The four Terrestrial planets are Mercury, Venus, Earth, and Mars. The one that has the coldest surface is actually Mercury! This may be surprising because it is the closest planet to the sun, but Mercury's nighttime side has the coldest surface temperature. The cold temperature is due to its thin atmosphere. Its thin atmosphere causes the temperatures on Mercury to vary back and forth between burning and freezing. While the side that is exposed to the seat heats up vastly, the side that is on the dark side can drop down to -184 degrees Celsius! Therefore, of the terrestrial planets, Mercury's dark side has the coldest surface.
