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

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. L 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: