NASA's Spitzer First to Crack Open Light of Far Away Worlds (Forwarded)

Tabatha Thompson
Headquarters, Washington Feb. 21, 2007
202-358-3895

Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-4673

RELEASE: 07-48

NASA'S SPITZER FIRST TO CRACK OPEN LIGHT OF FAR AWAY WORLDS

WASHINGTON -- 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 life on rocky exoplanets and comes years before astronomers
had anticipated.

"This is an amazing surprise," said Spitzer project scientist Michael
Werner of NASA's Jet Propulsion Laboratory (JPL), Pasadena, Calif.
"We had no idea when we designed Spitzer that it would make such a
dramatic step in characterizing exoplanets."

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
Jeremy Richardson of NASA's Goddard Space Flight Center, Greenbelt,
Md.

"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. Richardson is lead
author of a paper appearing in the Feb. 22 issue of Nature that
describes a spectrum for HD 209458b.

A team led by Carl Grillmair of NASA's Spitzer Science Center at the
California Institute of Technology in Pasadena, Calif., captured the
spectrum of HD 189733b. A team led by Mark R. Swain of JPL focused on
the same planet in the Richardson study and came up with similar
results. Grillmair's results will be published in the Astrophysical
Journal Letters. Swain's findings have been submitted to the
Astrophysical Journal Letters.

"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 Spitzer Science Center at the
California Institute of Technology conducts mission science
operations.

For artist's concepts and more information on the Web, visit:

http://www.spitzer.caltech.edu/Media.../visuals.shtml