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矮惑星マケマケのアルベドと大気の制約は,恒星の隠蔽から見た
J L Ortiz1, B Sicardy, F Braga-Ribas
1Instituto de Astrofísica de Andalucía, CSIC, Apartado 3004, 18080 Granada, Spain. ortiz@iaa.es
Nature
|November 23, 2012
まとめ
氷の矮惑星であるマケマケは,恒星隠蔽を用いて研究されました. 研究者は,その大きさ,アルベド,および密度を決定し,冥王星のように地球規模の大気がないことを発見しましたが,局所的な大気のポケットを持っている可能性があります.
科学分野:
- トランス・ネプチューンのオブジェクト
- 矮惑星の特徴について
- 惑星の大気圏
背景:
- 冥王星とエリスは,類似した特性を有する氷の矮星ですが,異なる大気状態です.
- 別の矮惑星であるマケマケは,冥王星とエリスの間の中間位置にあり,密度や大気の性質は不明である.
- 以前の研究では,マケマケの大きさとアルベドが示されていたが,密度や大気中の存在に関する制約はなかった.
研究 の 目的:
- マケマケの大きさ,アルベド,密度,大気条件など,マケマケの物理的性質を決定する.
- マケマケの特徴を冥王星とエリスの特徴と比較するために.
- マケマケの冥王星のような大気の可能性を調査する.
主な方法:
- 2011年4月23日に観測された恒星隠蔽イベント.
- 隠蔽コードの分析により,マケマケの予測軸と幾何学的なアルベドを決定する.
- 密度と大気圧の推論は,恒星の隠蔽の光の曲線から得られた.
主要な成果:
- マケマケの予測軸は1,430 ± 9 kmと1,502 ± 45 kmと決定されました.
- V帯の幾何学的アルベドは,p ((V) = 0.77 ± 0.03として計算され,冥王星より高く,エリスより低い.
- 表面圧力の上限が4〜12ナノバーで,地球大気の欠如が確認され,局所的な大気は可能である.
- 密度は1.7 ± 0.3 g cm(-3) と推論された.
結論:
- マケマケは,地球規模の大気がない,密度が高く,高度に反射する矮星です.
- その物理的性質は,冥王星やエリスと比較して,明確な進化の経路を示唆しています.
- 局所的な大気現象の存在を確認するためにさらなる観測が必要である.
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