Mercury
The smallest planet and closest to the Sun
Mercury is the smallest planet in our solar system and the closest to the Sun. Despite its proximity to the Sun, it is not the hottest planet—that title belongs to Venus. Mercury has no atmosphere to trap heat, resulting in extreme temperature variations.
Key Facts About Mercury
- Diameter: 4,879 km (3,032 miles)
- Distance from Sun: 57.9 million km (36 million miles)
- Day length: 59 Earth days
- Year length: 88 Earth days
- Moons: None
- Rings: None
Extreme Temperatures
Mercury experiences the most extreme temperature swings in the solar system. During the day, temperatures can reach 430°C (800°F), while at night they can plummet to -180°C (-290°F). This 600°C temperature difference is due to Mercury's thin atmosphere.
Surface Features
Mercury's surface is heavily cratered, similar to our Moon. The largest crater, Caloris Basin, is about 1,550 km in diameter. The planet also features long cliffs called scarps, which formed as Mercury's interior cooled and contracted.