A former comet-slammingspacecraft will swing by Earth on New Year's Eve before starting atwo-and-a-half-year journey to Comet Hartley 2.
Deep Impact will first spend six months using the larger of itstwo telescopes to search for Earth-sized planets around five candidate stars. Thesecond part of its extended mission involves a flyby of Hartley 2 that allowsclose observations of the comet's features.
"It's exciting that we can send the Deep Impactspacecraft on a new mission that combines two totally independent scienceinvestigations, both of which can help us better understand how solar systemsform and evolve," said Michael A'Hearn, Deep Impact leader and University of Marylandastronomer, in a statement about the spacecraft's new EPOXI mission.
NASA originally gave the go-ahead for the Deep Impactspacecraft to investigateComet Boethin, but scientists eventually realized they could not identifythe comet and its orbit in time to plan the mission flyby of Earth. Thespacecraft will use the planet's pull of gravity to redirect itself toward Comet Hartley 2 on December 31, 2007.
Deep Impact made history on July 4, 2005 when it smasheda probe into Comet Tempel. The resulting data differed greatly from what scientistsfound on previous comet missions Deep Space 1 and Stardust.
"One of the great surprises of comet explorations hasbeen the wide diversity among the different cometary surfaces imaged todate," said A'Hearn. "We want a close look at Hartley 2 to see if thesurprises of Tempel 1 are more common than we thought, or if Tempel 1 really isunusual."
The Deep Impact eXtended Investigation (DIXI) will follow upon those earlier findings not by smashing objects into Comet Hartley 2, butby mapping outbursts of gas from the comet surface, looking for waterice, and analyzing the cloud of gas and dust surrounding the comet.
However, starting in late January, the spacecraft will firstfocus on detecting alienworlds in the Extrasolar Planet Observations and Characterization (EPOCh)phase of its two-part mission.
Many extrasolar or alien planets normally remain hiddenbecause of the glaring light from their stars. Deep Impact's telescope candetect planets by subtracting the light of a star alone from the combined lightof both the star and its planet.
The mission will observe five nearby stars where large, Jupiter-likeplanets were already discovered. Deep Impact may detect neighboringplanets by watching for any gravitational pulls on the known planets' orbits.
The total journey – starting from December 31, 2007 to the closest comet encounter on October 11, 2010 – will be roughly 1.6 billion milesor some 18 times the distance from the Earth to the sun. The spacecraft willneed three trips around the sun before it can intercept Comet Hartley 2.
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- IMAGES: Smashing Science: Deep Impact's Top 10 Images
- Deep Impact: Comet Chaser