Photopolarimetric characterization of rough surfaces in regolith simulants

Aims. We experimentally examined the impact of the surface roughness of regolith simulants on the elements of the light-scattering Mueller matrix. Methods. We processed a Mojave Mars Simulant (MMS2) powder sample to produce a set of aggregates with a controlled degree of porosity. The final samples present a cylindrical shape of 0.2 cm radius by 0.4 cm height. The measurements, spanning scattering angles from 94° to 177°, were conducted at a wavelength of 640 nm at the IAA Cosmic Dust Laboratory (CODULAB), which was specifically adapted for surface studies. This marks the first scattering experiment on surfaces performed at CODULAB. Results. Our measurements reveal the influence of surface roughness on the scattering matrix elements, with trends directly correlated with the degree of roughness. Additionally, we observe an inverse relationship between surface roughness and albedo. Across all samples, a shallow negative polarization branch near the backward direction is detected, a characteristic attributed to the single-particle and coherent backscattering mechanisms commonly observed in comets and asteroids. The results also highlight the significant role of large-scale surface structures in determining the scattering behavior, particularly through enhanced multiple scattering. Future work will explore the wavelength dependence of the scattering properties of these rough surfaces.