A New High-pressure System to Investigate Clathrate Hydrates Stability and Role in Volatile Outgassing on Titan and Enceladus

The origin of Titan's atmospheric methane and of the volatiles measured in Enceladus' south pole plumes remain, to this day, unresolved. Clathrate hydrates are among the favored deep-seated reservoir candidates. However, the conditions allowing for their dissociation and the release of volatiles to the atmosphere (Titan) or the plumes (Enceladus) are still poorly constrained. This is mainly because there is a lack of knowledge on the stability of mixed clathrate hydrates in presence of anti-freeze agents such as ammonia. We present a new high-pressure system, a high-pressure cryogenic calorimeter, currently being developed at JPL that is designed to address this deficiency in the literature. We use a liquid nitrogen - cooled Setaram BT2.15 calorimeter, located at the Ice Physics Laboratory, JPL (see Figure 1). The temperature range achievable with this instrument is 77-473 K. This calorimeter uses Calvet elements (3D arrays of thermocouples), to measure the heat flux required to follow a predefined heating rate within a sample and a reference cell with a resolution of 0.1 μW. A high-pressure system is being implemented in order to develop the capability of investigating the pressure range 0-100 bars. This system includes: high-pressure cells with a gas flow system (from Setaram), a gas handling system to deliver the gas from 1K bottles of CH4, CO2, and N2, a vacuum system, and a vent system. With the calorimeter, clathrate hydrates will be synthesized within the cells from an H2O-NH3 aqueous solution. Then, cooling and heating tests will be conducted for several gas pressures in order to measure simultaneously the dissociation curve and thermodynamic properties (heat capacity, latent heat). Similarly, clathrate hydrates will be synthesized from the solution of interest within the fluid pressure cell. Dissociation curves will be measured by varying temperature, and following optically and via Raman and diffuse reflectance infrared spectroscopy the samples' evolution. We are nearing the end of the development phase for both apparatus, and will present preliminary tests and results at the meeting. This work has been conducted at the Jet Propulsion Laboratory, California, Institute of Technology, under contract to NASA.