Triton is the seventh-largest moon and sixteenth-largest object in the Solar System, and is modestly larger than the dwarf planets Pluto and Eris.
It comprises more than 99.5% of all the mass known to orbit Neptune, including the planet's rings and thirteen other known moons, and is also more massive than all known moons in the Solar System smaller than itself combined.
Also, with a diameter 5.5% that of Neptune, it is the largest moon of a gas giant relative to its planet in terms of diameter, although Titan is bigger relative to Saturn in terms of mass.
It has a radius, density (2.061 g/cm³), temperature and chemical composition similar to those of Pluto.

Triton's surface is covered with a transparent layer of annealed frozen nitrogen.
Only 40% of Triton's surface has been observed and studied, but it is possible that it is entirely covered in such a thin sheet of nitrogen ice.
Like Pluto's, Triton's crust consists of 55% nitrogen ice with other ices mixed in.
Water ice comprises 15–35% and frozen carbon dioxide (dry ice) the remaining 10–20%.
Trace ices include 0.1% methane and 0.05% carbon monoxide.
There could also be ammonia ice on the surface, as there are indications of ammonia dihydrate in the lithosphere.
Triton's mean density implies that it probably consists of about 30–45% water ice (including relatively small amounts of volatile ices), with the remainder being rocky material.
Triton's surface area is 23 million km², which is 4.5% of Earth, or 15.5% of Earth's land area.
Triton has a considerably and unusually high albedo, reflecting 60–95% of the sunlight that reaches it, and it has changed slightly since the first observations.
By comparison, the Moon reflects only 11%.
Triton's reddish colour is thought to be the result of methane ice, which is converted to tholins under exposure to ultraviolet radiation.

Because Triton's surface indicates a long history of melting, models of its interior posit that Triton is differentiated, like Earth, into a solid core, a mantle and a crust.
Water, the most abundant volatile in the Solar System, comprises Triton's mantle, enveloping a core of rock and metal.
There is enough rock in Triton's interior for radioactive decay to maintain a liquid subsurface ocean to this day, similar to what is thought to exist beneath the surface of Europa and a number of other icy outer Solar System worlds.
This is not thought to be adequate to power convection in Triton's icy crust.
However, the strong obliquity tides are believed to generate enough additional heat to accomplish this and produce the observed signs of recent surface geological activity.
The black material ejected is suspected to contain organic compounds, and if liquid water is present in Triton, it has been speculated that this could make it habitable for some form of life.
Triton is the seventh-largest moon and sixteenth-largest object in the Solar System, and is modestly larger than the dwarf planets Pluto and Eris. It comprises more than 99.5% of all the mass known to orbit Neptune, including the planet's rings and thirteen other known moons, and is also more massive than all known moons in the Solar System smaller than itself combined. Also, with a diameter 5.5% that of Neptune, it is the largest moon of a gas giant relative to its planet in terms of diameter, although Titan is bigger relative to Saturn in terms of mass. It has a radius, density (2.061 g/cm³), temperature and chemical composition similar to those of Pluto.
Triton's surface is covered with a transparent layer of annealed frozen nitrogen. Only 40% of Triton's surface has been observed and studied, but it is possible that it is entirely covered in such a thin sheet of nitrogen ice. Like Pluto's, Triton's crust consists of 55% nitrogen ice with other ices mixed in. Water ice comprises 15–35% and frozen carbon dioxide (dry ice) the remaining 10–20%. Trace ices include 0.1% methane and 0.05% carbon monoxide. There could also be ammonia ice on the surface, as there are indications of ammonia dihydrate in the lithosphere. Triton's mean density implies that it probably consists of about 30–45% water ice (including relatively small amounts of volatile ices), with the remainder being rocky material. Triton's surface area is 23 million km², which is 4.5% of Earth, or 15.5% of Earth's land area. Triton has a considerably and unusually high albedo, reflecting 60–95% of the sunlight that reaches it, and it has changed slightly since the first observations. By comparison, the Moon reflects only 11%. Triton's reddish colour is thought to be the result of methane ice, which is converted to tholins under exposure to ultraviolet radiation.
Because Triton's surface indicates a long history of melting, models of its interior posit that Triton is differentiated, like Earth, into a solid core, a mantle and a crust. Water, the most abundant volatile in the Solar System, comprises Triton's mantle, enveloping a core of rock and metal. There is enough rock in Triton's interior for radioactive decay to maintain a liquid subsurface ocean to this day, similar to what is thought to exist beneath the surface of Europa and a number of other icy outer Solar System worlds. This is not thought to be adequate to power convection in Triton's icy crust. However, the strong obliquity tides are believed to generate enough additional heat to accomplish this and produce the observed signs of recent surface geological activity. The black material ejected is suspected to contain organic compounds, and if liquid water is present in Triton, it has been speculated that this could make it habitable for some form of life.
Triton (moon)