Micro cold traps on the Moon

• Published in: Nature astronomy Vol. 5; no. 2; pp. 169 - 175
• Main Authors: Hayne, P. O., Aharonson, O., Schörghofer, N.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-02-2021; Nature Publishing Group
• Subjects: 704/445; 704/445/125; 704/445/845; 704/445/848; Astronomy; Astrophysics and Cosmology; Cold; Ice; Low temperature; Moon; Physics; Physics and Astronomy; Polar environments
• ISSN: 2397-3366; 2397-3366
• DOI: 10.1038/s41550-020-1198-9

Water ice is thought to be trapped in large permanently shadowed regions in the Moon’s polar regions, due to their extremely low temperatures. Here, we show that many unmapped cold traps exist on small spatial scales, substantially augmenting the areas where ice may accumulate. Using theoretical models and data from the Lunar Reconnaissance Orbiter, we estimate the contribution of shadows on scales from 1 km to 1 cm, the smallest distance over which we find cold-trapping to be effective for water ice. Approximately 10–20% of the permanent cold-trap area for water is found to be contained in these micro cold traps, which are the most numerous cold traps on the Moon. Consideration of all spatial scales therefore substantially increases the number of cold traps over previous estimates, for a total area of ~40,000 km
2
, about 60% of which is in the south. A majority of cold traps for water ice is found at latitudes > 80° because permanent shadows equatorward of 80° are typically too warm to support ice accumulation. Our results suggest that water trapped at the lunar poles may be more widely distributed and accessible as a resource for future missions than previously thought.
A reconstruction of the distribution of cold traps on the Moon at spatial scales varying from 1 km to 1 cm shows that the smallest ones are also the most numerous, 10–20% of the total. The total surface area of the Moon that can efficiently trap water is revised substantially upward, to 40,000 km
2
.