I'm of the opinion that there used to be a planet between Mars and Jupiter. The math says there should be one there, but all we have is an asteroid belt (the only place we have one). I say that whatever caused the planet to breakup sent debris in many directions which became some of the moons that we see around the larger planets (especially those with bizarre orbits) as well as creating Pluto and it's "moons."
Although I have not heard of anyone confirming it, supposedly someone spun all the planets back in time until all of their heaviest cratered sides were aligned to where the missing planet would have been. This time was about 12,500 years ago, a number that pops up in lots of places and, possibly, the time when the Earth was tilted giving us seasons (it took the Space Shuttles to see that, under miles of ice, the geography of the Antarctic matched very old maps that were found and that there are entire forests under the ice that were obviously frozen VERY fast). It all makes for some interesting theories!