Titan Regolith: Developing and Characterizing a Simulant

In January 2005, the Huygens probe successfully landed and examined the surface of Titan. The equatorial region is dominated by vast longitudinal dune fields composed of a dark undetermined material, possibly a combination of organic materials deposited from the atmosphere and water ice. The chemistry and material exchange mechanisms taking place between Titan’s surface and atmosphere are still poorly constrained so far, limiting our understanding of the chemical and geological processes occurring within this unique environment.

In order to better understand how Titan regolith forms and evolves into the topographical features that were observed by Cassini and Huygens, we measure the material properties of haze analogs prepared in the laboratory (the so-called “tholins”) and use this information to select, produce, and characterize a Titan regolith simulant. The simulant allows us to study Titan soil grains at relevant sizes (laboratory-produced tholins are often limited to sub-micron sizes while the grains on Titan’s dunes estimated to be on the order of hundreds of microns) as well as access larger quantities allowing for bulk material properties determination. The compression and shear strength of granular soils are key to the formation of surface topography, so that comparing our measurement on simulants with Titan’s surface features will ultimately both validate our simulants and constrain regolith formation and evolution processes on Saturn’s moon.

We present the production methodology and material properties measurements on our first simulants. Poly(methyl methacrylate) (PMMA) was chosen based on its comparable bulk modulus to laboratory tholins. Sub-micron PMMA particles (~200 nm; uniform, spherical particles) were first synthesized using a facile wet chemical polymerization reaction as an analogue to organic colloids comprising Titan’s atmospheric hazes. Batch syntheses were optimized to allow high yield (hundreds of grams per batch), mediating subsequent spray-drying of material products to micron-scale particles (~100 μm), in analogue to tholin surface sediment aggregates. Material crystallinity was assessed via differential scanning calorimetry and engineered via thermal treatments to best approximate native tholins. The bulk modulus was similarly analyzed via nano-indentation and optimized via control of polymer cross-linking. Finally, we measured the compression and shear strengths of granular material composed of these PMMA particles.