Cosmic Scale
Triton
Moon of Neptune · 4.5 billion km from the Sun
How big is Triton?
Triton is about 2,707 km across.
See Triton in 3D, at true scale
Triton orbits Neptune backwards, which almost certainly means it did not form there: it is a captured object from the Kuiper Belt, seized by Neptune's gravity. Voyager 2 flew past in 1989 and found nitrogen geysers erupting from one of the coldest surfaces ever measured.
At a glance
| Diameter | 2,707 km |
|---|---|
| Mass | 2.14 × 10²² kg |
| Diameter compared with Earth | 0.212 × Earth |
| Orbits | Neptune, backwards, every 5.9 days |
| Surface | −235 °C |
| Atmosphere | Thin nitrogen |
| Discovered | 1846, 17 days after Neptune |
Good to know
- Its retrograde orbit is slowly decaying; in a few billion years Neptune's tides will tear it into a ring.
- Geysers throw nitrogen gas and dust 8 km up, where winds smear them into dark streaks.
- Only about 40% of its surface was mapped by Voyager 2. No spacecraft has been back.