Cosmic Scale
Io
Moon of Jupiter · 778 million km from the Sun
How big is Io?
Io is about 3,643 km across.
Io is squeezed between Jupiter's gravity and the pull of the other large moons, and the friction melts its insides. The result is the most volcanically active world known: hundreds of erupting volcanoes, lava lakes, and plumes that rise hundreds of kilometres.
At a glance
| Diameter | 3,643 km |
|---|---|
| Mass | 8.93 × 10²² kg |
| Diameter compared with Earth | 0.286 × Earth |
| Orbits | Jupiter, every 1.8 days |
| Volcanoes | 400+ active |
| Surface flex | Up to 100 m of tides |
| Discovered | 1610, Galileo |
Good to know
- Its surface is repaved so fast that it has essentially no impact craters.
- The yellows, oranges and whites are sulfur and sulfur dioxide frost.
- Loki Patera, a lava lake 200 km wide, brightens on a roughly 500-day cycle.