No water found on distant planets

WASHINGTON -- Scientists taking their first "sniffs of air" from planets outside our solar system are a bit baffled by what they didn't find: water.

One of the more basic assumptions of astronomy is that the two distant, hot gaseous planets they examined must contain water in their atmospheres. The two suns the planets orbit closely have hydrogen and oxygen, the stable building blocks of water.

The planets' atmospheres -- examined for the first time using light spectra to determine the air's chemical composition -- are supposed to be made up of the same thing, H{-2}O.

But when two different teams of astronomers used NASA's Spitzer Space Telescope for extrasolar planet research, they both came up dry, according to research published in today's edition of Nature and the online version of the Astrophysical Journal Letters.

The study of one planet found hints of fine silicate-particle clouds. Research on the other planet found no chemical fingerprints for any of the molecules scientists were seeking.

"We had expected this tremendous signature of water ," said the study leader for one team, Carl Grillmair of the California Institute of Technology and Spitzer Science Center. "We obviously need to do some more work."

Grillmair's colleague, Harvard astronomy professor David Charbonneau, said these surprising "sniffs of air from an alien world" tell astronomers not to be so Earth-centric in thinking about other planets.

" These are unlike any other planets in the solar system," Charbonneau said. "We're limited by our imagination in thinking about the different avenues that these atmospheres take place in."

Our solar system has two planets without water in the atmosphere, Grillmair noted: Mercury, which doesn't have an atmosphere, and Venus, which is a different type of planet from the huge gaseous ones that would be expected to have the components of water in the air.

Scientists have found 213 planets outside our solar system, but only 14 have orbits that make it possible for extrasolar planet research; only eight or nine of those are close enough to see. Grillmair's team studied the closest, which goes by the name HD 189733b. The other planet, HD209458b, has the silicate cloud.

Scientists suggest the water could be under dust clouds, or all the airborne water molecules have the same temperature, making it impossible to see using an infrared spectrograph.

For more information, go to: Spitzer Space Telescope: http://www.spitzer.caltech.edu/ Nature: www.nature.com. The Astrophysical Journal Letters: http://www.journals.uchicago.edu/ApJ/rapid.html