Is the methane reservoir in Titan methane hydrate?

2019 Fiscal Year Final Research Report

• Project/Area Number: 17K14422
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Geochemistry/Cosmochemistry
• Research Institution: The University of Tokushima
• Principal Investigator: NOGUCHI Naoki 徳島大学, 大学院社会産業理工学研究部(理工学域), 助教 (50621760)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: メタンハイドレート / タイタン / 拡散 / 高圧 / 高圧氷 / メタン循環 / 振動分光

Outline of Final Research Achievements

Infrared (IR) absorption and Raman spectra of CH4 hydrate were measured under low temperature and high pressure in order to reveal the dynamics of CH4 in the phase-I (MH-I), -II (MH-II), and -III (MH-III) and their cage occupancies of CH4 and hydration numbers. For the IR spectra of MH-I, the bands due to ro-vibrational transition appeared in the wavenumber region of the CH stretching (ν3) mode of CH4 in the M cage below 40 K. It is the evidence for the quasi-rotor behavior of CH4. The ro-vibrational bands also were observed in the IR spectra of MH-II below 1.3 GPa. The shapes of the ν1 and ν3 band in the Raman and IR spectra of MH-II were drastically changed above 1.3 GPa. It suggests that the cage occupancy of the LL cage was changed from one to two by the dehydration at 1.3 GPa. The hydration number also changes from 5.36 ± 0.07 to 4.71 ± 0.22. The double occupied state in the LL cage may be realized by the formation of the dimer of CH4.

Free Research Field

地球惑星物質学

Academic Significance and Societal Importance of the Research Achievements

タイタンの大気中には2％のメタンが含まれており、探査によって発見されているアミノ酸前駆物質の原料であると考えられている。そのため、タイタンのメタンの存在量を確定し、メタンの循環過程を解明することは分子進化速度を解明するうえで重要である。この研究の成果は、タイタンにおけるメタンのリーザバ(貯蔵庫)であるメタンハイドレートの存在量を見積もるのに必要な基礎的なデータを実験によって導出したことである。