The largest moon of Neptune was an agent of chaos. It wasn’t born with Neptune itself. Instead, it was captured by the giant planet. As it spiraled in, it might have hit one of Neptune’s existing moons. And it scattered the others – knocking some of them out of orbit. Only one of them might have survived.

There’s a lot of evidence of that idea. Triton is about the same size and composition as Pluto. It contains more than 99 percent of the total mass of Neptune’s moons and rings. And it orbits in the opposite direction from Neptune’s rotation.

There’s no way for a moon to form in that kind of orbit, so Triton must have formed elsewhere in the solar system. It was captured when Neptune was young. It might have caromed off an existing moon. Or it might have had a companion. When the duo passed close to Neptune, it was ripped apart – Triton entered orbit, while its sibling was kicked off on its own. Triton then bludgeoned its way through the system.

A recent study says the only surviving moon is Nereid, Neptune’s third-largest moon. Researchers looked at it with Webb Space Telescope. They found that it’s made of the same materials as the moons of Uranus – not the other moons of Neptune. That suggests it was born with the planet, and survived Triton’s chaotic arrival.

Neptune is at its brightest this week. It’s in the east at nightfall, to the upper right of the bright planet Saturn. But you need a telescope to see it.

More tomorrow.

Script by Damond Benningfield

StarDate

Episodes 16

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