NASA's Spitzer
First to Crack Open
Light of Faraway
Worlds
from NASA Home
> Mission Sections > Spitzer > News at
http://www.nasa.gov/mission_pages/spitzer/news/spitzer-20070221-full.html
21 Feb 2007: NASA's Spitzer Space Telescope has captured for the
first time enough light from planets outside our solar system, known as
exoplanets, to identify 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, Pasadena, Calif. "We had no
idea when we designed Spitzer that it would make such a dramatic step in
characterizing exoplanets."
This artist's concept
shows a cloudy Jupiter-like planet that orbits very close to its fiery
hot star. NASA's Spitzer Space Telescope was recently used to capture spectra,
or molecular fingerprints, of two "hot Jupiter" worlds like the one depicted
here. This is the first time a spectrum has ever been obtained for an exoplanet,
or a planet beyond our solar system. Image Credit: Nasa/JPL-Caltech.
Spitzer, a space-based infrared telescope, obtained the detailed data,
called spectra, for two different gas exoplanets. Called HD 209458b and
HD 189733b, these so-called "hot Jupiters" are, like Jupiter, made of gas,
but orbit much closer to their suns.
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 surprisingly none was found
around HD 209458b and HD 189733b. According to astronomers, the water might
be present but buried under a thick blanket of high, waterless clouds.
Those clouds might be filled with dust. One of the planets, HD 209458b,
showed hints of tiny sand grains, called silicates, in its atmosphere.
This could mean the planet's skies are filled with 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 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 Nature
paper appearing Feb. 22 that describes a spectrum for HD 209458b.
In addition to Richardson's team, two other groups of astronomers used
Spitzer to capture spectra of exoplanets. A team led by Dr. Carl Grillmair
of NASA's Spitzer Science Center at the California Institute of Technology
in Pasadena, Calif., observed HD 189733b, while a team led by Dr. 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.
A spectrum is created when an instrument called a spectrograph splits light
from an object into its different wavelengths, just as a prism turns sunlight
into a rainbow. The resulting pattern of light, the spectrum, reveals "fingerprints"
of chemicals making up the object.
Until now, the only planets for which spectra were available belonged in
our own solar system. The planets in the Spitzer studies orbit stars that
are so far away, they are too faint to be seen with the naked eye. HD 189733b
is 370 trillion miles away in the constellation Vulpecula, and HD 209458b
is 904 trillion miles away in the constellation Pegasus. That means both
planets are at least about a million times farther away from us than Jupiter.
In the future, astronomers hope to have spectra for smaller, rocky planets
beyond our solar system. This would allow them to look for the footprints
of life -- molecules key to the existence of life, such as oxygen and possibly
even chlorophyll.
"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 was able to tease out spectra from the feeble light of the two
planets through what is known as the "secondary eclipse" technique. In
this method -- first used by Spitzer in 2005 to directly detect the light
from an exoplanet for the first time -- a so-called transiting planet is
monitored as it circles behind its star, temporarily disappearing from
our Earthly point of view. By measuring the dip in infrared light that
occurs when the planet disappears, Spitzer can learn how much light is
coming solely from the planet. 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 the new studies, Spitzer's spectrograph, which measures infrared light
at a range of wavelengths, stared at the two transiting planets as they
orbited their stars. This allowed the astronomers to subtract the spectra
of the stars from the spectra of the planets plus their stars to obtain
spectra of the planets alone.
"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."
Previous observations of HD 209458b by NASA's Hubble Space Telescope revealed
individual elements, such as sodium, oxygen, carbon and hydrogen, that
bounce around the very top of the planet, a region higher up than that
probed in the Spitzer studies and a region where molecules like water would
break apart. To do this, Hubble measured changes in the light from the
star, not the planet, as the planet passed in front. The observations indicated
less sodium than predicted, which again supports the idea that the planet
is socked in with high clouds.
Astronomers hope to use Spitzer for additional studies of transiting exoplanets,
which are those that cross in front of their stars from our point of view.
Of the approximately 200 known exoplanets, 14 are transiting. At least
three of these in addition to HD 209458b and HD 189733b are candidates
for obtaining spectra. Further spectral studies of HD 209458b and HD 189733b
will also yield more information about the planets' atmospheres.
NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer
Space Telescope mission for NASA's Science Mission Directorate, Washington.
Science operations are conducted at the Spitzer Science Center at the California
Institute of Technology, also in Pasadena. Caltech manages JPL for NASA.
Spitzer's infrared spectrograph was built by Cornell University, Ithaca,
N.Y. Its development was led by Dr. Jim Houck of Cornell.
For artist's concepts and more information,
visit:
http://www.nasa.gov/spitzer
and www.spitzer.caltech.edu/Media .
Tabatha Thompson
NASA Headquarters, Washington
202-358-3895
Whitney Clavin
Jet Propulsion Laboratory, Pasadena,
Calif.
818-354-4673 |
