Formerly the smallest planet in the Solar System. In August 2006 the International Astronomical Union redefined the term 'planet'. Now Pluto is classified as a dwarf planet.
Pluto is a small rocky object that lies at the very edge of the solar system. The planet is so far out it takes light from the sun about 5 and a half hours to reach Pluto in contrast to the 8 minutes it takes to reach Earth.
Its orbit of about 248 years sometimes takes it inside Neptune’s orbit. Pluto is so cold that nitrogen and oxygen, which we breathe so easily on Earth, become frozen solid.
The planet is only about two-thirds the size of our moon and up until recently was the biggest known object in the Kuiper Belt (an asteroid zone).
Pluto is the ninth, or last, planet in the solar system. The orbit, or path the planet takes around our Sun is an ellipse, or stretched out circle. For this reason there are times when Pluto is the furthest away from the Sun.
There are also times when it is closer to the Sun than Neptune. Right now, Pluto is the furthest planet. Pluto is a very long way from the Sun. Its average distance from the Sun is over 3.5 billion miles.
The closest Pluto gets to the Sun is over 2.7 billion (2,700,000,000) miles, and the furthest away it gets is over 4.5 billion (4,500,000,000) miles.
Pluto was discovered in 1930 by astronomer Clyde Tombaugh. After Neptune was discovered, astronomers noticed that something was changing the orbits of Uranus and Neptune and decided that there must be another undiscovered planet that was causing these changes. Mr. Tombaugh spent a long time taking photographs of the area of the sky where the unknown planet should be and finally discovered Pluto in one of the photographs.
Pluto is the Roman god of darkness and the underworld. Perhaps Pluto got its name because it is always in darkness.
It may have also gotten its name from the fact that its symbol "PL" are the initials of Percival Lowell, who founded the observatory where Mr. Tombaugh worked.
Pluto is the only planet in our solar system that we have not explored with a spacecraft. What we know about the dark, frozen world is the result of many years of work by dedicated scientists here on Earth. The current studies tell us that Pluto is made up of a mixture of rocks and several kinds of "ices". Scientists believe that most of the ices that make up Pluto are frozen methane and ammonia.
The surface of Pluto is very dark and extremely cold. Since the planet is so far away from the Sun, it gets almost no light or heat. Scientists believe that the temperature on the surface of the ninth planet is over 250 degrees celsius below zero.
At this low temperature, almost everything freezes solid. Scientists here on Earth have determined that Pluto does have a very thin atmosphere, but it is far too thin to support any kind of life.