Why are cometary orbits elliptical instead of circular?

Also, I was wondering whether the orbit of a comet can change over time and if so, which factors cause such a change. or:Also, I was wondering whether

Also, I was wondering whether the orbit of a comet can change over time and if so, which factors cause such a change.

or:Also, I was wondering whether the orbit of a comet can change over time and if so, which factors cause such a change.

or:If you analyze the gravitation, speed, and so forth, your equations eventually reduce to an ellipse. It is rather difficult to get a satellite into an exactly circular orbit. It's not only comets, it's all orbiting bodies.Orbits might change for various reasons. There are two moons of Saturn that share the same orbit. As one catches up to the other, gravity increases the speed of the one behind and slows the one in front. The one behind rises to a higher orbit, which takes longer to complete, and the one in front falls to a lower orbit, which completes faster. So the one ahead races away and the one behind falls farther behind, until they meet again from the opposite directions. www.google.com/search?q=two+moons+in+same+orbit

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