The Stratospheric Observatory for Infrared Astronomy (SOFIA) has detected evidence of molecular water in the regolith of Clavius Crater, a large crater visible from Earth in the Moon’s southern hemisphere. The airborne SOFIA observatory, a partnership between NASA and the German Aerospace Center, flies in a modified Boeing 747SP aircraft above the atmospheric water that blocks ground observation.
Satellites have had detected “hydrates” in the lunar regolith but could not distinguish between OH (hydroxyl) and H20 (molecular water). SOFIA was able to measure the precise being vibration of the H-O-H molecular bond at 6.1 µm in the infrared.
SOFIA targeted high lunar latitudes near the South Pole where low temperatures could allow migrating water to transiently remain on the surface and high hydroxyl abundances could create and trap water when impacted by small meteorites. Although Clavius has a relatively high concentration of water by lunar standards, says NASA, it is roughly one-hundredth of the water found in the Sahara desert.
Scientists theorize that the water is trapped in impact glasses or within/between grains sheltered from sunlight. “These results indicate that the water has a meteoric origin or is produced on the lunar surface itself from pre-existing hydroxyl.”
The team found that water “abundance’ varies with latitude, suggesting that meteorites may not be the only source of water. Further SOFIA observations will create water maps on the nearside lunar surface, enabling scientists to learn about the storage, retention and migration of water on the Moon’s surface.