The Effect of Luminosity Outbursts on the Abundance of Pebbles and Their Ice Mantles in Protoplanetary Disks

Dust growth is one of the key processes leading to planet formation in protoplanetary disks. Centimeter-sized dust grains, pebbles, are essential for the formation of planetesimals through streaming instability and play a crucial role in the formation of protoplanetary cores, giant planets, and the enrichment of their atmospheres with chemical elements. In this paper, the impact of luminosity outbursts on the amount of pebbles and icy mantles in a protoplanetary disk has been studied. We have performed global simulations of the formation and evolution of a self-gravitating, viscous protoplanetary disk using the two-dimensional thin-disk hydrodynamic code FEOSAD, which self-consistently produces luminosity outbursts. The model includes thermal balance, dust evolution and its interaction with gas, the development of magnetorotational instability, adsorption and desorption of four volatile species (H₂O, CO₂, CH₄, and CO), and the effect of icy mantles on the fragmentation properties of dust aggregates. Our results have shown that luminosity outbursts have a stronger impact on the CO₂, CH₄, and CO ice lines than on the water ice line. This is because the H₂O ice line resides in a region dominated by viscous heating during the early stages of disk evolution, whereas the ice lines of the other molecules lie in regions where stellar irradiation dominates the thermal structure, making them more sensitive to temperature variations induced by the outbursts. Nevertheless, luminosity outbursts lead to a twofold reduction in the total amount of pebbles in the disk due to the disintegration of dust aggregates into monomers following the loss of water ice, which acts as a binding agent. The reformation of pebbles occurs over several thousand years after the outburst, primarily through collisional coagulation. The characteristic timescales for pebble recovery significantly exceed the freezing timescales of water ice. The desorption of icy mantles occurs in a highly non-axisymmetric and intrinsically two-dimensional region of the disk due to the formation of spiral substructures during the early evolution of a gravitationally unstable disk.