24 April 1998

Orion's Water Factory

These days, it seems impossible to probe the Universe without stumbling across yet more water. Martian ice-caps, craters on the moon, Jupiter's Europa and recently Saturn's Titan - all look to be awash (or at least afrozen) with two parts hydrogen, one part oxygen. Yet such deposits are mere drops in the ocean compared to a mammoth water "factory" discovered close to the Orion nebula, say a team of astronomers from Cornell University.

Orion's giant interstellar gas cloud measures a trillion miles across and contains enough water vapour to fill the Earth's oceans sixty times a day, according to measurements made with the long-wavelength spectrometer aboard the Infrared Space Observatory (ISO), launched in 1995. The observations, reported in the April 20 issue of Astrophysical Journal Letters, could provide vital clues to the origin of water in our own solar system.

"It seems quite plausible that much of the water in the solar system was originally produced in a giant water vapour factory like the one we have observed in Orion," says ISO team-member David Neufeld. Eventually the vapour will freeze to ice particles, like the kind thought to have existed in the gas cloud from which our solar system was originally born.

Swirling around millions of stars fifteen-hundred light years from the sun, the Orion gas cloud might also trigger the formation of new stars and planets, says Cornell's Martin Harwit, leader of the project. Massive shock waves could compress the cloud, with the water vapour acting as a radiator to cool the gas sufficiently for star formation.

In the meantime, the findings confirm that the Universe is a far wetter place than previously suspected. Temperatures of 200 degrees Fahrenheit are sufficient to spark chemical reactions that convert most of the oxygen in interstellar gas into water. Which could dramatically improve the chances of there being extraterrestrial life. It's also good news for thirsty and unwashed astronauts.