Periodic microstructure in Saturn's rings A and B

Abstract

Diffraction of coherent radio waves transmitted by the Cassini spacecraft at 0.94- and 3.6-cm wavelengths indicates the presence of fine-scale structure in Saturn's rings A and B, characterized by a periodic radial variation in optical depth. Interpretation of the observed spectral signature in terms of a simple diffraction grating model yields estimates of the structural period λ _gr ~ 100-250 meters and orientation $\phi$ _gr ~ 0. In particular, two regions in Ring A of radial extent 123.05-123.4 × 10³ km and 123.6-124.6 × 10³ km yield average estimates of ${\overline{\lambda} _gr = 163 +/- 6 meters and ${\overline{\lambda} _gr = 217 +/- 8 meters, respectively. Three regions in Ring B of radial extent 92.1-92.6 × 10³, 99.0-104.5 × 10³ km, and 110.0-115.0 × 10³ yield average estimates of ${\overline{\lambda} _gr = 115_-15 ⁺²⁰, 146 +/- 14, and 250_-75 ⁺¹⁵⁰ meters, respectively. In all regions, the structure appears to be azimuthally symmetric with -3° <= $\phi$ _gr <= 3°.