M型星（M star）年龄依赖性紫外辐射对系外行星（exoplanet）生物特征探测与解释的影响

本文探讨了M型星的年龄如何通过影响紫外辐射通量，进而改变系外类地行星（terrestrial exoplanet）大气中的生物特征分子。研究通过模拟不同年龄的M型星周围的类地球行星（Earth-like planet）大气，揭示了恒星活动随年龄演化对行星大气化学成分及光谱特征的显著影响。

arXiv:2608.19328v1 Announce Type: new Abstract: Given their abundance and observational advantages, M stars will arguably be the best candidates for characterizing and searching for biosignatures on terrestrial exoplanets in the near future. However, photochemistry that can suppress or enhance key biosignature molecules in planetary atmospheres is primarily driven by UV flux from the host M star, which is influenced by stellar activity that decreases with age. Here, we simulate Pre-Industrial Earth-like and Archean Earth-like atmospheres around M4 and M8 stars from 650 Myr to 5 Gyr old. We find that our Pre-Industrial Earth atmospheres around 5 Gyr M stars have up to ten times more CH$_4$ than those around 650 Myr M stars, producing 68% stronger methane bands in NIR transit spectroscopy. Additionally, photochemical shielding from O$_2$ in our Pre-Industrial Earth atmospheres reduces the impact UV-driven photochemistry on composition, while the Archean Earth exhibits larger compositional changes due to weaker shielding from CO$_2$. Lastly, enhanced CO$_2$ photolysis, driven by the strong net UV flux and high Far/Near-UV ratios of 650 Myr and 1 Gyr M stars, cause our Archean Earth-like planets to produce up to 5.4 dex more O$_3$ than when around 5 Gyr M stars. The excess O$_3$ causes