- 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, barren, and cratered surface is 800° Fahrenheit (F) during the day, while at night the temperature falls to –280°F. Mercury has been baked by the Sun for 4.5 billion years. Not long after Mercury first formed, it may have collided with a giant asteroid that blasted off most of the planet’s outer covering. This means that today Mercury is mostly a ball of hot iron with a thin, rocky outer crust.