What theory explains why the Uranian system is on its side?

Astronomers have always assumed that Uranus must have been knocked onto its side by a collision. Now a new idea suggests that the planet's remarkable tilt could have another explanation.

Explanation:

I just know it

Astronomers have always assumed that Uranus must have been knocked onto its side by a collision. Now a new idea suggests that the planet’s remarkable tilt could have another explanation.

by Emerging Technology from the arXivarchive page

December 3, 2009

One of the great mysteries of our Solar System is why Uranus is tilted on its side. Surely, if the solar system formed from the same rotating cloud of dust and gas, then all the bodies within it should rotate in the same way. And yet Uranus’ axis of rotation lies at 97 degrees to the plane of the solar system.