Circular polarization of Iapetus’ leading side versus wavelength, obtained with FORS2 at the ESO VLT during the night 2012 January 02 at phase angles of 5.58°. The measurement technique was performed the same way as reported in Paper I for the trailing hemisphere; i.e., the solid green curve represents the average of the value of the signals obtained at 0.0° and 90.0° instrument position angles on the sky, so as to reduce the cross-talk effect from linear to circular polarization of the FORS2 instrument (e.g., Bagnulo et al. 2009).