The most intriguing places in our solar system might not be planets at all. This week we turn our attention to some of the most fascinating and unusual worlds in our solar system: its moons.

For most of human history, we assumed moons were quiet, lifeless companions like our own. But as spacecraft ventured deeper into the outer solar system, a very different picture emerged.

Some moons erupt with volcanoes. Some hide vast oceans beneath miles of ice. Some have weather, rivers, and lakes, made not of water, but methane. And a few of them may have the ingredients necessary for life.

We’ll explore these strange worlds, from Io and Europa to Titan and Enceladus, and take a closer look at what makes them so dynamic. Along the way, we’ll revisit Pluto and its surprisingly complex family of moons, and consider why the outer solar syste ...