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Location: UFOUpDatesList.Com > 1999 > Jan > Jan 9

In New Discoveries, a Planetary Mystery

From: Steven L. Wilson Sr <Ndunlks@aol.com>
Date: Sat, 9 Jan 1999 22:30:38 EST
Fwd Date: Sat, 09 Jan 1999 23:58:02 -0500
Subject: In New Discoveries, a Planetary Mystery


In New Discoveries, a Planetary Mystery

By John Noble Wilford


AUSTIN, Tex. -- In a stunning run of discoveries over the last
three years, astronomers have observed 17 nearby stars that
appear to be orbited by planets more or less the size of
Jupiter. The most recent detection of a planet around a star
other than the Sun was described here Saturday.

But while astronomers continue the search for more such objects,
they have now seen enough to be puzzled by an emerging pattern:
None of these extrasolar planetary systems seems to resemble the
Sun's family of planets. Is this an observational fluke? Or is
the solar system a cosmic oddball?

At a meeting of the American Astronomical Society, scientists
reviewed the mystifying evidence. All of these objects are found
in orbits much closer to their parent stars than Jupiter, the
solar system's giant, is to the Sun. Astrophysicists could only
speculate how such large planets, ranging in mass from one-half
to 10 times the mass of Jupiter, can orbit so close to a star
and survive what must be destabilizing gravitational stresses.

Other studies reveal that many of the stars orbited by large
bodies typically have two to three times more heavy elements
than exist in the Sun. And except for the extrasolar planets
extremely close to their host stars, most of these objects
appear to travel in orbits unlike those of planets around the
Sun.

"For the first time, we have enough extrasolar planets out there
to do some comparative study," said Dr. Geoffrey W. Marcy of San
Francisco State University, who is the leading discoverer of
these objects. "We are realizing that most of the Jupiter-like
planets far from their stars tool around in elliptical orbits,
not circular orbits, which are the rule in our solar system."

Dr. Marcy noted that 9 of the 17 detected extrasolar planets
sweep relatively close to their stars and then swing far out
again, giving an oval shape to their orbital paths. The others
travel in more circular orbits, presumably because they are even
closer to their stars and are regulated by gravitational tides.
One of these is only four million miles from its star and takes
only 4.2 days to complete its revolution, or "year."

An elliptical orbit was observed for the most recently
discovered extrasolar planet, around the star HD 168443 in the
constellation Serpens, the Snake. This new planet, Dr. Marcy
reported Saturday, orbits its star once every 58 days at an
average distance that is nearer to the star than Mercury, with
an 88-day orbit, is to the Sun.

The eccentricity of the newly discovered planet -- the degree
that it deviates from a circular path -- is 0.54, about 10 times
the eccentricity in the orbit of most solar system planets.

Theorists have proposed several possible explanations for such
eccentric orbits. When enough large planets orbit a star in
proximity, perhaps they generate a gravitational slingshot that
projects the planets into elongated orbits. Or perhaps a passing
star has upset the delicate balance of these planetary systems.

In some cases, the planets could be perturbed because their star
is part of a binary system, where two stars are locked in
gravitational embrace.

If elliptical orbits appear to be common for other planets as
massive as Jupiter, astronomers are wondering what different
circumstances in the solar system keep mighty Jupiter and Saturn
in circular orbits. It is not a trivial question, for the
emergence of life on Earth probably depended on the answer.

Jupiter-size bodies plunging toward and away from their stars
are likely to sweep aside smaller worlds, sending them crashing
into the star or flying out of orbit into interstellar space.
Current technology is incapable of detecting Earth-size planets
around other stars, but they almost certainly could not exist
near their star's warmth in a system so unsettled by large
planets in wrecking orbits, Dr. Marcy said.

"The implications are also profound for the search for
extraterrestrial life," Dr. Marcy said.

Yet of the all the Sun-like stars that have been studied so far
by planet seekers, only 5 percent have been found to have
Jupiter-mass planets in such eccentric orbits. Taking an
optimistic view, Dr. Marcy said that leaves 95 percent of stars
that may be free of these influences and could harbor habitable
planets.

Although nearly all astronomers agree that these detected
objects are extrasolar planets, a few holdouts are not so sure.
They have raised the possibility that these are brown dwarfs,
objects that formed like stars but lacked sufficient mass to
support nuclear fusion in their cores.

Dr. William D. Cochran, an astronomer at the University of Texas
here, said that too many of the objects had masses comparable to
Jupiter's for them to be brown dwarfs. But at the meeting, he
cautioned that they may not be planets, particularly because so
many of them have eccentric orbits and are so close to their
stars. They might be some new type of object unlike anything in
the solar system.

"To find a new type of object would be an extremely exciting
result," Dr. Cochran said. "Right now, we are still going to
call them 'planets,' even though they may really be something
slightly different."



Sunday, January 10, 1999
Copyright 1999 The New York Times

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