Pluto's Eccentric Orbit
Pluto's orbit sometimes takes it within the orbit of Neptune. The last occurence of this was from 1979 to 1999. Pluto is also orbitally locked to Neptune. This means that it takes exactly 1.5 times longer than Neptune, and crosses orbits at roughly the same point each time, therefore the two planets will never collide if nothing interrupts their orbits. Even if this was not the case, the odds against such a collision would be astronomical, due to the vast distances and times involved. Pluto's orbit is curious in two other respects. Firstly its orbit does not lie in the same plane as the other planets and secondly the plane of Pluto's equator is at almost exactly right-angles to the plane of its orbit, which is a similar situation to that of Uranus.