Far beyond the reach of the terrestrial and gas giant planets in our solar system exists an entirely different class of world known as ice giants. Uranus and Neptune are among this distinct class of chilly worlds, and astronomers have long been challenged to make close-up observations of these planets due to their sheer distance from the Earth. The closest we ever got was NASA’s Voyager 2 mission in the 70s, and it uncovered some particularly captivating details regarding Neptune’s largest natural satellite: Triton.
Triton is interesting because of its sheer size compared to other lunar bodies, and in the Neptunian system, it actually comprises of 99% of the lunar mass, with the other 1% being comprised of the rest of Neptune’s moons. The Voyager flyby also revealed what appeared to be frozen nitrogen and geysers erupting from the surface, which indicates some sort of geological activity from within.
Thanks to these geysers, Triton actually sports an atmosphere made almost entirely out of nitrogen. Albeit thin, the atmosphere is robust enough to support clouds, which are observable from up above. We can even observe winds on this distant world as those clouds are carried across the sky.
Another thing that makes Triton interesting to astronomers is its unique rotational pattern. While it appears tidally locked to Neptune just like the Moon is to Earth, it’s worth noting that Triton actually rotates in the opposite direction with regard to its parent planet. This observation, along with its unusual angle, gave rise to the idea that Triton may have once been a world in and of itself and was later stolen from space by Neptune’s gravitational influence.
Perhaps future missions will provide more insight into Triton’s unusual occurrence, but until now, its origins remain a mystery.