The Moon's Indigenous Water

Abstract

Planetary Science Until 5 years ago, the Moon was thought to be essentially bone dry. Analysis of the samples brought back by the Apollo and Luna missions had not revealed any hydrous components. Recent studies, however, using improved analytical techniques, reported the detection of water in some lunar rocks, and observations from orbiting spacecraft showed that water is present in the lunar surface. Some of this water is thought to have been delivered by meteorites and through solar-wind implantation of hydrogen; another part is thought be indigenous. Using Fourier transform infrared spectroscopy, Hui et al. have detected water in two Apollo samples representative of the Moon's primary crust, crystallized from the lunar magma ocean that is thought to have once covered the Moon. Water in these samples is indigenous—with solar-wind implantation ruled out by the use of grains that came from the interior of the individual Apollo rocks—and it was present at very early times, before the crust solidified. The authors estimate that the initial water content of the lunar magma ocean was around 320 parts per million. This water could have prolonged the crystallization of the magma ocean. Nat. Geosci. 10.1038/ngeo1735 (2013).