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初期の地球に有機分子が彗星から届いた
C F Chyba1, P J Thomas, L Brookshaw
1Laboratory for Planetary Studies, Cornell University, Ithaca, NY 14853, USA.
まとめ
初期の地球は,小惑星や彗星の衝突から生前生物の有機分子を受け取ったかもしれない. 初期の濃厚な大気は,生命の起源にとって極めて重要な有機分子の無傷な配送を可能にしました.
科学分野:
- 天体生物学 アストロバイオロジー
- 惑星科学は惑星科学である.
- 地質化学 地質化学
背景:
- 小惑星や彗星の衝突による地球上のプリバイオティックな有機分子の蓄積は,重爆撃 (4.5~38億年前) の間に発生したと推測されている.
- オーガニック分子の生存に対する大気への入り込みと衝撃の影響に関する以前の理解.
研究 の 目的:
- 彗星や小惑星から初期の地球に生前生物学的有機分子の生存と運搬を調査する.
- オーガニック分子を無傷に納入できる条件を決定する.
主な方法:
- 彗星と小惑星の大気相互作用のモデリング,空中ブレーキと衝撃熱分解を含む.
- 異なる衝撃速度と大気密度における有機分子生存率の分析.
- 初期の地球における有機分子増殖率の計算.
主要な成果:
- 有機分子は,約10 km/sを超える衝撃に耐えられない.
- 1バーの大気圏での空中ブレーキは,この臨界速度を下回る小さな彗星/小惑星を遅らせるには不十分です.
- 確固たる密度 (10バーCO2) の初期の大気は,45億年前の10^6-10^7kg/年という速度で彗星からの有機物の供給を可能にした.
結論:
- 密度の高い初期の大気は,地球外からの衝撃から,無傷のプリバイオティック有機分子を運ぶために極めて重要でした.
- オーガニック分子の増殖率は時間とともに低下し,半減期は約10^8年であった.
- この配送メカニズムは,地球上の生命の起源に関する有機物質の重要な源泉を提供します.
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