The Far Planets - Pluto

Pluto is the smallest planet in the solar system and usually the farthest planet from the Sun. It is named after the mythical Greek god of the underworld. It takes Pluto 248 Earth years to circle the Sun. Pluto's orbit is very erratic. For twenty of those 248 years the planet orbits closer to the Sun than does Neptune. This last occurred between 1979 and 1999.

Pluto is believed to be a dark and icy world with a surface of frozen nitrogen, methane, and carbon dioxide. It has been observed and photographed only from great distances. No spacecraft have ever been near the planet. In January 2006 NASA launched a robotic probe that should reach Pluto in 2015. It will provide the first-ever detailed images of the distant planet.

Tombaugh Discovers Pluto

Clyde Tombaugh (1906–97) is credited with discovering the planet Pluto. Tombaugh made the discovery on February 18, 1930, while working at the Lowell observatory in Flagstaff, Arizona. This famous observatory was founded in the 1890s by Percival Lowell. For years Lowell had searched for a planet believed by some astronomers to lie beyond Neptune. Following Lowell's death the observatory continued the search. Tombaugh found Pluto after diligently photographing the sky for many nights and studying the photographs for objects that changed position relative to the fixed stars.

The Naming of Pluto

Lowell's widow wanted to name the planet after her late husband. This was not allowed, because it would have broken the tradition of using names from Greek and Roman mythology. The name Pluto was finally selected from many suggestions made by the public.

Pluto was the Greek god of the underworld, and able to make himself invisible. The name seemed appropriate for the darkest planet in the solar system that had been so difficult to find. Also, the first two letters of the name matched the initials of Percival Lowell. The name Pluto was originally suggested by an eleven-year-old British girl named Venetia Burney.

Christy Discovers Pluto's Moon

Pluto has only one verified moon, Charon (pronounced "Karen"). It is named after a character in Greek mythology who ferried the souls of the dead across the river Styx to the underworld. On June 22, 1978, Charon was discovered by James Christy at the U.S. Naval Observatory in Washington, D.C. Christy was studying photographs of the planet when he noticed an odd shape in some of the images. After comparing photographs he realized that the shape moved over time compared with Pluto and the fixed stars. When the discovery was made public Christy suggested the name that was assigned to the moon. In November 2005 NASA announced that images from the Hubble Space Telescope suggested that Pluto has two additional moons orbiting far from the planet. As of December 2005 this finding had not been independently verified.