WASHINGTON, July 21 (Xinhua) -- A team of geologists at the California Institute of Technology (Caltech), working with colleagues at the University of Tennessee, has found structurally bound hydroxyl groups in a mineral in a lunar rock returned to Earth by the Apollo program.
Their findings are detailed in this week's issue of the journal Nature.
The team found the water in a calcium phosphate mineral, apatite, within a basalt collected from the moon's surface by the Apollo 14 astronauts.
To be precise, they didn't find "water" -- the molecule H2O. Rather, they found hydrogen in the form of a hydroxyl anion, OH-, bound in the apatite mineral lattice.
The Caltech team analyzed the lunar apatite for hydrogen, sulfur, and chlorine using an ion microprobe, which is capable of analyzing mineral grains with sizes much smaller than the width of a human hair. This instrument fires a focused beam of high-energy ions at the sample surface, sputtering away target atoms that are collected and then analyzed in a mass spectrometer.
"The moon, which has generally been thought to be devoid of hydrous materials, has water," says John Eiler, professor of geochemistry at Caltech and a coauthor on the paper.
"Hydroxide is a close chemical relative of water," explains coauthor George Rossman, Caltech's professor of mineralogy. "If you heat up the apatite, the hydroxyl ions will 'decompose' and come out as water."
The lunar basalt sample in which the hydrogen was found had been collected by the Apollo 14 moon mission in 1971; the idea to focus the search for water on this particular sample was promoted by Larry Taylor, a professor at the University of Tennessee in Knoxville, who sent the samples to the Caltech scientists last year.