SPACE.com Image Gallery: Exploring Mercury

Exploring Planet Mercury

Planet Mercury

Is that the moon? No! It's planet Mercury! Mercury and Earth's moon are similar in a number of ways. The surfaces of both objects are heavily cratered, tidal forces have changed their rotation and some low-lying areas are flooded in places with lava flows. Neither has an atmosphere and the surfaces of both are largely inactive. Of the nine planets, Mercury is the closest to the Sun and only Pluto is smaller. NASA's Mariner 10 -- the only spacecraft to have visited the planet -- took this image of Mercury in 1974 on one of its three 1974-75 flybys. Most of Mercury's surface remains to be studied and mapped, however, much of this region of the planet is too close to the Sun to be safely examined by a spacecraft. Notable facts about Mercury: Minimum Distance from Earth: 45 million km (28 million miles). Diameter: 4,878 km (3,030 miles). It takes 88 days to circle the sun. Mercury has no moons. Click to enlarge.

NASA/JPL