Due to Mercury's brightness and relative size in our night sky it was easily mistaken for a star rather than a Planet, in fact the ancients identified five so called rapidly moving "wandering stars" which we can correctly identify as Planets. Although first observed at some time prior the 3rd millennium BC, most of the info we know about Mercury is fairly recent, the majority of the info only being obtained in 1974-1975 by the US spacecraft Mariner 10. Only half of the Planets surface has been mapped to date.

How far is the Planet Mercury away from the Sun ?
This is the closest planet in our Solar system to the Sun, the average distance being 58 million Km (0.38 Au), Earth by comparison is nearly three times this distance further away.

How big is it ?
The Planet Mercury is not very big, it has a diameter of about 4880km which is only about a third of the size of the Earth,  it's a mass is approximately 3.30e23 kg, most of this mass can be accounted for by its very dense iron core. Of all the Planets, the only one smaller in our Solar System is Pluto.

What is it like on the surface of the Planet Mercury ?
There is a very wide range of surface temperature on this Planet, varying from 427°C on the side closest to the Sun to as low as -183°C on the side furthest away from the Sun, the largest variance found on any of the Planets in our Solar System. There is only a very slight atmosphere and the surface is both desolate, and heavily cratered by past meteorite impacts. It is hard to picture life ever evolving or existing in such an inhospitable place with such extremely varying conditions.

Does the Planet Mercury have any Moons ?
Although most of the Planets in the Solar System posses multiple moons Mercury is one of the few planets  which has neither moons nor satellites captive within it's gravity well.