Io
3,643 kmacross
Io is 3,643 km across and orbits Jupiter at 421,700 km, once every 1.8 days. The most volcanically active world in the solar system — hundreds of erupting volcanoes, kneaded hot by Jupiter’s tides.
▶ Visit Io in 3D
Why this moon matters
Io is caught in a gravitational tug-of-war: locked in resonance with Europa and Ganymede, it is endlessly squeezed by Jupiter’s tides, and the friction keeps its interior molten. The result is over 400 active volcanoes, lava lakes, and eruption plumes that fountain hundreds of kilometres into space. Its yellow-orange complexion is sulphur, repainted continuously.
Jupiter’s gravity flexes Io’s solid surface up and down by tens of metres every orbit — the ground tides here dwarf Earth’s ocean tides.
Io by the numbers
Diameter
3,643 km
Distance from Jupiter
421,700 km
Orbit period
1.8 days
Rotation
tidally locked
Surface gravity
1.80 m/s²
Temperature
−143 °C (lava: >1,000 °C)
Orbital speed
17.3 km/s
Sunlight travel time
43 minutes
In the interactive view you can fly to Io directly and ride along as it circles Jupiter.
Keep going
✓ Facts verified July 2026
Every figure on this page is a real, rounded value checked against primary sources. Found something out of date? See how we keep it accurate.