Answer: Io

For the most part, the objects in our solar system lead a rather sedate life. The solar system is filled with cold, lifeless, and essentially inert objects like distant moons, asteroids, and other objects just as desolate and still as you’d imagine.

Then, in contrast to the lack of activity you find on most solar system bodies, you have Jupiter’s moon Io. The surface of Io is covered with not just a few active volcanoes, not just enough volcanoes to put it ahead of Earth in the active geology department, but with over 400 volcanoes.

In the picture seen here, captured by the Galileo spacecraft in 1999, you can see the effects of the volcanic activity on Io. The surface is dotted with pock-mark like spots marking the volcanoes and their surrounding geography, and the coloration of the surface is a result of the lava flows and huge amount of sulfur-based compounds the volcanic eruptions rain down on the surface.