Mercury

Mercury is the first planet from the Sun.

Characteristics
Mercury's surface has many craters visible from space. Solar Radiation hits the planet commonly, due to the fact that Mercury does not have an actual atmosphere.

Atmosphere
Due to Solar Radiation from the Sun, Mercury has an extremely thin atmosphere. The atmosphere is instead classified as an exosphere.

Core
Mercury has a large core. The reason for this is unknown, but a theory proposes that Mercury was larger, but a collision evaporated some of the planet's surface.