Sat, Apr 14, 2007 - Page 7 News List

Obscure planet has signs of water in its atmosphere


There might be water beyond our solar system after all.

An alien planet that appeared to be dry, dark and dusty has water in its atmosphere, an astronomer said on Wednesday, but some of the astronomers who had made the earlier observations said his conclusions might be premature.

The planet, known as HD 209458b, circles a Sun-like star about 150 light-years away in Pegasus, passing between its star and Earth every 3.6 days. Last winter, two teams using the Spitzer Space Telescope failed to find signs of water in its atmosphere, causing consternation among planetary theorists.

All their models indicate that water vapor is one of the fundamental elements of planetary composition.

In the new work, Travis Barman of Lowell Observatory in Flagstaff, Arizona, made numerical models of the planet's atmosphere, assuming there was water. Barman then compared them with measurements made with the Hubble Space Telescope when light was shining through the edge of the planet's atmosphere as it passed in front of its star.

The Hubble observations were made by a team led by Heather Knutson, a graduate student at the Harvard-Smithsonian Center for Astrophysics.

The correlation between the bumps and wiggles predicted and observed, Barman said, "is a powerful clue that water is present."

Without water, the results would not match, he said in an e-mail message. "Water has been predicted to be present by many models [not just mine] for a long time," he said.

Barman said the earlier Spitzer observations, which were announced in February, might have failed to find water because they were made when the planet was passing behind its star, fully illuminated from the front.

That situation, observers say, could make it difficult to see water even if it were there.

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