The farther we penetrate the unknown, the vaster and more marvelous it becomes.

—Charles A. Lindbergh, 1974

The far planets are Jupiter, Saturn, Uranus, Neptune, and Pluto. They lie far from the Sun, in the coldest and darkest part of the solar system.

In ancient times people noticed that some lights in the sky followed odd paths around the heavens. The Greeks called them asteres planetos, or wandering stars. Later they would be called planets. The ancients could see only two of the far planets in the nighttime sky—Jupiter and Saturn.

Jupiter was named for the mythical Roman god of light and sky. He was the supreme god also known as Jove or dies pater (shining father). His counterpart in Greek mythology was named Zeus. Saturn was named after the god of agriculture, who was also Jupiter's father. His Greek counterpart was called Kronos...