Mercury is the solar system's sprinter. It races around the Sun in just 88 days, faster than any other planet.
But it turns slowly, so slowly that one sunrise to the next takes 176 Earth days. On Mercury, a single day lasts two of its years.
With almost no air to hold heat, it swings from 427 °C in sunlight to −173 °C at night. No planet has a wilder gap between day and night.
And yet there is ice here. NASA's MESSENGER spacecraft found it hiding in deep craters at the poles, where sunlight never reaches the floor.
Mercury is also shrinking. As its iron heart cools, the whole planet has tightened like a drying apple, leaving cliffs hundreds of kilometres long.
- Width
- 4,879 km
- One day
- 59 Earth days
- One year
- 88 Earth days
- Moons
- None
- Temperature
- −173 °C at night · 427 °C by day
- 70 kg on Earth weighs
- 26 kg here
