Clathrate hydrates (Fig. 1) are cage-like structures of water molecules that house guest gas species. They form when the gas interacts with ice under high-pressure and low-temperature conditions, and are thought to influence the surface geology and composition of icy bodies in the Solar System. Although the importance of clathrates has long been recognised, previous studies of their formation and physical properties have mostly involved theoretical thermodynamic calculations for structures produced from pure water solutions. In new research, published in Astronomy & Astrophysics, however, carbon dioxide (CO2) clathrate hydrates produced from weak saline solutions have been investigated. The team of researchers, including PhD student Ms Emmal Safi, used the High Resolution Powder Diffraction beamline (I11) at Diamond Light Source to conduct an in situ study of clathrates that are more relevant to those produced in the salty oceans of icy moons. The results indicate substantial differences in the formation characteristics and physical properties of CO2 clathrates compared with those that form from pure water solutions. The new findings can be used to help calibrate and inform models of clathrate formation on Earth, and other planetary bodies.
Figure 1: Crystal structure of a CO2 clathrate hydrate. The cage structure is formed from the interaction of CO2 gas with water molecules in ice (red and black: oxygen and hydrogen atoms, respectively). CO2 molecules (blue and purple: carbon and oxygen atoms, respectively) are then entrapped within the structure.
Clathrates in the outer Solar System
3. Day SJ et al. In situ apparatus for the study of clathrate hydrates relevant to solar system bodies using synchrotron X-ray diffraction and Raman spectroscopy. Astron. Astrophys. 574, A91 (2015).
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