はやぶさ２ 衝突装置による科学的成果

抄録

Hayabusa2, the 2nd Japanese asteroid explorer and sample return mission, has successfully brought samples of the C-type, Near-earth asteroid Ryugu back to the Earth on December 6, 2020. Hayabusa2 achieved a lot of outstanding missions, such as revealing the characteristics of Ryugu as a top-shaped, rubble pile asteroid, sampling from two different points on the surface of Ryugu, and making an artificial impact crater on Ryugu. The artificial crater was produced with the Small Carry-on Impactor (SCI) and as large as that formed in the gravity-controlled regime, in which the crater scale is determined not by the target strength, but by the target gravity. The crater formation in the gravity-controlled regime was also confirmed with the images of impact ejecta taken by Deployable Camera 3 (DCAM3). This is the most important result obtained by the first impact experiment on a real asteroid, suggesting that the surface strength of Ryugu is as small as that of sand. Other scientific results obtained from the SCI operation are also introduced in this paper to show the utility of impactors in planetary explorations.