Mercury

The smallest and fastest planet

Mercury is the closest planet to the Sun. It is tiny — only a bit bigger than our Moon. In the day it gets as hot as an oven, and at night it freezes. Mercury races around the Sun so fast that its year is only 88 days long!

Mercury is the smallest planet in the Solar System and the closest to the Sun. It has almost no atmosphere, so it can't hold heat: +430 °C by day, −180 °C at night. Its surface is covered in craters, just like the Moon. Mercury's core is enormous — 85% of the planet's radius. Curiously, one day on Mercury (a spin on its axis) lasts 59 Earth days, so only 1.5 Mercury days pass in a Mercury year (88 days).

Fun facts

• A day on Mercury is longer than its year!
• Mercury is closest to the Sun, but it's not the hottest planet — Venus is hotter.
• There is ice on Mercury: deep craters at the poles never see sunlight.
• Mercury zooms along at 170,000 km/h — the fastest planet in the Solar System.