- from Planets
Mercury is the nearest known planet to the Sun.
It is three times closer to the Sun than Earth. Mercury is hot. Its rocky, bare, and cratered surface is 800° Fahrenheit (F) during the day. At night, however, the temperature falls to –280°F. Mercury has been baked by the Sun for 4.5 billion years. Not long after it first formed, the planet may have crashed into a giant asteroid that blew away most of Mercury’s outer covering. Today, Mercury is mostly a ball of hot iron with a thin, rocky outer crust.