Triton is Neptune’s largest moon, orbiting backwards around its planet, almost certainly a captured Kuiper belt world with active geysers of nitrogen gas.
At a glance
| radius | 1,350 km (0.212 × Earth) |
|---|---|
| distance from its planet | 355,000 km |
| one orbit | 5.88 days |
| reflects | 76% of the sunlight it gets |
Read off the piece’s own catalogue, the same values it draws with.
About Triton
Triton is the only large moon in the Solar System that orbits opposite to its planet’s spin. A moon formed alongside its planet would not move that way, so Triton is thought to have been captured, probably a dwarf planet from the Kuiper belt, close kin to Pluto. William Lassell discovered it very soon after Neptune itself was found.
Voyager 2 flew past and found one of the coldest surfaces known, frozen nitrogen with a thin nitrogen atmosphere, a wrinkled region nicknamed the cantaloupe terrain, and dark streaks laid down by plumes rising from geyser-like vents. Few impact craters mean its surface is geologically young.
Because it orbits backwards, the tides it raises on Neptune slowly pull it inward. In the far future it is expected to be torn apart, perhaps forming a ring around the planet.
What you see in the piece
Triton’s bright frost reflects most of the faint sunlight that reaches it at Neptune’s distance, so it shows beside the planet as a small pale disc when you are close. From another star it cannot be seen at all.
Measured or modelled
Triton’s capture from the Kuiper belt is inferred from its backward orbit and is the accepted explanation, but how it happened, and how its orbit later settled, is modelled.
Questions
Why does Triton orbit backwards?
Because it was most likely captured by Neptune’s gravity rather than formed alongside the planet. A captured body can end up orbiting in either direction.
Does Triton have geysers?
Voyager 2 saw plumes rising from its surface and dark streaks laid down by them, thought to be nitrogen gas vented from beneath the frozen surface.