In the universe, cosmic dust might condense gases less than thought…
Ices are of paramount importance in the physical and chemical evolution of the universe. Their formation results from the cryo-condensation of atomic gases (H, O, C, …) on the surface of small grains of cold cosmic dust (T< 20 K). Several laboratory measurements have shown that, on flat surfaces with a chemical composition like that of dust grains (carbon, olivine), the condensation probabilities (or sticking coefficients) are close to 1 for most gases. Is this the case on nanometer-size particles, more representative of cosmic dust? Using X-ray photoelectron spectroscopy (XPS), we show that the sticking coefficients of H2O and CO2 are indeed close to 1 on flat surfaces but are far smaller than 1 on nanoparticles (carbon, olivine, alumina, etc.), bare or previously ice-covered. These new laboratory data will allow a better understanding of the interactions between dust, ice and gas, in diffuse molecular clouds, protoplanetary disks or planetary atmospheres.
Reference: “Laboratory-based sticking coefficients for ices on a variety of small-grain analogues”, C. Laffon, D. Ferry, O. Grauby, Ph. Parent, Nature Astronomy (2021).
Available on line: https://www.nature.com/articles/s41550-020-01288-7
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