太陽の酸素同位体組成は,捕捉された太陽風から推論された
K D McKeegan1, A P A Kallio, V S Heber
1Department of Earth and Space Sciences, University of California-Los Angeles (UCLA), Los Angeles, CA 90095-1567, USA. mckeegan@ess.ucla.edu
まとめ
太陽は,太陽系内部の岩質物質よりも,より豊富な酸素-16 (16O) を有しています. これは,初期の非質量依存化学が,より重い酸素同位体で地上の惑星を豊かにしていたことを示唆している.
科学分野:
- 宇宙化学 (コスモケミストリー)
- 惑星科学は惑星科学である.
- 天体生物学 アストロバイオロジー
背景:
- 太陽系材料の酸素同位体組成は,著しい変化を示しています.
- 決定的な原始太陽系酸素同位体組成は確立されていない.
- 太陽の光球は,リチウムよりも重い元素の太陽系の平均同位体組成を代表すると考えられています.
研究 の 目的:
- 太陽の酸素同位体組成を決定する.
- 太陽の酸素同位体と太陽系内部の惑星物質の同位体を比較する.
- 太陽系内部の同位体変動の起源を調査する.
主な方法:
- NASAのジェネシスミッションによって地球に戻された太陽風のサンプルを分析した.
- 太陽風における酸素同位体比の測定 ((16) O, (17) O, (18) O)
- 太陽風の同位体データと,地球,月,火星,隕石に関する既存のデータとの比較.
主要な成果:
- 太陽は,地球,月,火星,および大質量隕石と比較して,酸素-16 (16O) の濃度が大幅に増加しています.
- 太陽系内部の岩石体は,太陽に比べて16Oで枯渇しています.
- これらの発見は,岩石材料がより重い酸素同位体 ((17) Oと (18) O) で16Oに比べて約7%濃縮されていることを示唆しています.
結論:
- 太陽の同位体組成は,初期の太陽系の平均を反映しています.
- 太陽系内部の岩石物質は,おそらく17Oと18Oで濃縮された.
- この濃縮は,おそらく,惑星小惑星の蓄積前に発生した,質量に依存しない化学過程の結果である.
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