Mercury
Rocky planet
The smallest planet and the closest to the Sun, a grey, cratered world with almost no atmosphere.
Key facts
- Type
- Rocky planet
- Diameter
- 4,879 km
- Average distance from the Sun
- 57.9 million km
- One orbit
- 88 Earth days
- One day (sunrise to sunrise)
- About 176 Earth days
- Moons
- None
About the Mercury
How to recognise it
Mercury looks a lot like our Moon: grey, covered in craters and with no clouds. It is the smallest of the eight planets, only a little larger than the Moon.
What it is like
With almost no atmosphere to hold in heat, Mercury swings between scorching days and freezing nights. It races around the Sun in just 88 days, but turns so slowly that one day, from sunrise to sunrise, lasts about 176 Earth days.
Sources
Facts checked: 29 October 2026
