FIGURE 2.3 Radiation dose models for Europa, in rad [water] per month (30.4 days) of exposure below varying thicknesses of ice. The results of two independent evaluations are given, “JPL Total” and “APL Total.” For the JPL Total model, the separate contributions of electrons and photons (bremsstrahlung) are shown. The APL Total model has higher proton fluxes at very high energies. In addition to the theoretical uncertainties in Europa ’s radiation environment (as indicated by the differences between the APL and JPL models), natural variations of up to an order of magnitude have been observed in Jupiter’s trapped-particle intensities over the 25-year span between the Pioneer and Galileo missions. Information provided by J.M. Ratliff of the Jet Propulsion Laboratory and C.P. Paranicas of the Applied Physics Laboratory, Johns Hopkins University.

REFERENCES

1 Space Studies Board, National Research Council, A Science Strategy for the Exploration of Europa, National Academy Press, Washington, D.C., 1999.

2 G.C.Collins et al., “Evaluation of Models for the Formation of Chaotic Terrain on Europa, ” Journal of Geophysical Research 105: 1709, 2000.

3 M.H. Carr et al., “Evidence for a Subsurface Ocean on Europa,” Nature 391: 363, 1998.

4 N.A. Spaun, et al., “Conamara Chaos Region, Europa: Reconstruction of Mobile Polygonal Ice Blocks, Geophysical Research Letters 25: 4277, 1998.



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