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I wonder what would happen if an object in orbit were to be pushed outwards. I can imagine 2 outcomes: either it would keep spinning outwards away from whatever it is orbiting at a finite speed determined by the force that pushed it (the orbit growing longer and longer as the distance is growing) or it would move away from the object it is orbiting a finite length and then stabilize in orbit at an unchanging distance. Which of these would happen if it is not a third outcome?

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  • $\begingroup$ Could you be more specific on the way in which the object is pushed outward. Continuously with a constant force, a single, short push with a defined change in momentum ... this has a strong influence on the outcome. Also note that there is a third outcome: The object could enter an exit trajectory, leaving the gravitational binding of the orbited object. $\endgroup$ – Sebastian Riese Sep 7 '15 at 18:01
  • $\begingroup$ I was thinking of a short push or at least no force strong enough to make it leave the orbit. But I understand now that the result of it would be an elliptic orbit. $\endgroup$ – Malthe Andersen Sep 7 '15 at 18:08
  • $\begingroup$ That's right. It kind of bounces. To achieve a higher orbit you need to push the object along, not up. $\endgroup$ – John Duffield Sep 7 '15 at 18:43
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If, say, a comet slammed into it to push it outwards for a second then it would move on a new elliptical orbit with the sun at one focus and whip around that ellipse until it came to the same position having the same velocity as it had right after the comet hit it.

The new velocity at that point would just be part of the new and elliptical orbit.

So it does not mean anything that this motion will be about 90 degrees on the object's movement at that exact moment? My second interpretation is true then; that it will have a new orbit a little big bigger than before?

The velocity won't be entirely outwards unless the push had some backwards as well as outwards. So it will move on a ellipse. An ellipse has a part of the orbit where it is closer to the sun and a part where it is farther from the sun.

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  • $\begingroup$ So it does not mean anything that this motion will be about 90 degrees on the object's movement at that exact moment? My second interpretation is true then; that it will have a new orbit a little big bigger than before? $\endgroup$ – Malthe Andersen Sep 7 '15 at 17:16

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