Comet Encore 
A NASA spacecraft is taking a kinder, gentler approach to science today. After giving one comet a big whack five years ago, it’ll fly past a second comet with no violence at all.
The craft is Deep Impact. In July 2005, it fired a high-tech cannonball at Comet Tempel 1. The instrumented probe blasted a big hole in the comet, spewing gas, dust, and ice into space. The craft monitored the impact and studied the debris to learn more about how comets are made, and how they change over time.
NASA then re-targeted Deep Impact to visit Comet Hartley 2. The comet is about a half-mile across, and its six-year orbit brings it just outside Earth’s orbit around the Sun. In fact, it’s only a few million miles away from Earth right now, so telescopes on the ground will be getting a good look at it, too.
But the best view will come from Deep Impact, which will swing just a few hundred miles from the comet. It’ll snap thousands of pictures, and it’ll analyze the comet’s composition as well as the hazy gas and dust surrounding its nucleus and in its tail.
Scientists will compare the observations of Hartley 2 with those of other comets. That should provide a better overview of what comets are made of, how they formed, and how they’ve evolved over their long lifetimes.
After today, Deep Impact will keep an eye on the comet for several weeks. But so far, there’s no third destination for the two-time comet watcher.
We’ll post some of Deep Impact’s best pictures on our web site -- stardate.org.
Script by Damond Benningfield, Copyright 2010