[The Cajun]

The moon may since have been ejected by the tug of another planet passing nearby. Its fate is unclear, but it may have crashed into another gas giant if it is not still roaming the solar system.

Securely putting on tin foil hat. Venus?

[SunkenCiv]

The late Tom Van Flandern eventually attributed it to his Exploding Planet, some way or other, let’s see if that’s still online... hmm, not what I was looking for:

http://www.metaresearch.org/solar%20system/origins/original-solar-system.asp

[snip] Jupiter and Uranus have the most regular and apparently undisturbed large satellite systems: circular and co-planar orbits, orbit-synchronized spins, with orbital periods each roughly double that of the next moon in. Correspondingly, their patterns contain no exceptions to the requirements of the fission theory. Neptune, of course, has a highly disrupted satellite system. But the close resemblance between Pluto and Triton has been noted by many astronomers. [end snip]

(that is of course partly incorrect, insofar as the moons of Jupiter are MOSTLY the result of capture, based on their retrograde orbits; TVF refers here to )