火星の大気と表面の相互作用:デルタ17O ALH 84001から炭酸塩の測定
J Farquhar1, M H Thiemens, T Jackson
1Department of Chemistry, University of California San Diego, 92093-0356, USA. jfarquha@ucsd.edu
Science (New York, N.Y.)
|June 11, 1998
まとめ
火星の隕石 ALH 84001 は,火星の大気とシリケート惑星の異なる酸素同位体貯蔵庫を明らかにしています. これは,オゾン光分解のような大気中のプロセスが,炭酸塩鉱石に記録された同位体異常を生じさせたことを示唆している.
科学分野:
- 惑星科学は惑星科学である.
- 地質化学 地質化学
- 天体生物学 アストロバイオロジー
背景:
- 火星の隕石は,火星の地質学と大気の歴史を理解するために重要なサンプルを提供します.
- 鉱物中の酸素同位体は,惑星のプロセスと環境条件の敏感なトレーサーです.
研究 の 目的:
- 火星の隕石ALH 84001から炭酸塩の酸素同位体組成を調べるために.
- 炭素酸塩の形成の間に火星に明確な酸素同位体貯蔵庫が存在していたかどうかを決定する.
- 火星における大気中の酸素同位体異常の潜在的メカニズムを探求する.
主な方法:
- ALH 84001 の炭酸塩における酸素同位体比 (デルタ18O,デルタ17O,デルタ17O) の分析.
- 火星の炭素酸イソトープデータと,既知の地上および潜在的な火星のシリケート貯蔵庫の比較.
主要な成果:
- 炭酸塩酸素同位体測定 (デルタ18O = 18.3 ± 0.4‰,デルタ17O = 10.3 ± 0.2‰,デルタ17O = 0.8 ± 0.05‰) は,シリケート鉱物と比較して分化を示しています.
- これらの結果は,炭素酸塩の形成時に火星に少なくとも2つの異なる酸素同位体貯蔵庫が存在することを支持しています:大気とシリケート惑星です.
- 大気異常の潜在的なメカニズムは,オゾン光分解からのCO2と興奮した酸素 (O(1D)) を含む.
結論:
- ALH 84001炭酸からの酸素同位体データは,火星の大気の複雑な同位体の進化を示しています.
- 大気中の同位体シグネチャーは,CO2-H2Oの交換と鉱物の降水を通じて,地表鉱物へと移すことができる.
- 観測された同位体組成のバランスをとるために,おそらく火星のレゴリットの中に,17Oの枯渇した酸素のためのシンクが必要です.
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