@S1-A.ARPA,@MIT-MC.ARPA:ARG@SU-AI.ARPA (06/30/85)
From: Ron Goldman <ARG@SU-AI.ARPA>
a035 0233 28 Jun 85
PM-Other Worlds,0658
NASA Astronomer Expands List Of Possible Solar Systems
By LEE SIEGEL
AP Science Writer
FLAGSTAFF, Ariz. (AP) - A NASA astronomer says he has evidence eight
more nearby stars are surrounded by material that could hide planets
and he predicts scientists eventually will discover 1,000 such stars
orbited by planets, asteroids, comets or the dust that could form
them.
The evidence comes from a new analysis of observations of 500 nearby
stars by the orbiting Infrared Astronomical Satellite, or IRAS, said
Hartmut H.G. Aumann, of the agency's Jet Propulsion Laboratory in
Pasadena, Calif.
The stars are known as nearby stars because they are within 75 light
years of Earth. That's about 441 trillion miles - considered close to
Earth by astronomical standards.
Aumann outlined his findings Thursday at the annual meeting of the
Astronomical Society of the Pacific.
Astronomers believe that our solar system formed when a giant cloud
of dust and gas collapsed into clumps of material to create the sun,
the planets and orbiting asteroids and comets.
Many also believe it is reasonable to expect that solar systems
formed the same way around other stars under the proper conditions.
Under less favorable conditions, the initial dust-and-gas cloud might
not congeal into planets, but simply remain in the form of dust or
small bodies.
Aumann's conclusions increase to 12 the number of nearby stars
studied by IRAS that are believed to be surrounded by so-called
proto-planetary material.
Non-IRAS studies have indicated two other stars - HL Tau and R
Monceritos - may be surrounded by dust or larger bodies. And last
December, astronomers observed what may be a Jupiter-like planet
around the star Van Biesbroeck 8.
So astronomers now believe 15 stars are orbited by at least dust,
and possibly by asteroids, comets and planets.
The National Aeronautics and Space Administration announced in June
1984 that Aumann had identified more than 40 stars he suspected might
be surrounded by proto-planetary material.
At the time, he and other scientists were nearly certain such
material orbited four of those stars: Vega, Beta Pictoris, Epsilon
Eridani and Fomalhaut.
Another analysis by Aumann showed IRAS would be unable to detect
material that might surround dimmer stars, suggesting many more
''proto-solar systems'' might exist than can be detected with current
technology.
''There's a good chance that half the (2,000 known) nearby stars
eventually will be found to have material around them in significant
quantities that's either dusty or has accreted into planets,'' Aumann
said.
Don McCarthy, a University of Arizona astronomer who last year
observed the possible planet around Van Biesbroeck 8, said he agreed
with Aumann.
''It's a fair prediction that most stars have material around them
in the form of debris or planets,'' he said. ''It could easily be the
result of a common process.''
IRAS is capable of detecting such material, particularly dust,
because it measures infrared radiation, or heat, emitted by the
material as it is warmed by the central star.
IRAS cannot detect planets because they don't emit enough heat. So
astronomers who used IRAS can only infer the possible existence of
planets around stars surrounded by heat-emitting dust.
Aumann said he initially placed more than 40 stars on the suspected
proto-solar system list because their apparent excess heat emissions
suggested material orbited them. Using a tighter definition of excess
heat emission, he narrowed the list and concluded that eight of the
stars, plus the original four, were likely to be orbited by solid
material.
Aumann said the eight are Iota Eridani, Gamma Dorado, Beta Ursa
Major, Beta Leonis, Alpha Corona Borealis, Gamma Serpentis and stars
designated G-196 and G-838.
His second analysis concluded that many dimmer stars would emit too
little heat to warm surrounding material enough to be be detected by
IRAS. So it is conceivable they too are proto-solar systems, he said.
AP-NY-06-28-85 0531EDT
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