金星の上層大気の中性成分:ヴィーナス軌道探査機の先駆者からの予備的な結果

H B Niemann, R E Hartle, W T Kasprzak

Science (New York, N.Y.)

|February 23, 1979

まとめ

ヴィーナス軌道に乗ったパイオニア号の観測により,原子酸素は155km以上にある熱球の主要な構成要素であり,太陽の角度によって気温が大きく変動することが明らかになった. 同位体比は地球の値と一致する.

科学分野:

惑星科学は惑星科学である.
大気科学大気科学
宇宙物理学宇宙物理学

背景:

金星の熱球は,大気動力学と化学を理解するための重要な領域です.
金星の上層大気組成と気温プロファイルに関する以前の知識は限られていた.

研究の目的:

金星の熱圏の中性成分と温度を in situ で測定する.
主要なガスの相対的多量と,その高さや太陽光照明による変動を決定する.

主な方法:

ヴィーナス軌道探査機のパイオニア号に搭載された四極質量スペクトロメーターを利用した.
ニュートラル粒子の in situ 測定を行い,スケールの高さから温度を導出しました.

主要な成果:

主要成分である二酸化炭素 (CO2),一酸化炭素 (CO),窒素 (N2),原子酸素 (O),ヘリウム (He) の存在が確認されました.
ターミネーター領域の155km以下で最も豊富に存在するガスとしてCO2が特定されました.
原子酸素が155km以上で支配的な構成要素であることが判明し,O/CO2比率が予想以上に高かった.
観測された熱球気温は,太陽のゼニット角69度で約400Kから90度で230Kまでです.
酸素と炭素の同位体比が地上の値に匹敵することを決定した.

結論:

原子酸素は,これまで考えられていたよりも,金星の上部熱圏において,より重要な役割を果たしている.
熱球の温度は,太陽のゼニット角度に強い依存を示し,ダイナミックなプロセスを示しています.
同位体組成は,金星と地球の共通の起源または同様の進化過程を示唆しています.

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