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巨大な彗星のような水素雲が,暖かい海王星質量系外惑星GJ 436bから脱出しています
David Ehrenreich1, Vincent Bourrier1, Peter J Wheatley2
1Observatoire de l'Université de Genève, 51 chemin des Maillettes, 1290 Versoix, Switzerland.
Nature
|June 26, 2015
まとめ
熱い系外惑星は,恒星の放射線により大気を失う可能性があります. 系外惑星GJ 436bの観測は巨大な水素雲を明らかにし,時間の経過とともに大気質量の大幅な損失を示しています.
科学分野:
- 天文学と天体物理学について
- 惑星外科学とは,惑星外科学です.
背景:
- 恒星に近い軌道を回る系外惑星は,強い放射線を被り,大気質量損失につながる可能性がある.
- 低質量系外惑星は特に感受性があり,いくつかの理論は,大気を失って,海王星のような惑星から岩石の世界へと進化したと示唆しています.
研究 の 目的:
- 紫外線通過シグネチャーを分析することによって,系外惑星の大気質量損失を調査する.
- 大気圏の脱出と,その影響が系外惑星の進化に及ぼす観測的証拠を提供するためである.
主な方法:
- 紫外線スペクトロスコピーを用いて宿主恒星を通過する際の系外惑星GJ 436bの観測.
- 紫外線通過の深さと期間を光学通過データと比較する.
主要な成果:
- GJ 436bは,光学的な深さ (0.69%) に比べて,かなり大きな紫外線通過深さ (56.3 ± 3.5%) を示した.
- 紫外線通過は,光学通過の約2時間前に始まり,光学通過の3時間後に終了し,かなり長かった.
- GJ 436bの周りを囲む,水素が多大な外層雲の存在を推論した.
結論:
- 観測された延長紫外線通過は,GJ 436bからの大気質量損失が大きいことを示しています.
- 推定された質量損失率は,海王星のような大気を星が生涯にわたって枯渇させるには不十分ですが,過去より高い速度を示唆しています.
- これらの発見は,系外惑星の大気進化と,惑星が海王星のような状態から岩石状態への移行を理解するために重要な観測データを提供しています.
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