Io
Moon of Jupiter
The most volcanically active world in the Solar System, painted yellow, orange and white by sulphur.
Key facts
- Orbits
- Jupiter
- Diameter
- About 3,643 km
- One orbit
- 1.8 days
- Notable for
- Hundreds of active volcanoes
About the Io
How to recognise it
Io looks like a mottled yellow, orange and white ball dotted with dark spots, which are volcanoes. Its colours come largely from sulphur and sulphur compounds.
What makes it special
NASA describes Io as the most volcanically active world in the Solar System. It has hundreds of volcanoes, some throwing lava fountains dozens of miles high. The heat comes from Jupiter’s strong gravity squeezing and stretching the moon as it orbits.
Sources
Facts checked: 29 October 2026
