The origins of the irregular satellites of the giant planets are an important piece of the huge ‘puzzle’ that is the theory of Solar system formation. They are not in situ formation objects, around the planet, as one believes the regular satellites to be. Thus, the most plausible hypothesis to explain their origins is that they formed elsewhere and were captured by the planet. However, under restricted three-body dynamics, captures are temporary and must be assisted by an auxiliary mechanism in order to be permanent. Nevertheless, there does not exist one well-established capture mechanism. In this paper, we study the capture of binary-asteroids in order to try to understand which intrinsic features of this mechanism lead one member of the primordial binary, after it has been disrupted, to become a permanent capture. We have performed more than 105 simulations of binary-asteroid capture trajectories and considered four-body problem dynamics with the Sun, Jupiter and a pair of asteroids. Among the main results, we find the following: (1) the minor asteroid is much more susceptible to permanent capture than its major partner; (2) there exists an optimum binary-asteroid separation which makes permanent capture more favourable; and (3) a specific set of initial conditions whose capture probability is pretty expressive. Although we have studied only the planar prograde case, a fraction of ∼0.8 per cent of the captured objects match, in orbital shape, the irregular prograde satellites of Jupiter, without the aid of any other dissipative effect.