Importance of Biologically Active Aurora-like Ultraviolet Emission: Stochastic Irradiation of Earth and Mars by Flares and Explosions
Astrophysics, abstract
astro-ph/0307543
From: John M. Scalo <parrot@astro.as.utexas.edu>
Date: Wed, 30 Jul 2003 22:22:07 GMT (427kb)
Importance of Biologically Active Aurora-like Ultraviolet Emission:
Stochastic Irradiation of Earth and Mars by Flares and Explosions
Authors:
David S. Smith (1),
John Scalo (1),
J. Craig Wheeler (1) ((1) Univ. Texas at Austin)
Comments: 21 pages, 2 figures, accepted for publication in Origins of Life and
Evolution of the Biosphere
(Abridged) We show that sizeable fractions of incident ionizing radiation
from stochastic astrophysical sources can be redistributed to biologically and
chemically important UV wavelengths, a significant fraction of which can reach
the surface. This redistribution is mediated by secondary electrons, resulting
from Compton scattering and X-ray photoabsorption, with energies low enough to
excite atmospheric molecules and atoms, resulting in a rich aurora-like
spectrum. We calculate the fraction of energy redistributed into biologically
and chemically important wavelength regions for spectra characteristic of
stellar flares and supernovae using a Monte-Carlo transport code written for
this problem and then estimate the fraction of this energy that is transmitted
from the atmospheric altitudes of redistribution to the surface for a few
illustrative cases. Redistributed fractions are found to be of order 1%, even
in the presence of an ozone shield. This result implies that planetary
organisms will be subject to mutationally significant, if intermittent,
fluences of UV-B and harder radiation even in the presence of a narrow-band UV
shield like ozone. We also calculate the surficial transmitted fraction of
ionizing radiation and redistributed ultraviolet radiation for two illustrative
evolving Mars atmospheres whose initial surface pressures were 1 bar. Our
results suggest that coding organisms on planets orbiting low-mass stars (and
on the early Earth) may evolve very differently than on contemporary Earth,
with diversity and evolutionary rate controlled by a stochastically varying
mutation rate and frequent hypermutation episodes.
Full-text: PDF only
References and citations for this submission:
SLAC-SPIRES HEP (refers to ,
cited by, arXiv reformatted)