Mercury is the closest planet to the Sun and the smallest of the solar system's true planets. Due to it being so close to the sun, it is difficult to see it from Earth. One year on Mercury is 88 Earth days long and one day on Mercury lasts 59 Earth days. It is a barren planet with no atmosphere. It was named after Mercurius, the messenger of the Roman Gods and the Roman God of commerce. During the daytime, the planet is really hot, at nighttime, the planet is really cold. The polar caps are the only two regions of the planet that never see heat from the sun. It and Venus are the only two planets in the solar system that do not have any moons.