WASHINGTON -- Two NASA spacecraft now have new assignments after successfully completing their missions. The duo will make new observations of comets and characterize extrasolar planets. Stardust and Deep Impact will use their flight-proven hardware to perform new, previously unplanned, investigations.

An artist's concept shows the Deep Impact spacecraft. Credit: NASA

"These mission extensions are as exciting as it gets. They will allow us to revisit a comet for the first time, add another to the list of comets explored and make a search for small planets around stars with known large planets. And by using existing spacecraft in flight, we can accomplish all of this for only about 15 percent of the cost of starting a new mission from scratch," said Alan Stern, associate administrator for NASA's Science Mission Directorate, Headquarters, Washington. "These new mission assignments for veteran spacecraft represent not only creative thinking and planning, but are also a prime example of getting more from the budget we have."

The EPOXI mission melds two compelling science investigations -- the Deep Impact Extended Investigation (DIXI) and the Extrasolar Planet Observation and Characterization (EPOCh). Both investigations will be performed using the Deep Impact spacecraft, which finished its prime mission in 2005.

DIXI will involve a flyby of comet Boethin, which has never been explored. Boethin is a small, short period comet, or one that returns frequently to the inner solar system, from beyond Jupiter's orbit. This investigation will allow the recovery of some of the science lost with the 2002 failure of the COmet Nucleus Tour (CONTOUR) mission that was designed to make comparative studies of multiple comets. DIXI will be targeted to fly by comet Boethin December 5, 2008.

The EPOCh investigation also will use the Deep Impact spacecraft to observe several nearby bright stars, watching as the giant planets already known to be orbiting the stars pass in front of and then behind them. The collected data will be used to characterize the giant planets and to determine whether they possess rings, moons, or Earth-sized planetary companions. EPOCh's sensitivity will exceed both current ground and space-based observatory capabilities. EPOCh also will measure the mid-infrared spectrum of the Earth, providing comparative data for future efforts to study the atmospheres of extrasolar planets. This search for extrasolar planets will be made this year, en route to comet Boethin.

Michael A'Hearn of the University of Maryland, College Park, is EPOXI's principal investigator and the leader of the DIXI science team. L. Drake Deming of NASA's Goddard Space Flight Center, in Greenbelt, Md., is EPOXI's deputy principal investigator and leads the EPOCh investigation.

John Mather, Chief Scientist for NASA's Science Mission Directorate, said, "EPOXI is a wonderful opportunity to add to our growing body of knowledge of exoplanets. Watching planets go behind or in front of their parent stars can tell us about their atmospheric chemistry."

An illustration of the Stardust spacecraft. Credit: NASA

The other newly selected Discovery mission of opportunity is called New Exploration of Tempel 1 (NExT). The mission will reuse NASA's Stardust spacecraft to revisit comet Tempel 1. This investigation will provide the first look at the changes to a comet nucleus produced after its close approach to the sun. It will mark the first time a comet has ever been revisited. NExT also will extend the mapping of Tempel 1, making it the most mapped comet nucleus to date. This mapping will help address the major questions of comet nucleus "geology" raised by images of areas where it appears material might have flowed like a liquid or powder. The images were returned by Deep Impact from its encounter with the comet on July 4, 2005. NExt is scheduled to fly by Tempel 1 on Feb. 14, 2011.

Joseph Veverka of Cornell University, Ithaca, NY, is NExT's principal investigator.

Stardust launched in Feb. 7, 1999. It traveled over 2 billion miles to fly within 150 miles of the comet Wild 2 in January 2004 to bring back samples that may provide new insights into the composition of comets and how they vary from one another. The container with the comet samples returned to Earth in January 2006 while the rest of the spacecraft remained in space.

Created in 1992, NASA's Discovery Program sponsors frequent, cost-capped solar system exploration missions with highly focused scientific goals. In 2006, NASA received approximately two dozen proposals in response to an Announcement of Opportunity for Discovery missions and Missions of Opportunity. Proposals were evaluated for scientific merit, technical, management and cost feasibility.