SPACE.com -- String of Cosmic Pearls Photographed After Comet Breakup

Mosaic of several images of comet 57P. The main part of the comet is at left, with fragments stretching out to the right. The fragments all trail along behind the comet and have virtually the same motion.

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	String of Cosmic Pearls Photographed After Comet Breakup By SPACE.com Staff posted: 11:00 am ET 24 July 2002

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Like fuzzy pearls on a long cosmic necklace, the remains of a comet catastrophe strung out through space have been photographed by the University of Hawaii's 2.2-meter (7.2-foot) telescope on Mauna Kea.

The comet, called "57P/du Toit-Neujmin-Delporte," has broken into 19 pieces, 18 of which can be seen to the right of the main chunk in a newly released image, which is a mosaic of several pictures taken between July 17 and 19.

Astronomers don't know the exact details of why comets break apart, but they understand the basic process and they've observed a few similar events in the past. This breakup, however, could provide a long-lived natural laboratory for the investigation of comet innards.

The disaster in space was probably triggered by thermal stresses within the comet's nucleus as it was warmed by sunlight, according to a statement issued by the University of Hawaii.

Comets are made mostly of ice, dirt and rock. When comets approach the inner solar system, sunlight evaporates the ice in large quantities, sometimes generating a visible head, or coma, that glows from reflected sunlight. In extreme cases that can delight ground observers, a tail becomes visible. Since the ice and rock are intimately mixed, astronomers explain, the warming and evaporating ice produces great thermal and physical stresses on the body of the nucleus.

Most comets survive these close encounters with the Sun, then stream back out into the distant reaches of the solar system on their elongated orbits. For a few, however, the stress is so great that entire chunks of the nucleus break off.

Finding 19 comet fragments is a rare discovery. The situation is similar to the breakup of comet LINEAR C/1999 S4 in the year 2000, an event captured in pictures by the Hubble Space Telescope.

But LINEAR's pieces were only observable for a few days before they faded from view. The newly spotted pearls of 57P should be visible for several weeks, astronomers said. That ought to allow observations of how the fragments move and evolve, which scientists expect will yield insight into the constitution and fragility of this comet and possibly comets in general.

Comet 57P/du Toit-Neujmin-Delporte was discovered in 1941 by the 3 people for whom it is named. The "57P" means it is the 57th comet in the list of comets that have been seen on two or more of their passages around the Sun. (The first comet in this list, "1P", is the famous Halley's Comet.)

Astronomers can't always predict exactly when a comet will return to the inner solar system, and 57P was "re-acquired" on July 12 by Steven Pravdo of the Near-Earth Asteroid Tracking (NEAT) program.

University of Hawaii researchers Yanga Fernández, Scott Sheppard and David Jewitt identified the fragments by watching their slight movement with respect to background stars. The string of debris stretches across nearly 620,000 miles of space (1 million kilometers).

Backyard stargazers won't be able to see the comet's pieces. The brightest bit is about 250,000 times dimmer than what can be seen with the naked eye. Though the size of the pieces cannot be accurately determined, Fernández and colleagues said they are probably a few hundred yards (meters) in diameter.

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