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 Aubier et 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-Vernet et al. 1996. Icarus 123, 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 the r −6 law inferred for submicrometer grains by Showalter and Cuzzi (1993. Icarus 103, 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 an r − q law for the grains detected by PRA, we infer that the differential power law index q H ≈ 1200/( q − 1) km. When q varies in the range 3.5–2, H varies in the range 500–1200 km and the geometric cross section per unit area is a few times 10 −6 .