Triton (moon) - Physical Characteristics

Physical Characteristics

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 twelve other known moons, and is also more massive than all known moons in the Solar System smaller than itself combined. It has a radius, density (2.061 grams per cubic centimetre (0.0745 lb/cu in)), temperature and chemical composition similar to those of Pluto.

As with Pluto, 55% of Triton's surface is covered with frozen nitrogen, with water ice comprising 15–35% and dry ice (frozen carbon dioxide) forming the remaining 10–20%. Trace ices include 0.1% methane and 0.05% carbon monoxide. There could also be ammonia on the surface if ammonia dihydrate is present as suspected in the lithosphere. Triton's density implies it is probably about 30–45% water ice, 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 high albedo, reflecting 60–95% of the sunlight that reaches it. By comparison, Earth's moon reflects only 11%. Triton's reddish colour is thought to be the result of methane ice, which is converted to tholins under bombardment from 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 the moon's mantle, which lies over a core of rock and metal. There is enough rock in Triton's interior for radioactive decay to power convection in the mantle. The heat may even be sufficient to maintain a "subterranean ocean" similar to that which is hypothesized to exist underneath the surface of Europa. If present, a layer of liquid water would suggest the possibility, however unlikely, of life.