  We study galaxy populations and search for possible merging substructures in
the rich galaxy cluster A2142. Normal mixture modelling revealed in A2142
several infalling galaxy groups and subclusters. The projected phase space
diagram was used to analyse the dynamics of the cluster and study the
distribution of various galaxy populations in the cluster and subclusters. The
cluster, supercluster, BCGs, and one infalling subcluster are aligned. Their
orientation is correlated with the alignment of the radio and X-ray haloes of
the cluster. Galaxies in the centre of the main cluster at the clustercentric
distances $0.5~h^{-1}Mpc$ have older stellar populations (with the median age
of $10 - 11$~Gyrs) than galaxies at larger clustercentric distances.
Star-forming and recently quenched galaxies are located mostly in the infall
region at the clustercentric distances $D_{\mathrm{c}} \approx 1.8~h^{-1}Mpc$,
where the median age of stellar populations of galaxies is about $2$~Gyrs.
Galaxies in A2142 have higher stellar masses, lower star formation rates, and
redder colours than galaxies in other rich groups. The total mass in infalling
groups and subclusters is $M \approx 6\times10^{14}h^{-1}M_\odot$,
approximately half of the mass of the cluster, sufficient for the mass growth
of the cluster from redshift $z = 0.5$ (half-mass epoch) to the present. The
cluster A2142 may have formed as a result of past and present mergers and
infallen groups, predominantly along the supercluster axis. Mergers cause
complex radio and X-ray structure of the cluster and affect the properties of
galaxies in the cluster, especially in the infall region. Explaining the
differences between galaxy populations, mass, and richness of A2142, and other
groups and clusters may lead to better insight about the formation and
evolution of rich galaxy clusters.
