Asked by: Finn Gape, Kent
The reason for this is not known for sure. The most likely cause is that Uranus collided with a large object soon after its formation. The problem with this explanation is that if the planetary system were disrupted by a single impact it would result in the moons of Uranus having ‘retrograde’ orbits (orbiting in the opposite direction to the spin of the planet). However, this is not what is observed. Encouragingly, the latest research suggests that two or more impacts with Earth-sized protoplanets could result in exactly the kind of orbits displayed by Uranus’s moons.