New comet might be quite a sight in 1997.

Fickle by nature, comets may look tantalizingly bright far from Earth yet fizzle by the time they venture closer. So when it comes to predicting whether one of these icy objects will delight or disappoint, astronomer Brian G. Marsden usually remains cautious.

But new information has now inspired Marsden to compare a recently discovered comet to the great comet of 1811 and Tolstoy's poetic description of it in War and Peace:

". . .the radiant star which, after travelling in its orbit with

inconceivable velocity through infinite space, seemed suddenly--like an arrow piercing the earth--to remain fast in one chosen spot in the black firmament, vigorously tossing up its tail, shining and playing with its white light and the countless other scintillating stars."

Even if the newly found comet, dubbed Hale-Bopp, doesn't quite live up to Tolstoy's account as it passes near the sun in April 1997, it still might qualify as the first "really good" comet visible to the naked eye in 2 decades, says Marsden of the Smithsonian Astrophysical Observatory in Cambridge, Mass.

Marsden wasn't making literary allusions 3 weeks ago, when Alan Hale of Cloudcroft, N.M., and Thomas J. Bopp of Glendale, Ariz., independently discovered what ranks as the most distant comet ever found by amateur astronomers. Now residing in the constellation Sagittarius, Comet Hale-Bopp lies about seven times as far from the sun as Earth does. Yet even at that distance--beyond the orbit of Jupiter--the comet reflects sunlight well enough to be seen with 10-inch telescopes.

This could mean that the object is big and intrinsically bright. But at first Marsden, like other scientists, didn't let himself get too excited about the discovery, reported in a July 23 International Astronomical Union (IAU) circular. After all, Hale-Bopp's brightness could have a less intriguing explanation.

The observers may have imaged the comet just after an outburst, when a pocket of frozen, volatile material just beneath its surface vaporized, he notes. Expelled as a jet of gas, the material would drag dust out along with it, temporarily increasing the reflectivity of the comet and boosting its brightness.

"The question has been, Is this really a big comet, or is it just a comet that has had a big outburst?" says Marsden.

Astronomers have been fooled before by a comet's distant appearance. The highly publicized Comet Kohoutek, unusually bright when discovered, proved a dud when it neared the sun in 1973.

Comets are more likely to exhibit such behavior on their first visit to the inner solar system, explains Marsden. That's because they start their journey with a full supply of highly volatile compounds. These compounds vaporize at very low temperatures, giving the comets a promising glow far from the sun. But some first-timers don't have large reserves of a more crucial material, water-ice, which turns to steam only as a comet nears the sun. If they don't vent steam, comets can't fling out the dusty tails that give them their brilliance.

But recent evidence suggests that Hale-Bopp's current brightness isn't a fluke. Robert H. McNaught of the Anglo-Australian Observatory in Coonabarabran, Australia, reported in an Aug. 2 IAU circular that he has found an image of what appears to be the comet in a single photographic plate taken April 27, 1993. Marsden says that the image, if real, shows that Hale-Bopp already looked relatively bright 2 years ago. This argues against an outburst as the cause of its present appearance. And by comparing the comet's 1993 position with recent observations, Marsden deduces that Hale-Bopp visits the inner solar system about every 3,000 years.

With new data pouring in, Marsden says the location in the 1993 image looks more and more accurate.

"There's still a chance that the comet underwent an outburst," Marsden says. "But I think we can be optimistic that the comet does have a 3,000-year period and that it's been around many times before."

"Taking the situation at face value," Marsden writes in an Aug. 4 IAU circular, "one can note that the comet is in many respects similar to the great comet of 1811 . . . and may perform as spectacularly."