Io is only slightly larger than Earth’s moon and about one-quarter the diameter of Earth itself.​

Io orbits the planet Jupiter, which itself orbits the Sun at a distance of 484 million miles (778 million kilometers).

Tidal Lock: Over 1.8 Earth days, Io rotates once on its axis and completes one orbit of Jupiter, causing the same side of Io to always face Jupiter.

The moon Io is the most volcanically active world in the solar system. Io even has lakes of molten silicate lava on its surface.

Io’s very thin atmosphere is primarily sulfur dioxide, which on Earth is sometimes used to preserve dried food.

Io has no known moons of its own, but it is possible for moons to have moons.

Io has no known rings, but it does create a gaseous torus of material along its orbit around Jupiter.

Spacecraft have studied Io on flybys (Voyager and Cassini) or orbiting Jupiter (Galileo). Most recently, New Horizons observed Io en route to Pluto.

Io almost certainly could not support life as we know it. But that’s not to say it couldn’t harbor some form of life as we don’t know it.

Io’s volcanoes are at times so powerful that they are seen with large telescopes on Earth.