Triton is one of Neptune’s moons. It was discovered in 1846 by the British astronomer William Lassell.

Diameter: 2.71 x 106 m
Mass: 2.14 x 1022 kg
Composition: Nitrogen, water-ice, methane, carbon dioxide
Orbit: 3.54 x 106 m from Neptune

Triton is the largest of Neptune’s moons and the 7th largest moon in the Solar System. Neptune has 13 known moons. 6 are regular satellites with orbits in the same direction as the spin of the planet and there are 7 that orbit in the opposite direction to the planet’s spin.

Neptune’s moons take their name from Roman and Greek water gods because of Neptune’s (Poseidon’s) position as the god of the sea. Triton was the son of Poseidon and the messenger of the ocean. The name was first proposed by French astronomer Nicholas Camille Flammarion, though it was not adopted by the International Astronomical Union (IAU) until the 1950s.

Triton is composed of a frozen nitrogen crust and an interior of water-ice, carbon-dioxide ice and some frozen methane and carbon monoxide. There may be surface ammonia and ammonia hydrates. The moon is coloured red as a result of tholins. These are organic compounds created by the ultraviolet irradiation of ethane and methane. There may be a small rocky core and a liquid water layer in the interior. Heat from the radioactive decay of the rock may cause convection currents within Triton’s mantle.

Triton has a relatively flat surface, though there are features such as ridges, furrows, plateaus, plains and a few craters. Heights are usually less than one kilometre. The moon is geologically active. Some complex valleys and ridges could be the result of cryovolcanism – an extrusion of water-ice and ammonia rather than molten rock. There are a few eruptions of dust and nitrogen in plumes that reach heights of 8 km. There are reflective frozen nitrogen and methane caps on the polar region that are marked with impact craters. The oldest terrain on Triton resembles the skin of a cantaloupe melon and is called “cantaloupe terrain”. This is mostly dirty water-ice with depressions of about 30 to 40 km in diameter.

Triton’s atmosphere consists of nitrogen with additional traces of methane and carbon monoxide close to the surface. Turbulence on the surface of the moon creates weather conditions in its troposphere. There are no other higher atmospheric layers, such as the stratosphere on Earth that protects Earth from solar radiation. Consequently, a haze of hydrocarbons and nitriles – compounds of carbon and nitrogen such as cyanides – permeates through Triton’s troposphere.

Triton has a retrograde orbit, meaning that it orbits in the opposite direction to Neptune’s spin. This implies that Triton was a captured object that originated in the Kuiper Belt, the region of outer space beyond Neptune. The orbit is synchronous, meaning that the moon itself spins on its own axis in the same direction as its orbital movement. Triton always keeps the same hemisphere facing Neptune. It takes 5.87 Earth days to orbit Neptune. Along with Neptune and its other satellites, Triton takes 164.79 Earth years to orbit the sun.

The only spacecraft flyby of Triton was Voyager 2 in 1989. Its closest approach to Triton was 37,790 km.

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