Ice may be present a few centimetres below the Moon's surface in more areas of the lunar polar regions than was previously thought due to large, yet highly localised, variations in surface temperatures. The results, published in Communications Earth & Environment, are derived from direct measurements taken at the lunar surface in 2023 by the Indian Chandrayaan-3 mission.
Future long-term exploration (or habitation) of the Moon will likely depend on the availability of ice to provide water, with the likelihood of ice formation in a lunar area directly affected by the surface temperature. The only previous direct measurements of the lunar surface temperature were taken during the Apollo missions of the 1970s. However, these missions landed near the equator, several thousand kilometres from proposed landing sites for future manned missions, and where terrain slope has little effect on temperature.
Durga Prasad and colleagues analysed temperature readings taken at the lunar surface and to a depth of 10 centimetres below by ChaSTE — a temperature probe experiment on Chandrayaan-3's Vikram lander, which touched down at the edge of the south polar region (approximately 69 ° south). The authors found that temperatures at the landing site, a Sun-facing slope angled at 6 °, peaked at 355 Kelvin (82 degrees Celsius) and dropped to 105 Kelvin during the lunar night. However, a lower peak temperature of 332 Kelvin (59 degrees Celsius) was measured on a flat region approximately 1 metre from the lander.
The authors used the collected data to derive a model of how slope angle affects surface temperature at high lunar latitudes similar to the landing site. The model indicated that, for slopes facing away from the Sun and towards the nearest pole, a slope with a greater than 14 ° angle may be cool enough for ice to accumulate close to the surface. This is similar to conditions at the lunar poles, including those at the proposed landing sites for NASA's manned Artemis missions near the lunar south pole. The authors therefore suggest that areas on the Moon where ice can form may be more numerous and easier to access than previously thought.
