Radar images of asteroid 1998 QE2, taken when the cosmic traveler was about 3.75 million miles from Earth, revealed that the asteroid, with a 1.7-mile diameter, has a moon or satellite revolving around it. NASA/JPL-Caltech/GSSR hide caption

itoggle caption NASA/JPL-Caltech/GSSR

The famous Ring Nebula is shown here in striking detail, in a composite image made from images from NASA's Hubble Space Telescope and infrared data from telescopes on Earth. NASA, ESA, C.R. Robert O'Dell, G.J. Ferland, W.J. Henney and M. Peimbert hide caption

itoggle caption NASA, ESA, C.R. Robert O'Dell, G.J. Ferland, W.J. Henney and M. Peimbert

After a half-year mission at the International Space Station, Canadian astronaut Chris Hadfield lands in central Kazakhstan on Tuesday. Sergei Remezov/AFP/Getty Images hide caption

itoggle caption Sergei Remezov/AFP/Getty Images

This map, from the United States Geological Survey, shows the age of bedrock in different regions of North America. Scientists found ancient water in bedrock north of Lake Superior. This region, colored red, was formed more than 2.5 billion years ago. United States Geological Survey hide caption

itoggle caption United States Geological Survey