Neptune’s Moon Triton

Neptune is the furthest planet from the sun in our solar system at a distance of 2.8 billion miles (4.5 billion kilometres). Neptune is orbited by 14 individual moons. Of those 14 moons, one of them stands out among all others. The largest moon of Neptune is called Triton. Triton is the seventh largest moon in the solar system and composes 99.5% of the total mass of all moons in Neptune’s orbit. In fact, Triton is the only moon of Neptune massive enough to pull itself into a spherical shape. Triton has a diameter of 1,680 miles (2,710 kilometres), making it roughly 5.5% the diameter of Neptune. Triton is one of the most unique and interesting moons in the solar system. What makes this moon so unique?

Discovery Of Triton

Triton was discovered shortly after Neptune in 1846. Neptune was the first and only planet in our solar system found through mathematical predictions rather than direct observation. Irregularities in Uranus's orbit suggested the presence of another planet beyond Uranus, leading astronomers in 1846 to predict Neptune's existence. These predictions were soon confirmed through observations, and just 17 days after Neptune was validated, astronomer William Lassell discovered its largest moon, Triton. Following the tradition of naming solar system objects after Greek and Roman mythological figures, the moon was named Triton after Poseidon’s son in Greek mythology.

Orbit And Rotation

Triton’s orbit is one of its most distinctive and intriguing features. Unlike most moons in the solar system, Triton travels in a retrograde manner, meaning it moves in the opposite direction of Neptune’s rotation. Neptune spins counterclockwise, but Triton orbits clockwise. Moons around gas giants typically formed from small disks of material that surrounded the planets shortly after their formation. These moons usually coalesced from this material, which orbit in the same direction as their planet’s rotation. Since Triton orbits in the opposite direction, astronomers believe it did not form with Neptune. Instead, Triton was probably a dwarf planet in the Kuiper Belt that was eventually captured by Neptune’s gravity after passing too close. It takes about 5.8 Earth days for Triton to complete an orbit around Neptune. Additionally, Triton is tidally locked to Neptune, so one side constantly faces the planet, with no rotation of its own.

Composition Of Triton

Triton has only ever been observed by one spacecraft: Voyager 2, which is the only mission to have visited Neptune and captured images of the planet and its moons. Since this flyby, astronomers have only mapped about 40% of Triton’s surface, leaving much mystery about this moon. Its composition resembles that of Kuiper Belt dwarf planets like Pluto. Triton’s surface is layered with frozen nitrogen, making up roughly 55% of its crust; water constitutes 15-35%, and the rest is frozen carbon dioxide. Its interior mainly consists of water ice and rock, similar in structure to Earth, with a thin crust, a solid core, and a mantle. Notably, Triton’s interior likely contains abundant radioactive material, which decays and releases heat, melting subsurface ice and forming a liquid water ocean beneath the surface. The presence of this liquid water, along with surface organic compounds, suggests Triton could be a potentially habitable environment.

A Doomed Moon

Triton’s retrograde orbit around Neptune has a significant impact on its future. Neptune gradually absorbs Triton's rotational energy, causing Triton's orbit to slowly shrink. Over time, Triton’s orbit will become so small that it will either collide with Neptune or break apart while orbiting. Based on orbital decay rates, astronomers predict this will happen in about 3.6 billion years. When Triton reaches this end, debris from the collision will enter Neptune’s orbit, likely forming a vast ring system similar to Saturn’s.