CONSTRAINTS ON SATURN G-RING FROM THE VOYAGER-2 RADIO ASTRONOMY INSTRUMENT

We have reanalyzed the data acquired by the planetary radio astronomy (PRA) experiment during the passage of Voyager 2 through the outer par t of Saturn's G ring, originally published by Aubier et al. (1983. Geo phys. Res. Lett. 10, 5-8). This study closely parallels the reanalysis of the Voyager I PRA data during the E-ring passage (Meyer-Vernet et al. 1996. Icarus 123, 113-128). The instrument detected dust grain imp acts on the spacecraft in a region of approximate to 1000 km vertical extent around the ring plane with a maximum at ring plane crossing. Th e 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, 124-14 3) from photometric data. These results can be reconciled if the slope of the size distribution flattens above 0.5 mu. Assuming a rough cont inuity between the distributions deduced from the two data sets and an r(-q) law for the grains detected by PRA, we infer that the different ial power law index q < 3.5 for grain radii between about a half micro meter and a few micrometers. From the observed vertical profile, we de duce an effective ring vertical thickness H approximate to 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 ). (C) 1998 Academic Press.