Io

The volcano world

Vital statistics

• Mean radius: 1,822 kilometres
• Mass: 8.93 × 10²² kilograms
• Surface gravity: 1.79 metres per second squared
• Sidereal rotation: 42.5 hrs
• Orbital period: 1.77 days
• Mean temperature: -143 °C
• Axial tilt: 0 degrees

Field notes

• Io is the most volcanically active body in the solar system — hundreds of erupting volcanoes, some launching plumes 400 km into space.
• Jupiter's gravity kneads Io like dough: the ground itself rises and falls by up to 100 m every orbit. That friction is what melts its insides.
• Its surface repaints itself constantly with sulfur — yellow, orange, red — which is why Io looks like a moldy pizza and has almost no craters.

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