Size of icy grains after a heating event in a protoplanetary disk

Abstract

A heating event in a protoplanetary disk could sublimate H2O ice from icy aggregates. After the heating event, the temperature decreased, and the H2O vapor recondensed to form pure H2O grains through homogeneous nucleation or to form H2O ice layer covering the silicate aggregates left behind during the heating event. As a result, the size of the pure H2O ice grains could change from the commonly assumed value of 0.1μm of the aggregate composing ice-covered grains. Here, we numerically determined the final radii of the grains and the thickness of the H2O ice layer on the aggregates after the cooling. We also estimated the maximum radius of the aggregate consisting of the processed grains. If the size of the silicate aggregate left behind in the heating event was smaller than 0.073μm, continuous collisional growth of the aggregates of the processed grains was possible. If the size was larger than 0.073μm, a short cooling time depending on the heliocentric distance was required to achieve high mechanical strengths of the aggregates for the collisional growth.