Triton
What is Triton?
Moons· Diameter 2,707 km. Neptune's large moon that orbits backward, thought to be an object captured from outside. Even at −235 °C, geysers of nitrogen gas erupt from its surface.
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Orbit and size
| Diameter | 2,707 km |
|---|---|
| Parent | Neptune |
| Note | retrograde — a captured body |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Parent planet and sibling moons
Triton's cantaloupe terrain
The western hemisphere that Voyager 2 photographed is packed with dimples about 30 km across. Because it resembles the skin of a cantaloupe melon, it is called 'cantaloupe terrain'. The dimples are not impact craters: they are too even in size and never overlap. Scientists read them as the marks of heavier and lighter layers under the icy crust slowly trading places and pushing the surface up. No other body has yet been found with this pattern.
Triton was discovered on 10 October 1846, just 17 days after Neptune itself, by William Lassell in England. Lassell was an amateur astronomer who built his own telescope and observatory with money earned from brewing beer. The French astronomer Camille Flammarion proposed the name Triton in 1880, but for a long time the moon was simply called 'the satellite of Neptune'. The name came into general use only in the mid-twentieth century, after the second moon, Nereid, was found.
Triton's atmosphere is nitrogen, but it is so thin that it presses on the ground with about one seventy-thousandth of Earth's air pressure. No new mission to Triton has been approved. The Trident spacecraft, a NASA candidate in 2020, was not chosen in the final selection of 2021. Voyager 2's pictures from 1989 remain the only close-up view of Triton.
The moon in depth
Triton is the only large moon in the solar system that orbits in the opposite direction to its planet's spin. A moon born together with its planet would circle the same way. So scientists think Triton was once an object orbiting the Sun in the Kuiper Belt beyond Neptune, and was later captured. Its size and makeup, which are similar to Pluto's, support this idea.
When Voyager 2 flew past in 1989, it measured a surface temperature of −235 °C, among the lowest ever measured anywhere. Even so, Triton was not quiet. Voyager photographed geysers in which nitrogen gas carried dark dust up to 8 km high. The discovery showed that activity can happen even on such a cold world.
Its backward orbit also decides Triton's future. Neptune's gravity is slowly pulling it inward, and calculations show that in a few billion years it will come so close to Neptune that it breaks apart. The pieces could then form a ring around the planet. Zooming in on Neptune in the orbit view shows Triton circling the opposite way to the other moons.
Frequently asked
- How big is Triton?
- The diameter of Triton is 2,707 km.
- What is notable about Triton?
- The note of Triton is retrograde — a captured body.
- Which planet does Triton orbit?
- Triton orbits Neptune.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.