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NASA
Finds Extremely Hot Planet, Makes First Exoplanet Weather Map
05/09/07
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 gas planet HD 149026b is the hottest yet
discovered.
"We have mapped the temperature
variations with longitude 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 1,200 F on the dark side to 1,700 F 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
6,000 mph. The jet streams on Earth travel at 200 mph.
"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 3,700 F, 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.
Source:
NASA / JPL
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