Titan’s Prevailing Circulation Might Drive Highly Intermittent, Yet Significant Sediment Transport

Abstract

Titan, the largest moon of Saturn, is characterized by gigantic linear dunes and an active dust cycle. Much like on Earth, these aeolian processes are caused by the wind‐driven saltation of surface grains. It is still unclear, however, how saltation on Titan can occur despite the typically weak surface winds and the potentially cohesive surface grains. Here, we explore the hypothesis that saltation on Titan may be sustained at lower wind speeds than previously thought, primarily through granular splash rather than aerodynamic lifting of surface grains. We propose a saltation mass flux parameterization for Titan and use it to quantify sediment transport with a general circulation model. The results suggest that Titan's prevailing circulation can generate highly intermittent yet significant saltation, with mass fluxes of the order of 104 kg m−1 year−1, and that Titan dunes may be formed primarily by fine grains, approximately 0.1 mm in size.

Sand Transport on Titan: A Sticky Problem

“…The modeling in Comola et al (2022) disagrees with threshold speeds higher than actually measured in Titanlike laboratory measurements (Burr et al, 2015). The wind tunnel (a repurposed Venus tunnel, only 20 cm in diameter) in these experiments was not operated at Titan conditions, but at higher pressures (12 vs. 1.5 bar) and temperatures (293K vs. 94), aiming to match the ratio of density to viscosity on Titan.…”

“…With this counterintuitive assumption (for which there seems-Comola et al, 2019-at best limited experimental support), the optimum size would be only 0.1 mm and transport could be rather common. Comola et al (2022) calculate that sand transport rates can be quite high, but have not shown whether the resultant dune pattern is consistent with that observed on Titan.…”

“…The avalanche of recent papers on saltation topics attests to the interest in blowing sand in planetary environments. The wide digression from previously assumed Titan transport characteristics implied by Comola et al (2022) is disquieting: I can't quite put my finger on which of its many assumptions seems most improbable. But it makes some bold and interesting predictions which are testable by Dragonfly measurements, so time will tell.…”

“…The new work by Comola et al (2022) invokes strong cohesion, motivated by microscopic force measurements on Titan-like organic materials by Yu, Hörst, He, McGuiggan, & Bridges (2017), . The result is that the fluid threshold would be rather high, such that sand would very rarely move, and that the optimum particle size would be some 2 mm.…”

“…A penetrometer instrument on the Huygens probe in 2005 determined that the streambed sediments at the landing site were damp (Atkinson et al, 2010), data initially interpreted (in)famously as indicating mechanical properties similar to crème brûlée (e.g., Lorenz, 2020). Some new work (Comola et al, 2022) explores the implications of possibly enhanced cohesion of the carbon-rich sands elsewhere on Titan.…”