It has to do with the total angular momentum of a system composed of multiple smaller bodies. (Like the dust/debris cloud during solar system formation) This m

It has to do with the total angular momentum of a system composed of multiple smaller bodies. (Like the dust/debris cloud during solar system formation) This minute physics video (about the shape of the solar system) explains it probably better than I can put into words myself: http://www.youtube.com/watch?v=tmNXKqeUtJM http://www.youtube.com/watch?v=tmNXKqeUtJM The relevent part starts at about 1:03, but I recommend watching the whole thing.