隕石や火星の大気からの紫外線誘発メタン排出
Frank Keppler1, Ivan Vigano, Andy McLeod
1Department of Atmospheric Chemistry, Max Planck Institute for Chemistry, Hahn-Meitner-Weg 1, 55128 Mainz, Germany. frank.keppler@mpic.de
Nature
|June 9, 2012
まとめ
火星のメタンは,隕石から発生している可能性がある. 紫外線は隕石中の有機物質をメタンに変換し,大気中のメタンのレベルを説明する可能性がある. この地外的なメタンは,地球に似た炭素同位体シグネチャーを有しています.
科学分野:
- 惑星科学 惑星科学
- 天体生物学 アストロバイオロジー
- 地質化学 地質化学
背景:
- メタンは火星の大気中に検出され,その起源と観測の信頼性についての議論を巻き起こしました.
- メタンの寿命が短いため,生物学的または地質学的,継続的な供給源が必要になります.
- 以前の仮定では,隕石からのメタンの放出は無視できると考えられていた.
研究 の 目的:
- 火星の表面条件に曝された隕石からメタンの生成の可能性を調査する.
- 火星で観測された大気中のメタン濃度について,隕石由来メタンが説明できるかどうかを判断する.
- 隕石から生成されるメタンの同位体シグネチャーを分析するために.
主な方法:
- マーチソン隕石 (CM2炭酸性コンドライト) を,火星の表面条件をシミュレートした状態で紫外線に晒す.
- 実験的分析を通じてメタンの生産量を定量化する.
- 放出されたメタンの安定した水素と炭素同位体を分析する.
主要な成果:
- 重要な量のメタンは,紫外線に曝露した際にマーチソン隕石から生成されます.
- 隕石からの紫外線誘発によるメタンの形成は,火星の大気中のメタンの推定量のかなりの部分を説明することができます.
- 安定した水素同位体は,メタンの地球外起源を確認し,炭素同位体は,地上の微生物のメタンに似ている.
結論:
- 火星の隕石は,火星の大気中のメタンの信憑な源である.
- 火星表面の紫外線は,隕石の有機物からメタンの生成を促す可能性があります.
- 炭素同位体分析だけでは,火星の生物学的メタンと隕石由来メタンを区別できないかもしれません.
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