Degree of linear polarization, − P₂₁/P₁₁, versus phase angle α, obtained using the RT-CB model, along with the respective geometric albedo values p_MS retrieved in each computation run. The top panel(a) shows comparison of polarization measurements of Iapetus’ trailing side (circles with error bars) with the RT-CB model, while the bottom panel (b) shows comparison of the model with the polarization measurements of Iapetus’ leading side.