Washington D.C. Most of the 150 known extrasolar planets are discovered and studied through techniques such as finding the telltale wobble of a star tugged by an orbiting planet, or the “blink” of a star as a planet passes in front of it. Now for the first time scientists have observed an extrasolar planet through the light it emits in the infrared. “I feel we’ve been blind and have just been given sight,” commented co-author of the study* Dr. Sara Seager of the Carnegie Institution. “Detecting light from these other worlds is very exciting. It opens a whole new window on these objects. It’s the beginning of our ability to study their temperature, and composition,” she added. The study, published in the March 23 on-line edition of Nature, used measurements from NASA’s Spitzer Space Telescope, an infrared observatory launched in August 2003. Results of the work are announced today at NASA headquarters.

The planet, HD 209458b, is a so-called hot Jupiter—a massive gaseous world that orbits very closely to its parent star in only 3.5 days. It has not yet been possible to see these planets in the visible part of the spectrum because the light from the star vastly outshines that from the planet. However in the infrared, the planets show up more brightly than they do at visible wavelengths, making them detectable. As Seager explained: “This planet was discovered indirectly in 1999 and was later found to transit its star—the star dims as the planet moves in front of it during the course of the planet’s orbit. With Spitzer, we first measured the combined light of the planet and star just before the planet went out of sight. Then when the planet was out of view, we measured how much energy the star emitted on its own. The difference between those readings told us how much the planet emitted.” The results of the measurements agreed with models created to determine how much infrared radiation hot Jupiters are likely to emit. HD 209458b was found to be a scorching 1,574 F (1130 K), confirming that hot Jupiters are in fact intensely baked by their stars.

Another Spitzer study, led by Dr. David Charbonneau of the Harvard-Smithsonian Center for Astrophysics, also detected infrared light from a planet, TrES-1, using the same technique, making two infrared detections of hot Jupiters. That research will be published in an upcoming issue of The Astrophysical Journal.   “This first detection of light from two confirmed extrasolar planets is another major milestone along the way to the ultimate goal of finding Earth-like planets and examining their atmospheres for signs of life,” said Alan Boss, a star and planet formation theorist at Carnegie’s Department of Terrestrial Magnetism who advises NASA about the search for extrasolar planets. “This detection means that we are succeeding in the effort to combine astronomy and biology into the new field of astrobiology, which seeks to determine if life has originated and evolved elsewhere in the universe.”

The scientists got an added bonus in the Nature study. Researchers had thought that the seemingly bloated HD 209458b, with its particularly large radius, might have been stretched out from tidal tugs from the star due to an elongated orbit caused by gravitational interactions from yet another undetected planet. However, this scenario was ruled out because researchers found the orbit to be circular. “This finding adds to the growing number of mysteries that so many of these extrasolar planets seem to exhibit,” mused Seager.

*Researchers on the paper are Drake Deming, Goddard Space Flight Center; Sara Seager, Carnegie Institution; L. Jeremy Richardson, Goddard Space Flight Center; and Joseph Harrington, Cornell University. The research was supported by NASA, NASA’s  Origins of Solar Systems program,  and the NASA Astrobiology Institute.

 The Carnegie Institution (www.CarnegieInstitution.org) has been a pioneering force in basic scientific research since 1902. It is a private, nonprofit organization with six research departments throughout the U.S. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.

The Spitzer Space Telescope was launched in August 2003 for a 5-year mission. It detects energy from celestial objects in the infrared part of the spectrum, which is able to penetrate areas in space not visible in the optical spectrum such as dense clouds of gas and dust where stars form, new extrasolar planetary systems, and galactic centers.JPL manages the Spitzer Space Telescope for NASA.

NASA’s Astrobiology Institute (NAI), founded in 1997, is a partnership between NASA, 16 major U.S. teams, and five international consortia. NAI's goal is to promote, conduct, and lead integrated multidisciplinary astrobiology research and to train a new generation of astrobiology researchers. For more information about the NAI on the Internet, visit: http://nai.arc.nasa.gov/