triton

Triton orbits Neptune backward, spews nitrogen geysers from a surface colder than anywhere else in the solar system, and is gradually spiraling toward a catastrophic end. It almost certainly came from the Kuiper Belt — and its violent capture may have reshaped the entire Neptunian system.

Uranus and Neptune are the outermost planets in the solar system — massive worlds of water, methane, and ammonia ice that defy easy classification. Uranus spins on its side and is mysteriously cold, while Neptune radiates twice as much heat as it receives and harbors a giant storm. Both remain almost entirely unexplored.