Kepler Detects an Exoplanet Atmosphere
August 6, 2009: NASA's new exoplanet-hunting Kepler space telescope has detected the atmosphere of a known giant gas planet, demonstrating the telescope's extraordinary scientific capabilities. The discovery will be published Friday in the journal Science.
Right: An artist's concept of an exoplanet orbiting close to its sun. Image credit: NASA
Launched March 6, 2009, from Cape Canaveral Air Force Station in Florida, Kepler will spend the next three-and-a-half years searching for planets as small as Earth, including those that orbit stars in a warm "Goldilocks zone" where there could be water. It will do this by looking for periodic dips in the brightness of stars, which occur when orbiting planets transit, or cross in front of, the stars.
The observations were collected from a planet called HAT-P-7, known to transit a star located about 1,000 light years from Earth. The planet orbits the star in just 2.2 days and is 26 times closer than Earth is to the sun. Its orbit, combined with a mass somewhat larger than the planet Jupiter, classifies this planet as a "hot Jupiter." It is so close to its star, the planet is as hot as the glowing red heating element on a kitchen stove.
HAT-P-7 was known before Kepler turned its attention to the planet. Kepler's measurements are so precise, however, they show something new: a smooth rise and fall of the light caused by the changing phases of the planet, similar to the phases of our own Moon. Kepler could also see the planet's light vanish completely when it passed behind its parent star. This vanishing act is called an "occultation."
Above: A comparison of ground-based and space-based light curves for hot exoplanet HAT P7b. Image credit: NASA. [Larger image]
The new Kepler data can be used to study this hot Jupiter in unprecedented detail. The depth of the occultation and the shape and amplitude of the light curve show the planet has an atmosphere with a day-side temperature of about 4,310 degrees Fahrenheit. Little of this heat is carried to the cool night side. The occultation time compared to the main transit time shows the planet has a circular orbit. The discovery of light from this planet confirms the predictions by researchers and theoretical models that the emission would be detectable by Kepler.
The observed brightness variation is just one and a half times what is expected for a transit caused by an Earth-sized planet. Although this is already the highest precision ever obtained for an observation of this star, Kepler will be even more precise after analysis software being developed for the mission is completed.
"This early result shows the Kepler detection system is performing right on the mark," said David Koch, deputy principal investigator of NASA's Ames Research Center at Moffett Field, Calif. "It bodes well for Kepler's prospects to be able to detect Earth-size planets."
Stay tuned to Science@NASA for more results from Kepler.
Kepler is a NASA Discovery mission. Ames is responsible for the ground system development, mission operations and science data analysis. NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages the Kepler mission development. Ball Aerospace and Technologies Corp. of Boulder, Colo., is responsible for developing the Kepler flight system and supporting mission operations.
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