First Sign of Water on Planet Outside Our System

April 10, 2007

For the first time, astronomers have detected water in the atmosphere of a planet outside our solar system.

Astronomer Travis Barman announced today that he has discovered water around planet HD209458b by combining theoretical models with observations from the Hubble Space Telescope.

The results don't necessarily figure into the search for life on other planets, but they go far to reassure many astronomers that their predictions are on track, said Barman, of Lowell Observatory in Flagstaff, Arizona.

"It means that our theoretical understanding of these planets is in the ballpark," he said. "We understand enough about them to predict that water should be there, and then water is there."

Scientists have predicted water vapor in the atmospheres of most planets orbiting other stars.

The results are a "confidence booster," Barman said. They were recently accepted for publication in the Astrophysical Journal.

Planets in Transit

HD209458b and its star, HD209458, are 150 light-years from Earth in the constellation Pegasus.

Discovered in 1999, this was the first planetary system positioned in a way that allows scientists to observe the atmosphere of a planet outside our solar system. As of today, though, HD209458b is one of 14 such "transit systems."

Planets in transit systems pass between Earth and their host stars, allowing astronomers to calculate the planets' masses and measure their atmospheric compositions.

HD209458b, as seen from Earth, passes directly in front of its star every three and half days.

Using telescopes on the ground and in space, astronomers have heavily scrutinized the system.

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