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.

As Io moves closer to Jupiter, the planet's powerful gravity pulls hard on the moon, deforming it. This force decreases as Io retreats, and the moon bounces back.

Jupiter has an embarrassment of riches when it comes to moons. Among its 80 known moons is Io, which NASA describes as the most volcanically active world in the solar system.

Io, one of the four Galilean moons of Jupiter, as seen by the Galileo probe, 1997. Two volcanic eruptions are visible, one at the top, from the Pillan Patera, and the Prometheus plume at the ...

Jupiter, the largest planet in our solar system, is home to a fascinating array of moons. Among its 90-plus satellites, one stands out for its extraordinary geological activity: Io.

Io is Jupiter's third-largest moon, spanning roughly 2,300 miles (3,700 kilometers) across, which makes it slightly bigger than Earth's moon.

A NASA spacecraft made its closest-ever approach to Jupiter's moon Io, coming within 930 miles of the "surface of the most volcanic world," and the space agency released new images of the flyby.

As Io moves closer to Jupiter, the planet's powerful gravity pulls hard on the moon, deforming it. This force decreases as Io retreats, and the moon bounces back.

Io is probably one of the most well-known moons in the solar system. Orbiting 422,000 kilometers above Jupiter, Io is the innermost of the four Galilean moons. Io, along with the other three ...

With its famous volcanoes, Io produced about 30 times more heat than Earth per year. While scientists had guessed that a vast ocean of magma lies beneath the surface of the fiery moon, they couldn ...

Io was discovered by Galileo Galilei in 1610. It's the innermost of Jupiter's four large moons and is tugged on hard by the huge planet, as well as its sister satellites Europa and Ganymede.