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Autopsy report on dazzling comet demise

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Artist conception of a disintegrating comet  


By Richard Stenger
CNN

(CNN) -- Astronomers had a front row seat when comet LINEAR broke up in the inner solar system. Now they have wrapped up a post-mortem report, using an array of instruments trained on the comet to scrutinize its spectacular death.

"We were witnessing a rare view of a comet falling to pieces. By watching it unravel, we are essentially seeing its formation in reverse," said Hal Weaver, who observed the comet with the Hubble Space Telescope. "It was like hitting the rewind button."

Scientists had never seen the breakup of a comet's entire nucleus until last summer, when LINEAR erupted into dozens of pieces on an approach to the sun, which placed it in a prime viewing location for Earth observers.

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 Comet LINEAR Fast Facts
• Estimated radius of nucleus: .44 kilometers
• Time to complete one rotation: up to 12 hours
• Observed mass before break up: as high as 300 billion kilograms
• Total mass afterwards: 3 billion kilograms
• Discovered: September 1999 by the Lincoln Near Earth Asteroid Research (LINEAR) project.
• Broke up: July 2000 approximately 70 million miles from Earth.

Pristine chunks of ice and rock that date back to the early solar system, comets are thought to be the building blocks of planets. By witnessing the death of one, scientists hope to unlock secrets about the genesis of the solar system.

"We're very interested in how the planets formed, and figuring out how comets are put together is a very important step in that process," said Weaver, who along with other scientists were to publish their LINEAR studies in the May 18 issue of the journal Science.

The autopsy came up with some tantalizing glimpses into the life and death of LINEAR. Measuring its mass and how much ice boiled into gas during its demise, scientists determined that it was composed mostly of meteoric material.

In other words it was more of a snowy dirtball than a dirty snowball, which suggests that LINEAR formed relatively close to the sun, where less ice would have condensed on it rocky core.

The close-up view of the expiring comet provided scientists loads of data, but also left them more questions. LINEAR disintegrated into 16 big pieces, consistent with theories that many comets have cores composed of rubble piles.

But scientists cannot account for billions of kilograms of missing mass after the comet's dissolution last July. They speculate that more of the comet than expected broke up into pieces too small for detection by the array of watching observatories, which included the SOHO satellite and the Very Large Telescope in Chile.

Nor are they sure what exactly killed it. LINEAR contained low levels of carbon monoxide, a highly volatile compound that when warmed by the sun can spur comets to fracture with fatal consequences.

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This Hubble Space Telescope picture shows comet LINEAR's crumbling nucleus. The picture was taken on August 5  

But the autopsy did offer some possible causes of death. Some scientists said that LINEAR had rotated fairly rapidly, which could have contributed to its disintegration. Others said an earlier collision with an asteroid could have weakened its structural integrity.

"The bottom line is that there are still several things that are a bit puzzling about what happened to this comet," Weaver said.

Now little more than a trail of debris orbiting the sun, LINEAR is thought to have meandered into the inner solar system from the Oort Cloud, a reservoir of primordial comets on the outskirts of the solar system.

LINEAR was named for the astronomy program that first spotted it, the Lincoln Near Earth Asteroid Research observatory.







RELATED STORIES:
RELATED SITES:
• Space Telescope Science Institute
• Hubble Heritage Project
• NASA

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