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Analysis : Science
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The first image of a
possible
extrasolar planet
By Peter Symonds
4 June 1998
In the field of planetary science, remarkable discoveries are
being made rapidly, one after the other. Just four years ago,
extrasolar planets, or planets outside our own solar system, were
still a matter of speculation. Now a growing wealth of data not
only points to their existence but is challenging current theories
on the formation of planetary systems.
Last week, another first was announced. US National Aeronautics
and Space Administration (NASA) scientists released the first
photograph of what appears to be an extrasolar planet -- a large,
gaseous object apparently being catapulted into deep space by
its parent stars.
The planet, tentatively named TMR-1C, seems to be connected
by a strange filament of light to a nearby binary star system,
located in a star-forming region of the constellation Taurus at
a distance of about 450 light years.
Susan Terebey and her team from the Extrasolar Research Corporation
in Pasadena, California, made the discovery after meticulously
examining photographs of young star systems taken in the infra-red
spectrum using the Hubble Space Telescope.
The object may have been dismissed as a faint background star,
were it not for the 130 billion-mile-long trail of light linking
it to the binary pair of stars, TMR-1A and TMR-1B.
Terebey conjectures that the light trail could be a tunnel
produced by the planet as it escaped from its parent stars and
burrowed through the surrounding dust cloud. The tunnel would
act like a fibre optic cable channelling light from the two stars
deep inside their dusty surroundings.
Or, it may be caused by light reflecting from a trail of material
left behind by the escaping planet. Further observations of the
movement of TMR-IC and its spectrum are required to confirm that
it is a planet and that it has been ejected from the binary system.
According to astrophysicist Alan Boss of the Carnegie Institution
of Washington: "This is unbelievably exciting, seeing a possible
extrasolar planet for the first time. This is a major, unprecedented
observation. It is as important as the first indirect detection
of an extrasolar planet was."
Until now, the existence of extrasolar planets has been inferred
from the gravitational effect or "wobble" caused in
the motion of the stars they orbit. TMR-IC may turn out to be
the first to be observed directly.
If it proves to be the same age as its apparent parent stars
-- a few hundred thousands years -- then its mass is estimated
to be 2-3 times that of Jupiter, the largest planet in our solar
system. Its speed is calculated at up to 10 kilometres/second.
If the object is the same age as other nearby stars -- up to
ten millions years old -- it could not have been ejected from
the much younger binary star system. In this case, it is likely
to be much more massive and may even be a brown dwarf -- a star
too small to sustain nuclear fusion and glow brightly.
The discovery raises crucial theoretical challenges. Conventional
theories predict that giant gas planets take millions of years
to condense from dust in space. More recent explanations point
to another possibility -- that large, low-density planets can
condense very quickly out of gas clouds, at the same time as their
parent star.
"If this is a planet and the system is about 300,000 years
old, then the slower, conventional theory doesn't fit. It's like
Cinderella dropping her glass slipper after the ball. That slipper
is only going to fit one person. In the same way, I think the
fast-track theory is the only fit for explaining the formation
of this new planet," Boss said.
Being far smaller than its two parent stars, TMR-1C may have
gained enough momentum to be flung out of the stellar system by
a gravitational "slingshot" effect.
The release of the photograph of TMR-1C comes only weeks after
two groups of astronomers, using telescopes in Hawaii and Chile,
announced the first indirect evidence pointing to the existence
of rocky earthlike planets outside our own solar system.
As many as eight other extrasolar planets have been identified
since 1995, when the first signs were discovered of a planet orbiting
around a conventional star. The rapid advances in the field, despite
funding science cutbacks, have been possible in part through the
use of sophisticated new detectors, particularly in the infra-red
range.
The Hubble Space Telescope, a joint project of NASA and the
European Space Agency, was launched in 1990 and only became fully
functional in December 1993 after a space shuttle mission corrected
its instruments for spherical aberration.
The photograph showing TMR-1C was taken with Hubble's Near
Infrared Camera and Multi-Object Spectrometer (NICMOS). The highly
sensitive infra-red detectors must operate at very low temperatures
and are kept within a thermos bottle-like container filled with
frozen nitrogen gas. The aim is to keep the detectors cold and
the NICMOS operating for years, far longer than any previous space
experiment.
For further information and a range of downloadable images
of TMR-1C visit http://oposite.stsci.edu/pubinfo/pr/1998/19/
See Also:
The first evidence of new Earth-like
planets
[5 May 1998]
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