Gravitational Perturbation - How does it work?

[Bjarne]

It is easy to understand for example how Jupiter pulls (perturbation) the orbit of the Earth more elliptic.
But after a certain period the orbit will again be more circular.
How does that (the opposite) work ?

 

[Drakkith]

What exactly are you asking? How gravitational interactions cause an orbit to become unstable? It's simply that an object gets too close to another object and it's gravitational pull causes a large change in the orbit that cannot be corrected naturally. Was that what you were looking for?

 

[Jonathan Scott]

It is easy to understand for example how Jupiter pulls (perturbation) the orbit of the Earth more elliptic.
But after a certain period the orbit will again be more circular.
How does that (the opposite) work ?

If you have two bodies like Jupiter and the Earth orbiting the same source in near-circular ellipses with different orbital periods, then there will be systematic interaction effects depending roughly on the points in the orbit where they are closest to each other. If the relative orbital periods mean that these points of closest approach tend to occur near particular points in the Earth's orbit for several consecutive orbits, then this creates a systematic effect which tends to lift or drop some parts of the orbit. If the lifting effect occurs at a high point in the orbit, that will make it more elliptical, but if it occurs at a low point it will make it more circular. As the relevant orbits are not very far off circular, the overall effect makes the orbit sometimes more circular than average and sometimes more elliptical.