Changes

Pluto has an elliptical orbit.  It is usually further from the sun than any of the eight planets, but there are times due to its odd orbit when it is closer than [[Neptune]].<ref>http://science.jrank.org/pages/5352/Pluto.html</ref>

Pluto has an elliptical orbit.  It is usually further from the sun than any of the eight planets, but there are times due to its odd orbit when it is closer than [[Neptune]].<ref>http://science.jrank.org/pages/5352/Pluto.html</ref>

== Problems for evolutionary theory ==

== "Moon of Neptune" hypothesis ==

Pluto was initially supposed to have been a [[moon]] of [[Neptune]]. But with the discovery of [[Charon]] in 1978, and the subsequent discoveries of its other moons [[Hydra (moon)|Hydra]] and [[Nix]], that theory became far less plausible.

Pluto was initially thought to have been a [[moon]] of [[Neptune]]. But with the discovery of [[Charon]] in 1978, and the subsequent discoveries of its other moons [[Hydra (moon)|Hydra]] and [[Nix]], that theory became far less plausible.

 

Another hypothesis has held that Pluto entered the [[solar system]] from outside, and the [[Sun]] captured it. But if such a mass dived into the solar system from outside, then it would have followed a hyperbolic path. That it did not pass back ''out'' of the solar system to complete the hyperbola begs explanation.

== In popular fiction ==

== In popular fiction ==