[PPS07-02] Surface evolution of carbonaceous asteroid Ryugu revealed from touchdown operation of Hayabusa2
Keywords:Hayabusa2, Ryugu, touchdown
The ONC data show that Ryugu’s surface has almost homogeneous reflectance and color at the macro scale, but there is the regional variation in the spectral slope (b-x slope). The bluer materials are distributed at the equatorial ridge and in the polar regions, while the redder materials are widely spread over the mid-latitude regions (Sugita et al. 2019). The latitudinal variation of spectral slope suggests that exposure of Ryugu’s materials to space has led to their reddening by solar heating and/or space weathering. The ONC images obtained during the touchdown showed that a large amount of debris was produced by the impact of the projectile shot from the sampler system and the reaction control system (RCS) thrust immediately after the touchdown, and the entire field-of-view of ONC-W1 was darkened uniformly. Color changes of boulders observed during the touchdown suggest that the dark fine grains originate from the redder materials that covered the boulder surface. The stratigraphic relationship between the identified craters and the redder materials suggests that surface reddening occurred over a short period of time. These results suggest that Ryugu underwent an orbital excursion near the Sun.