An artist's rendering depicts the satellite ISEE-3/ICE during its planned lunar fly-by in August 2014. Mark Maxwell/Courtesy ISEE-3 Reboot Project hide caption

itoggle caption Mark Maxwell/Courtesy ISEE-3 Reboot Project

Mark Kelly (left) will stay on Earth while his brother, Scott Kelly, spends a year on the International Space Station. NASA will test how the environments affect them differently. NBC NewsWire/NBCU Photo Bank via Getty Images hide caption

itoggle caption NBC NewsWire/NBCU Photo Bank via Getty Images

An artist's rendering of Kepler-186f, the first validated Earth-size planet to orbit in the habitable zone of a distant star. T. Pyle/NASA/SETI Institute/JPL-Caltech hide caption

itoggle caption T. Pyle/NASA/SETI Institute/JPL-Caltech

The disturbance visible at the outer edge of Saturn's A ring in this image from NASA's Cassini spacecraft results from gravitational effects on ring particles by an object that may be replaying the birth process of icy moons. NASA/JPL-Caltech/Space Science Institute hide caption

itoggle caption NASA/JPL-Caltech/Space Science Institute

Where's the moon rock? Curators say national treasures are often overlooked in the museum's current display, which hasn't changed much since 1976. National Air and Space Museum, Smithsonian Institution hide caption

itoggle caption National Air and Space Museum, Smithsonian Institution