Surface of Mercury. Computer artwork of the Sun on the horizon, as seen from the planet Mercury. At its closest, Mercury is only 46 million kilometres from the Sun, less than a third of the Earth-Sun distance. The surface temperature extremes are the greatest in the solar system, ranging (day- night) from 400 to -170 degrees Celsius. A thin atmosphere is formed by the solar wind blasting material from its rocky surface. Due to the relative lengths of the day and year on Mercury, and the eccentricity of the orbit of Mercury, the Sun changes in apparent size and speeds up and slows down as it moves across the sky. The pattern on the surface of the Sun is granulation, caused by convection cells.