  The process of capture in the coorbital region of a solar system planet is
studied. Absolute capture likelihood in the 1:1 resonance is determined by
randomly constructed statistical ensembles numbering $7.24\times 10^5$ of
massless asteroids that are set to migrate radially from the outer to the inner
boundaries of the coorbital region of a Jupiter-mass planet. Orbital states
include coorbital capture, ejection, collisions with the Sun and the planet and
free-crossing of the coorbital region. The relative efficiency of retrograde
capture with respect to prograde capture is confirmed as an intrinsic property
of the coorbital resonance. Half the asteroids cross the coorbital region
regardless of eccentricity and for any inclination less than $120^\circ$. We
also find that the recently discovered retrograde coorbital of Jupiter,
asteroid 2015 BZ509, lies almost exactly at the capture efficiency peak
associated with its orbital parameters.
