Io
Io
Moon of Jupiter
Io facts
- Orbits
- Jupiter
- Distance from Jupiter
- 421,800 km (6.0 Jupiter-radii)
- Orbital period
- 1.8 days
- Diameter
- 3,643 km
- Mass
- 8.93 × 10²² kg
- Orbital inclination
- 0.04°
- Tidally locked
- Yes
- Discovered
- 1610, by Galileo Galilei
Io orbits Jupiter
Watch Io (highlighted) circle Jupiter. Press play; the moons run at their real relative speeds.
Relative sizes and spacing are compressed; orbits shown coplanar. Click a moon for its page.
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About Io
Io is the innermost of Jupiter's four large Galilean moons and the most volcanically active world in the Solar System. Constant flexing from Jupiter's gravity heats its interior, driving hundreds of volcanoes that repave its yellow, sulfur-covered surface. It is slightly larger than Earth's Moon.
- Named after a priestess of Hera in Greek myth
- Discovered: 1610, by Galileo Galilei
Io: frequently asked questions
- What is Io?
- Io is the innermost of Jupiter's four large Galilean moons and the most volcanically active world in the Solar System.
- What planet does Io orbit?
- Io orbits Jupiter at an average distance of about 421,800 km, completing one lap every 1.8 days.
- How big is Io?
- Io has a diameter of about 3,643 km and a mass of roughly 8.93 × 10²² kg.
- Why is Io famous?
- Io's claim to fame: the most volcanically active body in the Solar System, with hundreds of erupting volcanoes.
See Io in motion
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Data from NASA/JPL and NSSDCA. Source.