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Science File

Comet Shatters Close to Earth

April 29, 2006|John Johnson Jr. | Times Staff Writer

Astronomers are getting a close-up view of the death throes of a comet as it passes Earth and enters the inner solar system.

Comet 73P/Schwassmann-Wachmann 3 has broken into more than 40 fragments as it speeds toward a swing around the sun June 6, NASA said Thursday.

The main fragment will come closest to Earth on May 12, when it will be visible to ground observers.

None of the comet's pieces will come close to hitting Earth, NASA said. The closest fragment will pass at a distance of 5.5 million miles -- more than 20 times the distance from Earth to the moon.

"There is absolutely no danger to people on the ground," said Donald Yeomans, manager of NASA's Near-Earth Object Program.

It will still be the closest that any comet has come to Earth in two decades. But because it is not a large comet -- its largest fragment is thought to be 1 to 3 miles across -- observers will need binoculars to see it as it passes through the constellations Pegasus and Cygnus from May 12 to 14.

Comets, composed of loosely packed dust and ice particles, are wandering relics of the early solar system. Some theorists say a comet may have seeded early Earth with the basic ingredients for life.

Although comets sometimes exist for many millions of years, they can be pulled apart by gravitational forces when they pass by large objects, such as planets. The heat of the sun can also break them up.

Scientists do not know what caused the breakup of 73P/Schwassmann-Wachmann 3, which has orbited the sun every 5.4 years. It was first noticed during the comet's 1995 orbit, when it split into four chunks.

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