Mercury. Artwork of Mercury and the Sun, as they would appear to a spacecraft orbiting the planet. Mercury is the nearest planet to the Sun, its orbital radius being about 39% that of Earth's. It orbits the Sun every 88 days and revolves on its own axis every 58.7 days. Daylight temperatures can reach 430 degrees celsius (C), whilst the night temperatures plummet to -180C because the thin atmosphere does not retain heat. Mercury's surface is heavily cratered due to impacts from meteorites. The surface rocks are mostly dark and are a poor reflector of sunlight. Mercury has about the density of Earth, though only about 5% of the volume and mass of our planet.