  Measurements of the polarized reflected sunlight from atmosphereless solar
system bodies, over a range of phase angles, provide information about the
surface structure and composition. With this work, we provide analysis of the
polarimetric observations of the bright side of Iapetus at five different phase
angles, and over the full useful wavelength range (400-800nm), so as to assess
the light scattering behaviour of a typical surface water ice. Using FORS2 of
the ESO VLT, we have performed linear spectro-polarimetric observations of
Iapetus' bright side from 2009 to 2011 at five different phase angles, in the
range from 0.80-5.20^{0}, along with circular spectro-polarimetric observations
at one phase angle. By measuring, with high accuracy (~0.1% per spectral bin
for each Stokes parameter), the spectral polarization of the bright trailing
hemisphere of Saturn's moon Iapetus, we have identified the polarimetric
characteristics of water ice, and found that its linear degree of negative
polarization decreases with increasing phase angle of observation (varying from
-0.9% to -0.3%), with a clear dependence on wavelengths of observation.
