The planet closest to the Sun is the smallest in the system (only 0.055 the size of Earth). The diameter of Mercury is approximately 4,878 km, that is, equal to the Atlantic Ocean.
Mercury has no satellites.
The planet has a rarefied atmosphere consisting of atoms driven from its surface by the solar wind.
On the surface of Mercury, the difference between night and day temperatures is very different. Thus, in the night (opposite from the Sun) areas of the planet, the temperature can reach minus 180˚ C, and in the daytime (facing the Sun) areas it can rise to 430˚ C.
One day on Mercury corresponds to 58 days on Earth.
