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Location: UFOUpDatesList.Com > 2001 > Nov > Nov 27

Hubble Measures Atmosphere On World Around Another

From: NASANews@hq.nasa.gov
Date: Tue, 27 Nov 2001 12:10:11 -0500 (EST)
Fwd Date: Tue, 27 Nov 2001 15:22:23 -0500
Subject: Hubble Measures Atmosphere On World Around Another

Donald Savage
Headquarters, WashingtonNov. 27, 2001
(Phone: 202/358-1547)

Nancy Neal
Goddard Space Flight Center, Greenbelt, Md.
(Phone: 301/286-0039)

Ray Villard
Space Telescope Science Institute, Baltimore
(Phone: 410/338-4514)

RELEASE: 01-232


Astronomers using NASA's Hubble Space Telescope have made the
first direct detection and chemical analysis of the atmosphere
of a planet outside our solar system. Their unique observations
demonstrate it is possible with Hubble and other telescopes to
measure the chemical makeup of extrasolar planets' atmospheres
and potentially to search for chemical markers of life beyond

The planet orbits a yellow, Sun-like star called HD 209458, a
seventh-magnitude star (visible in an amateur telescope) that
lies 150 light-years away in the autumn constellation Pegasus.
Its atmospheric composition was probed when the planet passed in
front of its parent star, allowing astronomers for the first
time ever to see light from the star filtered through the
planet's atmosphere.

Lead investigator David Charbonneau of the California Institute
of Technology, Pasadena, and the Harvard- Smithsonian Center for
Astrophysics, Cambridge, Mass.; Timothy Brown of the National
Center for Atmospheric Research, Boulder, Colo.; and colleagues
used Hubble's spectrometer (the Space Telescope Imaging
Spectrograph, or STIS) to detect the presence of sodium in the
planet's atmosphere.

"This opens up an exciting new phase of extrasolar planet
exploration, where we can begin to compare and contrast the
atmospheres of planets around other stars," says Charbonneau.
The astronomers actually saw less sodium than predicted for the
Jupiter-class planet, leading to one interpretation that
high-altitude clouds in the alien atmosphere may have blocked
some of the light. The team's findings are to be published in
the Astrophysical Journal.

The Hubble observation was not tuned to look for gases expected
in a life-sustaining atmosphere (which is improbable for a
planet as hot as the one observed). Nevertheless, this unique
observing technique opens a new phase in the exploration of
exoplanets, or extrasolar planets, say astronomers. Such
observations could potentially provide the first direct evidence
for life beyond Earth by measuring unusual abundances of
atmospheric gases caused by the presence of living organisms.

The planet was discovered in 1999 through its slight
gravitational tug on the star. The planet was estimated to be 70
percent the mass of the giant planet Jupiter, or 220 times more
massive than Earth. Subsequently, astronomers discovered that
the tilt of the planet's orbit makes it pass in front of the
star -- relative to our line-of-sight from Earth -- making it
unique among all the approximately 80 extrasolar planets
discovered to date. As the planet passes in front of the star,
it causes the star to dim very slightly for the duration of the
transit. Transit observations by Hubble and ground-based
telescopes confirmed that the planet is primarily gaseous,
rather than liquid or solid, meaning that the planet is a gas
giant, like Jupiter and Saturn.

The planet is an ideal target for repeat observations because it
transits the star every 3.5 days -- which is the extremely short
time it takes the planet to whirl around the star at a distance
of merely four million miles from the star's surface. This close
proximity heats the planet's atmosphere to a torrid 2,000
degrees Fahrenheit (1,100 degrees Celsius).

Observations of four separate transits were made by Hubble in
search of direct evidence of an atmosphere. During each transit
a small fraction of the star's light on its way to Earth passed
though the planet's atmosphere. When the color of the light was
analyzed by STIS, the telltale "fingerprint" of sodium was
detected. Though the star also has sodium in its outer layers,
STIS precisely measured the added influence of sodium in the
planet's atmosphere.

The team, including Robert Noyes of the Harvard-Smithsonian
Center for Astrophysics and Ronald Gilliland of the Space
Telescope Science Institute in Baltimore, plans to look at HD
209458 again with Hubble in other colors of the star's spectrum
to see which are filtered by the planet's atmosphere. They hope
eventually to detect methane, water vapor, potassium and other
chemicals in the planet's atmosphere. Once other transiting
giants are found in the next few years, the team expects to
characterize chemical differences among the atmospheres of these

The Space Telescope Science Institute (STScI) is operated by the
Association of Universities for Research in Astronomy, Inc.
(AURA), for NASA, under contract with the Goddard Space Flight
Center, Greenbelt, Md. The Hubble Space Telescope is a project
of international co-operation between NASA and the European
Space Agency (ESA). The National Center for Atmospheric Research
is sponsored primarily by the National Science Foundation.

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