Astronomers thought they saw a big explosion in the nearby Andromeda galaxy. GALEX, JPL-Caltech/ NASA hide caption

itoggle caption GALEX, JPL-Caltech/ NASA

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

This diagram for the outer solar system shows the orbits of Sedna (in orange) and 2012 VP113 (in red). The sun and terrestrial planets are at the center, surrounded by the orbits (in purple) of the four giant planets — Jupiter, Saturn, Uranus and Neptune. The Kuiper belt, which includes Pluto, is shown by the dotted light blue region. Scott S. Sheppard/Carnegie Institution for Science hide caption

itoggle caption Scott S. Sheppard/Carnegie Institution for Science

Russian personnel are the first to meet space station crew members when they return to earth. Bill Ingalls/NASA hide caption

itoggle caption Bill Ingalls/NASA

An artist's concept of a narrow asteroid belt orbiting a star similar to our own sun. NASA/JPL-Caltech hide caption

itoggle caption NASA/JPL-Caltech

The Chinese flag is seen in front of a view of the moon at Beijing's Tiananmen Square in December, when China's first moon rover touched the lunar surface. That feat was widely celebrated — but observers believe the rover has now run into serious trouble. Mark Ralston/AFP/Getty Images hide caption

itoggle caption Mark Ralston/AFP/Getty Images