Hydrogen generation from ferrous saponite in reaction with H₂S-containing fluid: relevance to early Martian habitability

Natsumi Noda; Yasuhito Sekine; Yoshio Takahashi; Keisuke Fukushi; Hiroshi Sakuma; Takahiro Kawai; Mayuko Nakagawa; Norio KItadai; Kristin Johnson-Finn; Shawn Erin McGlynn

Article Hydrogen generation from ferrous saponite in reaction with H₂S-containing fluid: relevance to early Martian habitability

Natsumi Noda (Institute of Science Tokyo) ; Yasuhito Sekine (Institute of Science Tokyo) ; Yoshio Takahashi (Graduate School of Science, The University fo Tokyo) ; Keisuke Fukushi (Kanazawa University) ; Hiroshi Sakuma (Research Center for Electronic and Optical Materials/Functional Materials Field/Environmental Circulation Composite Materials Group, National Institute for Materials Science) ; Takahiro Kawai (Graduate School of Science, The University fo Tokyo) ; Mayuko Nakagawa (Institute of Science Tokyo) ; Norio KItadai (Japan Agency for Marine-earth Science and Technology) ; Kristin Johnson-Finn (Institute of Science Tokyo) ; Shawn Erin McGlynn (Institute of Science Tokyo)

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Natsumi Noda, Yasuhito Sekine, Yoshio Takahashi, Keisuke Fukushi, Hiroshi Sakuma, Takahiro Kawai, Mayuko Nakagawa, Norio KItadai, Kristin Johnson-Finn, Shawn Erin McGlynn. Hydrogen generation from ferrous saponite in reaction with H₂S-containing fluid: relevance to early Martian habitability. JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS. 2024, 130 (1), e2024JE008538.

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Molecular hydrogen is an important gas species for understanding the early Martian climate and redox chemistry. Through ancient aqueous alterations of crustal rocks, ferrous (Fe(II)) saponite formed abundantly on Mars. Subsequent intrusions of hydrothermal fluids may have resulted in the chemical reaction between the dissolved volatiles and the nearby rocks. Here we propose a new H₂ generating reaction between ferrous saponite and H₂S-containing fluids, possible on early Mars. A series of hydrothermal experiments at a relatively low temperature of 90°C were performed under anoxic conditions using synthesized ferrous saponite to compare the resulting H₂ concentration among various gas and fluid compositions. Based on the relationship with the existence of H₂S, reaction time, fluid pH, dissolved iron concentration, and amount of minerals, we found that high levels of H₂ (~0.1 mmol/g ferrous saponite) were generated in the presence of H₂S most rapidly in the moderate pH condition. Our microscopic chemical analysis of mineral phases suggested that ferrous saponite served as both the iron source of pyrite precipitation and the electron source to form H₂.

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