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

Abstract

Centimeter-sized dust grains-pebbles-are necessary for planetesimal formation via the streaming instability, they play an important role in forming protoplanetary cores and giant planets, as well as enriching their atmospheres with chemical elements. This work investigates the effect of luminosity outbursts on the abundance of pebbles and their ice mantles in protoplanetary disks. We perform global simulations of formation and evolution of a self-gravitating viscous protoplanetary disk using the 2D hydrodynamic thin-disk FEOSAD code, which self-consistently reproduces luminosity outbursts. The model includes thermal balance, dust evolution and its interaction with gas, development of magnetorotational instability, adsorption and desorption of four volatile compounds (H$_2$O, CO$_2$, CH$_4$ and CO), and the feedback of ice mantles on dust fragmentation properties. We show that luminosity outbursts have a stronger effect on the positions of CO$_2$, CH$_4$ and CO snowlines compared to the water snowline. This is because the H$_2$O snowline falls within the viscous heating dominated region during early disk evolution stages, while snowlines of other molecules are located in regions dominated by stellar irradiation heating and are thus more sensitive to temperature changes during outbursts. Nevertheless, luminosity outbursts reduce the total amount of pebbles in the disk by half due to destruction of dust aggregates into monomers following the loss of water ice that binds the aggregates together. Pebble recovery occurs over several thousand years after the outburst ends due to collisional coagulation, with recovery timescales significantly exceeding water freeze-out times. Ice mantle desorption occurs in a complex non-axisymmetric 2D region of the disk, associated with spiral substructure formation during early evolution of gravitationally unstable disks.