SEMINAR

Friday, September 18th, 2:00 p.m. 

ESRF Auditorium

"Probing Methane Clathrate Hydrates at Its Extremes: Implications for early Titan and ocean-exoplanet interiors"

Abstract

Katarzyna Skrzyńska¹, Erwan Le Menn², Baptiste Journaux³, Olivier Bollengier², Apostolos Pantousas¹, Mohamed Mezouar¹, Gabriel Tobie², and Anna Pakhomova¹

¹European Synchrotron Radiation Facility, Grenoble, France, katarzyna.skrzynska@esrf.fr ²CNRS UMR 6112, Universite de Nantes, LPG, Nantes, France ³University of Washington - Seattle, USA

Methane clathrate hydrates are unique compounds that bridge geoscience, planetary science, solid-state chemistry, and energy research. They are non-stoichiometric solids, which entrap variable amounts of methane within the cavities of a water framework. In extraterrestrial settings, deep methane clathrate reservoirs serve as a potential long-term source for atmospheric replenishment, a mechanism proposed to sustain the methane inventories of Titan, Pluto, and potentially many other large icy worlds and ocean planets. Beyond their role as volatile reservoirs, methane hydrates may govern the thermophysical state of the planet's interior, directly dictating the density, viscosity, and thermal conductivity profiles across the crust and mantle in icy planetary bodies. From a chemical perspective, the stability of methane hydrates is governed by a subtle compromise between attractive and repulsive Van der Waals forces between methane and water molecules. This unique balance makes methane hydrates a benchmark system for investigating hydrophobic hydration.

Despite the importance of methane hydrates, their behavior under high pressure is poorly understood and is the focus of scientific debate. Herein, using in situ single-crystal X-ray diffraction in a diamond anvil cell (DAC), we track subtle pressure-induced changes in methane clathrate hydrates. Our results show a pressure-driven increase in methane content within the clathrate hydrate framework and the emergence of a previously unknown clathrate hydrate phase that is stable at pressures of 1.3-2.1 GPa. Its formation is driven by methane–methane steric repulsion, which forces the formation of unconventional C–H···O hydrogen bonds. Furthermore, the new phase may serve as a methane reservoir in the outer part of the differentiating core of early Titan, thereby impeding degassing and accounting for the delay in the formation of Titan’s methane-rich atmosphere.