First Sign of Water on Planet Outside Our System

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Some of the more recently discovered planetary systems may be better candidates for such analysis, Barman said. But, he added, Hubble captured data from HD209458b with an instrument that is no longer working—so the particular kind of measurement used is no longer possible for other systems using Hubble.

Hot Jupiters

The mass of planet HD209458b is 220 times greater than Earth's. Like Jupiter, HD209458b is a gaseous planet, though it is only about seven-tenths the mass of our solar system's largest planet.

HD209458b orbits its star more closely than Mercury orbits our sun.

These traits put it into a class with other so-called hot Jupiters, which make up about 40 percent of known planets orbiting other stars. (Related: "'Hot Jupiters' Could Give Rise to Earthlike Worlds, Study Says" [September 7, 2006].)

Astronomers are interested in hot Jupiters because their size makes them the easiest exoplanets to study—and because their violent gravitational dynamics may both create and destroy Earth-size planets.

Jeremy Richardson, of NASA's ExoPlanets and Stellar Astrophysics Lab in Maryland, was lead author of an HD209458b report in the journal Nature in February.

Richardson's study found no evidence of water in the atmosphere.

But he said his team's observations were made using different techniques than Barman's—so they're not necessarily contradictory.

"The Barman paper looks at observations taken during transit," Richardson said.

"Our observations were made just before the planet disappears behind the star."

Other scientists, he said, have suggested that winds can obscure signs of water at this stage of a planet's orbit.

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