  We investigate a new theory of the origin of the irregular satellites of the
giant planets: capture of one member of a ~100-km binary asteroid after tidal
disruption. The energy loss from disruption is sufficient for capture, but it
cannot deliver the bodies directly to the observed orbits of the irregular
satellites. Instead, the long-lived capture orbits subsequently evolve inward
due to interactions with a tenuous circumplanetary gas disk.
  We focus on the capture by Jupiter, which, due to its large mass, provides
the most stringent test of our model. We investigate the possible fates of
disrupted bodies, the differences between prograde and retrograde captures, and
the effects of Callisto on captured objects. We make an impulse approximation
and discuss how it allows us to generalize capture results from equal-mass
binaries to binaries with arbitrary mass ratios.
  We find that at Jupiter, binaries offer an increase of a factor of ~10 in the
capture rate of 100-km objects as compared to single bodies, for objects
separated by tens of radii that approach the planet on relatively low-energy
trajectories. These bodies are at risk of collision with Callisto, but may be
preserved by gas drag if their pericenters are raised quickly enough. We
conclude that our mechanism is as capable of producing large irregular
satellites as previous suggestions, and it avoids several problems faced by
alternative models.
