Where Does Titan Sand Come From: Insight From Mechanical Properties of Titan Sand Candidates

Extensive equatorial linear dunes exist on Titan, but the origin of the sand, which appears to be organic, is unknown. We used nanoindentation to study the mechanical properties of a few Titan sand candidates, several natural sands on Earth, and common materials used in the Titan Wind Tunnel, to understand the mobility of Titan sand. We measured the elastic modulus (E), hardness (H), and fracture toughness (Kc) of these materials. Tholin's elastic modulus (10.4+/-0.5 GPa) and hardness (0.53+/-0.03 GPa) are both an order of magnitude smaller than silicate sand, and is also smaller than the mechanically weak white gypsum sand. With a magnitude smaller fracture toughness (Kc=0.036+/-0.007 MPa-m^(1/2)), tholin is also much more brittle than silicate sand. This indicates that Titan sand should be derived close to the equatorial regions where the current dunes are located, because tholin is too soft and brittle to be transported for long distances.

[1]  B. Crawford,et al.  Measuring substrate-independent modulus of thin films , 2011 .

[2]  J. Barnes,et al.  On the chemical composition of Titan’s dry lakebed evaporites , 2013, 1308.4856.

[3]  Chao He,et al.  A comprehensive NMR structural study of Titan aerosol analogs: Implications for Titan’s atmospheric chemistry , 2014 .

[4]  C. Sotin,et al.  Spectroscopy, morphometry, and photoclinometry of Titan's dunefields from Cassini/VIMS , 2008 .

[5]  S. K. Croft,et al.  Voyager 2 at Neptune: Imaging Science Results , 1989, Science.

[6]  C. Sotin,et al.  A 5-Micron-Bright Spot on Titan: Evidence for Surface Diversity , 2005, Science.

[7]  S. Hörst,et al.  Carbon Monoxide Affecting Planetary Atmospheric Chemistry , 2017, 1705.08468.

[8]  R. Lorenz.  Physics of saltation and sand transport on Titan: A brief review , 2014 .

[9]  K. Bowman.  Mechanical Behavior of Materials , 2003 .

[10]  George M. Pharr,et al.  Cracking During Nanoindentation and its Use in the Measurement of Fracture Toughness , 1994 .

[11]  M. Smith,et al.  Solubility and stability investigation of Titan aerosol analogs: New insight from NMR analysis , 2014 .

[12]  D. Thomas,et al.  Wind as a Geological Process on Earth, Mars, Venus and Titan , 1988 .

[13]  Rosaly M. C. Lopes,et al.  Material transport map of Titan: The fate of dunes , 2016 .

[14]  Sarah M. Horst,et al.  Titan's Atmosphere and Climate , 2017, 1702.08611.

[15]  L. Sklar,et al.  Influence of temperature, composition, and grain size on the tensile failure of water ice: Implications for erosion on Titan , 2012 .

[16]  M. Smith,et al.  Identification of nitrogenous organic species in Titan aerosols analogs: Nitrogen fixation routes in early atmospheres , 2013 .

[17]  J. Waite,et al.  The Process of Tholin Formation in Titan's Upper Atmosphere , 2007, Science.

[18]  T. Lauer,et al.  Dunes on Pluto , 2018, Science.

[19]  N. Bridges,et al.  Direct Measurement of Interparticle Forces of Titan Aerosol Analogs (“Tholin”) Using Atomic Force Microscopy , 2017, 1710.06400.

[20]  S. Debei,et al.  The morphological diversity of comet 67P/Churyumov-Gerasimenko , 2015, Science.

[21]  H. Heywood.  The Physics of Blown Sand and Desert Dunes , 1941, Nature.

[22]  A. Bar-Nun,et al.  Aging of Titan's Aerosols , 2002 .

[23]  P. Kuenen.  Experimental Abrasion 4: Eolian Action , 1960, The Journal of Geology.

[24]  Antoine Lucas,et al.  Methane storms as a driver of Titan’s dune orientation , 2015, 1504.03404.

