Presentation #124.01 in the session Laboratory Astrophysics Division (LAD): iPosters.
We have used the NASA Ames COsmic SImulation Chamber (COSmIC) facility  to produce several laboratory analogs (tholins) of (exo)planetary organic refractory materials generated from different gas mixtures at low temperature (150 K) using plasma chemistry in the stream of a supersonic jet expansion. Three samples were produced from N2:CH4 gas precursors (with different high-voltage discharges inducing different degrees of ionization in the plasma and with different concentrations of methane), one sample was produced from N2:CH4:C2H2, and one sample was produced from Ar:CH4 in order to produce a purely carbonaceous sample.
Spectral reflectance measurements were used to determine the complex refractive indices (or optical constants, n and k) of these tholins from 0.4 to 1.6 µm. We observe that both n and k appear to be correlated with the nitrogen content in the solid sample, with samples containing more nitrogen having higher n and k values. Comparisons to previous laboratory studies and Titan aerosol optical constants derived from observations show that the COSmIC tholins with a higher nitrogen content (higher n and k), are closer analogs of Titan aerosols .
We will present these new optical constants and the results of a new analysis of Cassini Visible Infrared Mapping Spectrometer (VIMS) observations of Titan’s atmosphere using the COSmIC tholin optical constants in a radiative transfer model . The COSmIC tholin sample produced from N2:CH4 with the lowest voltage has a spectral behavior that appears well suited to reproduce the observed Titan aerosol properties. This study has therefore demonstrated that this COSmIC tholin sample has valuable and promising optical properties for the analysis of Cassini’s Titan atmospheric observations. We will also present preliminary optical constants of tholins from 0.8 to 100 µm determined with the NASA Ames Optical Constants Facility .
References:  Salama F., et al., Proc. IAU S332 (2018),  Sciamma-O’Brien et al. PSJ (2023),  Sciamma-O’Brien et al. Proc. IAU S371 (2023).
Acknowledgement: The authors acknowledge the support of NASA SMD/APD and PSD and the technical support of E. Quigley.