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Posted by baalke on July 11, 2007, 9:54 pm
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http://www.jpl.nasa.gov/news/news.cfm?release=3D2007-077
NASA's Spitzer Finds Water Vapor on Hot, Alien Planet
Jet Propulsion Laboratory
July 11, 2007
A scorching-hot gas planet beyond our solar system is steaming up with
water vapor, according to new observations from NASA's Spitzer Space
Telescope.
The planet, called HD 189733b, swelters as it zips closely around its
star every two days or so. Astronomers had predicted that planets of
this class, termed "hot Jupiters," would contain water vapor in their
atmospheres. Yet finding solid evidence for this has been slippery.
These latest data are the most convincing yet that hot Jupiters are
"wet."
"We're thrilled to have identified clear signs of water on a planet
that
is trillions of miles away," said Giovanna Tinetti, a European Space
Agency fellow at the Institute d'Astrophysique de Paris in France."
Tinetti is lead author of a paper on HD 189733b appearing today in
Nature.
Although water is an essential ingredient to life as we know it, wet
hot
Jupiters are not likely to harbor any creatures. Previous measurements
from Spitzer indicate that HD 189733b is a fiery 1,000 Kelvin (1,340
degrees Fahrenheit) on average. Ultimately, astronomers hope to use
instruments like those on Spitzer to find water on rocky, habitable
planets like Earth.
"Finding water on this planet implies that other planets in the
universe, possibly even rocky ones, could also have water," said
co-author Sean Carey of NASA's Spitzer Science Center at the
California
Institute of Technology in Pasadena. "I'm excited to tell my nephews
and
niece about the discovery."
The new findings are part of a brand new field of science
investigating
the climate on exoplanets, or planets outside our solar system. Such
faraway planets cannot be seen directly; however, in the past few
years,
astronomers have begun to glean information about their atmospheres by
observing a subset of hot Jupiters that transit, or pass in front of,
their stars as seen from Earth.
Earlier this year, Spitzer became the first telescope to analyze, or
break apart, the light from two transiting hot Jupiters, HD 189733b
and
HD 209458b. One of its instruments, called a spectrometer, observed
the
planets as they dipped behind their stars in what is called the
secondary eclipse. This led to the first-ever "fingerprint," or
spectrum, of an exoplanet's light. Yet, the results came up "dry,"
probably because the structure of these planets' atmospheres makes
finding water with this method difficult.
Later, a team of astronomers found hints of water in HD 209458b by
analyzing visible-light data taken by NASA's Hubble Space Telescope.
The
Hubble data were captured as the planet crossed in front of the star,
an
event called the primary eclipse.
Now, Tinetti and her team have captured the best evidence yet for wet,
hot Jupiters by watching HD 189733b's primary eclipse in infrared
light
with Spitzer. In this method, changes in infrared light from the star
are measured as the planet slips by, filtering starlight through its
outer atmosphere. The astronomers observed the eclipse with Spitzer's
infrared array camera at three different infrared wavelengths and
noticed that for each wavelength a different amount of light was
absorbed by the planet. The pattern by which this absorption varies
with
wavelength matches that created by water.
"Water is the only molecule that can explain that behavior," said
Tinetti. "Observing primary eclipses in infrared light is the best way
to search for this molecule in exoplanets."
The water on HD 189733b is too hot to condense into clouds; however,
previous observations of the planet from Spitzer and other ground and
space-based telescopes suggest that it might have dry clouds, along
with
high winds and a hot, sun-facing side that is warmer than its dark
side.
HD 189733b is located 63 light-years away in the constellation
Vulpecula.
Other authors of the Nature paper include Alfred Vidal-Madjar,
Jean-Phillippe Beaulieu, David Sing and Nicole Allard of the Institute
d'Astrophysique de Paris: Mao-Chang Liang of Caltech and the Academia
Sinica, Taiwan; Yuk Yung of Caltech; Robert J. Barber and Jonathan
Tennyson of University College London in England; Ignasi Ribas of the
Institut de Ci=E8ncies de l'Espai, Spain; Gilda E. Ballester of the
University of Arizona, Tucson; and Franck Selsis of the Ecole Normale
Sup=E9rieure, France.
JPL 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,
Pasadena. JPL is a division of Caltech. Spitzer's infrared array
camera
was built by NASA's Goddard Space Flight Center, Greenbelt, Md. The
instrument's principal investigator is Giovanni Fazio of the
Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.
For graphics related to this research and more information about
Spitzer, visit http://www.spitzer.caltech.edu/spitzer and
http://www.nasa.gov/spitzer .
------------------------------------------------------------------------
Media contact: Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
2007-077
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