Uranus, the ice giant with a unique tilt, has long been a subject of fascination and mystery. The planet's 97.77-degree axial tilt, which is nearly perpendicular to its orbital plane, has led to numerous theories about its origin. The leading explanation is a giant impact, but the complexity of the Uranian system makes the mystery harder to unravel. The planet's rings, regular moons, and magnetic field all share the same sideways orientation, adding to the intrigue. The moons, in particular, provide powerful circumstantial evidence that whatever changed Uranus also reshaped its inner satellite system. A 2022 study explored a different route, suggesting that a substantial ancient moon migrating outwards could have changed the rate at which Uranus's spin axis precessed, allowing the planet to become trapped in a gravitational resonance. This scenario still ends with an impact, but not the traditional random strike by a passing planet-sized body. Most of the tipping happens gradually through gravity, with the lost moon's final collision fixing the result. NASA's Hubble overview of Uranus' seasons lists this alongside giant impacts and resonant torques from other giant planets. The tilt turns an 84-year orbit into extreme seasons, with one pole pointing towards the Sun while the other points away. The rings rotate into radically different viewing angles over the same orbit, and the seasonal polar cap has brightened as the northern pole has turned towards the Sun. Voyager 2, the only spacecraft to have visited Uranus, sampled one geometry during one season, leaving an entire history to infer. The familiar collision story should remain a hypothesis, as neither a giant impact nor a migrating lost moon has left a surviving impactor, timestamp, or unique signature that closes the case. Uranus was not literally knocked over in the sense that it once had a universal 'up'. Planets inherit spin from formation and then have that spin rewritten by collisions, migration, and resonance. What makes Uranus special is that the rewriting is still visible across the whole system: in the planet, the seasons, the rings, and the moons all circling on the same improbable plane.
