¹Zichen Wei, ¹Hao Zhang
The Astrophysical Journal, 1010, 63
Open Access Link to Article [DOI: 10.3847/1538-4357/aea69a]
¹Hubei Key Laboratory of Planetary Geology and Deep-Space Exploration, School of Earth and Planetary Sciences, China University of Geosciences, Wuhan, 430074, People’s Republic of China

We present a coordinated laboratory optical data set for three equilibrated ordinary chondrites (OCs; LL5/6, L6, and H6), including the recently witnessed Maoming fall of 2025 May 28, to investigate the coupled effects of grain size, surface structure, and simulated space weathering on their spectral, photometric, and polarimetric properties. Intact slabs and three grain-size fractions were measured in the fresh state and after two levels of pulsed-laser irradiation using Fourier-transform infrared reflectance spectroscopy, bidirectional reflectance distribution function (BRDF) measurements, and polarization phase curves. Irradiation generally produces spectral darkening, reddening, and weakening of the 1 and 2 μm absorption bands, although the degree of reddening depends on both composition and grain size. BRDF measurements reveal a systematic transition from nearly isotropic scattering in fine powders to enhanced backscattering in coarse powders and pronounced specular reflection from slabs. These scattering characteristics remain largely unchanged after irradiation, indicating that grain size and surface structure exert stronger control on angular scattering than irradiation-induced optical darkening. The specular component is strongly suppressed in the irradiated LL5/6 slab but remains evident in the L6 and especially H6 slabs, suggesting a contribution from metal-rich phases. Polarimetric measurements further show systematic differences between slabs and powders, with surface morphology influencing both the negative-polarization branch and the large-phase-angle polarization behavior. This dataset demonstrates that grain size and surface structure are as important as composition and space weathering in governing the optical properties of OCs, providing complementary constraints for interpreting OC-like asteroid surfaces.