Detailed chemical composition analysis of the Soi crater region on Titan

Creators: Solomonidou, A.; Malaska, M.J.; Lopes, R.M.C.; Coustenis, A.; Schoenfeld, A.M.; Schmitt, B.; Birch, S.P.D.; Le Gall, A.; Lawrence, K.; Matsoukas, C.; Wall, S.D.; Elachi, Charles¹

1. California Institute of Technology

Abstract

The Soi crater region (0° to 60°N, 180°W to −110°W), which includes the well-preserved Soi crater in its center, spans a region from Titan's aeolian-dominated equatorial regions to fluvially-dominated high northern latitudes. This provides a rich diversity of landscapes, one that is also representative of the diversity encountered across Titan. Schoenfeld et al. (2023) mapped this region at 1:800,000 scale and produced a geomorphological map showing that the area consists of 22 types of geomorphological units. The Visual and Infrared Mapping Spectrometer (VIMS) coverage of the region enabled the detailed analysis of spectra of 261 different locations using a radiative transfer technique and a mixing model, yielding compositional constraints on Titan's optical surface layer. Additional constraints on composition on the near-surface substrate were obtained from microwave emissivity. We have derived combinations of top surface materials between dark materials, tholins, water-ice, and methane suggesting that dark mobile organic material at equatorial and high latitudes indicates “young” terrains and compositions, while tholin/water-ice mixtures that dominate areas around latitude 35°N show a material that is older plains deposits that we interpret to be the end stage of aeolian and fluvial transport and deposition. We found no spectral evidence of CO₂, HC₃N, and NH₃ ice. We use the stratigraphic relations between the various mapping units and the relation between the geomorphology and the composition of the surface layers to build hypotheses on the origin and evolution of the regional geology. We suggest that sedimentary deposits, likely aeolian, are dominant in the region with fluvial activity and leaching changing the nature of the top surfaces of the midlatitude areas of the Soi crater region.

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Data Availability

Open research

All Cassini data used in this article can be accessed in the Planetary Data Systems (PDS), PDS Image Atlas (https://pds-imaging.jpl.nasa.gov/search/?fq=-ATLAS_THUMBNAIL_URL%3Abrwsnotavail.jpg&fq=ATLAS_MISSION_NAME%3Acassini&fq=ATLAS_INSTRUMENT_NAME%3Avims&fq=TARGET%3Atitan&q=*%3A*) for VIMS and (https://pds-imaging.jpl.nasa.gov/search/?fq=ATLAS_MISSION_NAME%3Acassini&fq=TARGET%3Atitan&fq=-ATLAS_THUMBNAIL_URL%3Abrwsnotavail.jpg&fq=ATLAS_INSTRUMENT_NAME%3Aradar&q=*%3A*) RADAR. The detailed product IDs for VIMS can be found in Table 2. The spectral library databases can be accessed here: http:// ghosst.osug.fr. Full descriptions of the radiative transfer model are provided by Hirtzig et al. (2013) (doi:https://doi.org/10.1016/j.icarus.2013.05.033). The VIMS analysis was done using the ENVI Imaging and Analysis software (https://www.l3harrisgeospatial.com/Software-Technology/ENVI) and the Interactive Data Language (IDL), both provided by L3Harris Geospatial.

Other data will be made available on request.

Contributions

Anezina Solomonidou, Michael Malaska, Rosaly Lopes, Athena Coustenis, Ashley Schoenfeld, Bernard Schmitt, Sam Birch, Alice Le Gall, Ken Lawrence, Christos Matsoukas, Steve Wall, and Charles Elachi are ALL authors of this manuscript. Anezina Solomonidou, Michael Malaska, Rosaly Lopes, Athena Coustenis, Ashley Schoenfeld, Sam Birch and Alice Le Gall by: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Software, Resources, Investigation, Formal analysis, Data curation. Bernard Schmitt, Ken Lawrence, and Christos Matsoukas by: Writing – review & editing, Software, Data curation. Steve Wall and Charles Elachi by: Writing – review & editing, Writing – original draft, Validation, Supervision.

Acknowledgement

We would like to thank the two anonymous reviewers for their thoughtful comments and efforts towards improving our manuscript. This research was partly supported by the NASA Astrobiology Institute through its JPL-led project entitled Habitability of Hydrocarbon Worlds: Titan and Beyond. This research was partly supported by the Cassini Data Analysis and Participating Scientists Program (CDAPS) grant #NH16ZDA001N to R.L. A.S. and A.C. acknowledge support from the CNES Appel annuel à Propositions de Recherche Program. A.S. was partly supported by the Czech Science Foundation (grant no. 20-27624Y). S.P.D.B. acknowledges support from the Heising-Simons Foundation (51 Pegasi b Fellowship). Part of this work was conducted at the Jet Propulsion Laboratory (JPL), California Institute of Technology (Caltech) under contract with NASA, and the Hellenic Space Center. ©2024 California Institute of Technology. Government sponsorship acknowledged.

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