Abstract
Previous authors have suggested that Titan’s individual sand particles form by either sintering or by lithification and erosion. We suggest two new mechanisms for the production of Titan’s organic sand particles that would occur within bodies of liquid: flocculation and evaporitic precipitation. Such production mechanisms would suggest discrete sand sources in dry lakebeds. We search for such sources, but find no convincing candidates with the present Cassini Visual and Infrared Mapping Spectrometer coverage. As a result we propose that Titan’s equatorial dunes may represent a single, global sand sea with west-to-east transport providing sources and sinks for sand in each interconnected basin. The sand might then be transported around Xanadu by fast-moving Barchan dune chains and/or fluvial transport in transient riverbeds. A river at the Xanadu/Shangri-La border could explain the sharp edge of the sand sea there, much like the Kuiseb River stops the Namib Sand Sea in southwest Africa on Earth. Future missions could use the composition of Titan’s sands to constrain the global hydrocarbon cycle.
Highlights
We chose to follow an unconventional format with respect to our choice of section headings compared to more conventional practice because the multifaceted nature of our work did not naturally lend itself to a logical progression within the precribed system
The dune spacing varies with latitude, perhaps resulting from changes in sand supply [13]
Radebaugh (2010) [15] noted the similarity of the heights and spacings to those seen in longitudinal dunefields on Earth, despite Titan’s differing gravity, atmospheric density, and composition
Summary
Builds sand from smaller particles (presumably haze) by agglomeration. By contrast, a top-down mechanism creates sand by breaking down larger rocks into smaller and smaller pieces until the requisite 300-micron size is reached, similar to how silica sand forms on Earth. A challenge to the flocculation model (shared by the evaporite mechanism suggested below) is that the sand originates with the lakes and seas at high latitude, whereas it accumulates near the equator. This requires a horizontal journey of over 3000 km, and a vertical ascent of almost 1 km. If haze-derived organic materials make up a large fraction of Titan’s crust (as they would if karstic processes drive lake basin formation) erosion due to small channels and gullies could produce sand without discrete sources.
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