The discovery, published in the October 21 issue of the journal Science, could help explain how Earth got its oceans and suggests that our planet may not be the only watery world in the cosmos.
"This new result shows that the reservoir of water ice in such a disk is huge," says Darek Lis, a senior research associate in physics at Caltech and a coauthor on the paper. If other planet-forming disks also have such copious amounts of water, then there's a greater chance that other planets are also wet. "Water-covered planets like Earth may be quite common," he says.
To make the discovery, the team of researchers, which includes Caltech professor of planetary science Geoff Blake and JPL's John Pearson, pointed the Herschel Space Observatory at a star called TW Hydrae, located 175 light years away. TW Hydrae, which is only about 10 million years old, is surrounded by a disk of gas—just as the young sun was about 4.6 billion years ago.
The team found the water vapor—which previously had never been detected in the outer regions of such a disk—using Herschel's Heterodyne Instrument for the Far Infrared (HIFI). The vapor, the researchers say, likely is produced when ultraviolet light from the central and other nearby stars bombards large reservoirs of ice in the disk.