[M-IS18] 水惑星学

[MIS18-02] 氷衛星における氷地殻底部環境を模擬したガスハイドレート生成観察装置の開発

*谷 篤史¹、須山 充¹、西谷 隆介² (1.神戸大学　大学院人間発達環境学研究科、2.大阪大学　大学院理学研究科)

キーワード：氷衛星、氷地殻、ガスハイドレート

Gas hydrates are clathrate compounds where hydrogen-bonded water cages include a guest gas molecule. Methane hydrate is one of famous gas hydrates because it is naturally found in deep-sea and permafrost sediments on the Earth. Gas hydrates would exist in icy moons as well. One of the most likely candidate is Saturn’s icy satellite Enceladus. Enceladus has a global ocean beneath the icy shell. INMS (Ion and Neutral Mass Spectrometer) aboard the Cassini spacecraft has investigated composition of the plumes that includes H2O (< 90 %), CH4, CO2, NH3, and other various organic materials. These results could reflect the composition of the subsurface ocean and imply the presence of clathrate hydrates in the ocean. Bouquet et al. (2015) suggests that the clathrate hydrate should be stable in the subsurface region deeper than 22 km. Density of gas hydrates depends on guest gas molecules. For example, methane hydrate is lighter than the water, whereas CO2 hydrate is heavier. If CO2 hydrate forms at the bottom of the icy shell, the average density may become large and the ice (water ice + CO2 hydrate) may try to sink locally. We have developed the observation system of gas hydrate formation and dissociation below the ice sheet. In the presentation, we report the progress of the observation system.