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The energetic charged particle absorption signature of Mimas

1980; American Geophysical Union; Volume: 85; Issue: A11 Linguagem: Inglês

10.1029/ja085ia11p05709

2156-2202

J. A. Van Allen, M. F. Thomsen, B. A. Randall,

Solar and Space Plasma Dynamics

Data are presented for a 1‐min dip in electron intensity that was observed coherently by four different University of Iowa detectors at 1546∶51 earth received time on day 244 of 1979 as Pioneer 11 crossed the orbit of Mimas inbound during its encounter with the Saturn system. By a detailed analysis we show that (1) this absorption microsignature in electron intensity is plausibly attributable to the particle sweeping effect of Mimas; (2) the radial width of the signature is caused primarily by energy dispersion in the longitudinal drift rate of electrons and not by radial diffusion; (3) the spectrum of trapped electrons at Mimas is nearly monoenergetic, centered at kinetic energy E =1.59 MeV with a spread δ E ∼0.1 MeV; (4) this narrow spectrum, which is unique in magnetospheric physics, is caused by the ‘band‐pass filtering’ action of the successive inner satellites, most importantly Enceladus, on an inward diffusing population of electrons; and (5) the radial diffusion coefficient D of electrons E = 1.0 MeV is 1.0 × 10 −10 R s ² s −1 at L =4 and probably in the range 3.7 × 10 −11 to 8.3 × 10 −12 R s ² s −1 at L =3.