SOME TERRESTRIAL-LIKE MORPHOLOGIES OF EXTRATERRESTRIAL CHANNELIZED FLOW (Invited Presentation)

Fluvial features are visible on Earth, Mars, and Titan (the largest satellite of Saturn). Although flow conditions on these bodies differ greatly, they result in some similar hydraulic and sediment transport processes. This process similarity allows for intercomparison among fluvial, flood, and submarine channel morphologies, which leads to better understanding of how extraterrestrial fluvial morphologies form(ed). At the smallest scale, meander bends, cutoffs and scroll bars are visible on Mars in inverted relief. Terrestrial meandering is correlated with vegetation, although data from the rock record as well as meanders forming today without significant vegetative influence show that this correlation is not absolute. The discovery of meanders on Mars adds impetus to investigations into what non-vegetative influence could provide the bank strength necessary for meandering. A few potential levees in the form of alternating or paired lateral ridge are also visible on Mars. However, multiple terrestrial analogs are available to explain these ridges, whose formation is not yet understood. In-channel bedforms on Mars are less energetically likely than on Earth due to the relative ease of fluvial sediment transport under lower gravity. However, flood-deposited bedforms are observed in outflow channels, where sediments form subaqueous dunes in shallow settings and streamlined plateaux behind flow obstacles. These features have morphological analogs to both submarine and flood-formed features on Earth. In Titan synthetic aperture radar (SAR) and visible light images, channel morphology is difficult to discern due to image resolution and quality. Narrow, deep features are inferred to be river valleys based on radar-illumination patterns indicative of sloping side walls. Wide, deep features may be incised channels, based on evidence of steep side slopes and sinuous planview forms. Some wide, shallow fluvial features are hypothesized to be multithread channels, based on variations in brightness and width. These potential multithread channels drain radar-bright terrain, hypothesized to be fluvially dissected below the SAR data resolution. If this hypothesis is correct, then dissected terrain would cover ~10% of Titan. A few stubby networks suggest formation by headward erosion processes.