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    Titan cryomineralogy: what discoveries in the laboratory can tell us about Titan’s surface
    (American Geophysical Union (AGU), 2021-12-17) Cable, ML; Vu, TH; Malaska, MJ; Choukroun, M; Maynard-Casely, HE; Runcevski, T; Hodyss, RP
    Titan hosts a large, diverse menu of organic molecules and is considered to be a prebiotic chemical laboratory on a planetary scale. Photochemistry in the atmosphere initiates a chemical cascade, starting with the dissociation of N2 and CH4 and generating a wide variety of molecules, ranging from small molecules (acetonitrile, acetylene) to incredibly large macromolecular species (>10,000 Da). We and others have demonstrated previously that some organic molecules readily form co-crystals in Titan-relevant conditions. These molecular minerals, or cryominerals, represent an exciting new class of compounds for Titan’s surface. Here we report on the latest experimental and theoretical characterization of Titan cryominerals, and discuss implications for physical and chemical properties of various terrains on Titan’s surface that could be studied in situ by missions like Dragonfly. Co-crystals may influence Titan surface material characteristics such structural hardness and resistance to erosion. Enhanced thermal expansion and decreased crystal size, for example, may lead to fracturing and/or more rapid erosion of co-crystal-based deposits. Density changes upon co-crystal formation compared to pure compounds may also play a role in organic diagenesis and metamorphism on Titan. Some cryominerals with stability only under certain conditions could preserve evidence of surface evolution and exchange, such as cryovolcanic activity, ethane fluvial/pluvial exposure, or outgassing of CO2 from the moon’s interior. On a hydrocarbon world like Titan where organic chemistry dominates the atmospheric chemistry and surface geology, chemists have the opportunity play a significant role in planetary science discoveries, and likewise, discoveries motivated by planetary science may help inform fundamental organic and physical chemistry research. Plain-language Summary Titan is the largest moon of Saturn, and the only moon in our solar system with a thick atmosphere. Titan has similar weather processes to Earth, including clouds, rain, rivers, and lakes. However, it is too cold for this weather cycle to be driven by water. Instead, methane and ethane, the main components of natural gas, make up the liquids on Titan’s surface. Titan’s surface materials also appear to be made of different ‘stuff’ compared to Earth. Instead of rocks with silica, iron, and other heavy atoms, Titan’s terrain seems to be made up of organic molecules containing carbon, nitrogen, and hydrogen. We have discovered that some of these molecules form crystals that behave like minerals do here on Earth; we call them ‘molecular minerals’ or cryominerals. So far, we and others have reported seven cryominerals, with one more predicted by theoretical modeling. We will give an overview of the different properties of each of these cryominerals, and how that might give us clues as to how Titan’s surface features formed, or might be observed with landed spacecraft like Dragonfly.