William R Somsky <wrsomsky@gmail.com> wrote:

Well, your "bouncing" planet only occurrs w/ point-like planets and sun which can pass through each other, so it's understandable that that is not normally considered.

Also, assuming it's a true radial orbit rather than an ellipse too narrow to see with my screen resolution, if the planet could pass through the sun it wouldn't bounce or whip around, it would leave the far side with the same speed it entered the near side, and its orbit would be bilaterally symmetrical. Of course I'm assuming that neither the sun's mass nor the planet's mass are concentrated at a point. If they are concentrated at a point, and the points collide, the program gets a division by zero error and terminates. Or the Runge-Kutta numerical simulation is swamped by noise and gives unpredictable results.

Any eccentricity zero orbit w/ non zero perihelion we'll be an escaping parabolic path.

No, an eccentricity zero orbit is a circle. I'm still curious as to how far out Earth's orbit can be gradually moved (to save us from the sun's red giant stage) before resonances with other planets increase eccentricities and cause planetary collisions or expulsions. We may need to move all the planets simultaneously.