Constraints on Saturn's G Ring from the Voyager 2 Radio Astronomy Instrument

Abstract

We have reanalyzed the data acquired by the planetary radio astronomy (PRA) experiment during the passage of Voyager 2 through the outer part of Saturn's G ring, originally published by Aubieret al.(1983.Geophys. Res. Lett.10, 5–8). This study closely parallels the reanalysis of the Voyager 1 PRA data during the E-ring passage (Meyer-Vernetet al.1996.Icarus123, 113–128). The instrument detected dust grain impacts on the spacecraft in a region of ≈1000 km vertical extent around the ring plane with a maximum at ring plane crossing. The signal is mainly produced by grains of radius of a few micrometers. We find a size distribution less steep than ther−6law inferred for submicrometer grains by Showalter and Cuzzi (1993.Icarus103, 124–143) from photometric data. These results can be reconciled if the slope of the size distribution flattens above 0.5 μ. Assuming a rough continuity between the distributions deduced from the two data sets and anr−qlaw for the grains detected by PRA, we infer that the differential power law indexq< 3.5 for grain radii between about a half micrometer and a few micrometers. From the observed vertical profile, we deduce an effective ring vertical thicknessH≈ 1200/(q− 1) km. Whenqvaries in the range 3.5–2,Hvaries in the range 500–1200 km and the geometric cross section per unit area is a few times 10−6.