Evolution of Uranus' spin-axis caused by a large moon (Gwenael Boue/Jacques Laskar)

Has the Mystery of Uranus' Tilt Been Solved?

Uranus orbits the sun on its side. Although the consensus is that the gas giant must have collided with something to make it this way, two researchers have modeled Uranus getting "wobbled" by a large moon, tugging it off axis.