Mercury is the smallest planet in our solar system and has a highly cratered surface, similar to the moon. It has a large iron core which is thought to make up about 75% of the planet’s radius. Mercury’s close proximity to the sun also allows it to be studied as a way to better understand the formation and evolution of planets in our solar system. Several missions, including NASA’s MESSENGER spacecraft, have been sent to Mercury to study its geology, composition, and magnetic field.