[25]  M A Smith,et al.  Formation of amino acids and nucleotide bases in a Titan atmosphere simulation experiment. , 2012, Astrobiology.

[26]  T. Proctor.  Low‐Temperature Speed of Sound in Single‐Crystal Ice , 1966 .

[27]  B. White,et al.  Higher-than-predicted saltation threshold wind speeds on Titan , 2014, Nature.

[28]  J. Rouzaud,et al.  Tholins and their relevance for astrophysical issues , 2008, Proceedings of the International Astronomical Union.

[29]  M. Tomasko,et al.  Possible tropical lakes on Titan from observations of dark terrain , 2012, Nature.

[30]  Brian R. Lawn,et al.  A Critical Evaluation of Indentation Techniques for Measuring Fracture Toughness: I , 1981 .

[31]  O. Anderson,et al.  A simplified method for calculating the debye temperature from elastic constants , 1963 .

[32]  R. Lorenz,et al.  Dune Worlds: How Windblown Sand Shapes Planetary Landscapes , 2014 .

[33]  C. Sotin,et al.  Shoreline features of Titan's Ontario Lacus from Cassini/VIMS observations , 2009 .

[34]  G. Pharr,et al.  Measurement of hardness and elastic modulus by instrumented indentation: Advances in understanding and refinements to methodology , 2004 .

[35]  K. Kaji,et al.  Relation between the crystal structure of polymers and the elastic modulus of polymer crystals in the direction perpendicular to the chain axis , 1975 .

[36]  V. Chevrier,et al.  Experimental determination of acetylene and ethylene solubility in liquid methane and ethane: Implications to Titan’s surface , 2017 .

[37]  A. Evans,et al.  Elastic/Plastic Indentation Damage in Ceramics: The Median/Radial Crack System , 1980 .

[38]  T. Cornet,et al.  Structure of Titan’s evaporites , 2015, 1512.07294.

[39]  C. Sotin,et al.  Evidence of Titan’s climate history from evaporite distribution , 2013, 1408.2899.

[40]  R. Kirk,et al.  Rain, winds and haze during the Huygens probe's descent to Titan's surface , 2005, Nature.

[41]  Rosaly M. C. Lopes,et al.  The Spectral Nature of Titan's Major Geomorphological Units: Constraints on Surface Composition , 2018 .

[42]  Mads Krabbe.  Fracture Toughness of Thin Films Estimated by Rockwell C Indentation , 2014 .

[43]  C. Sotin,et al.  Geological Evolution of Titan's Equatorial Regions: Possible Nature and Origin of the Dune Material , 2018 .

[44]  P. Willis,et al.  Titan tholins: simulating Titan organic chemistry in the Cassini-Huygens era. , 2012, Chemical reviews.

[45]  Rosaly M. C. Lopes,et al.  The Sand Seas of Titan: Cassini RADAR Observations of Longitudinal Dunes , 2006, Science.

[46]  C. Sotin,et al.  Organic sedimentary deposits in Titan's dry lakebeds: Probable evaporite , 2011 .

[47]  Chao He,et al.  Identification of nitrogenous organic species in Titan aerosols analogs: Implication for prebiotic chemistry on Titan and early Earth , 2014 .

[48]  N. Bridges,et al.  The effect of adsorbed liquid and material density on saltation threshold: Insight from laboratory and wind tunnel experiments , 2017, 1706.09986.

[49]  Randolph L. Kirk,et al.  Correlations between Cassini VIMS spectra and RADAR SAR images: Implications for Titan's surface composition and the character of the Huygens Probe Landing Site , 2007 .

[50]  U. Fink,et al.  The organic-rich surface of comet 67P/Churyumov-Gerasimenko as seen by VIRTIS/Rosetta , 2015, Science.

[51]  A. Hayes,et al.  Production and global transport of Titan’s sand particles , 2015 .

[52]  G. Pharr,et al.  An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments , 1992 .

[53]  C. Sotin,et al.  Cassini observations of flow‐like features in western Tui Regio, Titan , 2006 .