Polarimetry in Planetary Sciences and Astronomy

In recent decades, the relevance of polarimetry in planetary sciences and astronomy has increased rapidly. Polarization is a fundamental property of light and can be modified by any scattering event. As such, polarization yields additional information that cannot be obtained by only assessing light's scalar properties. For instance, the polarization state of starlight scattered by planetary surfaces can provide useful insights on the composition, size, morphology, and porosity of regolith particles and might even indicate the presence of life. Beside being useful for characterization, polarimetry can also greatly enhance the detection of exoplanets. Here, polarization can be harnessed to enhance the contrast between the bright light of a star, which can be considered to be fully unpolarized, and the very dim but polarized light reflected by an exoplanet. In this paper, we discuss and review the current developments and advances in optical polarimetry and polarimetric instrumentation in Switzerland within the framework of the National Centre of Competence in Research PlanetS. We focus on their implications for the vast range of science cases that polarimetry can address within the research fields of planetary science and astronomy.