3) Pluto is the biggest survivor of Neptune's wrath.
Still, even if they never physically smack into each other, Neptune's a big planet with a lot of gravity. How come it hasn't drawn Pluto in over all that time?
It's because of an odd fact about Pluto: it orbits the Sun twice for every three times Neptune goes around (this type of thing is called a 2:3 resonance) -- about 248 years for Pluto versus 165 for Neptune. This, together with its tilted orbit, means that it never really gets very close to Neptune. Every time Pluto is at its closest to the Sun, Neptune is 1/4 of the way away around its orbit! A really weird consequence of this is that
Pluto actually gets closer to Uranus than it can to Neptune!
But there's another conclusion we can draw too. You might think it's a huge coincidence that Pluto appears to avoid Neptune in its resonant orbit. But it's not coincidence. Imagine the solar system about 4.5 billion years ago. There may have been thousands, millions of icy balls orbiting the Sun near Neptune's orbit. But ones that were just inside or just outside Neptune's orbit would eventually interact with it, and get tossed into deep space, or dropped closer in to the Sun. Essentially, Neptune cleaned out any objects with orbits it didn't like.
But Pluto was safe! Its orbit never took it close enough to Neptune, and it survived the massacre. In fact, there are many objects in orbits similar to Pluto's; these are called
plutinos in honor of their largest member,
and quite a few have been discovered. Two of them are marked on the image above for your edification. Yes, Pluto is a plutino. I prefer the name Plutoid, but I didn't get a vote.