Neptune’s largest moon, Triton, is a frozen oddball.
One, it circles its parent planet in a retrograde orbit—that is, in a direction opposite to that of Neptune’s rotation. Which means that it must have begun life elsewhere, before being captured by the gas giant. It most likely came from the same place as Pluto—the inner edge of the Kuiper Belt.
Two, it’s also geologically active, showing signs of cryovolcanism.
Three, Triton is the only known moon in our solar system to have a surface made chiefly, of nitrogen-ice.
A new model suggests that it has an underground watery ocean that has a strong dose of ammonia, which keeps the liquid from freezing unless the temperature drops below minus 200 Fahrenheit.
So, while it may be the outermost ocean in the solar system, it’s not as cold as the hydrocarbon lakes on Saturn’s moon, Titan.
h/t: NEW SCIENTIST