Image courtesy NASA/UMD

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A bright spray appeared on the comet Tempel 1 shortly after the Deep Impact smash in 2005.

Image courtesy NASA/UMD

NASA Probe Has a Valentine's Date With a Comet

Stardust spacecraft will cozy up to Tempel 1 tonight.

NASA has set up a Valentine's Day date between a spacecraft and a battered, icy comet 208 million miles (336 million kilometers) from Earth. If mission matchmakers are right, the two bodies will swing close to each other tonight at 11:37 p.m. ET.

The comet, known as Tempel 1, is no stranger to spacecraft: NASA's Deep Impact mission got close enough in 2005 to launch an impactor into the core—or nucleus—of the icy object, sending up a cloud of debris.

The spacecraft took numerous pictures for study before speeding on toward its next rendezvous. (See "NASA Probe Closing in on 'Poisonous' Comet Hartley 2.")

The 3.7-mile-wide (6-kilometer-wide) Tempel 1 has since had plenty of time to get over its first "love"—the comet has made a complete trip around the sun.

Tonight Tempel 1 will be stepping out with a new dance partner, NASA's office desk-size Stardust probe. The cosmic meeting will allow astronomers to see how the comet's surface has been altered during its orbit.

"The biggest mystery now is what happens to a cometary nucleus after it goes around the sun once," said Peter H. Schultz, a Stardust co-investigator and an astrogeologist at Brown University in Rhode Island.

"This will be the first mission to actually have a chance to see if the landscape has changed, including new features or patches of ice."

Stardust to See How Comet's Scars Have Healed?

During its closest approach, the spacecraft and the comet will be within 120 miles (193 kilometers) of each other. At that time, Stardust will snap 72 high-resolution pictures and will test the density and composition of dust surrounding the comet.

If Schultz and his team have done their calculations right, the passing probe should also be able to see the crater made by Deep Impact five and half years ago—a first for science.

During the 2005 mission, "'airborne' debris from the impact prevented actual imaging of the crater," said Stardust team member Don Brownlee, an astronomer at the University of Washington in Seattle.

"We should get images of the crater and any other changes since the Deep Impact flyby. We will also get stereo images of the comet and some regions that were in the shade on the last flyby."

Comet Chaser May Escape, But Will Live On

Tonight's date also won't be the first cometary cuddle for the Stardust spacecraft, which has been roaming the solar system for the past 12 years.

In 2004, Stardust collected samples from the comet Wild (pronounced "Vilt") 2. When the craft passed Earth in 2006, Stardust jettisoned its sample capsule, becoming the first probe to deliver pieces of a comet. (See "Stardust's Space Cargo Thrills Scientists.")

Still, tonight's Valentine's Day encounter will probably be the last cosmic tryst for the plucky probe. Stardust is running out of propellant, which means that soon the craft will no longer be able to point its solar panels toward the sun to charge its battery.

Once out of juice, the aging comet-chaser will continue to quietly orbit the sun—unless a gravitational interaction with a larger body alters its course.

"Its most likely fate, like that of the comets it was designed to study, will be to be deflected by Jupiter onto an orbit that will escape the solar system," Brownlee said.

"Once outside the solar system, it will last billions of years probably, longer than the Earth itself."