Comet-Smasher to Hunt Alien Worlds

Feb. 8, 2008 -- A spacecraft that watched a probe smash into a comet has begun a new mission -- hunting for alien planets.

NASA's Deep Impact spacecraft, which gave astronomers a ringside seat to study the plumes and footprint of a man-made impact on Comet Tempel, is now searching for extrasolar planets as part of an extended mission.

"We're on the hunt for planets down to the size of Earth orbiting some of our closest neighboring stars," said lead scientist Drake Deming, with NASA's Goddard Space Flight Center in Greenbelt, Md.

Deep Impact, which sent a metal impactor crashing into Tempel-1 in July 2005, is en route to a new comet, Hartley 2. Though it has no more metal probes for kicking up material from inside the comet, Deep Impact will use its two telescopes for close-up studies of Hartley's surface.

The comet encounter won't happen until 2010, which leaves Deep Impact with plenty of time to scout nearby stars for signs of orbiting planets. Scientists have discovered more than 200 planets orbiting stars beyond our sun, mostly indirectly by measuring the small gravitational tugs they exert on their mother stars.

Direct observations are difficult because a star's radiance overwhelms light reflected by an orbiting planet. Occasionally however, from the perspective of Earth, a planet eclipses its star, allowing a direct measurement.