Surface Roughness of the Chang’E-5 and Chang’E-6 Lunar Samples: Implications for the Microscopic Processes Shaping the Lunar Surface

Although lunar surface roughness was studied extensively above micrometers before, it has not been investigated at smaller scales. In this study, we measured the surface topography of the Chang’E-5 and Chang’E-6 lunar samples by using atomic force microscopy. The obtained elevation datasets have a resolution of 117 nm pix –1 , and their power spectral densities were calculated to evaluate the surface roughness. The resulting topographic power decreases with increasing wavevector, indicating the surface becomes smoother at smaller scales. Depending on the distribution of strength weakness and impact condition, fragmentation processes can produce surfaces with various roughness, whereas melt cooling can produce smooth, curved surfaces. Surface roughness does not vary significantly among different crystalline minerals, but is systematically lower for glasses. Self-similarity of the sample surfaces was then examined by the Hurst exponent of topographic powers. Flat surfaces show the least self-similar pattern due to their smooth texture, whereas surfaces with rectangular features are the most self-similar linked to their highly ordered weakness planes. Notably, lunar grains can exhibit Hurst exponents greater than 1, which indicates a strength-dominated fragmentation regime rarely seen on larger-scale lunar surfaces. In the visible wavelengths, the single-scattering albedo decreases and the depolarization effect increases from spherical to prolate and rough grains. In the thermal infrared wavelengths, the absorption band depths of the selected samples may vary by 6%–21% due to different surface roughness. This study offers new insights into the microscopic processes shaping the Moon and contributes to a more accurate interpretation of lunar remote sensing data.