>>15302305
>Proto-Uranus rotating on a more typical axis compared to the ecliptic (a few degrees of tilt)
>Protoplanetary object, a few Earth masses, approaches proto-Uranus
>due to slight difference in inclination of orbits, the smaller object enters Uranus near its north or south pole (completely normal for solarsystem objects to do this)
>encounter velocity is slow, but the gravity of both objects accelerates them into each other at over 13 km/s
>impact occurs, and the protoplanet merges with proto-uranus, resulting in its incoming kinetic energy being converted into heat and rotational energy
>result is that Uranus now has an axial tilt of about 90 degrees
Hope this helps. Uranus never "tipped over", it was spun along a different axis due to a giant impact event.