Mercury is the closest planet to the Sun and the eighth largest.

Mercury is in many ways similar to the Moon: its surface is heavily cratered and very old; it has no plate tectonics. On the other hand, Mercury is much denser than the Moon (5.43 gm/cm3 vs 3.34). Mercury is the second densest major body in the solar system, after Earth, Actually Earth's density is due in part to gravitational compression; if not for this, Mercury would be denser than Earth. This indicates that Mercury's dense iron core is relatively larger than Earth's, probably comprising the majority of the planet. Mercury therefore has only a relatively thin silicate mantle and crust. 

Mercury actually has a very thin atmosphere consisting of atoms blasted off its surface by the solar wind. Because Mercury is so hot, these atoms quickly escape into space. Thus in contrast to the Earth and Venus whose atmospheres are stable, Mercury's atmosphere is constantly being replenished.

 Mercury has a small magnetic field whose strength is about 1% of Earth's.

  Mercury has no known satellites.

  Mercury is often visable  with binoculars or even the unaided eye, but it is always very near the Sun and difficult to see in the twilight sky. There are several web sites that show the current position of Mercury (and the other planets) in the sky. More detailed and customized charts can be created with a planetarium program such as Starry Night.