Researchers have used a new technique to analyze the gaseous atmospheres of such extrasolar planets and have made the first detection of water in the atmosphere of the Jupiter-mass planet orbiting the nearby star tau Bootis.
Scientists have previously detected water vapor on a handful of other planets, but these detections could only take place under very specific circumstances, says graduate student Alexandra Lockwood, the first author of the study.
The method used by scientists utilized the radial velocity (RV) technique-a technique commonly used in the visible region of the spectrum to which our eyes are sensitive-for discovering non-transiting exoplanets. Using the Doppler effect, RV detection traditionally determines the motion of a star due to the gravitational pull of a companion planet; the star moves opposite that of the orbital motion of the planet, and the stellar features shift in wavelength. A large planet or a planet closer to its host star provides a larger shift.
Lockwood, Blake, and their colleagues expanded the RV technique into the infrared to determine the orbit of tau Bootis b around its star, and added further analysis of the light shifts via spectroscopy-an analysis of the light's spectrum.
Since every compound emits a different wavelength of light, this unique light signature allows the researchers to analyze molecules that make up the planet's atmosphere. Using data of tau Bootis b from the Near Infrared Echelle Spectrograph (NIRSPEC) at the W. M. Keck Observatory in Hawaii, the researchers were able to compare the molecular signature of water to the light spectrum emitted by the planet, confirming that the atmosphere did indeed include water vapor.
The new results have been published online in The Astrophysical Journal Letters.
