Eccentric Orbits
Eccentric Orbits are based on planets that do not follow a circular motion as planets do in our solar system. In other words, an alien planet may come very close to its' star and then circle out to be very far away from it. This gives an interesting view to see how unique is our solar system. Scientists are only now discovering that Eccentric Orbits are the more common form of solar orbit and ours is very unique.
Scientists are now finding many planets. Many of the planets have eccentric orbits. As well, they are finding many that orbit much closer to their sun than mercury. We are indeed a unique solar system. How unique? Well, it will be years till be find out. We haven't even scratched the surface in looking for planets. Time will tell if we are the norm or the exception or somewhere in between.