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Re: Impacts and ETs

Tip over? Uranus currently has an inclination of almost 90 degrees. Do you
mean like that? Or our inclination stays the same while "tipping"?

Yes, sorry, I confused that in my last post. Polar wander is meant -- the process in which the angle between the Earth's rotation axis and the ecliptic stays the same. Rotating bodies are most stable when the mass is concentrated on the equator. Various processes (continental drift, reorganizations of mantle and core...) change the mass distribution of a planet, giving it a reason for fast and far polar wander.* The attraction of the Moon is greater than all such imbalances that the Earth can produce in itself, and therefore polar wander on Earth is either nonexistent or exceedingly slow.**

* The university library over here has an extraordinarily ignorant book from the 50s (read: before plate tectonics was discovered). The author did not accept continental drift and tried to explain all of geology and paleontology, especially the mass extinctions (including the frozen mammoths & stuff), by a series of catastrophic polar jumps.
** I don't know what has become of the idea, published last year or so, that polar wander on the scale of 16 to 20° happened in the Campanian -- taking two million years.