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Comet Sparks Awe Among Stargazers

Astronomy: Swooping past, 4.6-billion-year-old Hale-Bopp is a treasure trove for scientists.

March 28, 1997|K.C. COLE | TIMES SCIENCE WRITER

The giant comet Hale-Bopp, now headed for an April Fools' Day pass by the sun, is not accompanied by a planet-size spaceship carrying aliens, contrary to months of reports on late-night talk radio and the World Wide Web--and apparently the beliefs of 39 suicide victims in Rancho Santa Fe who reportedly hoped to hitch a ride on the ship by taking their lives.

However, the mountain-size chunk of the ancient solar system is carrying a treasure trove for scientists: a piece 25 miles in diameter of the early solar system, locked in frozen storage for the last 4.6 billion years.

Spewing out 90 tons of water per second in huge jets like a giant lawn sprinkler--along with cyanide, formaldehyde and other noxious gases--Hale-Bopp promises to reveal a great deal about Earth's birthplace, the ancient cloud of ice and stardust that formed the sun.

The toxic gases streaming from the comet's ink-black surface, says astronomer Stephen Edberg of the Jet Propulsion Laboratory in Pasadena, "are the building blocks of life--from bacteria on up to us."

Because this comet is so big and so bright, astronomers have an unprecedented opportunity to get up close and personal with material that has remained unchanged since the solar system was born. And because astronomers have all their hot new detectors trained on the interplanetary interloper, Edberg said, they have been able to see more, and sooner, than with any comet before.

Already, space-based cameras have to been able to see the spectra of molecules boiling off the comet, and discovered that the nucleus has a mottled structure more complex than previously thought. Observations also suggest that most of the gas and water is streaming from tiny ice grains surrounding the core, rather than from the nucleus.

"Astronomers have been looking for [this] for some time, and now we've found it," said Dale Cruikshank, a NASA Ames astronomer who is author of one of several papers on Hale-Bopp published today in the journal Science. "This is the first really large comet since we've had the techniques of modern astronomy."

"Everyone's dropped what they're doing," said JPL astronomer Donald Yeomans. Ground-based telescopes are tuned to signals in every wavelength from radio to infrared, while four NASA-funded rockets will be going up above the Earth's atmosphere get a better look.

Discovered by astronomer Alan Hale and amateur star watcher Thomas Bopp on July 23, 1995, Hale-Bopp gave scientists plenty of time to get ready, as it was visible well outside the orbit of Jupiter when first seen.

One of early images taken by a Houston observer contained what appeared to be a companion--a "Saturn-like object" with streaks coming out of the sides. Interpreted by some as an alien ship, the object turned out to be only a well-known star--its image distorted by the camera that took its picture.

Evidence of alien involvement, according to the late-night radio talk circuit, was a "course correction" the comet made as it passed by Jupiter. But as Krupp pointed out, all comets that pass Jupiter get pushed into new orbits by the giant planet's enormous gravity. While Hale-Bopp's last visit to Earth was about 4,200 years ago, it will be back in a mere 2,400 or so, thanks to its new, tighter path.

Many people have also been fascinated by the comet's double, blue and white tail. But all comets have double tails, said Krupp: the blue one composed of electrically charged particles, and the diffuse whiter tail of dust particles.

Even amateur astronomers have been able to see some of Hale-Bopp's most spectacular features, including a series of "hoods" or "shells" that surround it.

The gas and water jets gushing from the core get spun around by the comet's rapid, 11 1/2-hour rotation, forming rings, or hoods. In some images, these hoods look like jet trails, but Edberg said the jets may be the results of the way the pictures were made. "You do it one way, you see these halos or hoods," said Edberg, "you use another technique and it gives you radial lines."

One thing is certain: Hale-Bopp is huge--more than four times bigger than the comet that scientists think crashed into Earth 65 million years ago and threw up an enormous cloud of dust that killed the dinosaurs. Hale-Bopp poses no such danger. Its closest pass to Earth on March 22 was 122 million miles away--more distant than the sun.

Typical of comets, Hale-Bopp is extremely unpredictable. It has brightened in sudden outbursts only to dim again, and appears to be wobbling as well as spinning. Its huge tail spreads out as far as 40 million miles.

To a scientist, a comet is much more than a pretty sight. In recent years, researchers have concluded that most of the water, carbon and even gases required for life were brought to Earth by comets. "There is a growing consensus that Earth's oceans and atmosphere, and hence the biosphere, are products of cometary impacts," Cruikshank said.

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