Cosmic Scale
Mercury
Planet · 58 million km from the Sun
How big is Mercury?
Mercury is about 4,879 km across.
See Mercury in 3D, at true scale
Mercury is the smallest planet and the closest to the Sun, with almost no atmosphere to even out its temperature. It races around the Sun in 88 days while turning on its axis so slowly that a single day–night cycle takes 176 days.
At a glance
| Diameter | 4,879 km |
|---|---|
| Mass | 3.30 × 10²³ kg |
| Diameter compared with Earth | 0.383 × Earth |
| Year | 88 days |
| Day | 176 days, Sun to Sun |
| Temperature | −180 to 430 °C |
| Gravity | 38% of Earth's |
Good to know
- Its year is shorter than its day, so on parts of the surface the Sun rises, stops, backs up, then sets.
- Craters at its poles never see sunlight and hold water ice, a few metres from some of the hottest ground in the Solar System.
- Its huge iron core fills about 85% of its radius; the planet may have lost its outer layers in a collision.