^1,2Tianqi Zhang,^1,3Qi Tao,^1,2Xiaorong Qin,^2,4Yuchun Wu,^1,2Jiaxin Xi,^1,3Xiaoliang Liang,^1,3Hongping He,⁵Sridhar Komarneni
Journal of Geophyical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2024JE008619]
¹State Key Laboratory of Deep Earth Processes and Resources, & Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, PR China
²University of Chinese Academy of Sciences, Beijing, PR China
³CAS Center for Excellence in Deep Earth Science, Guangzhou, PR China
⁴State Key Laboratory of Solar Activity and Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing, PR China
⁵Department of Ecosystem Science and Management and Materials Research Institute, 204 Energy and the Environment Laboratory, The Pennsylvania State University, University Park, PA, USA
Published by arrangement with John Wiley & Sons

Despite the anticipated abundant carbonates due to historical atmospheric CO2 levels, Mars presents a geological puzzle with MgFe-smectites dominating the Noachian and early Hesperian terrains, contrasted by sparse carbonate deposits. To address this point, we explored the impact of CO2 on MgFe-smectite formation, emphasizing the role of variable Si concentrations within the simulated Martian environment. Hydrothermal experiments, conducted under a constant CO2 concentration (C0.5) and varying Si concentrations (Si0.5 to Si4), reveal a transformation from pyroaurite to MgFe-smectite via lizardite as an intermediary phase. This transformation underscores the crucial role of Si in this mineral sequence. Notably, experiments demonstrate that the interlayer CO32− in pyroaurite is released into aqueous environments during the mineral conversion, potentially impacting the Martian CO2 budget. These findings could explain isolated carbonate outcrops and the possibility of hydrotalcite-group minerals on Mars today. Further Mars exploration should consider identifying hydrotalcite-group minerals for their implications on the planet’s climate and habitability.

^1,2Shuya Tan,^1,3,4Yasuhito Sekine,²Takazo Shibuya
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2024JE008591]
¹Earth-Life Science Institute (ELSI), Tokyo Institute of Technology, Tokyo, Japan
²Institute for Extra-cutting-edge Science and Technology Avantgarde Research (X-star), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan
³Institute of Nature and Environmental Technology, Kanazawa University, Kanazawa, Japan
⁴Planetary Plasma and Atmospheric Research Center, Tohoku University, Sendai, Japan
Published by arrangement with John Wiley & Sons

Enceladus’ ocean could support methanogenic life in terms of the availability of chemical energy (H2 and CO2) and nutrients (N and P). However, excess energy and nutrients in the ocean raise the question of why they remain abundant if Enceladus is inhabited. Terrestrial methanogens require trace metals, such as Co, Ni, Cu, Zn, and Mo, for their enzyme activation; nevertheless, the availability of these trace metals is largely unknown in Enceladus’ ocean. Here, we investigate concentrations of dissolved trace metals in Enceladus based on hydrothermal experiments and thermodynamic equilibrium calculations in order to understand the minerals that control their concentrations in water-rock interactions. Our results show that Ni and Co concentrations in hydrothermal fluids can be controlled by dissolution of a sulfide mineral, pentlandite, in chondritic rocks. In a pH range for Enceladus’ ocean, our calculations show that hydrothermal environments would be the source of dissolved Ni and Co. Given a suggested range of water chemistry (pH and dissolved species) of Enceladus’ ocean, Ni, Zn, and Mo concentrations in hydrothermal fluids would be comparable to the levels required for terrestrial methanogens. However, both Co and Cu concentrations would be depleted compared with the levels required for terrestrial methanogens. We suggest that if methanogenic life in Enceladus requires trace metals at the same levels as for terrestrial methanogens, the availability of Co and Cu could control the activity of methanogenesis, possibly leaving excess chemical energy and nutrients in the ocean.