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Comet collision may tell of solar origin For the first time, NASA is setting off on a collision course with a comet, in hopes of blasting a huge hole in the celestial snowball and gazing upon the original ingredients of the solar system preserved inside.
NASA plans to stage the collision of Comet Tempel 1 and the Deep Impact probe on July 4, and in order to put the projectile in the right place for the encounter, Deep Impact must be launched by January 28. The earliest launch NASA planned was at 1:48 pm EST (2:48 am today Beijing time) from Florida's Cape Canaveral Air Force Station. Scientists do not know exactly what will happen when the comet barrels into Deep Impact's 372-kilogram copper-tipped projectile at about 37,000 kph. They expect, however, a giant explosion -- equivalent to the energy released by 4 1/2 tons of dynamite -- and a gouge into the comet's surface that could be as big as a football field and as deep as a 14-story building. "We put the impactor in the comet's path so that the comet overtakes it," said Rick Grammier, mission project manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "It's like standing in the middle of the road with a semi-truck bearing down on you," said lead scientist and University of Maryland astronomer Michael A'Hearn. "There is an outside chance that we could break the comet. We don't think that will happen." The comet is quite a bit larger than the projectile. Tempel 1 has an approximate radius of 3 kilometres, while the impactor spacecraft is about the size of a living room coffee table. While the collision is expected to obliterate the impactor, two telescopes aboard Deep Impact's mother ship will monitor the crash, then fly by the comet for close inspections. By probing below the comet's surface, scientists hope to learn about the conditions that existed more than 4 billion years ago when the solar system was formed. Comets are believed to contain frozen remains from the solar system's early years. The Deep Impact comet-buster may be the most direct way to search for the origin's of the solar system, said Ma Yuehua, a researcher at Nanjing's Zijinshan Astronomical Observatory. Chinese astronomers are closely following the search. The country has long been involved in theoretical research, but does not have any plans to launch comet probes, Ma said. Currently their focus is on the moon. A Chinese-made satellite is expected to orbit the moon by December of next year. Astronomers around the world are organizing a world-wide comet watch during the Deep Impact mission to collect as much information as possible. NASA also plans to train the Hubble, Spitzer and Chandra space observatories on the comet during and immediately after the collision. "My interest in comets all along has been trying to understand the chemical composition," A'Hearn said. "What we see coming out of comets as gas and dust is stuff that has been modified because it is very near the surface," he added. "Every time the comet goes around the sun, the surface gets heated. So there have been changes in the surface layers... What I really want to do is figure out how different the surface is from what's inside." |
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