超高温の巨大系外惑星における鉄の濃縮
David Ehrenreich1, Christophe Lovis2, Romain Allart2
1Observatoire Astronomique de l'Université de Genève, Versoix, Switzerland. david.ehrenreich@unige.ch.
Nature
|March 13, 2020
まとめ
研究者達は,超高温の系外惑星WASP-76bに不対称な大気のシグネチャを検出し, 鉄が夜側で凝縮していることを示しました. この発見により 極端な外惑星の気候と化学の理解が進んでいます
科学分野:
- 外惑星科学
- 大気化学
- 天体物理学
背景:
- 超高温の巨大系外惑星は,極端な温度 (>2,000 K) と高い日照度を有しており,惑星の気候を研究するのに理想的です.
- 大気モデルでは 雲のない昼側が 原子種に支配され 夜側よりも高い温度で 原子が分子に再結合することを予測しています
- 以前の観測では金属元素と温度相違が確認されましたが,系外惑星の表面における化学的グラデーションの直接的な測定は行われませんでした.
研究 の 目的:
- 超高温系外惑星の表面上の 化学的グラデーションを検知し特徴づけること
- 太陽系外惑星の昼と夜間の大気化学の違いを調査する
- 異なる大気組成を示す非対称な吸収シグネチャーを識別する.
主な方法:
- 大気シグネチャーをスペクトル的に,また一時的に解明するために,大きな光子収集領域を持つ高分散スペクトロスコーピーを利用した.
- 特定の要素からの吸収信号を特定するために,トランジットデータを分析した.
- 吸収信号のドップラーシフトを測定して 風のパターンと大気動態を推測した
主要な成果:
- WASP-76bの末端にニュートラル鉄 (−11 ± 0.7 km/s) に起因するブルーシフト吸収信号が検出されました.
- 夜の端にある朝のターミネーターの近くに 鉄の吸収信号は観測されなかった.
- 鉄の非対称性は 惑星の回転と昼から夜間の風の組み合わせによって説明されます
結論:
- WASP-76b系外惑星の 化学的な変化が確認されました
- 原子鉄は昼側から夜側へ 凝縮しているに違いない
- 極端な系外惑星環境における大気化学モデルを支持する観測証拠を提供した.
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