The Moon Is ‘Wetter’ Than First Believed

Geologists studying moon rocks have found evidence that water once existed on the lunar surface at levels 100 times greater than previously thought (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.1006677107). Using secondary ion mass spectrometry, Francis M. McCubbin and coworkers at Carnegie Institution for Science, in Washington, D.C., looked for hydroxyl groups in the mineral apatite from lunar samples collected during Apollo missions in the 1970s. The team extrapolated its findings to estimate the water content for the region of the moon from which the samples were collected at 64 ppb to 5 ppm. Previous estimates were less than 1 ppb. “The presence of hydroxyl in apatite from a number of different types of lunar rocks indicates that water may be ubiquitous within the lunar interior,” McCubbin and coworkers note in the paper. The researchers ruled out contamination of samples after they had been collected, observing that hydroxyl groups would have a tough time binding to and penetrating the moon rocks’ surface. The Carnegie Institution study complements the work of Alberto E. Saal of Brown University, who published a paper two years ago in Nature that first countered conventional wisdom that the moon was dry as a bone (C&EN, July 14, 2008, page 34). Saal’s work examined glass beads from one type of lunar volcanic rock.