Regolith grain sizes of Saturn's rings inferred from Cassini-CIRS far-infrared spectra

► Far-infrared emissivity spectra of Saturn's main rings are analyzed. ► In the modeling of spectra, the Hapke's model is used. ► The sizes of icy regolith grains are estimated to be 1 μm to 1-10 cm. ► The power law index for the size distribution is ∼3.