I Like Triton

I like Triton. About the size of Earth's own moon, Triton was once a Kuiper Belt Object (KBO), peer of Pluto, Charon, and Eris. Then, one fine sidereal day, something happened to cause Neptune to capture Triton. We know that it was captured, and not formed with Neptune, because its orbit is retrograde relative to the planet's direction of rotation. How that capture happen is still a bit unclear, but most likely Triton was in a double-planet system (like Pluto-Charon) that flew too close to Neptune; one partner ran off free, and Triton got stuck in the ice-giant's pull (Nature article, more papers). Triton has been visited once, by the Voyager 2 spacecraft on its way out of the solar system. NASA has considered going back with a mission called "Triton Explorer" (powerpoint fact sheet). I hope they do; Triton is a world of mystery, right on our doorstep...