Volcanic moon of JupiterThe Solar System's volcano world
Io
Tidal forces from Jupiter knead Io's interior and turn the moon into the most volcanically active world known.
- Host
- Jupiter
- Type
- Volcanic rocky moon
- Mean diameter
- 3,643 km
- Mean orbital radius
- 421,700 km
- Orbital period
- 1.77 days
- Rotation
- Synchronous
- Surface gravity
- 1.80 m/s²
- Surface temperature
- About −163 °C
Io up close
NASA imagery
A world squeezed by gravity
Io is caught in orbital resonances with Europa and Ganymede. Their gravitational nudges keep Io's orbit slightly elliptical, so Jupiter's pull changes in strength around every lap.
That changing pull flexes Io's solid body. Friction converts tidal energy into heat, sustaining a partially molten interior even far from the Sun.
Lava lakes and giant plumes
Io has hundreds of active volcanic centres. Some eruptions produce lava fountains and immense lava lakes; others launch sulfur-rich plumes hundreds of kilometres into space.
The volcanoes constantly resurface Io and supply material to Jupiter's magnetosphere. Juno and JWST now observe eruptions and volcanic hotspots in visible and infrared light.
Worth knowing
Io is roughly the same size as Earth's Moon but far more volcanically active.
Some volcanic plumes rise higher than the International Space Station's orbital altitude.
Io passes through Jupiter's intense radiation belts, which makes close spacecraft observations challenging.
Watch and explore
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A Huge Volcanic Eruption on Io V101 SPACE
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Research & further reading
Mission imagery and measurements are interpreted alongside orbital data. Follow the source links for the current NASA overview and precise satellite parameters.