Comet Holmes' display captivates stargazers

By Julie Steenhuysen

CHICAGO (Reuters) - The normally sedate Comet Holmes made a bright splash in the sky about two weeks ago, unexpectedly becoming a million times brighter than normal overnight and causing a stir among astronomers.

The comet and its expanding ball of dust have become the biggest object in the solar system, with a diameter appearing even bigger than the sun, according to astronomers at the University of Hawaii Institute for Astronomy.

The fireworks began on October 23, when the comet brightened in a 24-hour period. It is now fading but can still be seen by the naked eye in the northeastern sky.

"Something that spectacular is almost like a supernova going off," said Hal Weaver, a comet expert at The Johns Hopkins University Applied Physics Laboratory.

"Now, we're trying to observe the event and figure out what the heck happened," Weaver said in a telephone interview on Thursday.

Weaver and fellow astronomers, using the powerful Hubble telescope, have some clues that may help explain the display. So far they have noticed that the comet's nucleus, the small solid body that is the main source of all the comet's activity, is still surrounded by dust.

He and colleagues believe some sort of explosion sheared off a pancake-shaped slab of the comet, which crumbled into tiny dust particles that are being lit up by the sun.

Hubble images of the comet from June 1999 showed no dusty halo. At that time, they measured the comet's nucleus at some 2.1 miles, about the length of New York City's Central Park.