Some 340 million kilometers away, out beyond the orbit of Mars, the Stardust spacecraft is getting ready for a big Valentine's Day date. On February 14 the NASA craft will fly past Comet Tempel 1 at a planned distance of only 200 kilometers, getting a good look at the second comet it has investigated at close range since the probe's 1999 launch.
Stardust already visited Comet Wild 2 back in 2004. In an unprecedented feat, the spacecraft collected dust particles from Wild 2 and returned them to Earth in 2006 by dropping a sample-return package onto the Utah desert. Those samples are still producing new scientific findings about the conditions of the early solar system that primordial debris such as comets and asteroids preserve.
Having completed that mission, NASA trained its comet chaser on a new target: Tempel 1. This will be the second rendezvous for Tempel 1 as well. The comet was visited in July 2005 by another NASA probe called Deep Impact, which released an impactor to carve out a crater on Tempel 1 and get a better sense of its composition. The event kicked up so much debris, however, that Deep Impact did not get a good look at the resulting crater. When Stardust approaches, it may have a clearer view at the impact site. Scientists will also be keen to find out how the comet has changed over the course of its orbit. Comet Tempel 1 takes just over 5.5 years to make a lap around the sun, almost exactly the amount of time elapsed since Deep Impact's visit in 2005.
Photo of Tempel 1 taken by Stardust in January: NASA/JPL-Caltech