|Diameter||4880 km, 0.38 x Earth's|
|Average Distance from Sun||58 x 106km = 0.387AU|
|Length of Day||58.65 days|
|Length of Year||88 days|
|No. of Moons||None|
|Gravity||0.376 x Earth's|
Mercury is the closest planet to the Sun and the second smallest in our Solar System.
Only one spacecraft has ever been there. It was called Mariner 10, and took pictures of the surface of the planet. It found that Mercury is a rocky planet, covered in craters like the Moon. These craters are made when chunks of rock from outer space called meteorites smash into the surface. The biggest of these craters is 1300km across and is called the Caloris Basin.
Mercury has the biggest difference in temperatures in the Solar System. In the middle of the day, the temperature gets up to about 430 C, and at night it drops to –183 C.
Mercury doesn't have an atmosphere because it was blown off by a stream of particles from the Sun called the solar wind.
The planet has a very large amount of iron in its centre. This is surrounded by a layer of rock, which makes up the surface that we see.
Authors: Carolyn Brinkworth and Claire Thomas
Last updated: July 2001