|
Spacecraft setting off to shoot comet with 370kg bullet
American scientists are planning the ultimate drive-by shooting, 268m miles from home.They will launch a spacecraft next month on a six-month crash course in cometary science. On July 4 the spacecraft, Deep Impact, will blast a copper bullet about a metre in diameter into the path of 4-mile-wide block of ice and dust called Comet 9P/Tempel 1. With luck, and if the calculations are right, the comet will hit the 370kg (820lb) projectile at 23,000mph. The projectile will be vapourised, but it should also blow a hole in the comet big enough to house the RomanColosseum. The mothership will witness the whole thing, and send pictures back to scientists in Pasadena. It will be the closest ever study of a phenomenon that medieval observers thought to herald disaster. In one sense, they were right: a direct collision between a comet the size of Tempel 1 and the Earth could effectively wipe out human civilisation. Such impacts have happened many times in geological history, and could do so again. Researchers have begun to think of ways to prevent them, but nobody has any idea of the mass, or density, of a comet - whether they are like frozen concrete, or have the texture of frosted candyfloss. Deep Impact is a carefully planned act of celestial vandalism designed to deliver an answer. "We will be capturing the whole thing on the most powerful camera to fly in deep space," said Michael A'Hearn of the University of Maryland, the scientific leader of the project. "We know so little about the structure of cometary nuclei that we need exceptional equipment to ensure that we capture the event." Deep Impact will take off from Cape Canaveral on January 12, make half an orbit around the sun, and cross the comet's path on July 4. The collision with the projectile will happen when the mothership is several thousand miles away, and the impact will release the energy equivalent to 4.4 tonnes of TNT, throwing out a cloud of dust and ice. If all goes well, enough of this will settle to allow Deep Impact a clear view of the damage as it gets to within about 300 miles of the comet. By that time, the Earth will also have moved through half of its annual orbit, keeping pace with the spacecraft, so that the collision can be seen by earthbound astronomers and space telescopes such as the Hubble. A spacecraft sailed through the coma of Comet Wild-2 in January, and will bring samples back to Earth in 2006. Another craft, Rosetta, was launched this year to land on a comet in 2014. But Deep Impact will be the first to send back data from such a meeting. Comets delivered water for the Earth's oceans, and they carry complex organic molecules that may have played a role in triggering life on Earth. Tempel 1, first spotted in 1867 by Ernst Wilhelm Tempel of Marseilles orbits the sun every five and a half years. It is not likely to suffer any permanent damage in the collision, or to be knocked into a more dangerous orbit. "This is the astronomical equivalent of a 767 airliner running into a mosquito," said Don Yeomans, a mission scientist at the Jet Propulsion Laboratory in Pasadena. Posted by: tipper 2004-12-31 |
| http://www.rantburg.com/poparticle.php?ID=52560 |