Surface of Mercury. Computer artwork showing the surface of the planet Mercury with the Sun overhead. 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. Some of Mercury's thin ???tmosphere??is captured material which streams off the Sun, while other gases are released by chemical processes on the planet's rocky surface.