Mercury

Smallest of the four inner planets, and the planet closest to the Sun. It has no known satellite...


DATA
Diameter: 4878km (3031miles)
Mass: (Earth=1) 0.055
Volume: (Earth=1) 0.056
Density: (water=1) 5.44
Orbital Period: 89.97 Earth days
Rotation Period: 68.646 Earth days
Av. Surface Temp: 427°C (800°F)

The Planet Mercury

Hardly anything at all was known about Mercury by the people of Earth, until they sent the Mariner 10 probe to investigate in 1974 and 1975. The probe’s findings were fairly extensive, having photographed nearly half the planets surface during its three close approaches of Mercury. The pictures show a heavily cratered, Moon-like world with frequent valleys and ridges. Earth scientists gathered more information through radar mapping in 1991 and 1992, revealing what may be water-ice on the floors of some of the craters permanently in shadow. Mercury has an atmosphere of helium and sodium that is tenuous at best, with a weak magnetic field.