Field data analysis, laboratory experimentation, and mapping Cassini radar images to characterize fluvial sediments on Titan

Maue, Anthony David (2022) Field data analysis, laboratory experimentation, and mapping Cassini radar images to characterize fluvial sediments on Titan. Doctoral thesis, Northern Arizona University.

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Abstract

The icy surface of Saturn’s largest moon, Titan, has been modified by fluvial processes, as evidenced in flyby radar images from the Cassini spacecraft and near-surface images from the Huygens lander. Some features interpreted as gravel-bed braided rivers on Titan exhibit anomalously high radar backscatter, which may be due to the particular size, shape, and distribution of rounded fluvial sediments. In this dissertation, I characterize fluvial sediment on Titan and related processes by exploring the sedimentological controls on radar backscatter using ground truth for Earth-observing radar images, tracking the evolution of icy clasts in Titan-analog abrasion mill experiments, and assessing downstream variations in radar backscatter in Titan’s fluvial features that may indicate sedimentary processes. To provide ground truth for a coarse-grained sedimentary environment, sediment properties were measured at field sites on alluvial fans in the Mojave Desert. These hand measurements were compared to radar backscatter at C-band (λ = 5.6 cm) and L-band (λ = 23.5 cm) wavelengths to find strong correlations with median grain size, and little or no effect from shape or sorting. Differences with expectations from theoretical models support the importance of empirical evaluations. To observe how sediment properties may change in transport on Titan, water ice clasts were tumbled at cryogenic temperatures. The measured abrasion rates are comparable to that of weak terrestrial materials and rounding occurs very rapidly, indicating that clast comminution may occur over comparatively short distances on Titan. The dominance of fragmentation over attrition produces relatively few fine particles, suggesting fluvial abrasion is unlikely to be a significant source of Titan’s dune sands. The field study of radar backscatter and laboratory tests of fluvial abrasion are synthesized to assist interpretation of backscatter variations occurring in Titan’s radar-bright fluvial features. The measured backscatter trends are frequently found to be non-monotonic, both increasing and decreasing over a feature’s length, in contrast to the steady decrease in backscatter expected for simple downstream fining. Causes for local variation are explored and a typical fining rate is proposed that is most consistent with the lowest abrasion rates of the Titan Tumbler, indicating Earth-like downstream fining that may be explained by fluvial sediment more durable than pure water ice.

Item Type:	Thesis (Doctoral)
Publisher’s Statement:	© Copyright is held by the author. Digital access to this material is made possible by the Cline Library, Northern Arizona University. Further transmission, reproduction or presentation of protected items is prohibited except with permission of the author.
Keywords:	fluvial processes; radar; sediment; Titan; Clasts; Backscatter
Subjects:	Q Science > QB Astronomy
NAU Depositing Author Academic Status:	Student
Department/Unit:	Graduate College > Theses and Dissertations College of the Environment, Forestry, and Natural Sciences > Physics and Astronomy
Date Deposited:	06 Jun 2023 17:06
Last Modified:	06 Jun 2023 17:06
URI:	https://openknowledge.nau.edu/id/eprint/5967

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