Mercury is the closest planet to the Sun. It rotates three times in two of it's years. It's orbit is highly eccentric, varying from 46 million km from the Sun to 70 million. There are extreme temperature variations on Mercury ranging from 90 K to 700 K.
Mercury's surface is very cratered, very old and has no plate tectonics. It is the second densest major body in the solar system. It is believed that Mercury's dense iron core probably comprises the majority of the planet and that Mercury has a relatively thin mantle and crust.It might surprise that Mercury has a very thin atmosphere. But in fact, this consists of atoms blasted off the surface by the solar wind. These atoms soon escape into space. So in fact Mercury does not have a stable atmosphere but one that is constantly being replenished.
In addition to the craters, Mercury's surface has very large escarpments, some hundreds of kilometers long and up to 3 km high. One of the largest features on Mercury is Caloris Basin which is about 1300 km in diameter. It was probably caused by a very large impact early in the planet's history. This, it is believed, was also responsible for the strange features on the exact opposite side of the globe.
Incredibly, radar evidence indicates the presence of water ice in the protected shadows of some craters at the North pole.
Mercury has a small magnetic field and no satelite