Ganymede, a satellite of the planet Jupiter. With a diameter of 3,270 miles (5,260 km), Ganymede is the largest satellite in the solar system, and is larger than the planet Mercury. Its surface is composed of ice and has distinct dark and light areas. The dark areas are heavily cratered and the light areas are covered by long, parallel channels. Ganymede was discovered by Galileo Galilei in 1610.
A lunar land rush is the most likely thing in the world (or, rather, out of it). As private companies gaze spaceward with dollar signs in their eyes, it's time to start settling some questions about space ownership, use and management.
A single pulsar is fascinating enough, but as a set, these rapidly rotating neutron stars help scientists figure out mysteries of the universe.