Tim Larson, EPOXI Project Manager from the Jet Propulsion Laboratory in Pasadena, Calif., speaks during a press conference, Thursday, Nov. 18, 2010, at NASA Headquarters in Washington. The press conference was held to discuss the Nov. 4 successful flyby of Comet Hartley 2 by NASA's EPOXI Mission Spacecraft. Images from the flyby provided scientists the most extensive observations of a comet in history. Photo Credit: (NASA/Paul E. Alers)

Tim Larson, Stardust NExT Project Manager, speaks during a news briefing, Wednesday, Jan. 19, 2011, at NASA Headquarters in Washington. On Feb. 14, 2011 NASA's Stardust-NExT (New Exploration of Tempel 1) mission will encounter Comet Tempel 1, providing a unique opportunity to measure the dust properties which will also provide a comparison between two observations of a single comet, Tempel 1, taken before and after a single orbital pass around the sun. Photo Credit: (NASA/Paul E. Alers)

Jessica Sunshine, EPOXI Deputy Principal Investigator, University of Maryland, far right, discusses imagery sent back from the EPOXI Mission spacecraft during a press conference, Thursday, Nov. 18, 2010, at NASA Headquarters in Washington. The press conference was held to discuss the Nov. 4 successful flyby of Comet Hartley 2 by NASA's EPOXI Mission Spacecraft. Images from the flyby provided scientists the most extensive observations of a comet in history. Photo Credit: (NASA/Paul E. Alers)