Images from Hayabusa2 revealed many more boulders on the surface of asteroid Ryugu than were expected. Asteroid Itokawa also has a large number of boulders, but Ryugu appears to have more per unit area. Figures 1 and 2 show boulders marked in green that appear to be between 8 m to more than 10 m in size, based on images taken from the home position (about 20 km away from Ryugu) on June 30, 2018.

• Figure 1: Distribution of boulders on the surface of Ryugu (asteroid is pictured at 300 degrees longitude). A green marker indicates a boulder that appears to be between 8 m to 10 m or more. In this figure the north pole of the asteroid is at the image top.
  Image credit ※: Kindai University, JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University. University of Aizu, AIST.

Figure 1 shows a region of Ryugu’s surface where the boulder coverage is comparatively low. By contrast, Figure 2 shows a region where there seems to be far more boulders (although it is possible that this will change with more detailed analysis in the future). Both regions in Figure 1 and Figure 2 have hundreds of identified boulders, but there is also considerable variation between places where the boulder number is particularly high and regions where there are fewer. In general, boulders provide valuable evidence about the kinds of collision that an asteroid has been subjected to over its lifetime. The number, shape and variation of these boulders will therefore be examined in detail and, when compared with other observational data, allow the formation of asteroid Ryugu to be revealed.

• Figure 2: Distribution of boulders on the surface of Ryugu (asteroid is pictured at 60 degrees longitude). A green marker indicates a boulder that appears to be between 8 m to 10 m or more. In this figure the north pole of the asteroid is at the image top.
  Image credit ※: Kindai University, JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu, AIST.

※ Please use the displayed credit when reproducing these images. In the case where an abbreviated form is necessary, please write "Kindai University, JAXA & collaborators".

Tatsuhiro Michikami (Faculty of Engineering, Kindai University), Hayabusa2 ONC Team.
2018.08.31