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Triton, a picture taken by Voyager 2 in 1989Triton, a picture taken by Voyager 2 in 1989 At 2700 kilometres (about 1700 miles) in diameter, Triton is Neptune’s largest moon, and the seventh largest of all the moons in the Solar System. It orbits its parent planet in a reverse direction, the only large moon to do so (the others that do are tiny, irregular objects). Beneath its icy crust lies a mantle of water, which may be liquid if underground temperatures are high enough. On the surface, however, it is extremely cold. With an average surface temperature of -238°C (-396°F), Triton is the coldest world in the Solar System.

A close-up view of the surface of TritonA close-up view of the surface of TritonThe rugged cantaloupe terrain of TritonThe rugged cantaloupe terrain of Triton

Cantaloupe terrain

Scientists gained knowledge of the surface of Triton when the Voyager 2 space probe flew past Triton in 1989 at a distance of 40,000 kilometres (25,000 miles), sending back detailed images.

They revealed an icy surface featuring few craters, but covered by a dense network of ridges and valleys. This is described as "cantaloupe" terrain, because of its similarity—when viewed from space—to the skin of a cantaloupe melon. It is probably the result of the ice melting to a slush, then refreezing. Triton’s granite-hard surface is made up of 55% nitrogen ice, with water ice and frozen carbon dioxide mixed in. A thin coating of nitrogen ice is believed to cover the moon's entire surface.



Triton comprises more than 99.5% of the total mass of objects that orbit around Neptune.

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