An exoplanet with some fizz: C[O.sub.2] detection bolsters search for signs of life.

Moving one step closer to finding distant fingerprints of life, astronomers have for the first time detected carbon dioxide in the atmosphere of a planet that orbits a star other than the sun.

The extrasolar planet and its star lie about 63 light-years from Earth. Slightly bigger than Jupiter, the gaseous body circles its parent star at a proximity that renders it far too hot to support life. But the finding bodes well for ultimately detecting carbon dioxide and other potential markers of life on planets that lie far enough from their parent stars to be habitable, says Mark Swain of NASA's Jet Propulsion Laboratory in Pasadena, Calif.

In the atmospheres of more temperate planets, carbon dioxide--along with water, methane and oxygen--can be made by biological processes. "In that context," Swain says, "the carbon dioxide measurement constitutes a dress rehearsal ... for our long-term goal of trying to detect signs of life or signs of habitability on terrestrial-mass planets or super Earths in the habitable zone" around a star, which is where water could exist as a liquid.

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Using the Hubble Space Telescope's Near Infrared Camera and Multi-Object Spectrometer, Swain and his colleagues recorded infrared spectra from the planet, which periodically crosses in front of its parent star as seen from Earth. When the hot planet lies side by side with its parent star, HD 189733, astronomers can detect the spectra of infrared radiation, or heat, from both star and planet. When the planet dives behind the star, only the infrared radiation from the star reaches Earth. Subtracting the two measurements provides the amount of infrared radiation given off by the planet alone.

The spectra of the planet's radiation, recorded by the Hubble instrument, reveal chemical constituents of the planet's atmosphere. The team found evidence of water vapor, which was previously detected in the planet's atmosphere, as well as carbon monoxide and the never-before-seen carbon dioxide, the researchers report in an upcoming Astrophysical Journal Letters. Team member Gautam Vasisht of JPL also presented the findings on November 19 in Paris at the Molecules in the Atmospheres of Extrasolar Planets meeting.