  Laboratory experiments revealed that CO$_{2}$ ice particles stick less
efficiently than H$_{2}$O ice particles, and there is an order of magnitude
difference in the threshold velocity for sticking. However, the surface
energies and elastic moduli of CO$_{2}$ and H$_{2}$O ices are comparable, and
the reason why CO$_{2}$ ice particles were poorly sticky compared to H$_{2}$O
ice particles was unclear. Here we investigate the effects of viscoelastic
dissipation on the threshold velocity for sticking of ice particles using the
viscoelastic contact model derived by Krijt et al. We find that the threshold
velocity for sticking of CO$_{2}$ ice particles reported in experimental
studies is comparable to that predicted for perfectly elastic spheres. In
contrast, the threshold velocity for sticking of H$_{2}$O ice particles is an
order of magnitude higher than that predicted for perfectly elastic spheres.
Therefore, we conclude that the large difference in stickiness between CO$_{2}$
and H$_{2}$O ice particles would mainly originate from the difference in the
strength of viscoelastic dissipation, which is controlled by the viscoelastic
relaxation time.
