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Beyond Pluto. Though Ikeya-Seki is the fourth new comet to be discovered this year, and there are some 1,700 already on record, astronomers are still not sure exactly what comets consist of. For centuries they were objects of excitement and superstition, often feared as precursors of grave and cataclysmic events. Today some astronomers speculate that comets are the debris flung off by larger planets out beyond the earth. The most widely accepted theory holds that a vast cloud completely surrounds the solar system. According to Fred Whipple of the Smithsonian Observatory, about 4.6 billion years ago the cloud (a giant snowstorm") began to condense into separate bodies—"dirty snowballs" of dust and ices made up of methane, ammonia and water. Some of these bodies were captured by the outer planets and fell onto them, and some fell into the sun. About 1% of them, Whipple thinks, have gone into orbit around the sun as periodic comets ranging in size from tiny bits to as much as 20 miles in diameter.
Despite their fiery appearance, comets are not actually aflame but glow mostly from fluorescence due to solar radiation. The closer they get to the sun, the brighter and larger they grow. One of the rare "sungrazing" comets, Ikeya-Seki will whip around the sun at a maximum speed of about 300 miles per second, passing within 300,000 miles of the sun's surface. Astronomers discounted some predictions that the comet will collide with the sun. But it could be broken up by the sun's radiation and gravitational field. If it survives its solar encounter, the comet discovered by a piano-key polisher and a guitar instructor will then disappear into the nether reaches of space—considerably beyond Pluto—and will not come hack into view for some 500 to 1,000 years.