QUESTION:
Why has Jupiter got so many moons?

ANSWER from Glenn Orton on 20 February, 1996:
Jupiter's gravity is large enough to have captured several asteroids from
the nearby asteroid belt between Jupiter and Mars.  Their orbits are
chaotic, as well, which lends credibility to this interpretation.  On the
other hand, the large "Galilean" satellites which are co-planar and in
regular orbits probably formed at or near the same time as Jupiter. 

Note that Saturn also has a potpourri of small satellites for much the
same reasons probably.  ...plus Titan, the one "biggie".