Italian astronomer Galileo Galilei, known as the father of modern astronomy, discovered Io on January 8, 1610. But the moon’s ...

On March 8, 1979, NASA's Voyager 1 spacecraft discovered active volcanoes on Jupiter's moon Io. Before Voyager 1 flew by Io, scientists believed the moon to be a dead world much like Earth's moon.

Voyager 1 took this photo of Jupiter and two of its satellites (Io, left, and Europa) on Feb. 13, 1979. Io is about 220,000 miles above Jupiter's Great Red Spot; Europa is about 375,000 miles ...

Io is an incredibly active and extreme place, with glistening lava lakes and volcanic eruptions shooting sulfur and magma to ...