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.
Deming and his colleagues have begun using Deep Impact's larger telescope for follow-up studies of some of these so-called transiting planets.
First, they measure the combined light of a star and the known orbiting planet. As the planet passes behind the star, Deep Impact makes another measurement of just the starlight. Subtracting the light from the star from the combined readings leaves researchers with measurements of just the planet.
"We can analyze this light to discover what the atmospheres of these planets are like," Deming said.
Observations of the giant transiting planet HAT-P-4 began Jan. 22, but a problem aiming the telescope caused the star to move out the field of view about 20 percent of the time, Deming said in the project's blog. The problem was resolved, and by this week, Deep Impact had made thousands of observations.
"Ongoing efforts to improve the calibration of the data will allow sensitivity to small planets that we hope to discover," Deming added.
Scientists plan to calibrate Deep Impact's findings by looking at a planet they know well: Earth. Observing the home planet in visible and infrared light will give scientists a better idea of what an alien Earth looks like in Deep Impact's eyes.
Related Links:
Irene Klotz's blog: Space Diary
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