A new study using the now-defunct Stratospheric Observatory for Infrared Astronomy (SOFIA) has produced the first detailed map of water distribution on the Moon. SOFIA was a joint project between NASA and the German space agency DLR. With clear, identifiable Moon features highlighted using water data, the study provides clues as to how water might move on the Moon’s surface, particularly near the South Pole, an important area for space exploration.

The new map covers roughly a quarter of the Earth-facing side of the lunar surface at 60 degrees latitude and extends to the moon’s south pole. Given the large region covered, the researchers were easily able to determine how water relates to the elements on the lunar surface, avoiding sunlight and preferring cold regions.

“When we look at the water data, we can actually see the rims of the craters, we can see the individual mountains, and we can even see the difference between the day and night sides of the mountains due to the higher water concentration in those places. We are the director of the SOFIA Science Center at NASA’s Ames Research Center in Silicon Valley, California, and Bill Rich, lead author of the study presented at the 2023 Lunar and Planetary Exploration Conference.

In late 2024, NASA’s Volatiles Investigating Polar Exploration Rover (VIPER) will land at the top of Monts Mouton at the SOFIA study site to conduct the first extraterrestrial resource mapping mission. The flat-topped moon mountain will be a special topic in the follow-up article by the team leading the current study of SOFIA data.

This current discovery tracks water’s unique light signature, along with two previous SOFIA results on the amount and distribution of water on the moon’s sunny surface. Other missions observing large areas of the lunar surface have studied light of different wavelengths, which cannot distinguish water from similar molecules such as hydroxyl. Moonwater is found in the soil and can be found as ice crystals or water molecules chemically bonded to other materials.

Rather than determining the absolute amount of water in the area, the researchers compared data collected around the moon’s south pole with a relatively dry reference region near the moon’s equator to see how the amount changed. Just as skiers on Earth know that snow lasts longer on slopes with less direct sunlight, higher concentrations of water were found on the shaded edges of craters and mountains. This suggests that the local geography of the Moon plays an important role in the amount of water available.

As NASA prepares to send astronauts back to the moon, led by Artemis, the agency has identified 13 candidates to land near the moon’s South Pole. Through Artemis, NASA will land the first woman and the first human of color on the moon, and lunar water could become a critical resource for establishing long-term human existence.

“With this map of SOFIA data and others to come, we’re examining how water is concentrated in different environmental conditions on the Moon,” said Casey Honniball, visiting scientist at NASA’s Goddard Space Flight Center and member of the VIPER research team. in Greenbelt, Maryland, who participated in the study. “This map will provide valuable information about potential exploration sites for the Artemis program, as well as provide regional context for future science missions such as VIPER.”

In addition to the southern region, where new map results are generated, SOFIA observations of objects associated with other missions are archived and are currently being analysed. NASA’s missions to Artemis will target both polar and nonpolar regions, including the Lunar Trailblazer, which will orbit the moon to map its hydroxyl and water content.

Where the Moon’s water might come from—whether it is ancient and present in lunar minerals from early volcanic processes on the moon, whether it is modern, whether it was carried by asteroids, comets, or the solar wind, and migrated across the lunar surface—is another important question. SOFIA observation left open. VIPER aims to better understand this difference, which is important for determining whether water is diffused and deep at the surface, or just dispersed at or near the surface.

It is clear, however, that even at its lowest limit the Moon contains much more water than we once thought.

“Our general knowledge that the Moon was dry from the Apollo era was wrong,” said Paul Lucy, a professor at the University of Hawaii at Manoa and co-author of the paper. “We already know this is wrong, but the real question is to what extent.”