumulate ice," said Aharonson. "This trend began at least 1.5 billion years ago and has continued even over the past 100 million years. This suggests that ice has been building up on the Moon from a nearly continuous source -- or sources -- rather than through a single event such as a large comet impact."

A key finding concerns Shackleton Crater, long considered one of the most promising candidate sites for lunar ice. The team determined that although Shackleton has been permanently shadowed for about 3.5 billion years, it only became cold enough to function as a cold trap approximately 500 million years ago. Its ice accumulation history is therefore substantially shorter than its shadowing history. In contrast, Haworth Crater was identified as a cold trap more than 3.3 billion years ago and emerged from the analysis as a significantly better-stocked target for future sampling.

"The longer a given region has been a cold trap, the more ice it has accumulated," Aharonson said. "To identify targets for future missions, we searched for the oldest cold traps and found several extensive ones more than 3.3 billion years old near the Moon's South Pole."

To explore what the ice distribution implies about the history of lunar water, the team built a mathematical model incorporating three competing processes: water supply, evaporation, and impact gardening -- the repeated disturbance and redistribution of surface material by small impacts, which can bury ice beneath a protective layer of regolith. The model, combined with the observation that younger cold traps hold relatively little ice, points to water supply and water loss both occurring at comparatively rapid rates -- described by the researchers as analogous to a faucet filling a leaking bucket.

Proposed sources of that water supply include volcanic outgassing from the lunar interior, solar wind hydrogen reacting chemically with surface minerals, and a succession of asteroid and comet impacts distributed over millions of years rather than a single catastrophic delivery event. The study does not resolve which source dominates but constrains what any viable model must explain.

The results are particularly timely given the launch of NASA's Artemis II mission on April 1, 2026, and the broader international push toward permanent lunar infrastructure. Water ice at the south pole represents a potential resource for drinking water, irrigation, and rocket propellant production for deep-space missions. A physical sample would also allow direct chemical comparison with terrestrial water and with water detected elsewhere in the solar system.

"The gold-standard proof of the existence of ice on the Moon would be a sample of it," Aharonson said. "It would allow us to compare the chemical composition of water on the Moon with that on Earth, and to assess whether -- and how -- crewed lunar missions could make use of this resource."

"Future spacecraft missions would be able to collect extensive data on the ice from the crater's surface, and rovers would be able to approach, enter and sample the ice deposits," said Hayne.

Research Report: Observational constraints on the history of lunar polar ice accumulation