Why do Venus, Uranus and Pluto have retrograde rotation?
The only ideas we have are that soon after, or even during their formation process, there were lots of very large bodies orbiting the Sun. Some relics of these objects survive today in the satellites and asteroids that measure from 400 to 2000 kilometers in radius. Every large body with a solid surface we have looked at so far, shows the scars of enormous ancient impacts by bodies many hundreds of kilometers across. Presumably, during the last age of planet formation, there were many such impacts and these may have been the ones that tilted some of the planets to their current orientations. Retrograde rotators have had their ‘north poles’ tilted by more than 90 degrees so that their south poles are now pointed into the hemisphere where the earth’s north pole is. The planets may have originally all rotated in the same direction, but with such extreme tilts, their rotation now proceeds in the opposite directions.
