Recent flybys of the fiery world refute a leading theory of its inner structure—and reveal how little is understood about geologically active moons.

Since the late 1970s, scientists have believed that Io could have an ocean of lava hidden beneath its surface, causing much of the Jovian moon’s surface-level volcanic activity.

Because Io is so close to its massive host planet, the moon is subjected to a tremendous gravitational pull as it orbits Jupiter once about every 42 hours, according to the Planetary Society.

Jupiter’s moon Io is the best example of a world of fire, freckled with volcanoes and cracked by lava spills. There are many competing theories to explain the workings of this fire-orb.

Io, one of the most fascinating moons in our solar system, continues to mystify scientists with its intense volcanic activity and bizarre behavior. This moon, known for its towering volcanoes, ...

Galileo measured Io’s polar gravity when it flew by this large moon in May 1999. From the gravitational field, says Dr. Jerry Schubert of the UCLA, it’s possible to determine Io’s internal ...

Observations made of Jupiter’s moon Io during the Juno mission’s flybys helped astronomers confirm how and why Io became the most volcanic world in the solar system. CNN values your feedback 1.

NASA's robotic Juno spacecraft is delivering the fresh data on Io with a series of flybys, each getting closer to Jupiter's volcanic moon until a pair of close-up encounters at a range of less ...

Recent strange activity around Jupiter’s volcanic moon, Io, confused and excited scientists. By Oliver Whang Io, the third largest of Jupiter’s moons, is caught in a pressurized, explosive ...

No moon in our solar system is likely as chaotic as Io, Jupiter’s third largest. The rocky body looks like a pepperoni pizza because of the constant, numerous eruptions on its surface. The ...