comet
Image: NASA, HAROLD WEAVER, the HST Comet LINEAR Investigation Team and the University of Hawaii

It's been almost a year since astronomers using the Hubble Space Telescope chanced upon comet LINEAR at death's door. They watched in awe as part of the comet's crust blew off and its core lit up in a fiery blaze. Within four short hours from that initial explosion, LINEAR burned 50 percent brighter than normal, and during the next few days it slowly disintegrated, shooting house-size fragments down its smoking tail. Now researchers have fully analyzed those final momentsand no fewer that six teams report findings in today's issue of Science.

The new information about comet LINEAR's makeup and breakup raises old questions about comets in general. For one thing, researchers had presumed that comets contained equal parts of snow or ice and meteoritic material. But based on the new studies, LINEAR appears to have had little ice, leading some scientists to speculate that it formed relatively close to the sun, near Jupiter's orbit. Also, the comet's core seems to have been a pile of rocky rubble and not a homogeneous body, as some astrophysicists have suggested.

Finally new spectrographic data reveal that LINEAR contained very little carbon monoxide. Some scientists suspected that this supervolatile compound, found in certain comets, had contributed to LINEAR's demise. Instead they now propose that LINEAR's seemingly rapid rate of rotationcoupled with its approach to the sunhelped to send it to the brink. "As we debate these issues, we also have to keep in mind that it's possible that LINEAR was just an odd comet," says Hal Weaver of Johns Hopkins University. Weaver is a co-author on three of the six Science papers. "But to get a sense for that, we have to keep looking for evidence from other comets and try to build up some statistics."