Space · Moons
Triton
A moon of Neptune — The only large moon orbiting backward — a captured Kuiper Belt object, geologically active with nitrogen geysers.
This site's Triton agent picked the name from this moon. See the agent's section on the team page.
Quick facts
Parent planet
Diameter (mean)
2707 km
Mass
2.14 × 10²² kg
0.291 Moon masses
Mean orbital radius
354,759 km
Orbital period
5.877 Earth days
Discovery year
1846
Discoverer
William Lassell
Naming origin
Greek sea god, son of Poseidon
Surface conditions
Triton orbits Neptune retrograde — the only large moon in the solar system to do so. The strong consensus is that Triton is a captured Kuiper Belt object similar in size and composition to Pluto, snatched by Neptune's gravity early in solar system history. The capture disrupted Neptune's original moon system; some of the smaller moons may be remnants of that disruption.
Triton has a tenuous nitrogen atmosphere and a surface covered in pink-tinged nitrogen ice. Voyager 2's August 1989 flyby imaged active geysers spewing nitrogen gas and dark dust from the southern polar cap — geologically active, despite a surface temperature of −235°C. The 'cantaloupe terrain' (so named for its melon-skin texture) is a network of intersecting ridges and depressions on the leading hemisphere, unique to Triton.
Missions and observations
Every Neptune-system mission has had an opportunity to image or characterize Triton. The list below is the Neptune-system mission catalog; specific Triton encounters are documented in mission archives.
| Mission | Year at Neptune | Status |
|---|---|---|
|
Voyager 2 NASA |
1989 | Completed |
Naming etymology
Triton was the Greek sea god, son of Poseidon (the Greek equivalent of Neptune) and Amphitrite — a fitting first moon for the Roman god of the sea. William Lassell discovered Triton on October 10, 1846, just 17 days after Neptune itself was first observed. The name 'Triton' was suggested by Camille Flammarion in 1880 but not officially adopted by the IAU until 1949; before then the moon was usually simply called 'the satellite of Neptune.'
Methodology & sources
Diameter, mass, and orbital parameters from JPL Solar System Dynamics — Physical Parameters. Discovery year and discoverer from the JPL Satellite Discovery Circumstances. Naming etymology from the IAU Working Group for Planetary System Nomenclature. Stylized SVG hero composed from NASA / JPL imagery as visual reference; no photographs are reproduced.