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Unwelcome encounter with Swift-Tuttle?

Astronomers last month hailed Comet Swift-Tuttle's return to Earth's vicinity after an absence of 130 years. The visit set a record, making Swift-Tuttle the longest-period comet whose calculated orbit has been confirmed by observations (SN: 10/10/92, p.230). But Swift-Tuttle's next visit to the inner solar system may prompt a less enthusiastic greeting.

Brian G. Marsden of the Smithsonian Astrophysical Observatory in Cambridge, Mass., calculates that there's a small chance - no greater than one in 10,000 - that the 10-kilometer-wide comet will crash into Earth in the year 2126. He predicts that the comet will reach perihelion - its closest approach to the sun - on July 11, 2126. If so, not to worry: By the time Swift-Tuttle crosses Earth's orbit some 19 days later, our planet will be about 15 million miles away. Marsden notes, however, that the unpredictable nature of such nongravitional effects as cometary outbursts of gas may mar his prediction. And if Swift-Tuttle reaches perihelion 15 days later, on July 26, then Earth could be in for big trouble.

Astronomers can improve this prediction by monitoring Swift-Tuttle for the next five years, Marsden says, when nongravitational effects dominate. As for the myriad schemes to avoid a future doomsday, such as bombing the comet, he says these are best left to future generations. Besides, he notes, in the 2060s two asteroids -- Hathor and the apt-sounding Nereus -- may pass even closer to Earth than Swift-Tuttle.
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Title Annotation:comet may not return to earth until 2126
Publication:Science News
Article Type:Brief Article
Date:Nov 14, 1992
Words:237
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