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Mystery dust postpones comet probe launch

Drawing of Contour approaching the rocky, icy core of a comet.
Drawing of Contour approaching the rocky, icy core of a comet.  

By Richard Stenger

(CNN) -- NASA will wait until at least Wednesday to send a comet-chasing mission into space, giving the space agency time to study some mysterious particulate matter found on the $160 million craft.

Designed to take the most detailed pictures ever of comet nuclei, the robot ship could shed light on the behavior and evolution of the primordial ice boulders, among the oldest objects in the solar system.

The Comet Nucleus Tour (Contour) probe, which could pass within 62 miles (100 km) of two or more comets, was slated to lift off onboard a Delta rocket on Monday from Cape Canaveral, Florida.

On Friday, mission managers said they decided to push back the launch at least two days, after technicians placing the launch rocket nose cone over Contour noticed unknown contaminants on one of the probe's solar panels.

"There's some dust here. It's probably not a problem. But we need to check it out to make sure it won't affect the launch or the instruments," NASA spokesperson Helen Worth said.

The new tentative liftoff time is 2:41 a.m. EDT on Wednesday. If necessary, the launch can be postponed until July 25 without affecting the mission, NASA said.

After orbiting Earth for some weeks, Contour will fire its main engine and begin looping around the sun, which will give it gravity boosts as it approaches its intended destinations.

The first stop is comet Encke in November 2003. The second is comet Schwassmann-Wachmann 3 in June 2006.

Both will be relatively close to Earth during the encounters -- within 31 million miles (50 million km). But besides proximity, the two comets have hardly anything else in common.

Interactive comet tour 

Encke, one of the most observed comets for centuries, has passed near the sun thousands of times and releases little gas and dust. In contrast, Schwassmann-Wachmann 3 was first detected only 70 years ago and has proven much more volatile, splitting recently into several pieces.

Armed with high-resolution cameras and instruments to study comet dust, gas and nuclei, Contour might even visit a third comet if the conditions are right, mission scientists said.

Besides serving as the building blocks of planets, comets might have seeded Earth with the complex organic chemicals from which life arose, scientists speculate.

Detailed studies of comets could do more than offer clues about the origins of the solar system and life. They could help humans learn how to divert a potential killer comet on a collision course with Earth, space scientists said.

Previous comet mission include NASA's Deep Space 1, which last year snapped the best images yet of a comet nucleus when it passed within 1,200 (2,000 km) of comet Borrelly.

There are other NASA comet expeditions in progress or in the works. Stardust, launched in 1999, should fly near a comet in 2005 and return to Earth with dust samples in 2006. Deep Impact, scheduled to lift off in 2004, is slated to collide with a comet in 2005.

The closest comet encounter so far took place in 1992 when the European Space Agency's Giotto passed within about 120 miles (200 km) of a comet.

Rosetta, another ESA probe, could launch as early as January. It is designed to fly to a comet, go into orbit around its nucleus and drop a mini-lander on its surface.


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