Laboratory-based sticking coefficients for ices on a variety of small grains analogs

TL;DR

This study measures how the shape and composition of cosmic dust analogs affect gas sticking and desorption, revealing that grain curvature reduces adsorption rates and influences ice formation in space.

Contribution

It provides the first laboratory measurements of sticking coefficients on curved dust grain analogs, highlighting the impact of grain morphology on gas adsorption and desorption processes.

Findings

Sticking coefficients of H2O and CO2 decrease on curved, porous grains.

Grain size does not affect H2O thermal desorption temperatures.

Reduced gas accretion rates influence ice growth and gas-ice partitioning.

Abstract

Abundances and partitioning of ices and gases produced by gas-grain chemistry are governed by adsorption and desorption on grains. Understanding astrophysical observations rely on laboratory measurements of adsorption and desorption rates on dust grains analogs. On flat surfaces, gas adsorption probabilities (or sticking coefficients) have been found close to unity for most gases. Here we report a strong decrease of the sticking coefficients of H2O and CO2 on substrates more akin to cosmic dust, such as submicrometer-sized particles of carbon and olivine, bare or covered with ice. This effect results from the local curvature of the grains, and then extends to larger grains made of aggregated small particles, such as fluffy or porous dust in more evolved media (e.g. circumstellar disks). The main astrophysical implication is that accretion rates of gases are reduced accordingly, slowing the growth of cosmic ices. Furthermore, volatile species that are not adsorbed on a grain at their freeze-out temperature will pertain in the gas phase, which will impact gas-ice partitions. We also found that thermal desorption of H2O is not modified by grains size, and thus the snowlines temperature should be independent on the dust size distribution.