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Published June 2017 | public
Journal Article

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

Abstract

This paper presents the first results of the solid phase analysis of the Titan tholins generated in the Titan Haze Simulation (THS) experiments. This study complements the gas phase analysis study that was presented in a previous publication introducing the THS capabilities. In the THS experiment, the chemistry is simulated by plasma in the stream of a supersonic jet expansion. With this unique design, the gas is jet-cooled to Titan-like temperature (∼150 K) before inducing the chemistry by plasma, and remains at low temperature in the plasma discharge (∼200 K). 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: N_2 ── CH_4, N_2──CH_4──C_2H_2, N_2──CH_4──C_6H_6 and N_2──CH_4──C_2H_2──C_6H_6. 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.

Additional Information

© 2017 Elsevier Inc. Received 9 August 2016, Revised 10 December 2016, Accepted 9 February 2017, Available online 21 February 2017. This research is supported by NASA SMD (SSW). K. T. Upton wishes to acknowledge the support of the NASA Harriet Jenkins Pre-Doctoral Fellowship Program, and the continuous support of Ph.D. advisor Dr. J. L. Beauchamp. The authors acknowledge the support provided by Ames' Advanced Studies Laboratory (ASL), a partnership between NASA Ames Research Center (ARC) and the University of California, Santa Cruz (UCSC). The authors wish to acknowledge Dr. Abdessamad Benidar for the new modeling of the pressure and temperature in the expansion done in 2012 to update the values from Biennier et al., 2006, with the current dimensions of the experimental setup. The authors also gratefully acknowledge the outstanding technical support of R. Walker and E. Quigley (NASA ARC), as well as the contributions of M. McMahon and J. Hellgeth at Fisher Scientific where the IR measurements were performed, and Scott Sandford for the use of his IR microscope.

Additional details

Created:
August 21, 2023
Modified:
October 25, 2023