Pluto's orbit lies in a different plane from all the other planets.

It probably consists of a core of icy rock covered by a thick layer of water ice. The surface is reddish in color and contains frozen methane, nitrogen and carbon monoxide. There is a thin atmosphere.

The following information was kindly contributed by Russell Odell.

Pluto is the black sheep of the solar system. Astronomers ignore it. It is the only planet in the solar system that lacked the importance of being visited by a space probe. Because of its large size moon, Charon, in relation to the size of the planet itself, some are apt to call it a "double planet".

Charon is about half the size of the planet. Moons are always much smaller than the planet they orbit. As an example, our moon is about one fourth the size of our earth. The moons of Jupiter, Saturn and Neptune are much smaller than their respective planets.

Some speak of Pluto and Charon as odd ball satellites of Neptune that somehow, broke loose from Neptune's gravitational domain.

It took many years of intense research to find Pluto. Astronomers knew there was another planet out there but they couldn't find it. It began in earnest when the astronomer Percival Lowell who built, at his own expense, an observatory, because he was obsessed he could find life on the planet Mars. He died in 1916 without finding life on Mars or the missing planet.

Clyde Tombaugh, a 22 year old farm boy from Illinois, with no formal training, came to work as a temporary employee at the observatory. He stayed for 13 years. It was he, who on February 18, 1930, located the missing planet. It took the observatory until March 13, 1930, to announce the discovery to the world. That date, was the birthday of Percival Lowell.

Pluto is a tiny planet, only a dim speck of light reflected off the sun, 3,667,000,000 miles (5,913,520,000 km) away. Its diameter in 1976 was calculated to be 3,700 miles. In 1980 it was recalculated to only 1,800 miles. With further research in 1990, the diameter was found to be only 1,404 miles. The smallest planet in the solar system. The Lilliputian planet of the universe. Its moon Charon, has a diameter of a little less than 790 miles. Through most telescopes Pluto appears as a yellowish point of light. The 200 inch scope at Palomar sees it as a very small disk.

Pluto rotates on its axis once in 6.39 days. It is thought that, like Venus, it rotates retrograde (clockwise). Its temperature is minus 400ºF. Being so far from the sun it receives about 1/1600th the amount of heat and light that the earth does. Light traveling at 186,000 miles per second takes nearly seven hours to reach the planet. Pluto and Charon are two of the coldest bodies in the solar system. Charon is very close to Pluto, about 12,200 miles. They are so close it is thought they share the same common atmosphere of frozen nitrogen, carbon monoxide and methane. Pluto orbits the sun at 2.9 miles per second (10,140 m.p.h.), the slowest of all the planets and takes 248 years to complete its orbit.

All the planets have nearly a circular orbit around the sun, but Pluto's is more oval, and at times, it is closer to the sun than Neptune. Because of it oval orbit, it even swings through Neptune's orbit.

The reason the two planets never collide is because Pluto's orbit is 1.5 times greater than Neptune's. Because of this, the two planets will never get closer than 250 million miles.

Useful Links

Buy links to your science site