Wandering Gas Giants and Lunar Bombardment

--- Outward migration of Saturn might have triggered a dramatic increase in the bombardment rate on the Moon 3.9 billion years ago, an idea testable with lunar samples.

Written by G. Jeffrey Taylor
Hawai'i Institute of Geophysics and Planetology
posted August 24, 2006

Actually any appreciable change in the orbit of any of the four gas giants will inevitably cause a cataclysmic bombardment through "resonance sweep".
A small body cannot be stable in an orbit that is in resonance with a gas giant, so if a gas giant changes orbit a number of these "forbidden zones" will move with it and "sweep" the asteroid and Kuiper belt ejecting large numbers of objects into excentric orbits.

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