Scientists insisted that although the experiment was somewhat reminiscent of the 1998 movie "Deep Impact," in which a US spaceship attacks a monster comet with nuclear weapons to ward off its collision with Earth, the real-life attack on comet Tempel 1 was in pursuit of exclusively scientific goals.

"The impact simply will not appreciably modify the comet's orbital path," . Don Yeomans, a mission scientist with NASA's Jet Propulsion Laboratory, told reporters. "Comet Tempel 1 poses no threat to the Earth now or in the foreseeable future."

The cosmic sniper shot, in which both the target and the projectile move at least 20 times faster than bullets, is expected to provide a glimpse beneath the surface of the comet and offer new clues to the origins of the solar system.

The projectile, the size of an oil drum, was fired at 2:07 am (0607 GMT) by US spacecraft Deep Impact that had undertaken a 173-day, 431-million-kilometer (268-million-mile) journey to get closer to the comet, which is about as large as half Manhattan Island.

Shortly after the separation, a camera-equipped probe peeled off from the projectile and set on a separate path that will get it as close as 500 kilometers (310 miles) to Tempel 1 shortly after the copper-laden impactor slams into it.

"Everything appears to have gone as planned," Alan Buis, a spokesman for the JPL, told AFP in a brief telephone interview.

The collision with the gas-spewing rock that is hurtling through in the solar system at approximately 37,100 kilometers (23,000 miles) per hour is set for about 2:00 am (0600 GMT) Monday.

It will likely gouge a large crater on the surface of the comet, sending up a cloud of ice, dust and debris that researchers hope will offer a load of valuable information.

That is when the fly-by probe will swing into action. It will have approximately 13 minutes to take infrared and other images of the collision and the resulting cloud before it is swallowed by a potential blizzard of particles from the nucleus of the comet.

Images will also be snapped and beamed back to the mother spaceship by the impactor in the final minutes of its life, allowing a glimpse into the cloud of gases and dust constantly enveloping Tempel 1.

Deep Impact is equipped with four data collectors that will help it monitor the collision and conduct spectral analysis.

It will be backed up by numerous other spaceborne platforms, including the US Hubble and Spitzer space telescopes, Chandra X-ray observatory as well as the European Space Agency's XMM-Newton X-ray observatory and Rosetta spacecraft.

Comets circling the Sun, which are numbered in billions, are seen as leftovers from a massive cloud of gas and dust that condensed to form the Sun and planets about 4.6 billion years ago.

Therefore, their geological and chemical structure is believed to contain important clues to the nature of the Universe.

"With the information we receive after the impact, it will be a whole new ballgame," noted Deep Impact principal investigator Michael A'Hearn. "We know so little about the structure of cometary nuclei that almost every moment we expect to learn something new."

National Aeronautics and Space Administration scientists will spend most of the upcoming 24 hours guiding the impactor towards the comet.

But two hours before Monday's collision, the kamikaze probe will fire up its own navigational system and use thrusters to maneuver itself toward impact. Community
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