I need your help on a possible (but perhaps low probability) scenario for how the distance between Earth and the moon could change: say a large object from the Kuiper Belt manages to make its way into the inner system. It passes by our moon such that its gravity changes the moon's orbit around Earth into a more pronounced ellipse. So there will be times when the moon is much closer to Earth and other times when it's further away than its current distance from Earth.

Say that this change in the moon's orbit isn't enough to cause an apocalyptic scenario for life on Earth but that the tides are of course much, much more pronounced. I surmise that the greatest impact would be felt in costal towns and cities around the world. My question is: how long would it take for the change in the moon's orbit to be felt on Earth? Are we talking almost immediately/ within the hour for some unlucky areas that are now much closer to the moon on its new orbit, and at most within 12 hours for the "luckier" areas? Or would the time frame be much longer?

Thank you in advance for any insights you could offer on this.

  • $\begingroup$ I think this question is simply too broad: there are a practically infinite number of ways in which the moon's orbit can be perturbed, and the time-scale of the effects on Earth will depend on the exact nature of the perturbation. Gravitational effects propagate at light speed so in a strict physical sense Earth would be affected in 1.3 seconds, but you seem to be asking something more along the lines of "when would the effects become noticeable/significant" which (as stated) is impossible to answer in general. $\endgroup$ – Pont Oct 10 '17 at 6:41

The moon's orbit might have changed, but obviously it would take some time before this would become visible. The moon's position iself would probably not be that affected by the event as its inertia is too huge. So the tides would probably not be noticeably affected in the first hours.

I have no idea really how long, but it might not take too long before, depending on what point of its new, elliptical orbit the moon is now positioned - is it now approaching earth, or more or less staying at the same distance, or to the contrary getting farther away - the tides will start to be affected.

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