Lunar Poles Show Ice Accumulation Over 1.5 Billion Years

Moon's Polar Ice Accumulating for Billions of Years, New Study Reveals

A recent study by scientists from Israel and the United States indicates that ice has been accumulating at the Moon's poles for at least 1.5 billion years. Published in Nature Astronomy, the research highlights "cold traps"—permanently shadowed craters—as key locations for these ancient ice deposits. The findings, derived from data collected by NASA's Lunar Reconnaissance Orbiter, suggest a continuous build-up of ice over vast timescales.

Ice has been accumulating at the Moon's poles for at least 1.5 billion years, primarily within permanently shadowed "cold traps." This continuous build-up has significant implications for future lunar exploration, particularly NASA's Artemis program which plans to focus on these polar regions.

Persistent Polar Ice: A Billion-Year Accumulation

The study, led by researchers at Israel's Weizmann Institute of Science in collaboration with U.S.-based scientists, determined that ice has persisted and accumulated at the lunar poles for a minimum of 1.5 billion years. Analysis revealed that older, permanently shadowed regions contain higher quantities of ice, suggesting a gradual, ongoing process rather than a single large deposition event, such as a comet impact.

The Crucial Role of Lunar Cold Traps

The accumulation of ice occurs within "cold traps," which are deep craters located near the Moon's poles. These regions remain permanently shadowed due to the Moon's minimal axial tilt, preventing direct sunlight from reaching their interiors. Temperatures within these cold traps average around minus 160 degrees Celsius, which is cold enough for ice to persist for billions of years. While many permanently shadowed regions function as cold traps, some do not due to heat radiated from surrounding crater walls.

Historically, the Moon's axial tilt was greater than it is today. As the tilt decreased over geological time, more polar craters became permanently shadowed and cooled sufficiently to become cold traps. Researchers calculated the age of these regions based on when they lost exposure to sunlight.

Detecting Ancient Ice: Methodology and Key Observations

The research team, including Prof. Oded Aharonson, Prof. Paul Hayne, and Dr. Norbert Schörghofer, utilized ultraviolet-sensitive data from NASA's Lunar Reconnaissance Orbiter. Ultraviolet light, originating from the Sun and distant stars, can penetrate shadowed areas, and ice reflects specific ultraviolet wavelengths differently from rock, allowing for its detection.

Their analysis showed a clear correlation between the age of a permanently shadowed region and its ice coverage: regions that became shadowed earlier accumulated larger ice areas. This trend has been observed over at least 1.5 billion years and continues into the last 100 million years. Geometric calculations were used to identify which permanently shadowed regions also function as cold traps and when they acquired this status. For example, Shackleton Crater, shadowed for 3.5 billion years, is estimated to have become a cold trap approximately 500 million years ago. Several extensive cold traps, over 3.3 billion years old, were identified near the Moon's South Pole, including Haworth Crater.

Implications for NASA's Artemis Program and Future Exploration

These findings are highly relevant to NASA's Artemis missions, which aim to land astronauts at the Moon's South Pole. The lunar ice represents a potential resource that could be converted into water, oxygen, and fuel to support future space missions and potentially a permanent lunar base, which NASA envisions as a possible transit point for future Mars missions.

Future missions are anticipated to collect samples of this lunar ice. Such samples could provide crucial data on its chemical composition, allowing for comparisons with Earth's water, and help assess its usability for crewed missions. The research provides guidance for targeting the most ancient cold traps for ice deposit sampling.

Unraveling the Origins of Lunar Water

Researchers developed a mathematical model suggesting that the amount of surface ice is influenced by factors such as water supply, evaporation, and impact gardening—the redistribution and burial of ice by lunar soil. The observation of slow ice accumulation over hundreds of millions of years, despite relatively little ice in younger cold traps, indicates both rapid water supply and loss rates on the Moon. Proposed sources of lunar water include volcanic activity, reactions from the solar wind, and multiple asteroid and comet impacts over millions of years.