enhances the probability of the bubble coalescence and makes bubble larger. On the other hand, in the present study the dimention of the apparatus is far larger than that of the distributor and the depth of the liquids is shallow. Therefore, the probability of the bubble coalescence over the distributor is less than that of the Houghton et al.'s case, because the circulation of the liquid in the apparatus makes bubbles easy to apart each other. This fact is recognized when the porous plate distributor is used for liquid of group A and C in the bubble column with continuous liquid flow. Summary Bubbles which have been just generated from the porous plate are small and have an equal size, but sometime coalescence of these small bubbles occurs at a location

The Hayabusa2 spacecraft arrived at the near-Earth carbonaceous asteroid 162173 Ryugu in 2018. We present Hayabusa2 observations of Ryugu’s shape, mass, and geomorphology. Ryugu has an oblate ‘spinning top’ shape with a prominent circular equatorial ridge. Its bulk density, 1.19 ± 0.02 g cm–3, indicates a high porosity (>50%) interior. Large surface boulders suggest a rubble-pile structure. Surface slope analysis shows Ryugu’s shape may have been produced if it once spun at twice the current rate. Coupled with the observed global material homogeneity, this suggests that Ryugu was reshaped by centrifugally induced deformation during a period of rapid rotation. From these remote-sensing investigations, we identify a suitable sample collection site on the equatorial ridge.