Hydrogen cyanide and butadiene as cryominerals on the surface of Titan
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Date
2021-12-17
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Publisher
American Geophysical Union (AGU)
Abstract
The Cassini-Huygens mission has revealed a wide variety of Earth-like landforms on Titan’s surface: plains, mountains, plateaux, dunes, lakes, seas and rivers. Titan’s surface appears to be constructed from organic materials and ice, rather than rocks and minerals that make up Earth’s surface. At a surface temperature of ~92 K, non-covalent interactions such as hydrogen bonding and van der Waals forces are sufficiently strong to enable stable interactions among these organic molecules, which form an entirely new class of cryogenic organic minerals (naturally occurring compounds with a specific composition). Photochemical models, partially validated by Huygens surface measurements and Cassini spacecraft measurements as well as Earth-based observations, allow us to make an initial guess for the composition of Titan’s surface. Simple organic molecules like acetylene, hydrogen cyanide, acetonitrile, etc. in their solid form are expected to be important constituents of the surface. However, many of their crystal structures and properties in solid state, at Titan relevant temperatures, are ambiguous. It is highly likely that crystalline polymorphs of some of these molecules are yet to be discovered. The crystal structure of a solid material is one of its most fundamental properties, and is necessary for understanding of intermolecular interactions and for prediction of mechanical and chemical properties – such as the ability to support deep valleys, high canyon walls, and resistance to erosion. We will present new data on the crystal structure and physical properties of two molecules thought to be present in significant quantities on Titan’s surface: hydrogen cyanide and butadiene. We have used Raman spectroscopy and cryogenic powder X-ray diffraction to better understand the phase behavior and structure of these materials under Titan conditions. While hydrogen cyanide is known to undergo a phase transition at ~170 K, the behavior of butadiene at low temperature has not been explored in detail. Our data indicates a new monoclinic structure for butadiene, and a possible new structure for HCN at low temperature. We will also present the implications of these results for Titan’s geology and evolution.
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Keywords
Moon, Saturn planet, Hydrogen cyanides, Butadiene, Surface area, Rocks, Minerals, Temperature range, Molecules, Canyons, Raman spectroscopy
Citation
Hodyss, R. P., Vu, T. H., Maynard-Casely, H. E., Cable, M. L., Malaska, M., & Choukroun, M. (2021). Hydrogen cyanide and butadiene as cryominerals on the surface of Titan. Presentation to the AGU Fall Meeting 2021, New Orleans, Louisiana and Online, 13-17 December 2021. In AGU Fall Meeting Abstracts (Vol. 2021, P45G-2515). Retrieved from: https://agu.confex.com/agu/fm21/meetingapp.cgi/Paper/912386