Jupiter is like a mini solar system. The Sun’s largest planet has a family of almost a hundred known moons. Most of them are little more than cosmic flotsam – chips of rock and ice no more than a couple of miles wide. But a few rank among the most interesting worlds in the solar system.

The four largest moons are Io, Europa, Ganymede, and Callisto. They account for more than 99.9 percent of the combined mass of all of Jupiter’s moons. They probably formed along with Jupiter itself, from dust and gas that encircled the newborn planet.

Io is the most volcanically active body in the solar system. It’s covered by hundreds of volcanoes, lakes of molten lava, and other features. The other three big moons appear to have oceans of liquid water buried below their icy crusts. And Europa’s ocean is considered one of the most likely homes for life in the solar system.

Some of Jupiter’s little moons could have formed at the same time as the big guys, then perhaps moved into different orbits. But most of them appear to be the remains of asteroids that Jupiter captured when they wandered close. The asteroids were blasted apart in big collisions, leaving small chunks of ice and rock in orbit around the planet.

Jupiter is low in the east-northeast at nightfall, and climbs high overhead during the night. It looks like a brilliant star. Through binoculars, the four big moons look like tiny stars lined up near the planet.

Script by Damond Benningfield