Deep Impact Headed for July 4 Crash with Comet

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An artist's rendition of the moment of impact and forming of a crater on comet Tempel 1.

An artist's rendition of the moment of impact and forming of a crater on comet Tempel 1. NASA/JPL/UMD hide caption

itoggle caption NASA/JPL/UMD
An image of comet Tempel 1 taken by Deep Impact on June 27, 2005.

An image of comet Tempel 1 snapped by Deep Impact on June 27, 2005. NASA/JPL-Caltech/UMD hide caption

itoggle caption NASA/JPL-Caltech/UMD

Tips for Skywatchers

The following sites offer tips for spotting the comet after NASA's spacecraft crashes into it, brightening it significantly in the night sky.

This July 4, NASA is preparing for fireworks in space, when the comet Tempel 1 will smash into a probe set in its path. Scientists hope the mission, called Deep Impact, will reveal what comets are made of and how they're put together.

As it nears Tempel 1, the Deep Impact mother ship will release an impactor to be hit by the comet at 23,000 mph. The impactor carries a copper slug weighing more than 300 pounds — to ensure the collision packs a punch — and an onboard guidance system to keep the oncoming comet in its crosshairs.

Just before 2 a.m. Eastern Monday, the spacecraft will crash into Tempel 1, creating a crater that could be as big as a football field. NASA scientists hope that will reveal fresh material beneath the surface — pristine ice and debris left over from the very early days of planet formation.

The trickiest part of the mission will be making sure the collision takes place. The impactor is aiming for a spot lit by the sun on a comet just 10 miles wide. The crash may make the comet bright enough to be seen on Earth with binoculars and possibly with the naked eye.

Carey Lisse, a professor at the Johns Hopkins applied physics lab, says the mission could reveal how planets formed from what was essentially space dust.

"Comets are the first step," Lisse says. "They are baby planets. And if we understand them fully, we'll understand how all this material got together and started forming planets. "

The Deep Impact mother craft will start sending back photos of the collision shortly after impact. The impactor will also send back pictures of the comet, taken in the moments before it meets its fiery end.

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