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Are You A Crater? A Potential Open-Basin Crater Lake Crosscut by Radar-Bright Fluvial Features on Titan

Presentation #413.05 in the session “Titan”. Cross-listed as presentation #405.04.

Published onOct 03, 2021
Are You A Crater? A Potential Open-Basin Crater Lake Crosscut by Radar-Bright Fluvial Features on Titan

Titan has only 90 known craters, due in part to its active surface where aeolian deposition infills craters and fluvial processes erode crater walls [1]. Fine-grained aeolian material is dark in Cassini’s radar. Inactive fluvial features appear either radar-bright from icy cobbles on the valley floor acting as retroreflectors [2] or have a radar-bright/dark pairing due to valley topography.

Our mapping of radar-bright fluvial features in Cassini’s T121 flyby revealed that one feature flows across a ~77 km wide circular form (31.7°S, 74.3°W) identified as a crater in Titan’s global geologic unit map [3]. Although not included in Titan’s updated crater catalogue [1], we find this feature fulfills two of four crater qualifications: circularity with a radar-dark interior, but a discontinuous rim and lacking ejecta. These factors suggest a C3 (Probable crater) designation under the classification scheme of [1].

Whether or not this feature was formed by impact, the radar-bright fluvial feature that cuts across it could be the inlet and outlet valleys of an open-basin paleolake, such as those found on Mars. Open-basin paleolakes on Mars give insight into regional liquid levels and past climate. In the Titan crater-form, the system of fluvial features seems to flow east to west, with singular inlet/outlet valleys that exhibit the radar-bright/dark pairing associated with topography, possibly because the valleys incise the crater walls. On the crater floor, the valley has a uniform radar-bright cross-section and splits into three branches that rejoin on the western edge. This branching could indicate that flow speed decreases and incision is shallower along the crater floor, which might allow pooling during Titan’s intense, infrequent precipitation events.

Liquid would drain via the radar-bright valleys into Hotei Arcus in the North-West. Hotei Arcus is thought to have paleolakes [3] and at least four radar-bright fluvial features flow into it. A crater lake for the cross-cut feature would be consistent with regional paleolakes. However, as the fluvial feature crosses the crater floor, this fluvial activity is likely more recent than, and unrelated to, a paleolake. In that respect, the feature is more similar to Algeria’s Ouarkziz Crater than Mars’ paleolakes which lack continuous channels. Future study will contribute to understanding the hydrologic history of the Hotei region.

[1] Hedgepeth et al., 2020. Icarus 344

[2] Le Gall et al., 2010. Icarus 207

[3] Lopes et al., 2020. Nat Astro 4

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