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Posted by baalke on May 9, 2007, 8:38 pm
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http://www.jpl.nasa.gov/news/news.cfm?release=2007-055
NASA Finds Extremely Hot Planet, Makes First Exoplanet Weather Map
Jet Propulsion Laboratory
May 09, 2007
Pasadena, Calif. - Researchers using NASA's Spitzer Space Telescope
have
learned what the weather is like on two distant, exotic worlds. One
team
of astronomers used the infrared telescope to map temperature
variations
over the surface of a giant, gas planet, HD 189733b, revealing it
likely
is whipped by roaring winds. Another team determined that the gas
planet
HD 149026b is the hottest yet discovered. Both findings appear May 9
in
Nature.
"We have mapped the temperature variations across the entire surface
of
a planet that is so far away, its light takes 60 years to reach us,"
said Heather Knutson of the Harvard-Smithsonian Center for
Astrophysics
in Cambridge, Mass., lead author of the paper describing HD 189733b.
The two planets are "hot Jupiters" - sizzling, gas giant planets that
zip closely around their stars. Roughly 50 of the more than 200 known
planets outside our solar system, called exoplanets, are hot Jupiters.
Visible-light telescopes can detect these strange worlds and determine
certain characteristics, such as their sizes and orbits, but not much
is
known about their atmospheres or what they look like.
Since 2005, Spitzer has been revolutionizing the study of exoplanets'
atmospheres by examining their infrared light, or heat. In one of the
new studies, Spitzer set its infrared eyes on HD 189733b, located 60
light-years away in the constellation Vulpecula. HD 189733b is the
closest known transiting planet, which means that it crosses in front
and behind its star when viewed from Earth. It races around its star
every 2.2 days.
Spitzer measured the infrared light coming from the planet as it
circled
around its star, revealing its different faces. These infrared
measurements, comprising about a quarter of a million data points,
were
then assembled into pole-to-pole strips, and, ultimately, used to map
the temperature of the entire surface of the cloudy, giant planet.
The observations reveal that temperatures on this balmy world are
fairly
even, ranging from 650 degrees Celsius (1,200 Fahrenheit) on the dark
side to 930 degrees Celsius (1,700 Fahrenheit) on the sunlit side. HD
189733b, and all other hot Jupiters, are believed to be tidally locked
like our moon, so one side of the planet always faces the star. Since
the planet's overall temperature variation is mild, scientists believe
winds must be spreading the heat from its permanently sunlit side
around
to its dark side. Such winds might rage across the surface at up to
9600
kilometers per hour (6,000 miles per hour). The jet streams on Earth
travel at 322 kilometers per hour (200 miles per hour).
"These hot Jupiter exoplanets are blasted by 20,000 times more energy
per second than Jupiter," said co-author David Charbonneau, also of
the
Harvard-Smithsonian Center for Astrophysics. "Now we can see how these
planets deal with all that energy."
Also, HD 189733b has a warm spot 30 degrees east of "high noon," or
the
point directly below the star. In other words, if the high-noon point
were in Seattle, the warm spot would be in Chicago. Assuming the
planet
is tidally locked to its parent star, this implies that fierce winds
are
blowing eastward.
In the second Spitzer study, astronomers led by Joseph Harrington of
the
University of Central Florida in Orlando discovered that HD 149026b is
a
scorching 2,038 degrees Celsius (3,700 Fahrenheit), even hotter than
some low-mass stars. Spitzer was able to calculate the temperature of
this transiting planet by observing the drop in infrared light that
occurs as it dips behind its star.
"This planet is like a chunk of hot coal in space," said Harrington.
"Because this planet is so hot, we believe its heat is not being
spread
around. The day side is very hot, and the night side is probably much
colder."
HD 149026b is located 279 light-years away in the constellation
Hercules. It is the smallest and densest known transiting planet, with
a
size similar to Saturn's and a core suspected to be 70 to 90 times the
mass of Earth. It speeds around its star every 2.9 days.
According to Harrington and his team, the oddball planet probably
reflects almost no starlight, instead absorbing all of the heat into
its
fiery body. That means HD 149026b might be the blackest planet known,
in
addition to the hottest.
"This planet is off the temperature scale that we expect for planets,"
said Drake Deming, a co-author of the paper, from NASA's Goddard Space
Flight Center, Greenbelt, Md.
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.
For more information about the Spitzer Space Telescope, visit
www.spitzer.caltech.edu or http://www.nasa.gov/spitzer .
------------------------------------------------------------------------
Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
Grey Hautaluoma 202-358-0668
NASA Headquarters, Washington
2007-055
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