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太陽系外惑星HD209458bの周囲に広がった上層大気圏
A Vidal-Madjar1, A Lecavelier Des Etangs, J-M Désert
1Institut d'Astrophysique de Paris, CNRS/UPMC, 98bis boulevard Arago, F-75014 Paris, France. alfred@iap.fr
Nature
|March 14, 2003
まとめ
天文学者は,通過中にガス巨人HD209458bから脱出する原子水素を検出しました. ライマン・アルファ線で観測されたこの発見は,惑星のロシュ限界を超えた大気の脱出を示唆しています.
科学分野:
- 外惑星科学とは,外惑星科学のこと.
- 大気物理学 大気物理学
- 星の天文学 星の天文学
背景:
- HD209458bは,観測された通過を観測した最初の系外惑星であり,ガスの巨星としての地位を確認しました.
- 以前の観測では,HD209458bの下層大気 (中性ナトリウム) のみ検出されました.
- エクソプラネットの大気の理解は,潜在的に居住可能な世界の特徴づけに不可欠です.
研究 の 目的:
- HD209458b系外惑星の上層大気を検知し,特徴づけること.
- ガス巨人の大気の脱出メカニズムを調査する.
- 検知方法としてトランジット中のライマンアルファ線吸収を活用する.
主な方法:
- HD209458bが宿主星を通過した3回の通過を観測した.
- 星のライマンアルファ線における吸収を測定する.
- 観測データを大気逃避モデルと比較する.
主要な成果:
- HD209458bの通過中に検出された15 +/- 4%の原子水素吸収.
- 観測された吸収は,ロシュ限界を超えた大気の脱出を示しています.
- これは,HD209458bの大気中に原子水素が初めて検出されました.
結論:
- HD209458bの上層大気は,活発に脱出しています.
- 原子水素の脱出は,惑星のロシュ限界を超えて発生します.
- ライマン・アルファ観測は,系外惑星の大気逃避を研究するのに有効です.
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