The Moon and the planet Jupiter stand side by side as they climb across the southeastern quadrant of the sky late tonight. They rise around 1 a.m., with brilliant Jupiter to the right of the Moon.
The lunar surface shows the aftermath of an era of intense volcanic activity, when molten rock bubbled to the surface in vast pools. The pools long ago hardened to form plains of volcanic rock -- the dark areas on the lunar surface.
On one of the moons of Jupiter, the volcanic activity never stopped. And today, Io is the most volcanically active body in the solar system. It has many more volcanoes than Earth does, and they belch out a hundred times more lava.
A recent study shows that the volcanoes most likely are fed by a massive underground ocean of magma -- rock that's heated to more than 2200 degrees Fahrenheit.
Planetary scientists analyzed observations by the Galilo spacecraft, which orbited Jupiter for several years. The craft measured the magnetic fields of Jupiter and Io, and the way the magnetic fields interact. A careful analysis of the Galileo data revealed evidence of the magma ocean. It forms a layer that's about 30 miles deep, and begins 20 to 30 miles down.
The rock is melted by a gravitational tug of war between Jupiter and some of its other large moons, which twists and squeezes Io's interior. That generates enough heat to melt the rocks below the surface -- keeping Io sizzling long after our own Moon cooled off.
Script by Damond Benningfield, Copyright 2011