NASA Principal Investigator for New Horizons mission Alan Stern (L) and Co-Investigator Will Grundy (R) hold up an enlarged, out-dated U.S. postage stamp with the "NOT YET" crossed out, during the celebration of the spacecraft New Horizons flyby of Pluto, at NASA's Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, July 14, 2015. REUTERS/Mike Theiler 

NASA's New Horizons spacecraft, to be launched toward the planet Pluto, is displayed at the Kennedy Space Center in Cape Canaveral, Florida November 4, 2005. REUTERS/Charles W Luzier 

Hubble Space Telescope images, taken by the Advanced Camera for Surveys, show Pluto, its large moon Charon, and the planet's two new putative satellites June 11, 2002. REUTERS/NASA