Do we really know that?
Uranus is twice the distance from the Sun that Saturn is resulting in an orbit that takes 84 years to complete relative to Saturn's 29 year orbit. Neptune is another situation as its orbit takes so many more years to complete than Uranus' orbit.
No, they don't switch orbits, each stays in its own orbit and those orbits are not close together. You may perhaps be confusing Pluto with Neptune. While Neptunes orbit is more circular (all orbits are actually oval-ish), Pluto's orbit is highly eccentric -- an elongated oval whose close point to the Sun is just a bit closer than Neptune's orbit. However due to the great stretch in its orbit, more like a comet to some degree, Pluto takes about twice as long as Neptune to complete its circuit, Neptune taking about twice as long as Uranus, Uranus taking about 2 1/2 times as long as Saturn, etc. -- all in very rought terms.
You can go to
www.nineplanets.org/ to find out the specifics of these planets and their orbits. Dave
