Pluto is the smallest planet in this solar system and only has a diameter of 1,440 miles (2,320km). Because of its size and orbit, many astronomers doubt the fact that Pluto is a planet and until more can be learned about Pluto, it will continue to be debated. William Pickering and Percival Lowell in 1905 believed that a ninth planet must exist because of the irregularities in the orbits of Neptune and Uranus. However, Pluto wasn't discovered till 1930 by Clyde Tomsbaugh and even then, he found Pluto was too small to have an effect on the orbits of Uranus or Neptune.

Since Pluto is so far away, approximately 7.5 billion kilometers away from earth at its maximum distance, it has been almost impossible to view Pluto from Land based telescopes. The atmosphere on earth prevents telescopes on earth to view Pluto accurately. However, with the help of the Hubble telescope in outer-space, Pluto can be seen more clearly. The most noticeable feature on Pluto is the north pole which is covered by what is believed to be byproducts of the methane and nitrogen in Pluto's atmosphere. Pluto has never been explored by any human made satellites and even Voyager 2 which has already flown out of this solar system never reached Pluto.

Pluto also has an unusual orbit. Pluto can be considered both the ninth and eighth planet because the orbit of Pluto overlaps the orbit of Neptune. This occurs because Pluto's orbit is very elliptical and has a 17.2 degree orbital plane inclination from the solar system. As a matter of fact, Pluto is currently closer to the sun than Neptune is and will be until 1999. It takes Pluto more than 248 earth years to orbit the sun once.

SATELLITES

Surprisingly, Pluto has one known moon called Charon. Charon is about 790 miles (1,270km) in diameter and was also discovered during an occultation. Most unusual of all, it is believed that the methane-nitrogen atmosphere on Pluto is shared by Charon. It is also believed that Charon could be a planet since it is more than half the size of Pluto and has a high mass ratio. This is proved by the fact that the center of gravity on Pluto is actually in the space between Pluto and Charon.

Pluto and its satellite Charon as taken with ESA's Faint Object Camera on the Hubble Space Telescope.  This is the clearest view yet of the distant planet Pluto and its moon, Charon, as revealed by NASA's Hubble Space Telescope (HST). The image was taken by the European Space Agency's Faint Object Camera on February 21, 1994 when the planet was 2.6 billion miles (4.4 billion kilometers) from Earth.

DOWNLOAD THIS MOVIE!

Click here to download this movie of the Pluto Express Spacecraft making an expected flyby around Pluto and Charon (1.05Mb).

If you want to view this page in a new window, click here.