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From: Stig Agermose <Stig_Agermose@online.pol.dk>
Date: Fri, 25 Sep 1998 01:05:04 +0200
Fwd Date: Fri, 25 Sep 1998 11:15:27 -0400
Subject: Double Pleasure In Planet Quest


Source: MSNBC

http://www.msnbc.com:80/news/198947.asp

Go to the page for images and links!

Stig

*******

Double pleasure in planet quest

Two teams of researchers come up with new surprises

By Alan Boyle
MSNBC

Sept. 23 -- Two revelations about possible planets beyond our
solar system have astronomers seeing double: One team of
researchers has seen signs of planet creation in a double-star
system. Another team has found evidence of yet two more planets
- one of which appears to have an Earthlike orbit around its
parent star. 

THE PLANET HUNT is only a few years old, but in the past few
months the pace of the quest has accelerated dramatically. So
far, several planets have been detected indirectly by analyzing
variations in the light from distant stars. Such variations,
scientists believe, are caused by the gravitational effect of
giant planets circling those stars.

A research team including two pioneers in the field, San
Francisco State University's Geoffrey Marcy and the
Anglo-Australian Observatory's Paul Butler, announced Wednesday
that they have detected two more planets using the technique.
That brings the number of extrasolar planets found so far up to
at least a dozen, the researchers said, with nine discovered by
Marcy and Butler. Scores more are likely to follow in the months
and years ahead.

At the same time, other planet-searching strategies are being
developed - including the use of powerful radio telescopes to
sense the dusty disks that are thought to spawn planets around
young stars. Another research team led by Luis Rodriguez of the
National Autonomous University in Mexico City announced that
they have found two such disks in what appears to be a binary
star system.

If multiple-star systems can indeed develop planets, that opens
up a whole new front in the planet search - and, eventually, in
the search for extraterrestrial life.

Here are further details about the day's revelations:

A PLANET IN THE RIGHT SPOT


Marcy, Butler and their colleagues were particularly intrigued
by a planet detected around HD 210277, a sunlike star in the
constellation Aquarius, 68 light-years from Earth. (One
light-year equals about 6 trillion miles.)

Based on an analysis of the star's gravitational wobble, the
planet appears to be about the size of Jupiter, with an orbit
just a little wider as Earth's. One year on this planet would
equal 437 Earth days, the researchers said.

"We had discovered planets that orbit much closer and much
farther from their stars than the Earth-sun distance," Marcy
said in a statement. "We wondered if nature rarely puts planets
at one Earth-sun distance. Now we know that such planets are not
rare."

Marcy said the next goal would be to find Jupiter-size planets
that have Jupiter-size orbits as well.

"What we're all about is discovering (planets) where evolution
might have gotten a toehold," he said. "Jupiter-sized planets at
a greater distance from their star would suggest a solar system
that could host a rocky Earthlike planet."

If no such worlds are found circling the hundreds of stars being
targeted by planet-hunters, that could lead to a different
conclusion.

"It might be the first sign that Earth is truly unusual and so
life may be rare," Marcy said.

The second planet appears to orbit HD 187123, a sunlike star in
the constellation Cygnus, 154 light-years away. The researchers
say this planet is also about Jupiter's size, but whirls only
about 4 million miles away from its parent star, well within
Mercury's distance from our own sun. Each "year" takes only
3.097 Earth days, the researchers said.

In both cases, the observations were made using the Keck
telescope in Hawaii. The planet with the Earthlike orbit is the
subject of a paper to be submitted to the Astrophysical Journal
Letters, while a paper on the close-in giant planet has been
accepted by Publications of the Astronomical Society of the
Pacific.


BINARY-STAR BONANZA


Not too long ago, the prevailing view was that the gravitational
interplay within multiple-star systems would tear apart any
planets before they were even born. But new observations appear
to show disks of dust - the suspected birthplace of planets =97
surrounding twin stars about 450 light-years away in the
constellation Taurus.

The latest findings were developed using the National Science
Foundation's Very Large Array radio telescope in New Mexico and
published in Thursday's issue of the journal Nature.

Rodriguez and his colleagues focused on a source of infrared and
radio emissions within a giant cloud of gas and dust where
sunlike stars are being born.

Observations of the source, known as L1551 IRS5, were made in
the 7mm wavelength using radio receivers built in 1993 and 1994
by the National Radio Astronomy Observatory. The resolution of
the source was 10 times as good as previous observations at
similar wavelengths, making out structures measuring seven times
as wide as the radius of Earth's orbit around the sun (that's
about 650 million miles).

For the first time, astronomers were able to see two swirling
disks of dust, presumably with a star at the center of each
disk. The disks appeared to be separated by slightly more than
the distance between our own sun and Pluto, the solar system's
outermost planet. Each disk was as wide as Saturn's orbit around
the sun.

Astronomers hadn't thought such disks could hold enough mass to
form planets, but the new results indicate otherwise.

"Each of these disks contains enough mass to form a solar system
like our own," David Wilner of the Harvard-Smithsonian Center
for Astrophysics said in a statement. "However, we don't think
these solar systems would be able to form outer, icy planets
like Uranus and Neptune, because of the small size of the dust
disks."

The stars might well develop hot planets that could be thrown
off into deep space due to the complex orbital mechanics of a
multiple-star system, astronomer Alan P. Boss of the Carnegie
Institute of Washington said in a commentary written for Nature.

Boss said such a process might explain the recent observations
of what appears to be a "runaway planet" - although he
acknowledged that the planet could be a "background star
masquerading as a planet."

Rodriguez said the theories spawned by the new observations
broadened the possibilities in the search for distant planets.

"Most stars in the universe are not alone, like our sun, but are
part of double or triple systems," he said, "so this means that
the number of potential planets is greater than we realized."