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Tabatha Thompson NASA Headquarters, 202-358-3895
Whitney Clavin Jet Propulsion Laboratory, 818-354-4673
NEWS RELEASE: 2007-020 Feb. 21, 2007
NASA's Spitzer First to Crack Open Light of Faraway Worlds
NASA's Spitzer Space Telescope has captured for the first time enough light from planets outside our solar system, known as exoplanets, to identify signatures of molecules in their atmospheres. The landmark achievement is a significant step toward being able to detect possible life on rocky exoplanets and comes years before astronomers had anticipated.
"This is an amazing surprise," said Spitzer project scientist Dr. Michael Werner of NASA's Jet Propulsion Laboratory,
Spitzer, a space-based infrared telescope, obtained the detailed data, called spectra, for two different gas exoplanets: HD 189733b is 370 trillion miles away in the constellation Vulpecula, and HD 209458b is 904 trillion miles away in the constellation Pegasus.
Just as a prism disperses sunlight into a rainbow, Spitzer uses an instrument called a spectrograph to reveal a spectrum by splitting light from an object into different wavelengths. The process uncovers "fingerprints" of chemicals making up the object. The exoplanets Spitzer observed are known as "hot Jupiters" because they are gaseous like Jupiter but orbit much closer to their stars.
The data indicate the two planets are drier and cloudier than predicted. Theorists thought hot Jupiters would have lots of water in their atmospheres, but were surprised when none was found around HD 209458b or HD 189733b. In addition, one of the planets, HD 209458b, showed hints of tiny sand grains, called silicates, in its atmosphere. This could mean the water is present in the planet's atmosphere but hidden under high, dusty clouds unlike anything seen around planets in our own solar system.
"The theorists' heads were spinning when they saw the data," said Dr. Jeremy Richardson of NASA's
"It is virtually impossible for water, in the form of vapor, to be absent from the planet, so it must be hidden, probably by the dusty cloud layer we detected in our spectrum," he said.
A team led by Dr. Carl Grillmair of NASA's
"With these new observations, we are refining the tools that we will one day need to find life elsewhere if it exists," said Swain. "It's sort of like a dress rehearsal."
Spitzer teased out spectra from the feeble light of the two planets through the "secondary eclipse" technique. In this method, the telescope monitors a planet as it transits, or circles behind its star, temporarily disappearing from view.
By measuring the dip in infrared light that occurred when the planets disappeared, Spitzer's spectrograph was able to obtain spectra of the planets alone. The technique will work only in infrared wavelengths, where the planet is brighter than in visible wavelengths and stands out better next to the overwhelming glare of its star.
In previous observations of HD 209458b, NASA's Hubble Space Telescope measured changes in the light from the star, not the planet, as the planet passed in front. Those observations revealed individual elements, such as sodium, oxygen, carbon and hydrogen, which bounce around the very top of the planet.
"When we first set out to make these observations, they were considered high risk because not many people thought they would work," said Grillmair. "But Spitzer has turned out to be superbly designed and more than up to the task."
JPL manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. The
For artist's concepts and more information on the Web, visit: http://www.nasa.gov/spitzer andwww.spitzer.caltech.edu/Media .
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