地球上の惑星の蓄積に対するシリコン同位体の制約
Isaac J Onyett1, Martin Schiller2, Georgy V Makhatadze2
1Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, Copenhagen, Denmark. isaac.onyett@sund.ku.dk.
Nature
|June 14, 2023
まとめ
原始的な隕石は 地球上の惑星の構成要素ではありません 代わりに,早期に形成された微分小惑星は,惑星の形成中に内外太陽系物質の混合をたどるシリコン同位体の変異で,重要な惑星構成要素です.
科学分野:
- 惑星科学
- 宇宙化学
- 同位体地化学
背景:
- 地上の惑星の形成を理解するには,前体物質の知識が必要です.
- 岩石の核合成の変異は 惑星の構成要素をたどります
- シリコン同位体 (μ30Si) は,耐火性元素の主要なトレーサーである.
研究 の 目的:
- 隕石におけるシリコン (μ30Si) の核合成成分を決定する.
- 地球のような惑星の原材料を特定する
- 太陽系内部の 蓄積の歴史を再構築する
主な方法:
- 原始隕石と微分隕石におけるシリコン同位体の構成 (μ30Si) の分析
- 内部と外部の太陽系天体のSi値の比較.
- μ30のSi値と蓄積年齢および他の同位体トレーサー (Mo,Zr,Ni) の相関
主要な成果:
- 太陽系内部の天体 (火星を含む) はSi不足を示し,コンドライトはSi過剰を示している.
- 塩基体は主要な構成要素ではなく,分化された小惑星物質が主要な構成要素である.
- 地球の前身は ~26%のSiが豊富な太陽系外部の物質を含んでいたが,火星は早期に形成され,この濃縮を回避した.
- 火星と原地球のSi組成は,衝突成長と小石の蓄積による急速な形成 (<300万年) と一致しています.
- 地球のイソトープの組成は,流動性と月形成の影響を考慮して,小石の蓄積モデルと一致しています.
結論:
- 惑星の形成には,太陽系の内側と外側の異なる物質が混ざり合っていた.
- 早期に形成された微分小惑星は,コンドライトではなく,地上の惑星の重要な構成要素を表しています.
- 火星と地球のイソトープのサインを説明し,小石の蓄積の役割を強調しています.
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