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NASA plans on having a smashing time

点击量:   时间:2019-03-08 07:19:00

By Charles Seife in Washington DC SIX years from now, a huge copper bullet will slam into the surface of a comet, gouging out a crater seven storeys deep. The project, dubbed Deep Impact, is one of two space missions announced by NASA last week. The other, named Messenger, is to put a spacecraft into orbit around Mercury. When scientists study the clouds of gas emitted by a comet as it nears the Sun, they’re never certain what originates from the comet itself and what comes from the dirt picked up during the comet’s travels through the Solar System. Deep Impact, which will cost $240 million, should solve this puzzle. When the spacecraft approaches comet P/Tempel 1 on 4 July 2005, it will release a half-tonne projectile that should strike the comet at ten kilometres a second, hurling cometary material out into space. “The ejecta will be pristine material from inside the comet,” says project manager James Graf of the Jet Propulsion Laboratory in Pasadena. Messenger, costing $286 million, will be the first spacecraft to visit Mercury since Mariner 10 made three flybys in 1974. After settling into orbit around the planet in 2009, the spacecraft will photograph its surface, record the composition of its thin atmosphere, and map its magnetic field. An altimeter will also measure any wobbles as the planet turns, which will help determine whether there is liquid sloshing around beneath Mercury’s crust. “Whether there’s a fluid core or not will help us understand the origin of Mercury’s magnetic field and its thermal history,