Mercury is the smallest and closest planet to the sun. It’s a rocky planet, with craters all over it, and doesn’t have a moon or an atmosphere. This planet spins very slow, so one day would seem to take a long time. Since Mercury is the closest to the sun, it doesn’t have to make a humungous rotation and takes a shorter time. If you lived on Mercury, one year would only be 88 Earth days. Fun Fact: Mercury has been known from ancient times because it can be seen without a telescope.