Mercury
Mercury - Rotating Model
Credit: Almond/NASA
It is quite similar to the Moon, with lots of craters, but it has no moon of its own.
Mercury was the Roman god of travel, and the planet probably got its name because it moves so fast across the sky.
The first spacecraft to visit Mercury was Mariner 10 in 1973, and again in 1974, but it only mapped about half of the surface.
More recently (January 2008) the Messenger spacecraft captured more
of the rocky planet's surface during a close approach. After 2 more
fly-bys, Messenger is will enter orbit around Mercury in March 2011.
| Facts and Figures | |
| Orbit | 57,910,000 km from the Sun or 0.38 AU |
| Radius | 2,440 km |
| Mass | 3.30 x 1023 kg or 0.055 Earths |
| Length of Year | 88 Earth days |
| Length of Day | 176 Earth days |
| Surface Gravity | 0.38 g |
| Surface Temperature | about -200 to 400 °C |
