Links
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- Io on Wikipedia
Io
Details
Io is Jupiter's third-largest moon and the most volcanically active world in the Solar System. Tidal flexing from Jupiter, Europa, and Ganymede keeps its interior hot enough to renew the surface with lava flows and sulfur-rich deposits.
Io matters because it makes a moon feel more like a furnace than a quiet companion world. It is only a little larger than Earth's Moon, but its surface is covered by the evidence of hundreds of volcanoes. NASA describes it as the most volcanically active world in the Solar System, a place where eruptions can throw lava fountains dozens of miles or kilometers high.
That activity is not a local accident. Io is caught between Jupiter's enormous gravity and the timed pulls of Europa and Ganymede, which keep its orbit from settling into a simple circle. The result is tidal flexing: Io is squeezed and released hard enough to generate internal heat, driving material toward the surface through volcanoes, rifts, and lava plains.
That is why Io stands apart among the Galilean moons. Europa and Callisto invite attention because of ice and possible hidden oceans; Io is exposed, hot, and visibly rewritten. Its pastel yellows, reds, whites, and dark volcanic centers are not decoration. They are the visible skin of a world where geology is happening fast enough to erase craters and repaint the surface.
1,592km
Key facts
- Scale fact
- 3,643 kmdiameter
- Estimated age
- ~4.5 billion years
- Composition
- Silicate rock with sulfur-rich surface deposits
Scale context
Where Io sits on the full axis
Shared physical scale
4,022km
Together, these objects make the size change around Io easy to compare at a glance.
Sources
References for Io
Measurements and descriptive context are compiled by the Scale of Space team from the references below. If you find an error, please let us know.
- Io — Wikipedia
- Visual reference: Wikimedia Commons (NASA / JPL / University of Arizona, Public domain)
Between the smallest and the largest, perspective is everything.
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Scale of Space is a scroll-based journey through the universe, placing objects on a single logarithmic scale so you can compare size across an unbroken range.
Guides turn parts of that scale into curated essays, while focused views let you explore the same range through specific groups of objects.