Space
NEPTUNE’S largest moon, Triton, and the dwarf planet Pluto may have shared a common origin before being separated, an analysis of their composition suggests.
Triton and Pluto are both icy bodies smaller than Earth’s moon, have similar densities and appear to have hosted subsurface oceans at some point in the past.
Unusually, Triton, which is about 50 per cent more massive than Pluto, orbits in the opposite direction to its planet’s rotation – the only large moon to do so in the solar system. This has led to suggestions it may have originated in the Kuiper belt, a region of icy objects like Pluto that exist beyond Neptune, because moons that formed with Neptune should match its spin.
Kathleen Mandt at NASA’s Goddard Space Flight Center in Maryland and her colleagues have now gone further by suggesting that Triton and Pluto formed close to each other before the solar system settled down. “They probably formed in the same region, which wouldn’t be where the Kuiper belt is now – it would have been either closer or further away,” says Mandt.
Studying prior data on the two bodies, the team found that both have a large amount of nitrogen and trace amounts of methane and carbon monoxide, which could have accumulated in the outer regions of the young nebula surrounding our sun 4.5 billion years ago (arXiv, doi.org/m4jc).
This suggests they both formed in cold outer regions of the early solar system, which were rich in nitrogen. But they also have low amounts of water, similar to some known icy comets such as comet C/2016 R2 (PanSTARRS) that may hav
