NASA revisits Deep Impact comet

New close-up imagesof a comet smashed by a specialized NASA spacecraft six years ago as part of a research mission will be beamed to Earth during a Valentine's Day encounter with another NASA spacecraft.

The unmanned Stardust spacecraft will come within 200 kilometres of the comet Tempel 1 shortly after 11:30 p.m. ET Monday, NASA estimates.

It will take 72 high-resolution photographs and beam them 336 million kilometres back to Earth early Tuesday morning. It will also count dust particles from the comet and analyze their chemical composition, said Joe Veverka, principal investigator of the mission, in an interview on CBC's Quirks & Quarks Saturday.

Tempel 1 is a relatively large, pock-marked comet that was smashed by a NASA spacecraft in 2005 during a mission to uncover what lies underneath the outer layers of a comet.

That mission, called Deep Impact, included a second spacecraft some distance away that monitored the collision.

"While the spacecraft taking pictures was still around, the dust never settled, so we never saw the crater that was made," Veverka said. "So, we never finished the experiment."

Stardust's latest mission will allow researchers to see how big a crater was left by Deep Impact and therefore provide information about how strong the materials on the surface of the comet are. It will also help researchers see the difference between older features and "fresh" craters on a comet's surface. They'll also be able to tell how the surface changes as the comet loses ice after moving to the point in its orbit closest to the sun, said Veverka, a professor of astronomy at Cornell University.

It will be the first time a comet has ever been photographed up close on two different occasions. Right now, Tempel 1 is on the opposite side of the sun relative to the Earth. It passed its closest point to the sun 39 days ago.

Stardust was launched in 1999. Its earlier missions involved observing the asteroid Annefrank and visiting the comet Wild 2. Stardust collected dust particles from Wild 2 and sent them back to Earth in a capsule in 2006. Its mission to Tempel 1, dubbed Stardust-Next, will consume the last of its fuel.