[B-BC03] 地球惑星科学　生命圏フロンティア

[BBC03-05] Habitable aqueous environment on Early Mars inferred from reconstructed water chemistry at Gale

★Invited Papers

*福士 圭介¹、関根 康人^2,1、佐久間 博³、森田 康暉⁴、Robin Wordsworth⁵ (1.金沢大学環日本海域環境研究センター、2.東京工業大学地球生命研究所、3.（独）物質・材料研究機構、4.金沢大学大学院自然科学研究科自然システム学専攻、5.ハーバード大学)

キーワード：初期火星、ゲールクレータ、水質

There is a wealth of geomorphological and mineralogical evidence indicating the presence of liquid water on early Mars. However, the chemical properties of the water such as pH and salinity, which are crucial to habitability on early Mars, have not been clarified so far. The NASA rover Curiosity has conducted a geological survey of Gale crater, a former lake on Mars, and provided mineralogical and geochemical data on the lacustrine sediment. The present study quantitatively estimates the water chemistry of the pore water based on exchangeable cation compositions in the smectite and the salt mineralogy in the sediment. Results show that the liquid water was of Na-Cl type with moderate salinity (0.1-0.5 mol/kg) and circumneutral pH. The estimated Na-Cl concentrations reflect hyposaline lakes developed in 10^4--10^6-year-long semiarid climates. The mild aqueous conditions and redox disequilibria in secondary minerals under this estimated water chemistry suggests that there was a habitable aqueous environment on early Mars.