Io
Io is the innermost of Jupiter’s four Galilean moons and the third-largest moon of Jupiter.
Io is Jupiter’s innermost Galilean moon and the most volcanically active world in the Solar System. Discovered by Galileo Galilei in 1610, it is a key example of tidal heating in action.
What it is
Io is a natural satellite of Jupiter, about 3,643 km in diameter — slightly larger than Earth’s Moon. It is one of the four Galilean moons (along with Europa, Ganymede, and Callisto) and orbits Jupiter in roughly 42.5 hours.
Why it matters
Io’s extreme volcanism — hundreds of volcanoes and active lava fountains — is powered by tidal heating from Jupiter’s gravity and gravitational interactions with Europa and Ganymede. This makes it a natural laboratory for studying planetary geology and internal heating processes.
Key details
Io’s surface is constantly reshaped by eruptions and sulfurous deposits, leaving few impact craters. Its thin atmosphere is mostly sulfur dioxide, and its colourful surface (yellow, red, white, black, green) comes from sulfur and silicate materials.
In short
- Io is the most volcanically active world in the Solar System.
- Its volcanism is driven by tidal heating from Jupiter and neighbouring moons.
- Discovered by Galileo Galilei on 8 January 1610.
- Slightly larger than Earth’s Moon, with a thin sulfur dioxide atmosphere.
Io is a major object of interest for Canadian astronomy education and public science outreach because it is a nearby, well-studied example of tidal heating and active volcanism in the Solar System.
Quick questions
What is Io?
Why is Io so volcanically active?
How big is Io?
Sources
- NASA Science — https://science.nasa.gov/jupiter/jupiter-moons/io/facts/Supports: Discovery date, volcanic activity, Galilean moon status, size relative to Earth's Moon, orbital position.
- NASA Science — https://science.nasa.gov/jupiter/jupiter-moons/io/Supports: Most volcanically active world, tidal heating explanation, lava fountains, lava lakes, general overview.
- The Planetary Society — https://www.planetary.org/worlds/ioSupports: Innermost Galilean moon, volcanic activity, atmosphere composition, orbital and physical context.
- Encyclopaedia Britannica — https://www.britannica.com/place/Io-satellite-of-JupiterSupports: Discovery by Galileo, innermost Galilean moon, naming context, volcanic activity.
- European Space Agency — https://sci.esa.int/web/hubble/-/39830-the-volcanic-moon-ioSupports: Sulfur dioxide frost, extremely tenuous atmosphere, discovery context, volcanism observations.