Key figures: Carle Pieters (Principal Investigator, Moon Mineralogy Mapper, Brown University), Anthony Colaprete (Principal Investigator, LCROSS, NASA Ames), NASA, Indian Space Research Organisation (ISRO)
Summary
On September 24, 2009, the journal Science published findings from the Moon Mineralogy Mapper (M3), a NASA imaging spectrometer carried aboard India’s Chandrayaan-1 orbiter, which launched October 22, 2008. Led by Carle Pieters of Brown University, the M3 team identified absorption features near 2.8–3.0 micrometers across the lunar surface, indicating the presence of hydroxyl and water molecules bound within the top few millimeters of soil. The signal was strongest at cooler high latitudes and around several fresh craters, and appeared to vary over the lunar day, suggesting an active process — possibly solar wind hydrogen interacting with oxygen in surface minerals — was continually forming and releasing the molecules.
Weeks later, NASA’s Lunar Crater Observation and Sensing Satellite (LCROSS) mission targeted the search for water ice in a permanently shadowed region. On October 9, 2009, LCROSS’s spent Centaur rocket stage struck the floor of Cabeus crater near the lunar south pole at approximately 11:31 UTC, followed four minutes later by the LCROSS shepherding spacecraft, which flew through the resulting debris plume to collect spectroscopic data before itself impacting the surface. The impacts excavated an estimated 350 metric tons of lunar material.
On November 13, 2009, NASA announced that analysis of the ejecta plume had confirmed the presence of water. Mission scientists, led by principal investigator Anthony Colaprete of NASA’s Ames Research Center, later reported in a peer-reviewed Science paper (2010) that the instruments detected roughly 155 ± 12 kilograms of water vapor and ice within their field of view, corresponding to a regolith concentration of about 5.6 percent water ice by mass at the Cabeus impact site — a far higher concentration than the trace hydroxyl detected by M3 across sunlit regions.
Significance
The two 2009 findings together dismantled the long-standing assumption, dating to the Apollo era, that the Moon was essentially anhydrous. The M3 result showed that water-related molecules are widespread across the lunar surface, while LCROSS demonstrated that substantial reservoirs of water ice can be trapped in permanently shadowed polar craters, where temperatures never rise above roughly -170°C.
These discoveries reshaped lunar science and became a central input into subsequent NASA planning, including the Artemis program’s targeting of the lunar south pole, since accessible water ice could support drinking water, breathable oxygen, and rocket propellant production for future crewed missions without needing to be transported from Earth.
Sources
- Water on the Moon — Wikipedia
- Moon Water and Ices — NASA Science (LCROSS results, announced November 13, 2009)
- Colaprete et al., “Detection of Water in the LCROSS Ejecta Plume,” Science (2010)