Planet
Mercury
Terrestrial planet
The swift, scorched innermost world
The smallest planet and closest to the Sun. Mercury has almost no atmosphere, so its surface swings from about 430 °C in daylight to −180 °C at night. It is always seen near the Sun, low in twilight.
In your sky
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Key facts
Distance
0.39 AU from the Sun (mean)
Diameter
4,879 km
Orbital period
88 days
Day length
176 Earth days (solar day)
Moons
0
Did you know
- A solar day on Mercury lasts two of its years.
- NASA's MESSENGER found water ice in permanently shadowed polar craters.
- Its iron core takes up about 85% of its radius.
