The Infrared Astronomical Satellite has found another unusual member of the solar system: an object, possibly an asteroid or dead comet, that passes closer to the Sun than any known planet or asteroid.
The object, temporarily designated minor planet 1983TB, adds to the growing collection of objects that the orbiting telescope has detected. IRAS discoveries include five comets this past summer and evidence of solid material around the star Vega.
Its latest discovery appears to be less than 2 kilometers (1.2 miles) in diameter. The object was about 30 million kilometers (19 million miles) from Earth when first observed last month.
While examining the IRAS data of Oct. 11, Simon Green, postgraduate student in astronomy at Leicester University, England, noted rapidly moving object that the satellite observed in seven consecutive orbits spaced 100 minutes apart.
The news was flashed immediately to astronomical observatories around the world, and the object was quickly located and photographed by the Palomar Observatory in California and the Lowell Observatory in Flagstaff, Ariz.
Observers at both sites reported the object to be very dim, 16th-magnitude asteroid. (On the brightness scale used by astronomers, the smaller the magnitude number, the brighter the object. With an apparent visual magnitude of 16, 1983TB is about 6 million times fainter than the brightest star in the sky.)
From the object's position in the sky at the various times it was seen, Brian Marsden of the International Astrophysical Union calculated its orbit. He determined that it belongs to the Apollo class of asteroids, which periodically cross Earth's orbit.
While there are many "Earth-crossing" asteroids - and new one is discovered about every few months -- 1983TB is of exceptional interest, according to Dr. Conway W. Snyder, IRAS deputy project manager for science.
1983TB passes within 15 million kilometers (9 million miles) of the sun, closer than any planet or known asteroid and 10 times closer than Earth.
Furthermore, Snyder said, its orbit is almost exactly the same as that of the Geminid stream of meteroids, which are visible as shower of meteors ("shooting stars") in December.
Astronomers know that several meteoroid streams move along the orbits of comets, the material apparently having been shed by the comets over the centuries. The Orionid shower in October is associated with Halley's comet, for example, and the Perseid shower in August is apparently related to the short-period comet Swift-Tuttle.
Comets are believed to be composed mainly of ice mixed with dust and rock, whereas asteroids are miniature planets, mostly dust and rock.
Although 1983TB looks like an asteroid in telescopes, Snyder said, its apparent relation to the Geminids suggests that it may actually be dead comet whose ice and other voltatile materials have boiled away during its many close passes by the Sun.
On the other hand, it is somewhat larger than the nuclei of most comets are believed to be. In addition, its aphelion (the point in its orbit farthest from the Sun) is right in the "main belt" of asteroids out beyond Mars.
The orbital period of 1983TB is about 1.5 years, and its plane is inclined about 20 degrees to Earth's orbit.
Astronomers are planning additional observations with photometers and spectrometers in an effort to clear up the mystery of the identity of 1983TB.
IRAS was launched Jan. 25, 1983, from the Western Test Range at Vandenberg Air Force Base, Calif.
The IRAS project was developed and is operated by the Netherlands Agency for Aerospace Programs (NIVR), the U.S. National Aeronautics and Space Administration (NASA) and the United Kingdom's Science and Engineering Research Council (SERC). The Rutherford Appleton Laboratory operates the tracking station and preliminary science analysis center in England. Jet Propulsion Laboratory is the U.S. management center for the project.
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