How Neptune snagged a passing moon

Finally, a plausible explanation for how Neptune captured its errant moon Triton. Surprise, surprise, it may in fact involve gravity. It seems that Triton was wandering through space locked in the gravitational embrace of a companion when the pair happened to pass by Neptune. The gravity of the giant planet extricated Triton from its partner, flinging one into deep space and keeping the other as a moon.

About 40 per cent larger than Pluto, Triton moves through its tilted orbit in the opposite direction to Neptune’s rotation. This is the hallmark of a captured body, rather than one formed in situ, but astronomers have never been able to work out how Neptune managed to capture Triton.

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