标题： 系外行星的紫外线宜居带 显示英文标题

标题： The ultraviolet habitable zone of exoplanets

摘要： 在宜居带（CHZ）发现的数十颗岩石系外行星目前代表了太阳系外最适合居住的地方。然而，假设在CHZ行星上存在液态水并不能保证适合生命出现的环境。根据实验研究，生命的构建块最有可能在存在最小紫外线（UV）通量的情况下通过光化学反应产生。另一方面，高紫外线通量可能对生命构成威胁，导致大气侵蚀并损害对生命至关重要的生物分子。这些论点引发了关于其他恒星周围CHZ行星实际宜居性的疑问，特别是那些具有不同紫外线与总辐射亮度比值的恒星。通过结合“平均原理”和最近的实验研究，我们定义了紫外线边界条件（紫外线宜居带，UHZ），在此范围内生命可能产生并进化。我们调查了在CHZ发现的系外行星是否确实经历了这样的条件。通过分析Swift-UV/光学望远镜数据，我们测量了17颗拥有23颗行星位于其CHZ的恒星的近紫外（NUV）亮度。我们推导出NUV亮度与恒星有效温度之间的经验关系。我们发现，实际上有18颗CHZ系外行星围绕着其M矮星宿主运行的位置超出了UHZ，即它们的M矮星宿主的NUV亮度明显太低，无法通过氰硫化学触发非生物起源。只有有效温度大于3900 K的恒星能用足够的NUV辐射照亮其CHZ行星以触发非生物起源。否则，较冷的恒星需要高能耀发活动。 显示英文摘要

摘要： The dozens of rocky exoplanets discovered in the Circumstellar Habitable Zone (CHZ) currently represent the most suitable places to host life as we know it outside the Solar System. However, the presumed presence of liquid water on the CHZ planets does not guarantee suitable environments for the emergence of life. According to experimental studies, the building blocks of life are most likely produced photochemically in presence of a minimum ultraviolet (UV) flux. On the other hand, high UV flux can be life-threatening, leading to atmospheric erosion and damaging biomolecules essential to life. These arguments raise questions about the actual habitability of CHZ planets around stars other than Solar-type ones, with different UV to bolometric luminosity ratios. By combining the "principle of mediocricy" and recent experimental studies, we define UV boundary conditions (UV-habitable Zone, UHZ) within which life can possibly emerge and evolve. We investigate whether exoplanets discovered in CHZs do indeed experience such conditions. By analysing Swift-UV/Optical Telescope data, we measure the near ultraviolet (NUV) luminosities of 17 stars harbouring 23 planets in their CHZ. We derive an empirical relation between NUV luminosity and stellar effective temperature. We find that eighteen of the CHZ exoplanets actually orbit outside the UHZ, i.e., the NUV luminosity of their M-dwarf hosts is decisively too low to trigger abiogenesis - through cyanosulfidic chemistry - on them. Only stars with effective temperature >3900 K illuminate their CHZ planets with enough NUV radiation to trigger abiogenesis. Alternatively, colder stars would require a high-energy flaring activity.