Satellite Discovers Evidence of Water in Distant Solar System
(From the September/October 2001 issue of StarDate magazine)
Astronomers using an Earth-orbiting radio telescope have found evidence that a star 500 light-years away in Leo is vaporizing a surrounding swarm of comets, thus releasing a huge cloud of water vapor. The detection, made by the Submillimeter Wave Astronomy Satellite (SWAS), is the first evidence that planetary systems other than our own contain water, a molecule essential to life on Earth.
“What makes the results we are reporting today so unusual is that we have found a cloud of water vapor around a star where we would not ordinarily have expected to find water,” said Gary Melnick of the Harvard-Smithsonian Center for Astrophysics, principal investigator of the SWAS mission. “IRC+10216 is a carbon-rich star in which the concentration of carbon exceeds that of oxygen,” he said. “In such stars we expect all the oxygen atoms to be bound up in the form of carbon monoxide, with almost nothing left over to form water.…The most plausible explanation for this water vapor is that it is being vaporized from the surfaces of orbiting comets, ‘dirty snowballs’ that are composed primarily of water ice.”
It would take several hundred billion comets to produce the amount of water vapor detected by SWAS. “That sounds like a lot,” said Saavik Ford, a graduate student at The Johns Hopkins University and co-author of the discovery. “But the total mass required of this swarm of orbiting comets is similar to the original mass of the Kuiper Belt, a collection of comets that orbits our own Sun beyond the orbit of Neptune.”
Launched December 5, 1998, SWAS is the third spacecraft in NASA’s Small Explorer Program. The spacecraft studies star formation by determining the composition of interstellar clouds and establishing how these clouds cool as they collapse to form stars and planets. Rebecca Johnson
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