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J. Scalo, D. Smith (UT Austin), E. Vazquez-Semadeni (UNAM, Mexico)
The solar wind modulates the low-energy galactic cosmic ray flux in our solar system, but this modulation depends on the size and other properties of the heliosphere and the details of cosmic ray propagation. It has been repeatedly suggested that the cosmic ray flux on Earth, and presumably other habitable planets, should be greatly enhanced when the solar system passes through denser regions of the interstellar medium, but the importance of such events remains uncertain. We attempt to improve this situation using calculations of test planetary systems and their associated heliosphere analogues moving through a realistic continuous density and velocity field based on 3-dimensional hydrodynamical simulations representing the interstellar medium. Using simplified approximations for the dependence of heliosphere size on external density and relative velocity and for the dependence of cosmic ray modulation on heliosphere size and distance from the parent star, we follow the time series of cosmic ray fluxes at various distances from the parent star. From ensembles of these test particle time series' we estimate the probability distribution of cosmic ray fluxes and associated durations for a variety of model planetary systems. Implications for long-term fluctuations in planetary mutation rates and atmospheric chemistry are briefly discussed.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.