The Titan Haze Simulation (THS) experiment on COSmIC. Part II. Ex-situ analysis of aerosols produced at low temperature

Here, we present and discuss the results of scanning electron microscopy and infrared spectroscopy studies of THS solid aerosols produced in the four gas mixtures already studied by mass spectrometry in the gas phase: N2CH4, N2CH4C2H2, N2CH4C6H6 and N2CH4C2H2C6H6. Differences in the morphology of the grains and aggregates produced in the volume of the gas phase in the plasma cavity, depending on the initial precursors, have been observed by scanning electron microscopy, that appear to be linked to differences in the growth processes and might have an impact on microphysical models. The mid-infrared spectroscopic analysis highlights changes in the nitrogen chemistry, and the abundance of aromatic compounds, depending on the initial gas mixture. A preliminary study of the aging and degradation of the THS samples with time and exposure to air and light has shown the importance, for future studies of laboratory-generated planetary aerosol analogs, of collecting, storing and characterizing samples under controlled environment. A comparison to VIMS data shows that the THS tholins produced in simpler mixtures, i.e., with a higher level of nitrogen incorporation, are more representative of Titan's aerosols.