Callisto

The ancient witness

Vital statistics

• Mean radius: 2,410 kilometres
• Mass: 1.08 × 10²³ kilograms
• Surface gravity: 1.24 metres per second squared
• Sidereal rotation: 17 days
• Orbital period: 17 days
• Mean temperature: -139 °C
• Axial tilt: 0 degrees

Field notes

• Callisto is the most heavily cratered world in the solar system — its 4-billion-year-old surface is a fossil of the early solar system.
• It orbits far enough from Jupiter's radiation belts that it's been proposed as the safest base for future human missions to the Jovian system.
• Even this battered iceball probably hides a subsurface ocean — they seem to be everywhere out here.

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