A big space crash likely made Uranus lopsided
Phys.org - Fri 21 Dec 18Uranus is a lopsided oddity, the only planet to spin on its side. Scientists now think they know how it got that way: It was pushed over by a rock at least twice as big as Earth.
How Uranus ended up lopsided: Simulations reveal collision with another planet billions of years ago, Daily Mail - Fri 21 Dec 18Uranus Was Likely Hit By a Rock Which Made the Planet Lopsided, Scientists Say
TIME - Fri 21 Dec 18The massive planet tilts about 90 degrees on its side