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A New Planet in Pegasi?
The following report is from a December 1995 article in the
Encarta Yearbook.
Planet Detected Orbiting a Star Similar to the Sun, Astronomers
Say
Swiss astronomers reported in the November 23, 1995, issue of
the journal Nature that theyhad detected a companion
object—possibly a planet—in a close orbit around the star 51Pegasi.
The star is located in the constellation Pegasus, 45 light-years
(425 trillion km, or 264trillion mi) from the earth. The orbiting
object cannot be observed directly, but theastronomers inferred its
existence from a slight oscillation of 51 Pegasi that the
investigatorssuggest is caused by the gravitational pull of an
unseen object.
Astronomers Michel Mayor and Didier Queloz of the Geneva
Observatory in Switzerland
first announced their detection of the object on October 6 at an
astronomy conference inFlorence, Italy. Two teams of astronomers in
the United States observed 51 Pegasi followingthe announcement and
reported that they had confirmed Mayor and Queloz's discovery
usingthe same measurements and methods. The scientific community
greeted the teams' resultswith excitement; if the results hold up
over time, the object would be the first planetidentified outside
our solar system that is circling a star similar to the sun.
The star 51 Pegasi is much like the sun in age and size, but its
suspected companion objectresembles nothing in our solar system.
According to the astronomers' measurements, thesuspected planet is
approximately 7.5 million km (4.7 million mi) from 51 Pegasi—only
one-twentieth the distance from its star as the earth is from the
sun. In contrast, the planet closestto the sun, Mercury, is about
58 million km (36 million mi) from the sun. The newly
detectedobject's proximity to 51 Pegasi means it would be very hot,
with an estimated temperature ofabout 1025° C (1880° F).
According to the astronomers' measurements, the reported object
also orbits 51 Pegasi veryquickly, making a full revolution every
4.23 days. The planet that circles the sun most rapidlyis Mercury,
which makes a full circuit in 87.6 days. The mass of the suspected
object near 51Pegasi is estimated to be one-half to two times the
mass of Jupiter, the largest planet in oursolar system.
Scientists have confirmed and generally accepted the detection
of only one planetary systemoutside our solar system. The objects
in this system orbit a star very different from the sun,however. In
1992, radio astronomers identified two planets orbiting a pulsar—a
dense,rapidly spinning remnant of a supernova explosion that emits
a stream of low-frequencyradiation.
The astronomers reported that two objects circling the pulsar
each had about the same massas the earth. They also found evidence
of a third orbiting object about as massive as themoon. It was
unclear whether these objects were created when the star itself
came into being,as the planets in our solar system are believed to
have formed. The objects near the pulsarmay have been created from
matter blown off of the pulsar in the supernova explosion
butremaining in the gravitational grip of the exploded star.
Scientists are also intrigued by the possibility that a second
object may be circling 51 Pegasiin a larger, slower orbit. Mayor
and Queloz observed a secondary variation in the light from51
Pegasi that shifted much more slowly and slightly than the
variation that suggested the
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closer object. Astronomers were working to confirm this result
at the time the study was published.
One question raised by the Swiss astronomers' discovery was how
51 Pegasi's suspectedcompanion was formed. Mayor and Queloz offered
two explanations for the origin of such anobject: either it formed
as a gas giant like Jupiter, or it was a brown dwarf (a starlike
objectlarger than a planet but smaller than most stars) that was
stripped of some of its mass byradiation from 51 Pegasi. If the
latter were true and the hypothesized object was beingquickly
devoured by the star, then it would not be considered a planet. If
the object was aJupiter-like gas giant, however, a different set of
questions would be raised. Astronomers arenot accustomed to the
idea of gas giants existing so close to a star and have no
clearexplanation of how one could come to be in the position that
51 Pegasi's companionoccupies.
Source: Encarta Yearbook, December 1995.
Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft
Corporation. All rights reserved.
Page 2A New Planet in Pegasi?
Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation.
All rights reserved.
