A telescope on Spain's Canary Islands last month saw that the comet LINEAR, named for MIT's Lincoln Laboratory, has completely blown apart. Before its annihilation, it was the brightest comet of the year.
"The central condensation was highly condensed and showed the typical 'teardrop' form in the evenings of July 23 and July 24, although its brightness decreased by a factor of about three between the two nights," reported Dr. Mark Kidger of the Instituto de Astrofisica de Canarias.
"In the evening of July 25, something very odd was happening to the comet: the central condensation was seen to be strongly elongated, with a very flat brightness distribution. The condensation's brightness faded further and its length increased on the following nights. On July 27, there was no evidence of any local brightness peaks that would indicate the presence of subnuclei."
Comet LINEAR was a "new" comet, which means that it made its first passage through the inner solar system. It was named for the observatory that originally discovered it in September 1999. LINEAR is the acronym for Lincoln Near Earth Asteroid Research, a project operated by Lincoln Laboratory to search for Earth-approaching objects.
When discovered, Comet LINEAR was immediately regarded as a candidate likely to reach naked-eye visibility based on its relative brightness and large heliocentric distance.
The comet was expected to stay in northern skies until the second week of August, when it was to dip below the hori-zon. But the observations with Spain's Jacobus Kapteyn Telescope suggest that the comet was dying very quickly.
Using NASA's Hubble Space Telescope earlier in July, researchers were surprised to catch the comet LINEAR in a brief, violent outburst when it blew off a piece of its crust, like a cork popping out of a champagne bottle. The surfaces of new comets are believed to be covered almost completely by a very thin, fragile layer of highly volatile ices such as carbon dioxide mixed with dust.
The eruption, the comet's equivalent of a volcanic explosion (though temperatures are far below freezing, at about -100���F. in the icy regions of the nucleus or core), spewed a great deal of dust into space.
This mist of dust reflected sunlight, dramatically increasing the comet's brightness over several hours. Hubble's sharp vision recorded the entire event and even snapped a picture of the chunk of material jettisoned from the nucleus and floating away along the comet's tail.
When Hubble and the Chandra X-ray observatory observed the comet for a few days in July, astronomers caught an eyeful.
"We lucked out completely," said Hubble comet-watcher Harold Weaver of Johns Hopkins University. "In one surge of brilliance, this under-performing comet showed us what it could have been. Comet LINEAR generally has not been as bright as we had hoped, but occasionally does something exciting."
A version of this article appeared in MIT Tech Talk on August 9, 2000.
