火星の炭酸塩消失の謎を解明か(NASA’s Curiosity Rover May Have Solved Mars’ Missing Carbonate Mystery)

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2025-04-17 NASA

NASAのキュリオシティ探査車は、長年謎とされてきた「火星に炭酸塩鉱物が見つからない問題」に対する有力な解答を発見した。ゲール・クレーター内のセントラル・ビュート(Central Butte)での観測から、かつて炭酸塩が存在していた可能性のある地層が酸によって溶解したことが判明。これは酸性の地下水が炭酸塩を溶かした結果とされ、炭酸塩鉱物が検出されなかった理由を説明するもの。この発見は、火星の古代気候、環境変化、生命存在可能性を理解するうえで重要な一歩とされている。

<関連情報>

キュリオシティ探査機によって確認された炭酸塩は、太古の火星で炭素循環が行われていたことを示している Carbonates identified by the Curiosity rover indicate a carbon cycle operated on ancient Mars

Benjamin M. Tutolo, Elisabeth M. Hausrath, Edwin S. Kite, Elizabeth B. Rampe, […], and Ashwin R. Vasavada
Science  Published:17 Apr 2025
DOI:https://doi.org/10.1126/science.ado9966

火星の炭酸塩消失の謎を解明か(NASA’s Curiosity Rover May Have Solved Mars’ Missing Carbonate Mystery)

Editor’s summary

The Curiosity rover is gradually climbing a mountain located in Gale crater on Mars. Higher levels of the stratigraphy expose rocks that formed at later times. Tutolo et al. studied the composition of drill samples taken from a sulfate-rich layer (see the Perspective by Bishop and Lane). They found that the rocks contained abundant iron carbonate, which was invisible in previous orbital observations. If there are similar abundances of carbonate in other sulfate-rich layers across Mars, then those layers may contain a substantial reservoir of carbon dioxide extracted from the atmosphere. The carbonates found by the authors have partially decomposed, returning some carbon dioxide to the atmosphere: an ancient carbon cycle. —Keith T. Smith

Abstract

Ancient Mars had surface liquid water and a dense carbon dioxide (CO2)–rich atmosphere. Such an atmosphere would interact with crustal rocks, potentially leaving a mineralogical record of its presence. We analyzed the composition of an 89-meter stratigraphic section of Gale crater, Mars, using data collected by the Curiosity rover. An iron carbonate mineral, siderite, occurs in abundances of 4.8 to 10.5 weight %, colocated with highly water-soluble salts. We infer that the siderite formed in water-limited conditions, driven by water-rock reactions and evaporation. Comparison with orbital data indicates that similar strata (deposited globally) sequestered the equivalent of 2.6 to 36 millibar of atmospheric CO2. The presence of iron oxyhydroxides in these deposits indicates that a partially closed carbon cycle on ancient Mars returned some previously sequestered CO2 to the atmosphere.

0303宇宙環境利用
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