Mercury is the eighth largest planet (or second smallest) in the Solar
System.
Mercury is a heavily cratered planet, composed of rock with a central
iron core that is three-quarters of the diameter of the planet (3,600
km). Following the Earth, Mercury is the second densest planet in the
Solar System.
Covered with thousands of craters, the surface of Mercury closley
resembles the Earth's Moon. Mercury has few non-cratered areas on the
surface, with the exception of the large flat area known as the Caloris
Basin, and a few other small areas. The Caloris Basin, the result of an
asteroid impact, is 1300 km in diameter.
The surface temperature of Mercury is characterized by major
fluctuations. The daytime side of the planet reaches over 400 degrees C
(752 degrees F), but on the night side the temperature falls to -170
degrees C (-274 degrees F).
Mercury has no atmosphere and no known satellites.
The only visit to Mercury was made by the Mariner 10 spacecraft in
1974.
Mercury was believed by the Greeks to be two different stars. Mercury's
appearance in the morning was called Apollo, and its evening appearance
was referred to as Hermes.
Mercury, often identified with the Greek god, Hermes, is the messenger
of the gods in Roman mythology. Mercury is often characterized with
winged sandals.
