Why is the planet pluto the furtherest plant from the sun?

Dear Cati,

Well, I could answer that one planet has to be the furthest out and in
this case it is Pluto. However, Pluto has an eccentric orbit which
means that for about 20 years of its 249 year orbit Pluto is slightly
closer to the sun than Neptune the eighth planet.
See http://dosxx.colorado.edu/Pluto/orbits.jpg

There had been much debate about the existence of another planet
beyond Neptune following its discovery in 1846. Pluto was finally
discovered February 18th 1930 by Clyde Tombaugh and officially labeled
the ninth planet by the International Astronomical Union.

Pluto has a single moon called Charon (discovered in 1978). There is a
debate among astronomers that Pluto and Charon is a double planet.
Others argue that Pluto should be downgraded to a large asteroid or
comet for it is even smaller than our Earth’s moon.

The existence of a further planet beyond Pluto was also debated but
following information received from Voyager 2’s encounter with
Neptune, this is now generally discounted.

Please ask for clarification of the research, or if the links do not
work, before rating the answer.

Sources with images and detailed information:
http://www.solarviews.com/eng/pluto.htm
http://seds.lpl.arizona.edu/nineplanets/nineplanets/pluto.html

answerfinder-ga

Search strategy
Pluto
://www.google.com/search?hl=en&ie=UTF-8&oe=UTF-8&q=pluto

Maybe Pluto isn't the farthest planet from the sun.

Some astronomers consider Pluto to be so unlike the other planets,
especially because of the extreme tilt of its orbit relative to the
plane that the other planets' orbits are in, that it should not be
considered a planet at all. That would leave Neptune as the most
distant "proper" planet. But this opinion seems to be in the minority.

Then you have the recent (October 2002) discovery of the object named
Quaoar. This object is relatively large, though still much smaller
than PLuto, revolves around our sun, and is well outside the orbit of
Pluto. Because the tilt of its orbit is quite similar to that of the
other planets except Pluto, in that one respect it looks more like a
planet than Pluto does. You can read more about Quaoar here:
  http://news.nationalgeographic.com/news/2002/10/1003_021007_quaoar.html

So one might argue that Quaoar is the tenth planet. You will see some
of that discussion if you follow the link above.