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J. F. Cooper (Raytheon Technical Services Company, NASA GSFC), A. C. Cummings, R. A. Mewaldt (Space Radiation Laboratory, Caltech), J. D. Richardson (Center for Space Research, MIT), C. Wang (Center for Space Research, MIT and Laboratory for Space Weather, Chinese Academy of Sciences, Beijing, China), R. E. Johnson (Engineering Physics, U. Virginia)
Abundant data are available from operational interplanetary spacecraft to construct model flux spectra and dosage profiles for irradiation of icy bodies including Centaurs, Kuiper Belt Objects, and Oort Cloud comets by ions at plasma to cosmic ray energies. Data sources include the Advanced Composition Explorer (ACE) and other spacecraft in interplanetary space near Earth, the Ulysses spacecraft in an eccentric six-year polar orbit around the Sun, and the two Voyager spacecraft now moving through the outer Solar System towards the boundaries of the heliosphere. For applications to irradiation of solar system objects there is a need to compile flux averages of past and future data extending over the 11-year solar activity cycle, and the 22-year solar magnetic cycle, as approximations to irradiation over much longer periods of time. Heliospheric plasma and cosmic ray transport models can be used to extrapolate from multiple spacecraft observation points to heliocentric orbits of specific bodies at given phases of these cycles. In this report we focus on interstellar pickup ions accelerated from initial plasma (eV - keV) energies up to 100 MeV/nucleon at the solar wind termination shock, thought to be located at 90 - 100 AU from the Sun, and propagated by diffusion and gradient-curvature drifts throughout the heliosphere. These ions show large changes in intensity and spatial gradients during both cycles, while being very important for surface irradiation of small bodies in the outer solar system. Overall positive radial gradients are predicted for ACR ion intensities averaged over 22 years at orbits of Centaurs and KBOs, possibly contributing to perihelion and eccentricity gradients in visible color of the Classical KBO population. Compression of heliospheric boundaries inward in response to increasing density of local interstellar gas could occasionally expose these objects to stronger radial gradients and higher irradiation dosages over billions of years.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.