Mercury
The first planet from the Sun
The smallest planet and the closest to the Sun, Mercury is only about 40 % wider than our Moon, and looks much like it: a grey world covered in craters, with almost no atmosphere. With nothing to hold the heat, its ground reaches 430 °C by day and falls to -180 °C at night, the widest swing of any planet.
It turns three times for every two trips round the Sun, so that one sunrise to the next takes 176 of our days, two of its years. Seen from Earth it never strays far from the Sun, which is why few people have ever seen it. The map comes from NASA's MESSENGER probe, which orbited it from 2011 to 2015; BepiColombo, from ESA and Japan, is due to enter orbit in November 2026.
Key figures
- Diameter
- 4,879 km, 0.38 × Earth
- Mass
- 0.0553 × Earth
- Surface gravity
- 3.7 m/s², 38% of Earth's
- Surface temperature
- -180 °C at night, 430 °C by day
- Rotation period
- 58.6 days
- Sunrise to sunrise
- 176 days
- One orbit of the Sun
- 88 days
- Mean distance from the Sun
- 57.91 million km
- Atmosphere
- None, only a thin exosphere
- Moons
- None