Growth and Morphology of Water-, Methanol-, and Ethanol-ice Dust Grains Formed in an Astrophysically Relevant Plasma Experiment

Ice dust grains composed of water, methanol, and ethanol are successfully produced in a laboratory plasma experiment operating at astrophysically relevant temperatures. Both methanol- and ethanol-ice grains grow in an elongated and branched way similar to water-ice grains formed in a plasma. The experiment reveals that methanol- and ethanol-ice grains grow faster, larger, and more branched (spikier) than water-ice grains. The observed growth features seem to be related to the fact that more source molecules and monomer grains can exist in the system at the same temperature. The observed morphology is in agreement with the characteristics of the diffusion-limited aggregation. We also find that larger and more branched ice grains form when the ambient gas pressure is low or the mass of the ambient gas is light, indicating that the aggregation of small grains is enhanced under these conditions.