An Analysis of the Electron Flux and Electron Microsignatures Observed in the Vicinity of Mimas at Saturn

An analysis of the electron absorption signature observed by the Cosmic Ray System on Voyager 2 near the orbit of Mimas is presented. We find that these observations cannot be explained as the absorption signature of Mimas. Combining Pioneer 11 and Voyager 2 measurements of the electron flux at Mimas's orbit (L = 3.1), we find an electron spectrum where most of the flux above ~ 100 keV is concentrated near 1 to 3 MeV. This spectral form is qualitatively consistent with the band-pass filter model of Van Allen et al. (1980b). The expected Mimas absorption signature is calculated from this spectrum neglecting radial diffusion. Since no Mimas absorption signature was observed in the inbound Voyager 2 data, a lower limit on the diffusion coefficient for MeV electrons at L = 3.1 of D > 10 -8 Rs 2 s -x is obtained. With a diffusion coefficient this large, both the Voyager 2 and the Pioneer 11 small-scale electron absorption signature observations in Mimas's orbit are enigmatic. Thus we refer to the mechanism for producing these signatures as the Mimas ghost. A cloud of material in orbit with Mimas may account for the observed electron signature if the cloud is at least 1% opaque to electrons across a region extending over a few hundred kilometers.