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Another belt of icy debris is thought to reside within the so-called Kuiper Belt, which unlike the Oort Cloud, lies in the plane of the solar system, 500 times further out than the distance between the Sun and Earth.
In contrast to the planets, comets orbit the Sun along highly elliptical paths. Some "short-period" comets take up to 200 years to orbit the Sun. Other "long-period" comets exhibit far longer orbital periods, lasting up to hundreds of thousands, even a million years.
Occasionally passing stars outside the Solar System tug at the icy objects, hurtling them inwards into orbit around the Sun and its cohort of planets. Only last year Comet Shoemaker-Levy slammed into the giant planet, Jupiter: a spectacle recorded in extraordinary detail thanks to the far-reaching gaze of the Hubble Space Telescope.
As a comet nears the Sun, its icy layers begin to evaporate, releasing dust and dirt to form a curved dust tail. The liberated gases glow as they become heated, producing the coma, a luminous envelope surrounding the solid core. Ionized by the Sun's radiation and pushed backwards by the solar wind, the heated gas trails behind and also glows, forming a second, straight tail.
When approaching closer to the Sun, a comet's nucleus heats up. As gas and dust molecules previously bound inside the nucleus are released into the coma, they emit millimeter radiation. Much of what astronomers learn about the composition of comets will come from spectral line studies rather than through images. In order to map the distribution of gas and dust molecules in comets, researchers are now beginning to use the BIMA array's high spectroscopic resolutioncapabilities.
Lew Snyder, University of Illinois, on-camera
Knowing the distribution of gas and dust within comets might also indicate how these same materials were distributed
the region of space in which they formed. In turn, this information could yield clues on the composition of the giant
gas cloud from which the solar system is thought to have condensed some 4.5 billion years ago.
QuickTime Movie (1.5 MB); Sound File (802K); Text
Lew Snyder, on-camera
QuickTime Movie (1.5 MB); Sound File (899K); Text
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