Mercury Mercury is the closest planet to the sun. It’s average distance from the sun is approximately fifty-eight million km and it’s diameter is 4875 km, making it the second smallest planet in our solar system. It’s volume and mass are about 1/18 that of the earth and it’s average density is approximately equal to that of the earth. Mercury’s magnetic field is one-hundred times weaker than that of Earth’s. Mercury has the shortest revolution of all the planets in our solar system and revolves around the sun in about eighty-eight days. Radar observations of the planet show that its period of rotation is 58.7 days, or two-thirds of its period of revolut