Newtonian gravity shows us that not only can you have nearly circular orbits, and not only can you have nearly elliptical orbits, but it admitted two new classes of orbits.

One is called a parabola, so it can go on a parabolic orbit. It comes in, let’s say, from the Oort Cloud or from the Kuiper Belt. It comes on in, it circles the sun once, and then it goes back out, never to be seen again.

You can also have hyperbolic orbits. And maybe you remember some of these terms from geometry. So you have parabolas and hyperbolas. And so, you can have a comet or an asteroid come in on a hyperbolic orbit.

Again, it comes in, goes around the sun once, and then goes on out back to the Kuiper Belt and infinity, never to return again.

So we have two types of orbits. One is called bound orbits, where it’s caught in the gravitational field, and bound orbits are things like ellipses or circles.

Unbound orbits are the parabolas and the hyperbolic orbits. They’re called this because each of the types of orbits can be taken strictly geometrically