Spectro-polarimetry of the bright side of Saturn's moon Iapetus

TL;DR

This study provides detailed spectro-polarimetric measurements of Iapetus's bright side, revealing how water ice's polarization characteristics vary with phase angle and wavelength, enhancing understanding of surface properties.

Contribution

The paper presents high-precision spectro-polarimetric data of Iapetus's surface across multiple phase angles and wavelengths, offering new insights into its ice surface scattering behavior.

Findings

Polarization decreases with increasing phase angle

Negative polarization varies from -0.9% to -0.3%

Wavelength dependence observed in polarization behavior

Abstract

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.