Mercury: the quick little world
Mercury is the smallest of the eight planets and the closest to the Sun. Its rocky ground is marked by craters.
One trip around the Sun takes about 88 Earth days. Sunlit ground gets extremely hot, but nights can be extremely cold.
Wonder about this
Why does being nearest the Sun not make Mercury hottest?
A science clue
Venus’s dense atmosphere traps much more heat; Mercury has almost no atmosphere to retain it.