Exploring the potential of exoplanet polarimetry

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Thanks to the ongoing development of high-precision polarimeters, the investigation of the polarized radiation of exoplanets is expected to provide essential insights, complementary to those observables obtained through "classical techniques". An already broad range of studies has been performed during the past two decades with the goal to identify the impact of various physical properties of atmospheric and surface properties (land masses, oceans) on the resulting polarization signal of exoplanets. However, the OBSERVABLE polarization at optical to infrared wavelengths is not determined by that of the exoplanet alone. In particular, the absorption and scattering by potentially existing exoplanetary rings and exomoons, the local debris disk of the exoplanetary system, the dust phase of the interstellar medium as well as the impact of intrinsically polarized stellar radiation have to be taken into account. The main goals of this project are (A) To study the impact of external sources of polarization that potentially interfere with and modify the polarization signal of exoplanets and (B) To derive observing strategies that allow discriminating between the polarization signal of the exoplanet and that of various external sources, to separate the polarization signal of the exoplanet, and to quantify the level of uncertainty due the contribution of the external sources. While these goals are ambitious, they are essential for the identification of limitations of polarimetric exoplanet studies and approaches to overcome them and thus for exploiting the potential of exoplanet polarimetry. As such, the results of this study will provide a necessary complement to already existing as well as future numerical and observational polarization studies of exoplanets.