Resurfacing processes on asteroid (162173) Ryugu caused by an artificial impact of Hayabusa2’s Small Carry-on Impactor

Resurfacing process on Ryugu accompanied by an artificial impact crater formation caused by Hayabusa2’s SCI was studied from comparison of pre- and post-impact images of this region observed by ONC-T. Three different aspect of resurfacing process was examined, the crater rim profiles, the motion of boulders and the appearance of new boulders, and the motion vectors of Ryugu’s surface around the SCI crater. Thus, the averaged crater rim height, h, was derived as follows: h=h_rexp[-(r/R_rim-1)/λ_rim], where R_rim is the SCI crater rim radius of 8.8 m, and the fitted parameter of h_r is 0.475 m, and that of λ_rim is 0.245 m. The ejecta blanket thickness of the SCI crater was thinner than that estimated both from the conventional relationship for natural craters and with calculated from the crater formation theory. But, this discrepancy of the ejecta blanket thickness is solved taking in account of new boulders appeared in the post-impact images were included in the volume. The motion of boulders discovered could be classified by its mechanisms as follows: excavation flow, pushed by falls of ejecta, surface deformation by dragged by slight motion of Okamoto boulder, and seismic shaking caused by the SCI impact itself. The seismic shaking has made motion to boulders to move farther than 10cm in most of the area within 15 m apart from the SCI crater center where its maximum acceleration of the impact induced seismic wave has induced acceleration 7 times larger than Ryugu’s surface gravity, and the evidence of the seismic shaking with the movement of >3cm were detected in small fraction of the area farther than 15 m where these regions should have experienced acceleration larger than the Ryugu’s surface gravity.