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.
Following the invention of the telescope, three more of the far planets were discovered—Uranus, Neptune, and Pluto. Uranus was named for the father of the god Saturn. Neptune was the god of the sea and Jupiter's brother in Roman mythology. Pluto was named after the Greek god of the underworld.
When the Space Age began humans sent robotic spacecraft to investigate the far planets. They returned images of strange and marvelous worlds composed of gas and slush instead of rock. Many new moons were revealed. Some of these moons are covered with ice and have atmospheres. There could be liquid water beneath that ice teeming with life. This possibility is particularly appealing to space scientists and to all people who wander if we are alone in the universe.
FUTURE MISSIONS TO THE FAR PLANETS
As of March 2004 NASA's next mission to a far planet is expected to be the Jupiter Icy Moons Orbiter (JIMO). This mission will focus on the three large moons of Jupiter named Europa, Ganymede, and Callisto. The Voyager and Galileo spacecraft provided tantalizing evidence that these three moons may have oceans of liquid water beneath their icy surfaces. The JIMO project is expected to launch sometime in 2012.