
The Moons of Uranus
Voyager 2 photographed the five major moons at close range. All have icy surfaces, but they are darker and rockier than Saturn's moons. Early in their history three were geologically vigorous

The Moons of Uranus
Voyager 2 photographed the five major moons at close range. All have icy surfaces, but they are darker and rockier than Saturn's moons. Early in their history three were geologically vigorous

Io
The solar system's most active volcanic world is a moon of Jupiter whose geyser like eruptions and massive lava flows yield evidence of exotic volcanic fluids. Their source of energy is gravitational

The Moons of Saturn
The 17 icy bodies that orbit the planet display a surprising range of geological evolution. Many of them show craters more than four billion years old, but one of them has terrain so new that no craters are seen

The Galilean Moons of Jupiter
In viewing the four largest Jovian satellites last year the Voyager spacecraft increased to nine the number of earthlike bodies that can be closely compared to gain an understanding of how they evolved