Photometric behavior of Ryugu’s NIR spectral parameters

Context. JAXA’s Hayabusa2 mission rendezvoused the Ryugu asteroid for 1.5 years to clarify carbonaceous asteroids’ record Solar System origin and evolution. Aims. We studied photometric behavior of spectral parameters characterizing near-infrared (NIR) spectra provided by Hayabusa2/NIRS3 instrument, that is say 1.9 µm reflectance, 2.7 2.8 band depths (ascribed phyllosilicates), NIR slope. Methods. For each parameter, we applied following empirical approach: (1) retrieval equigonal albedo applying Akimov disk function (this step was only performed reflectance correction); (2) median parameter value at phase angle bin; (3) a linear fit. Results. Ryugu’s shows steepness similar Ceres, according same taxonomy two asteroids. Band decrease with increasing angle: this trend opposite observed on other asteroids explored space missions ascribed very dark albedo. visible reddening are similar, contrary asteroids, where larger: could be due surface darkness or particle smoothness. Albedo globally uncorrelated, but locally anticorrelated. A correlation between darkening observed.