Meteoritic Evidence for the History of Water on Mars: (Fostering Joint International Research)

2019 Fiscal Year Final Research Report

• Project/Area Number: 15KK0153
• Research Category: Fund for the Promotion of Joint International Research (Fostering Joint International Research)
• Allocation Type: Multi-year Fund
• Research Field: Petrology/Mineralogy/Economic geology
• Research Institution: Japan Aerospace EXploration Agency (2018-2019); Tokyo Institute of Technology (2015-2017)
• Principal Investigator: Tomohiro Usui 国立研究開発法人宇宙航空研究開発機構, 宇宙科学研究所, 教授 (60636471)
• Project Period (FY): 2016 – 2019
• Keywords: 火星 / 火星隕石 / 水 / 水素同位体

Outline of Final Research Achievements

We conducted in situ hydrogen isotope (D/H) analyses of Martian meteorites. The hydrogen isotope analyses provide evidence for the existence of a distinct but ubiquitous water reservoir (D/H = 2-3 times Earth’s ocean water: SMOW). The origin of this reservoir appears to predate the current Martian atmospheric water (D/H = ~5-6 x SMOW) and is unlikely to be a simple mixture of atmospheric and primordial water retained in the Martian mantle (D/H ~SMOW). We conclude that this intermediate-D/H reservoir (2-3 x SMOW) is likely a global surficial feature that has remained relatively intact over geologic time. We propose that this reservoir represents either hydrated crust or ground ice interbedded within sediments. Our results corroborate the hypothesis that a buried cryosphere accounts for a large part of the initial water budget of Mars.

Free Research Field

地球化学

Academic Significance and Societal Importance of the Research Achievements

惑星表層環境は，その惑星近傍だけではなく，太陽系全体のダイナミクスの結果を反映しているため，異なる惑星間での表層環境の違いを理解することが，地球表層環境を理解する上でも非常に重要となってくる。地球以外で過去に液体の水を保持していた太陽系天体は火星のみであり，火星は地球との比較対象として，惑星表層環境の解明に適した天体と言える。本研究により，火星の水の散逸史および表層環境進化が明らかとなるだけでなく，異なるサイズ・太陽距離を持つ地球表層環境の理解が飛躍的に進むと期待される。