Axial Tilt of Uranus

Every other planet spins more or less upright as it orbits; Uranus lies on its side. At 97.77° the axis points past the perpendicular, so the planet effectively rolls around the Sun, offering first one pole, then its equator, then the other pole to the light across its 84-year orbit. The moons and rings share the tilt exactly, orbiting in the equatorial plane like a bullseye when a pole faces Earth — which is the central clue: whatever tipped Uranus happened early, before or during the assembly of its satellite system.

The standing explanation is one or more giant impacts by Earth-sized bodies in the young solar system, though a slower alternative — a resonance that pumped the tilt while a massive early moon was later lost — remains alive. Strangest of all, the extreme geometry barely shows in the climate: sluggish heat transport smooths the 42-year polar days and nights into temperature differences of only a few kelvin.