Axial tilt
Uranus: Uranus, the blue planet, rotates on its side. One result of this axis orientation is that, averaged over the Uranian year, the polar regions get more energy from the Sun than its equatorial regions. Nevertheless, Uranus is colder at its poles than at its equator. What causes this is unknown. The reason for Uranus's unusual axial tilt is also not known for sure, but the usual idea is that during the formation of the Solar System, an Earth-sized protoplanet collided with Uranus, causing the skewed orientation.