STS-127 shuttle mission crew members from left, Commander Mark Polansky, Pilot Doug Hurley, Mission Specialists Christopher Cassidy, Tom Marshburn, Dave Wolf and Julie Payette of the Canadian Space Agency, give a presentation at the NASA Tweetup event held at NASA Headquarters, September 24, 2009 in Washington. The NASA Tweetup featured a presentation and a question and answer session with the crew of the STS-127 shuttle mission to install new hardware and expand the Japanese Kibo laboratory on the International Space Station. Photo Credit: (NASA/Carla Cioffi)

Canadian Space Agency Astronaut and STS-127 Mission Specialist Julie Payette answers questions at the NASA Tweetup event held at NASA Headquarters, September 24, 2009 in Washington. Nearly 200 of NASA’s Twitter followers are in attendance. Photo Credit: (NASA/Carla Cioffi)

Guests use their laptop computers to "Tweet" and follow a NASA STS-127 crew presentation on Twitter at the NASA Tweetup event held at NASA Headquarters, September 24, 2009 in Washington. Nearly 200 of NASA’s Twitter followers are in attendance. Photo Credit: (NASA/Carla Cioffi)

NASA Astronaut and STS-127 Mission Commander Mark Polansky, far left, answers questions at the NASA Tweetup event held at NASA Headquarters, September 24, 2009 in Washington. Nearly 200 of NASA’s Twitter followers are in attendance. Photo Credit: (NASA/Carla Cioffi)

NASA Astronaut and Mission Specialist Dave Wolf, center, answers questions at the NASA Tweetup event held at NASA Headquarters, September 24, 2009 in Washington. Nearly 200 of NASA’s Twitter followers are in attendance. Photo Credit: (NASA/Carla Cioffi)

Roger Clark, team member, Cassini spacecraft Visual and Infrared Mapping Spectrometer and co-investigator, Moon Mineralogy Mapper, U.S. Geological Survey in Denver answers questions on NASA’s discovery of water molecules in the polar regions of the moon at a press conference at NASA Headquarters, September 24, 2009, in Washington. Photo Credit: (NASA/Carla Cioffi)

Jim Green (far left), director, Planetary Science Division, Science MissionDirectorate at NASA Headquarters in Washington; Carle Pieters, principal investigator, Moon Mineralogy Mapper, Brown University; Rob Green, project instrument scientist, Moon Mineralogy Mapper, at NASA's Jet Propulsion Laboratory; Roger Clark, team member, Cassini spacecraft Visual and Infrared Mapping Spectrometer and co-investigator, Moon Mineralogy Mapper, U.S. Geological Survey in Denver and Jessica Sunshine (far right), deputy principal investigator for NASA's Deep Impactextended mission and co-investigator for Moon Mineralogy Mapper,Department of Astronomy, University of Maryland discuss their findings of water molecules in the polar regions of the moon at a press conference at NASA Headquarters, September 24, 2009, in Washington. Photo Credit: (NASA/Carla Cioffi)

Al Feinberg from NASA Television, center, interviews a guest at the NASA Tweetup event held at NASA Headquarters, September 24, 2009 in Washington. Nearly 200 of NASA’s Twitter followers are in attendance, which features a presentation and a question and answer session with the crew of the STS-127 shuttle mission to install new hardware and expand the Japanese Kibo laboratory on the International Space Station. Photo Credit: (NASA/Carla Cioffi)

NASA Astronaut and STS-127 Mission Commander Mark Polansky, also known as @Astro_127 on Twitter, answers questions at the NASA Tweetup event held at NASA Headquarters, September 24, 2009 in Washington. Nearly 200 of NASA’s Twitter followers are in attendance. Photo Credit: (NASA/Carla Cioffi)

Jim Green (second from left), director, Planetary Science Division, Science Mission Directorate at NASA Headquarters in Washington discusses NASA’s findings of water molecules in the polar regions of the moon at a press conference at NASA Headquarters, September 24, 2009. Photo Credit: (NASA/Carla Cioffi)

NASA Astronaut and Mission Speciliast Tom Marshburn answers questions at the NASA Tweetup event held at NASA Headquarters, September 24, 2009 in Washington. Nearly 200 of NASA’s Twitter followers are in attendance. Photo Credit: (NASA/Carla Cioffi)

Rob Green, project instrument scientist, Moon Mineralogy Mapper, at NASA's Jet Propulsion Laboratory in Pasadena, CA answers questions on NASA’s discovery of water molecules in the polar regions of the moon at a press conference at NASA Headquarters, September 24, 2009, in Washington. Photo Credit: (NASA/Carla Cioffi)