- Astronomers have detected a planet around
a star just 15 light-years from the sun, the closest world ever found outside
our solar system.
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- At least 1.8 times as massive as Jupiter,
the planet orbits a stellar weakling -- a dim, low-mass star called Gliese
876 -- every 61 days. Though assumed to be a Jupiter-like ball of gas with
no solid surface, not particularly hospitable to life, scientists estimated
that the planet's interior could be warm enough to harbor a key requirement
of life -- liquid water in the form of a mist.
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- Located in the direction of the constellation
Aquarius, Gliese 876 is about a third of the distance to the next nearest
star known to have a planet, or about 87 trillion miles away.
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- Astronomers have detected a dozen or
so planets beyond the family of the sun in recent years, but this one --
located in the direction of the constellation Aquarius -- has riveted their
interest because of the nature of its parent star. Gliese 876 is a red
dwarf, the first such dim, low-mass star ever found to have a planet.
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- With just a third the mass of the sun,
the star is only about one-fortieth as luminous as the sun and therefore
hard to study. But red dwarfs are believed to be the most common stars
in the universe, and they "live" virtually forever.
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- The new findings mean that "planets
may be a dime a dozen," Geoffrey Marcy, of San Francisco State University
(SFSU) and the University of California at Berkeley, said in a telephone
interview. He and colleagues Paul Butler of the Anglo-Australian Observatory,
Steven S. Vogt of the University of California at Santa Cruz and Debra
Fischer of SFSU were first to report detection of the new planet this week
at a scientific meeting in Victoria, British Columbia. Their findings were
confirmed within hours by a team led by Xavier Delfosse of Geneva Observatory
in Switzerland and Grenoble University in France.
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- "The Milky Way galaxy contains 100
billion stars. Most are these red dwarfs, these little runts of stars,"
Marcy said. Now that scientists know even such tiny stars can form planets,
he added, they can plausibly hypothesize that there are "at least
billions of planets just within our galaxy alone."
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- "This is an incredibly important
finding," said Stephen Maran, a spokesman for the American Astronomical
Society. "This has to mean there are planets all over the Milky Way.
Who's to say we aren't floating in a sea of planets?" And, he added,
because red dwarfs never change, "you have forever for life to evolve."
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- Unlike the sun, such stars do not puff
up and die in a span of 10 billion years, turning any nearby worlds to
cinders.
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- The possibility that planets form easily,
around all kinds of stars, was hinted at in 1992 when a few little worlds
were detected in orbit around a whirling, dead star called a pulsar. But
the rush of planet discoveries -- powered by advances in technology and
observing techniques -- has focused primarily on stars like the sun. It
did not start in earnest until October 1995, when Swiss astronomers announced
the detection of a planet around the sun-like star 51 Pegasi, in the constellation
Pegasus. Since then, new worlds have been found in such a startling variety
of odd configurations that scientists are struggling to explain how they
might have formed.
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- None of the widely accepted planets beyond
the sun have been observed directly, because the glare of the starlight
overwhelms them. Astronomers instead study the planets' gravitational tugs
on the parent stars.
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- The new discovery brings the number of
worlds found with this method to 12, said Marcy, whose team has found most
of those. (The Hubble Space Telescope has taken a direct image of an object
announced last month as a planet candidate, but it has yet to be confirmed.)
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- Marcy's team first studied Gliese 876
in 1994 using instruments at Lick Observatory in California and, beginning
last year, used the much more powerful Keck I telescope atop the extinct
volcano Mauna Kea in Hawaii, with a high-resolution spectrometer attached.
They are surveying 400 nearby stars.
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- The planet travels an egg-shaped path
around Gliese 876, at an average distance about one-fifth that between
sun and Earth, or half that of Mercury, the innermost planet to the sun.
Theorist Didier Saumon, of Vanderbilt University in Nashville, told Science
News, whose June 27 issue reports on the new planet findings, that he calculates
the average surface temperature at minus 75 degrees centigrade (minus 103
degrees Fahrenheit), far below the freezing point of water. But in warmer
layers not far below the surface, he said, water droplets could exist.
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- Because of the planet's elongated two-month
orbit, its seasons must be brutal, he added in a telephone interview. As
the planet swings twice as far out in the winter as in the summer, it shifts
from one extreme to the other every month.
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- Marcy cautioned that giant gas planets
are probably poor platforms for life. Lacking hard surfaces, they make
it difficult for water to pool. However, Saumon speculates, should the
planet have solid moons, they might be temperate enough to offer a foothold
for organisms. Scientists have hypothesized that frozen water on Jupiter's
moon Europa and on the planet Mars might harbor primitive microorganisms.
A team from Oregon State University reports in today's issue of the journal
Science that they have discovered colonies of microbes growing deep inside
layers of ice in Antarctica.
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- The Marcy team finished its final key
observation of Gliese 876 at Keck in the predawn hours of last Friday.
Then came a sleep-deprived scramble to catch a flight that same day to
the Canada symposium of the International Astronomical Union, with the
just-analyzed data "hot off the printer," Marcy said.
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- At the conference, a rival planet hunter
called Delfosse at the European Southern Observatory in La Serena, Chile,
to inform him of Marcy's announcement. Within hours, the gathering received
a fax of ESO observations of Gliese 876, confirming Marcy's findings. "It
was a wonderful day," Marcy said.
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