Polarimetric properties of Mercury-like and Venus-likeexoplanets

The polarization phase curves are presented at effective wavelengths of 0.55 μ m from photometry and polarimetry of Mercury and Venus when the two planets are treated as both the spatially resolved planets and corresponding unresolved exoplanets. The discrepancy between the theoretical curves by others and these curves are pointed out. It is found that the polarization amplitude of the unresolved Mercury is smaller than that of the unresolved Venus by two or three orders with 1 AU distance from a host star at the same observation distance. And their polarization phase curve patterns are highly in contrast to each other. In both the observational coordinates and the coordinates defined by the scattering plane, the Mercury-like curve takes an appearance of dominantly positive polarization while the Venus-like has a feature of negative polarization dominance. This feature does not vary with planetary radius, distance from the host star or distance from the observer. Further, the phase angle of polarization turning point where the polarization changes sign is also independent of these parameters. These properties can help us to distinguish those exoplanets with atmospheres from those without atmosphere and thus to be instructive to figure out types of exoplanets.