MERCURY

If an explorer were to step onto the surface of Mercury, he would discover a world resembling lunar terrain. Mercury's rolling, dust_covered hills have been eroded from the constant bombardment of meteorites. Craters dot the surface.

Mercury, the closest planet to the Sun, was named by the Romans after the fleet-footed messenger of the gods because it seemed to move more quickly than any other planet. But is it?

This photomosaic of Mercury was constructed from photos taken by Mariner 10 six hours before the spacecraft flew past the planet on March 29, 1974. These images were taken from a distance of 5,380,000 kilometers (3,340,000 miles). (Courtesy USGS, and NASA)