Mercury is the smallest and fastest planet in the solar system. It is also the closest planet to the sun. It is named after the Roman messenger god Mercury, the fastest Roman god. The planet Mercury was known by ancient people thousands of years ago. It has no moons.
How Big Is Mercury?
Mercury is the smallest of the eight planets in our solar system. It is only a little bigger than Earth's moon. It would take more than 18 Mercurys to be as big as Earth. If you could weigh Mercury and the moon, Mercury would weigh much more. Mercury has a rocky surface, but deep inside is a heavier material, probably iron.
Where Is Mercury?
Mercury is the closest planet to the sun. On average, it is a little more than one-third the distance from the sun than Earth is. Or, put another way, Earth is almost three times farther from the sun than Mercury. Mercury orbits the sun once every 88 Earth days. So one year on Mercury is 88 Earth days. But a day on Mercury is longer than an Earth day. One Mercury day lasts for 59 Earth days.