Comet Trekking

Halley 's heavenly body returns

For five years, astronomers have been scanning the skies to become the first to sight one of history's most celebrated objects. Last week a Caltech team led by British Graduate Student David C. Jewitt, 24, and Staff Astronomer G. Edward Danielson, 43, won the cosmic sweepstakes. Using Palomar Observatory's 200-in. telescope, they spotted Halley's comet as a faint moving dot in the constellation Canis Minor. The comet has not been seen since 1911. A year earlier, its fiery appearance caused a rash of doomsday forecasts and end-of-the-world parties.

More than a billion miles away, just beyond Saturn's orbit, the lump of icy debris is only dimly lighted by the sun and distant stars. Even the big Palomar mirror could not have found it without a highly sensitive silicon-chip light detector called a charge-coupled device (CCD), used in place of a photographic plate. When the comet approaches for its hairpin swing around the sun in 1986, solar radiation will boil off volatile material, creating a glowing head and characteristic tail and perhaps another heavenly spectacle.

Before Edmund Halley (pronounced Hal-ee) identified them in 1705 as periodic visitors to the inner solar system, comets were widely viewed as omens of disaster. Astronomers now look upon them as primordial chunks of matter that offer clues to the solar system's formation. The budget-conscious U.S. has bowed out of the race to intercept Halley's comet with a robot spacecraft, thus leaving the field to the Soviets, Western Europeans and Japanese. But NASA plans a relatively cheap ($2 million) alternative: diverting an unmanned ship already in orbit for an inspection of a comet called Giacobini-Zinner, which will appear a few months ahead of its famous kin.

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