The Surface UV Environment on Planets Orbiting M-dwarfs: Need for Experiments & Implications for Origins-Of-Life Chemistry
Abstract
Rocky, temperate planets orbiting M-dwarf stars are of intense astrobiological interest because they are the only potentially habitable worlds accessible to biosignature search over the next 10+ years (e.g., Proxima Centauri b, LHS1140 b, TRAPPIST-1 system). Simultaneously, recent experimental and theoretical work suggests that ultraviolet (UV) light may have played a key role in the origin of life on Earth, and especially the origin of RNA. Characterizing the UV environment on M-dwarf planets is crucial to understanding whether life as we know it could emerge on such worlds. In this work, we couple radiative transfer models to observed M-dwarf spectra to determine the surface UV environment on prebiotic Earth-analog planets orbiting M-dwarfs. We calculate dose rates to quantify the impact of different surface UV environments on prebiotically-important photoprocesses. We consider factors that could influence the surface UV environment, including flares, atmospheric surface pressure, and varying UV output early in the star's life. We find that M-dwarf planets have access to 1000 times less bioactive UV fluence than the young Earth. It is uncertain whether UV-dependent prebiotic chemistry, such as recently discovered pathways for the synthesis of ribonucleotides and sugars, could function on UV-poor M-dwarf planets. Laboratory studies are required to determine whether UV-dependent prebiotic chemistry can proceed on M-dwarf planets and, if not, whether elevated UV irradiation during stellar flares can substitute. Our work suggests a potential advantage for active M-dwarfs relative to quiet M-dwarfs as habitable planet hosts. Further, if laboratory studies confirm that UV-dependent prebiotic chemistry cannot proceed on M-dwarf planets, then biosignature searches on such worlds will empirically test whether UV light is required for the emergence of life.
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E2787R