82-1 Sticking Together: Turbulent Flocculation of Tholins to Create Saltatable Dune Sand on Titan.

Session: Friends of Hoth, Episode IX: The Rise of Icy Ocean Worlds

Presenting Author:

Adis Husić

Authors:

Husić, Adis¹, Yu, Xinting², Martinez, Beauxregard³, Cordts, Charles⁴, Blase, Ryan⁵, Patrick, Edward⁶, Birch, Sam⁷, Lapotre, Mathieu GA⁸, White, Erik⁹

(1) Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX, USA, (2) University of Texas at San Antonio, San Antonio, TX, USA, (3) University of Texas at San Antonio, San Antonio, TX, USA, (4) University of Akron, Akron, OH, USA, (5) Southwest Research Institute, San Antonio, TX, USA, (6) Southwest Research Institute, San Antonio, TX, USA, (7) Brown University, Providence, RI, USA, (8) Stanford University, Geological Sciences, Stanford, CA, USA, (9) University of California, Santa Cruz, Santa Cruz, CA, USA,

Abstract:

 

Titan is the only known moon with a dense atmosphere and stable surface liquids of methane and ethane. The atmosphere forms aeolian features similar to those on Earth, such as dunes. Cassini’s VIMS instrument found the dunes are organic in composition with little or no water ice. These organics likely come from the atmospheric haze as it settles on the surface. Dune particles have an optimal saltation size of 100 to 1000 microns, depending on factors such as cohesiveness, while the haze particles are only 0.5 to 2 microns in size as measured by the Huygens probe. Laboratory analogs of the hazes, known as ‘Tholins’, are also 1 to 2 microns, with natural clusters reaching 10 microns.

To address this discrepancy, Barnes et al. 2015 proposed four growth mechanisms for organics on Titan, including flocculation and evaporitic deposition. We explored whether flocculation could create sand-sized particles in Titan’s river channels. Hirai et al. 2023 showed that wetting and drying tholin with liquid methane causes growth, but not over 20 microns. Earth-based models link floc sizes to viscosity, turbulence, and time. Thus, we tested turbulent mixing in hexane to stimulate floc growth.

We have four aliquots of 4 mg of tholin in 100 mL of hexane. Hexane is used since it is liquid at room temperature and has a similar viscosity to Titan’s methane/ethane liquid. For aliquot 1, tholin sits in hexane for 30 minutes with no mixing; Aliquot 2 sits until full hexane evaporation; Aliquot 3 is turbulently mixed (Re>4000) for 30 minutes; Aliquot 4 is turbulently mixed until full evaporation. The unevaporated solution from aliquots 1 and 3 are separated and allowed to evaporate, creating aliquots 5 and 6 respectively.

Our results for no mixing match Hirai et al. 2023, with no mixing showing growth but few aggregates being over 30 microns. The case is enough to grow aggregates from 1-10 microns to over 100 microns in as little as 30 minutes. Mixing for longer times increases this growth to have many particles over 300 microns, and some even over 1000 microns. Thus, flocculation and fluvial transport appear promising for forming sand-sized particles which may then saltate and lead to dune formation on Titan.

[1] Barnes+2015, PlSci, 4, 1, 1-19  [2] Hirai+2023, GeoRL, 50

 

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-4542

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