Modeling Repeated M Dwarf Flaring at an Earth-like Planet in the Habitable Zone: Atmospheric Effects for an Unmagnetized Planet
Por:
Tilley, Matt A., Segura, Antigona, Meadows, Victoria, Hawley, Suzanne, Davenport, James
Publicada:
1 ene 2019
Resumen:
Understanding the impact of active M dwarf stars on the atmospheric equilibrium and surface conditions of a habitable zone Earth-like planet is key to assessing M dwarf planet habitability. Previous modeling of the impact of electromagnetic (EM) radiation and protons from a single large flare on an Earth-like atmosphere indicated that significant and long-term reductions in ozone were possible, but the atmosphere recovered. However, these stars more realistically exhibit frequent flaring with a distribution of different total energies and cadences. Here, we use a coupled 1D photochemical and radiative-convective model to investigate the effects of repeated flaring on the photochemistry and surface UV of an Earth-like planet unprotected by an intrinsic magnetic field. As input, we use time-resolved flare spectra obtained for the dM3 star AD Leonis, combined with flare occurrence frequencies and total energies (typically 1030.5 to 1034 erg) from the 4-year Kepler light curve for the dM4 flare star GJ1243, with varied proton event impact frequency. Our model results show that repeated EM-only flares have little effect on the ozone column depth but that multiple proton events can rapidly destroy the ozone column. Combining the realistic flare and proton event frequencies with nominal CME/SEP geometries, we find the ozone column for an Earth-like planet can be depleted by 94% in 10 years, with a downward trend that makes recovery unlikely and suggests further destruction. For more extreme stellar inputs, O3 depletion allows a constant ∼0.1-1 W m-2 of UVC at the planet's surface, which is likely detrimental to organic complexity. Our results suggest that active M dwarf hosts may comprehensively destroy ozone shields and subject the surface of magnetically unprotected Earth-like planets to long-term radiation that can damage complex organic structures. However, this does not preclude habitability, as a safe haven for life could still exist below an ocean surface. © Matt A. Tilley et al., 2018; Published by Mary Ann Liebert, Inc.
Filiaciones:
Tilley, Matt A.:
Department of Earth and Space Sciences, University of Washington, Johnson Hall Rm-070 Box 351310, Seattle, WA 98195-1310, United States
NASA Astrobiology Institute, Virtual Planetary Laboratory Lead Team, United States
Astrobiology Program, University of Washington, Seattle, WA, United States
Univ Washington, Dept Earth & Space Sci, Seattle, WA 98195 USA
NASA, Astrobiol Inst, Virtual Planetary Lab, Lead Team, Washington, DC USA
Univ Washington, Astrobiol Program, Seattle, WA 98195 USA
Segura, Antigona:
NASA Astrobiology Institute, Virtual Planetary Laboratory Lead Team, United States
Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Mexico
NASA, Astrobiol Inst, Virtual Planetary Lab, Lead Team, Washington, DC USA
Univ Nacl Autonoma Mexico, Inst Ciencias Nucl, Mexico City, DF, Mexico
Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Mexico
Meadows, Victoria:
NASA Astrobiology Institute, Virtual Planetary Laboratory Lead Team, United States
Astrobiology Program, University of Washington, Seattle, WA, United States
Department of Astronomy, University of Washington, Seattle, WA, United States
NASA, Astrobiol Inst, Virtual Planetary Lab, Lead Team, Washington, DC USA
Univ Washington, Astrobiol Program, Seattle, WA 98195 USA
Univ Washington, Dept Astron, Seattle, WA 98195 USA
Hawley, Suzanne:
NASA Astrobiology Institute, Virtual Planetary Laboratory Lead Team, United States
Astrobiology Program, University of Washington, Seattle, WA, United States
Department of Astronomy, University of Washington, Seattle, WA, United States
NASA, Astrobiol Inst, Virtual Planetary Lab, Lead Team, Washington, DC USA
Univ Washington, Astrobiol Program, Seattle, WA 98195 USA
Univ Washington, Dept Astron, Seattle, WA 98195 USA
Davenport, James:
NASA Astrobiology Institute, Virtual Planetary Laboratory Lead Team, United States
Department of Physics and Astronomy, Western Washington University, Bellingham, WA, United States
NASA, Astrobiol Inst, Virtual Planetary Lab, Lead Team, Washington, DC USA
Western Washington Univ, Dept Phys & Astron, Bellingham, WA 98225 USA
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