| |
 |
|
|
Science Forum Index » Astro Forum » Hubble Probes Layer-Cake Structure of Exoplanet's Atmosphere
Page 1 of 1
|
| Author |
Message |
| Guest |
 Posted: Wed Jan 31, 2007 3:26 pm |
|
|
|
|
HUBBLE PROBES LAYER-CAKE STRUCTURE OF ALIEN WORLD'S ATMOSPHERE
(Forwarded from STScI by Lori Stiles, UA, 520-626-4402)
- Wednesday, January 31, 2007
---------------------------------------------------------------
SUMMARY: Astronomers at the University of Arizona Lunar and Planetary
Lab
are the first to see structure in the atmosphere of a planet outside
our
solar system. They report it today in Nature. The following news
release is
being forwarded from the Space Telescope Science Institute in
Baltimore, Md.
Contact information and Web links are listed at the end of the
release.
-----------------------------------------------------------------
The powerful vision of NASA's Hubble Space Telescope has allowed
astronomers
to study for the first time the layer-cake structure of the atmosphere
of a
planet orbiting another star. Hubble discovered a dense upper layer of
hot
hydrogen gas where the super-hot planet's atmosphere is bleeding off
into
space.
The planet, designated HD 209458b, is unlike any world in our solar
system.
It orbits so close to its star and gets so hot that its gas is
streaming
into space, making the planet appear to have a comet-like tail. This
new
research reveals the layer in the planet's upper atmosphere where the
gas
becomes so heated it escapes like steam rising from a boiler.
"The layer we studied is actually a transition zone where the
temperature
skyrockets from about 1,340 degrees Fahrenheit (1,000 Kelvin) to about
25,540 degrees (15,000 Kelvin), which is hotter than the Sun," said
Gilda
Ballester of the University of Arizona in Tucson, leader of the
research
team. "With this detection we see the details of how a planet loses
its
atmosphere."
The findings by Ballester, David K. Sing, of the University of Arizona
and
the Institut d?Astrophysique de Paris, and Floyd Herbert of the
University
of Arizona will appear Feb. 1 in a letter to the journal Nature.
Intense ultraviolet radiation from the host star heats the gas in the
upper
atmosphere, inflating the atmosphere like a balloon. The gas is so hot
that
it moves very fast and escapes the planet's gravitational pull at a
rate of
10,000 tons a second, more than three times the rate of water flowing
over
Niagara Falls. The planet, however, will not wither away any time
soon.
Astronomers estimate its lifetime is more than 5 billion years.
The scorched planet is a big puffy version of Jupiter. In fact, it is
called a "hot Jupiter," a large gaseous planet orbiting very close to
its
parent star. Jupiter might even look like HD 209458b if it were close
to the
Sun, Ballester said.
The planet completes an orbit around its star every 3.5 days. It
orbits 4.7
million miles from its host, 20 times closer than the Earth is to the
Sun.
By comparison, Mercury, the closest planet to our Sun, is 10 times
farther
away from the Sun than HD 209458b is from its star. Unlike HD 209458b,
Mercury is a small ball of iron with a rocky crust.
"This planet's extreme atmosphere could yield insights into the
atmospheres
of other hot Jupiters," Ballester said.
Although HD 209458b does not have a twin in our solar system, it has
plenty
of relatives beyond our solar system. About 10 to 15 percent of the
more
than 200 known extrasolar planets are hot Jupiters. A recent Hubble
survey
netted 16 hot Jupiter candidates in the central region of our Milky
Way
Galaxy, suggesting that there may be billions of these gas-giant star
huggers in our galaxy.
HD 209458b is one of the most intensely studied extrasolar planets
because
it is one of the few known alien worlds that can be seen passing in
front
of, or transiting, its star, causing the star to dim slightly. In
fact, the
gas giant is the first such alien world discovered to transit its
star. HD
209458b is 150 light-years from Earth in the constellation Pegasus.
The transits allow astronomers to analyze the structure and chemical
makeup
of the gas giant's atmosphere by sampling the starlight that passes
through
the planet's atmosphere. The effect is similar to finding fingerprints
on a
window by watching how sunlight filters through the glass.
Previous Hubble observations revealed oxygen, carbon, and sodium in
the
planet's atmosphere, as well as a huge hydrogen upper atmopshere with
a
comet-like tail. These landmark studies provided the first detection
of the
chemical makeup of an extrasolar planet's atmosphere.
Additional observations by NASA's Spitzer Space Telescope captured the
infrared glow from the planet's hot atmosphere.
The new study by Ballester and her team is based on an analysis of
archival
observations made in 2003 with Hubble's Space Telescope Imaging
Spectrograph
by David Charbonneau of the Harvard-Smithsonian Center for
Astrophysics in
Cambridge, Mass. Ballester's team analyzed spectra from hot hydrogen
atoms
in the planet's upper atmosphere, a region not studied by
Charbonneau's
group.
-----------------------------------------------------
Science Contact Information
Gilda Ballester 520-621-4073 gilda@lpl.arizona.edu
David K. Sing 33 1 4432 8028 sing@iap.fr
Floyd Herbert 520-621-4569 herbert@vega.lpl.arizona.edu
Media Contact Information
Donna Weaver, Ray Villard
Space Telescope Science Institute
410-338-4493/4514
-------------------------------------------------------
Related Web sites
http://hubblesite.org/news/2007/07
http://vega.lpl.arizona.edu/~gilda
Download illustrations:
http://hubblesite.org/news/2007/07
http://uanews.org/silk/request/ballester.jpg
CAPTION for the image immediately above:
The solar-type star, HD 209458, and its 'hot Jupiter" planet in
transit are
shown in simulated violet light. As in this illustration, the star
would
appear as a limb-darkened purple disk if seen in near-ultraviolet and
violet
light. The newly detected dense, narrow layer of hot hydrogen atoms is
represented by the dark absorbing ring around the opaque planetary
disk. The
bulk of hydrogen atoms in the upper atmosphere, which forms an
extensive
cloud and also a comet-like tail, is shown in white. The absorbing
layer was
drawn at twice the altitude and 10 times the thickness to be more
easily
visible in this illustration, the rest of which has been drawn to
scale.
(Art credit: Loretta McKibben, UA Lunar and Planetary Lab). |
|
|
| Back to top |
|
| |
|
Page 1 of 1
All times are GMT - 5 Hours
The time now is Sat Oct 11, 2008 1:16 pm
|
|