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CORRECTED: NASA comet crash seeks info on earth

Posted on: Thursday, 30 June 2005, 20:01 CDT

In June 29 story headlined "NASA comet crash to seekbuilding blocks of life" please read in second paragraph...during the creation of the solar system... instead of ...during the creation of the universe...

A corrected version follows:

LOS ANGELES (Reuters) - NASA scientists are preparing toslam a coffee table-sized spacecraft into a comet half the sizeof Manhattan on July 4 in a cosmic smashup aimed at discoveringthe building blocks of life on Earth.

The mission, known as Deep Impact, aims to uncover andphotograph pristine material formed billions of years agoduring the creation of the solar system by blasting a craterthe size of a football stadium into comet Tempel 1.

Comets are composed of ice, gas and dust from the solarsystem's farthest and coldest regions. They often show burstsof activity, during which parts of their crusty surfaces liftoff to create fan-shaped jets of dust.

They are also "carriers of basic chemical building blocksfor allowing life to occur," Rick Gremmier, project manager forthe NASA mission, said on Wednesday. "We want to find out whatthose materials were ... and put a piece in the puzzle of howthe solar system was formed."

One theory, Gremmier said, is that comets first broughtwater to Earth by crashing into its surface.

At 1:52 a.m. EDT (0552 GMT) on Monday, the 771-pound (350kg) copper-fortified impactor is expected to smash into Tempel1 at 23,000 miles an hour, a speed that would pare the flightfrom New York to Los Angeles down to 6 minutes.

Scientists anticipate the crash will eject a spray of iceand dust from the comet's crusty surface and reveal thematerial beneath it.

The comet will be about 83 million miles away from Earth.

BLIZZARD OF PARTICLES

Deep Impact, the spacecraft that carried and will launchthe impactor, will be about 310 miles away from the comet atthe time of the planned collision and will have about 13minutes after the blast to capture images and data before itweathers a blizzard of particles thrown out of the comet'snucleus.

The crash is expected to produce a hole that could range insize from that of a small house to a football stadium,depending on the density of comet's nucleus. It is not expectedto change the comet's path.

There are cameras aboard both the impactor and the maincraft, and the blast will also be observed by the Hubble,Spitzer and Chandra space telescopes.

There is also the chance that the mission could drift offcourse. The biggest challenge is the comet itself, Gremmiersaid, as each is different in its makeup and behavior.

"The ultimate challenge is just trying to target a cometthat is moving that fast, and also have independently thefly-by spacecraft observing the same spot as that impact,"Gremmier said.

Even if the impact fails, the mission will still producethe best images to date of a comet nucleus, Gremmier said.

Earlier this week, astronomers got a preview of the orbitalpyrotechnics when Tempel 1's volatile nucleus blew off a streamof dust captured by the Hubble Space Telescope.

Because scientists do not know how bright the impact willbe, they cannot say how easy it will be for backyardastronomers to see it. Those with the best chance are peoplewith medium-powered telescopes in the western United States,parts of Mexico, and New Zealand, they said.

Source: REUTERS

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