Subj:	Hubble Telescope Sees Alien Planet's Atmosphere
Date:	11/27/01 2:28:41 PM Pacific Standard Time

November 27 3:56 PM ET

Hubble Telescope Sees Alien Planet's Atmosphere

WASHINGTON (Reuters) - The Hubble Space Telescope has spied
the atmosphere of a planet orbiting a star 150 light-years
from Earth in the constellation Pegasus, NASA said on
Tuesday.

The planet, about the size of Jupiter and orbiting close to
the star HD209458, has an atmosphere loaded with sodium and
is inhospitable to earthly life, officials at the National
Aeronautics and Space Administration said at a briefing.

Still, the discovery for the first time of an atmosphere
around a planet outside our solar system was heralded as a
breakthrough in planetary exploration.

"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," said David
Charbonneau, the lead investigator on the project.

"This is a just a remarkable result," said Alan Boss, an
astronomer at the Carnegie Institution of Washington. "The
first detection of the atmosphere of a planet means that for
the first time we have entered into a new phase in the era
of extrasolar planet discovery and characterization."

Known as HD209458b -- neither the planet nor the star it
orbits are famous enough for a more euphonious name -- the
planet is one of about 80 discovered in the last decade
outside Earth's solar system.

Most of these are giant planets made of gas, like Jupiter in
our own system. About 15, including this one, are "hot
Jupiters", giant planets about 100 times closer to their
star than Jupiter is to the sun.

That makes them far too hot for life as we know it. Not only
would any hypothetical human traveler to this planet die but
the planet's intense heat would quickly melt any coins in
the person's pockets, the scientists said.

INHOSPITABLE, BUT STILL BREAKTHROUGH

The planet's hospitality is not the issue, however. What is
important to scientists is the notion that Hubble, an
orbiting

telescope designed to avoid the distortion of Earth's
atmosphere, managed to detect an atmosphere outside our
immediate neighborhood.

At 150 light-years, the planet is considered close by cosmic
standards. A light-year is about 6 trillion miles, the
distance light travels in a year.

Even so, it is much more distant than any other atmosphere
scientists have detected.

They did it by watching the planet make a three-hour transit
in front of its star, and trained Hubble's spectrograph on
both. This instrument can "see" the different materials in a
planet or other celestial feature.

When the planet passed in front of the star, astronomers
looked at the star to see its light filtered by the planet's
atmosphere. They saw sodium in the atmosphere, but actually
a bit less than expected for a Jupiter-class planet, which
might indicate high-altitude clouds above the alien planet
that could have blocked some of the light.

Boss envisioned an intensified search for Earth-type planets
with this technique and others over the next decade.

"Those (future) observations will hopefully find us planets
where there is evidence of carbon dioxide, water vapor,
ozone and methane," Boss said. "If you can find all four of
those signatures in the same planet, you can make a very
strong case that that planet is habitable, if not actually
inhabited."

Up until now, the young science of extrasolar planet
detection has generally found alien worlds by finding a
distinctive wobble in stars that indicates the gravitational
pull of a circling planet or planets.

Hubble's success in seeing this planet's atmosphere could
point the way to searching for new Earth-like planets using
the transit technique.

This is not an entirely new method: Bruce Margon of the
Space Telescope Science Institute in Baltimore noted that
the atmosphere of Venus, Earth's next-door neighbor, was
detected by watching its transit in front of the sun three
centuries ago.