Comet erupts violently as Hubble watches

A sequence of images shows debris streaming away from the comet -- along its tail

By Richard Stenger
CNN.com Writer

(CNN) -- Comet LINEAR dazzled astronomers when it violently blew off a piece of its crust "like a cork popping off a champagne bottle," Hubble researchers announced Friday.

The explosion jettisoned a large amount of fine debris into space, reflecting sunlight and markedly brightening the comet for several hours.

The Hubble Space Telescope took exceptionally clear pictures of the entire eruption sequence, including the ejected material as it drifted away along the tail of LINEAR.

"We lucked out completely," said Hubble comet hunter Harold Weaver of the Johns Hopkins University in Baltimore, Maryland.

"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," he said in a statement.

Telescopes on the ground did not appear to detect the latest eruption, according to Hubble scientists. But Hubble's sensitive instruments were able to reveal precise details of the event.

The pictures offer clues about the interior composition of comets, thought to be clumps of dust and ice that formed in the early history of the solar system.

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Scientists have several theories

Comets create their trademark tails when, heated by sunlight, they eject gas and dust. The Hubble telescope first located the streaking comet 74 million miles (120 million km) from Earth. It recorded the violent drama during observations in early July.

Weaver observed similar fragments when he trained the Hubble telescope on comet Hyakutake in 1996.

His scientific team offered some possible explanations for the cause of the eruption.

In one scenario, part of the core may have vaporized after it was exposed to sunlight for the first time. Core ice sublimated quickly into gas, causing intense pressure that "blew the lid off" the surface crust.

Another possibility is that fragment came from one of numerous house-sized pieces that comprise the comet nucleus.

Some astronomers think comet cores are essentially loosely bound piles of such "cometesimals."

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