Photometry of (162173) Ryugu and its artificial crater as inferred by Hayabusa2/ONC images

The JAXA/Hayabusa2 rendezvoused with the (162 173) Ryugu asteroid from June 2018 to November 2019, performing an artificial impact experiment on 5th April 2019. The goal of this work is to study the photometric properties' variation of the target area (latitude 7-10 degrees N; longitude 303-305 degrees E) after the artificial impact experiment. This is done by applying an empirical method based on the statistical analysis of the Optical Navigation Camera (ONC)'s data set (in particular, of the v band, centred at 0.55 $\mu$m), similar to that applied to other asteroids explored by space missions and to the NIRS3 data set of Ryugu. The method was firstly applied on the entire data set acquired between March and April 2019, covering most of the Ryugu surface. The retrieved average phase function of Ryugu is very similar to that obtained on the NIRS3 data set, according to the similar visible and near-infrared albedo values. Nevertheless, this phase function is flatter than other asteroids belonging to the same Ryugu taxonomic class. This can be attributed to the higher spatial resolution of Hayabusa2 observations, which flattens the phase function of dark asteroids by minimizing the effects of shadowing, as confirmed by photometric studies of other asteroids. Then, the photometric properties of the artificial impact crater area revealed a slight phase function steepening and narrowing after the impact: this could indicate that the exposed surface has a larger roughness and more porous particles.