Exploring titan in the laboratory and in situ

Abstract

Titan, the largest moon of Saturn, contains a vast inventory of org. mols. on the surface of a water-ice-dominated ocean world, making it a prebiotic chem. lab. on a planetary scale. Many of the org. mols. on Titan's surface appear to assoc. in a manner akin to minerals on Earth, forming mol. solids, co-crystals, and hydrates. These 'mol. minerals' exhibit unique phys. and mech. properties compared to their pure components, and may affect formation mechanisms and timescales of landscape evolution on Titan. We have discovered three co-crystals to date, which have been characterized using Raman spectroscopy and cryogenic powder X-ray diffraction. The benzene-ethane co-crystal, the equiv. to a 'hydrated mineral' on Titan as ethane is liq. at 90 K, is readily formed at Titan surface temps. and would likely be the first material to ppt. from an evapg. hydrocarbon lake. The acetylene-ammonia co-crystal could form via co-condensation in the atm., or if acetylene dissolved in liq. methane or ethane flowed over an ammonia-rich surface deposit during a fluvial/pluvial event. The acetylene-butane co-crystal might be ubiquitous in the polar regions of Titan, as both of these compds. should be abundant on Titan and both are highly sol. in liq. hydrocarbons, making them the major components of evaporite materials in and around the Titan lakes. Intermol. interactions of mol. minerals such as these might change dissoln. and repptn. kinetics and equil., and therefore could affect the chem. erosion, transport, and deposition of mols. in terrain on Titan's surface. In situ data will be crit. for validating this lab. work. Dragonfly is a rotorcraft lander recently selected under the NASA New Frontiers Program to explore Titan's surface. The aerial mobility of Dragonfly enables sampling of materials and detailed measurement of surface compn. at dozens of sites in different geol. settings up to hundreds of kilometers apart. Dragonfly will perform wide-ranging in situ exploration and discovery to study prebiotic chem. and document the habitability of this extraterrestrial environment, including possible characterization of any mol. minerals as predicted by lab. work.

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