Climates and spectral signatures of rocky planets around low-mass stars

2023 Fiscal Year Final Research Report

• Project/Area Number: 18K13601
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 17010:Space and planetary sciences-related
• Research Institution: National Astronomical Observatory of Japan (2020-2023); Tokyo Institute of Technology (2018-2019)
• Principal Investigator: Fujii Yuka 国立天文台, 科学研究部, 准教授 (20713944)
• Project Period (FY): 2019-02-01 – 2024-03-31
• Keywords: 系外地球型惑星 / ハビタブルゾーン

Outline of Final Research Achievements

I calculated the three-dimensional atmospheric structures of (synchronously-rotating) terrestrial planets in the habitable zones of low-mass stars, as a function of atmospheric pressure and composition. Based on these insights, I examined the observability of spectral signatures of atmospheric species in the planetary thermal emission, using (a) the time variation of the absolute flux (“phase curves”), and (b) the Doppler shift of the spectral lines. These methods can, in principle, be applied to non-transiting exoplanets in the solar neighborhood once a stable spectrograph (a high-resolution spectrograph in the case of (b)) is available, and the detectability with future observatories was evaluated. In addition, I studied the stability of one type of biosignature, volatile organic compounds, under the ultraviolet irradiation of low-mass stars.

Free Research Field

系外惑星

Academic Significance and Societal Importance of the Research Achievements

ハビタブルゾーンの地球型惑星の中で、暗い低質量星周りのものは、発見や詳細観測に比較的有利であり、詳細観測に期待が高まっている。実際に発見されているターゲットで大気組成や大気圧を変えたときの大気構造を求め、また、検出器のノイズを考慮して大気分子の検出のための観測の条件を求めたことは、JWSTおよびその後の将来計画で想定されている中間赤外線の高感度観測によって惑星表層を制約する可能性を開く。また、バイオシグニチャーと考えられる揮発性有機物の大気中の安定性を系統的に調べたことで、観測しやすい分子の傾向が明らかになった。