Distribution of test particles on the (ϕ, a) plane as the 1:2 resonance approaches. Four snapshots at different moments with t = 0 kyr representing exactly when the nominal resonance reaches the initial position of test particles are given in each of the four panels. Objects later captured by the leading and trailing island are in red and blue, respectively, while those not captured by any asymmetric resonance are in purple. The horizontal line stands for the nominal position of 1:2 resonance.