Mercury

The scorched sprinter

Vital statistics

• Mean radius: 2,440 kilometres
• Mass: 3.30 × 10²³ kilograms
• Surface gravity: 3.7 metres per second squared
• Sidereal rotation: 59 days
• Orbital period: 88 days
• Mean temperature: +167 °C
• Known moons: 0
• Axial tilt: 0.034 degrees

Field notes

• One Mercury day — sunrise to sunrise — lasts 176 Earth days, two full Mercury years. Near the poles you could outrun the sunset at walking pace.
• Mercury is shrinking. As its giant iron core cools, the whole planet has contracted, wrinkling its crust like a drying apple.
• It is not the hottest planet, despite being closest to the Sun. With no atmosphere to hold heat, days hit +430 °C and nights crash to −180 °C — the wildest temperature swing in the solar system.
• There is water ice on Mercury: crater floors at the poles sit in permanent shadow and have stayed cold enough to hoard ice for billions of years.

Data: NASA Planetary Fact Sheets. Explore the full interactive 3D map at the home page — every orbit is computed from real Keplerian elements.