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The Largest Kuiper Belt Object Isn't Pluto Or Eris, But Triton
StartsWithABang writes: Out beyond Neptune, the last of our Solar System's gas giants, the icy graveyard of failed planetesimals lurks: the Kuiper Belt. Among these mixes of ice, snow, dust and rock are a number of worlds — possibly a few hundred — massive enough to pull themselves into hydrostatic equilibrium. The most famous among them are Pluto, the first one ever discovered, and Eris, of comparable size but undoubtedly more massive. But there's an even larger, more massive object from the Kuiper Belt than either of these, yet you never hear about it: it's Triton, the largest moon of Neptune, a true Kuiper Belt object!
Actually, its name is mythological in origin (like most bodies in our solar system):
http://en.wikipedia.org/wiki/M...
http://en.wikipedia.org/wiki/M...
William George
It's the other way around, the retrograde (which is only "counterclockwise" when viewed from one side) motion causes tidal drag which causes the orbit to decay.
Tidal forces produce bulges on large objects, and the resulting non-spherical shape allows gravity to apply torque to objects and transfer angular momentum between their rotation and their orbital revolution. This tends to bring rotation and orbital revolution into sync: it locked the moon's rotation to its orbit around the Earth, and the reverse process transferred angular momentum from Earth's rotation to the moon's orbit, slowing the Earth's rotation and pulling the moon to a higher orbit. Triton happened to be captured on the "wrong" side of Neptune and end up in a retrograde orbit, so the same tidal drag is pulling it into a lower orbit.
Phobos is in a similar situation despite having a prograde orbit: it's low enough that it orbits faster than Mars rotates (appearing from the surface to cross the sky in the opposite direction as Deimos), so the tidal drag that is pulling the more distant and slower-orbiting Deimos into an even higher orbit is pulling Phobos into a lower one.