Fig. 33. Comparison of Lunar Micrometeorite Gardening Rates with Galilean Satellite Ice Sublimation Rates.

The point `A12' shows the depth of the regolith at the Apollo 12 landing site (Nakamura et al, 1975). The lines `Gault model' and `Arnold model' show the lunar regolith mixing time as a function of depth as determined from expected meteorite fluxes by Gault et al (1974), and Arnold (1975, Fig. 7). The point `Apollo microcraters' shows the surface exposure times of typical 100--500\mic\ lunar soil grains, based on microcrater counts (Poupeau et al, 1975). `Durand model' shows the surface residence time for 1--50\mic\ grains, derived from a Monte Carlo model tied to observed cosmic ray exposure ages (Durand et al, 1975). The arrow shows the expected 100-fold increase in gardening rates on the Galilean satellites relative to the moon in the depth range of tens of\mic\ (Humes et al, 1974). The diagonal lines show, for comparison, the diurnally-averaged sublimation rates for equatorial ice with the given albedo at 5.2 A.U., assuming instantaneous equilibrium with sunlight.
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