Triton🌙

Triton is the largest moon of Neptune and one of the most unusual moons in the Solar System, discovered in 1846 only weeks after Neptune itself. It is a huge icy world about 2,700 kilometers wide—almost the size of Earth’s Moon—but with a very different history. Triton orbits Neptune in a retrograde direction, meaning it moves opposite to the planet’s rotation, which is extremely rare and strong evidence that Triton was captured long ago from the distant Kuiper Belt instead of forming with Neptune.

Triton’s surface is incredibly cold, around –235°C, and covered in frozen nitrogen, methane, and water ice, giving it a smooth, bright, sometimes slightly pink look. Even though it is freezing, Triton is active: Voyager 2 discovered geysers that shoot nitrogen gas high into the sky, along with smooth plains, deep cracks, icy cliffs, and the strange bumpy “cantaloupe terrain” found nowhere else in the Solar System. Triton even has a thin atmosphere made mostly of nitrogen—unusual for a moon—and this atmosphere changes slightly with Neptune’s long seasons.

Many scientists think that under Triton’s icy crust there could be a liquid ocean kept warm by tidal forces and leftover heat, which raises the possibility that it could support simple forms of life. Because Triton was captured, its orbit is slowly shrinking, and far in the future it may be torn apart to create a new ring around Neptune. Since only Voyager 2 has ever visited it, Triton remains a mysterious and exciting world that scientists hope to explore again someday.