A new comet leaves Halley’s trailing behind

Peter Kauffner

A giant comet with enormous destructive potential is rapidly approaching the earth — but it won’t be coming any closer than 122 million miles.
Comet Hale-Bopp, already hyped in astronomy circles as “the big bopper” and “the comet of the century” because of its size, is believed to have a nucleus with a diameter of about 25 miles.
This is significantly larger than the potato-shaped Halley’s Comet, which is only 10 miles across at its widest. Hale-Bopp will also be much brighter than Halley’s — a comet which returns approximately every 76 years and was last visible in 1986 — dbecause of its diameter and distance from the sun.
Hale-Bopp is barely visible at the moment and will be obscured by the moon after Jan. 21.
“Right now, it’s just about impossible to see. It’s on almost the same line as the sun,” said Robert Gehrz, a professor of astronomy at the University who will be supervising observation of the comet.
Hale-Bopp will be reappearing in more impressive style on Feb. 5. As it hurtles toward the sun, its icy surface will warm, causing gas and dust to evaporate. This evaporated material creates the tail — millions of miles long — that makes a comet visible.
Hale-Bopp’s brightness will continue to increase as it approaches the sun. The comet will reach perihelion — its closest approach to the sun — on April 1. At that point, Hale-Bopp will be about 85 million miles from the sun.
The Jet Propulsion Laboratory of the National Aeronautics and Space Administration projects that Hale-Bopp will achieve a magnitude of minus one at perihelion. This means that the comet is expected be even brighter than last year’s Comet Hyakutake, which had a magnitude of zero (brightness increases with decreasing magnitude numbers). In fact, it may become almost as bright as Sirius (magnitude -1.45), the brightest star in the sky.
But experienced comet watchers warn against taking such predictions too seriously. “Comets are like cats,” David Levy, co-discoverer of Comet Shoemaker-Levy 9, said in a World Wide Web posting. “They have tails, and they do precisely what they want.”
Shoemaker-Levy collided with Jupiter in 1994 and created a zone of destruction much larger than the earth. A somewhat larger comet hit the earth about 65 million years ago and is commonly blamed for the extinction of the dinosaurs.
Hale-Bopp has a nucleus more than twice as wide as that of Shoemaker-Levy. While it is not expected to cause any trouble, University researchers will be keeping an eye on it.
The University O’Brien Observatory in Marine on St. Croix will be making infrared observations of the comet.
“This will help us determine the chemical composition of the comet,” said Gehrz. “We look at the emission spectrum. It’s the same procedure that the FBI uses to analyze the composition of paint,” Gehrz said.
Several dozen other comets have been analyzed in this way. Most of them have been found to consist of silicates, the same type of material as granite.
Comets are believed to be composed of material that has changed little since the beginning of the solar system. Scientists hope data from comets can provide insights into the formation of the planets.