All it took to verify a lava lake on Io was a fortunate transit by an icy world.
Radio Jupiter
In the visible spectrum, Jupiter is a bright, star-like point in the night sky. Viewing it with the naked eye, it would be easy to confuse it with a star except for the fact that it doesn’t twinkle. At radio frequencies Jupiter appears very different. It doesn’t have a simple round shape, for example, and it is extraordinarily bright. So bright that it can outshine the Sun at some radio frequencies.
Looking for Lava in All the Wrong Places
In 1979 Linda Morabito was processing an image taken by the Voyager 1 spacecraft. It was an image of Io, one of Jupiter’s moons. She discovered what appeared to be a plume of material erupting from Io’s surface. Upon further analysis it was found to be due to a volcanic eruption, as was the first evidence of active volcanism on a body other than Earth. We now know that Io is the most geologically active body in our solar system.