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.
It's tough to wrap your mind around a time when the Earth wasn't here. So how do Earth and the rest of the planets out there get their start in the universe?
The occasional sunspot can interrupt communications here on Earth. But major solar flares have the potential to cause more havoc. Could a flare-up wipe out all our electronics?