Mercury is the first and the smallest planet in the solar system. It is also the first of the four terrestrial planets of our solar system. The first recorded observation goes back to one millennium BC. Mercury is very similar to our own moon, it is gray and has a lot craters. However, Mercury is 1.5 times bigger than the moon. Greek astronomers believed that it consisted of two objects: Apollo and Hermes. Hermes was only visible at evening twilight while Apollo was visible overday. Later the Romans called it Mercury, after their god of messengers.
Exploration of Mercury
There were two flyby missions from NASA: Mariner 10 and MESSENGER.
MESSENGER made a fly-by of Mercury on 14 January 2008, to further investigate the observations made by Mariner 10 in 1975. A third mission, BepiColombo will carry two probes to Mercury.
BepiColombo is an collaboration between Japan and ESA.
Mercury's gravity is too weak to hold an atmosphere. However, there is a sort of 'exosphere' which holds: oxygen, sodium, hydrogen, helium and potassium.
There are traces of argon, nitrogen, carbon dioxide, water vapor, xenon, krypton and neon. The source of these elements is still uncertain. However, scientists believe that the oxygen and helium is coming from the solar winds. The other elements come from evaporating volcanoes.