Home > Encyclopedia of Science > Pluto

• The search for Pluto
• The properties of Pluto
• Its only moon
• The origin of Pluto
• Trips to Pluto

Pluto, the ninth and farthest planet from the Sun, is one of the least well understood objects in the solar system. It is the smallest of the major planets and has a most unusual orbit. Pluto is only 1,428 miles (2,300 kilometers) in diameter. Since the planet is 3.66 billion miles (5.89 billion kilometers) away from the Sun, it takes almost 250 years for it to complete one revolution around the Sun. However, it takes Pluto only 6.39 Earth days to complete one rotation about its own axis.

In Greek mythology, Pluto is the god of the underworld. The planet was given its name for several reason. First, due to its great distance from the Sun, Pluto is...