The asteroid explorer "Hayabusa2014" launched in December 12 arrived at Ryugu, a carbonaceous asteroid (C-type asteroid) in June 2.From near-field observations for about a month, Ryugu is a coma-shaped (abacus ball-like) object with an equator crater (a high zone that goes around the equator), and many rock masses (boulders) are found on the entire surface. It was found to be characterized by the existence of a large crater near the equator.

　Ryugu was found to be a celestial body formed by the accumulation of debris, and it is presumed that it was formed by deformation due to high-speed rotation in the past.Numerical calculation showed that the strength inside the celestial body is weak, and if it is uniform, the deformation progresses from the inside.

　For the surface where rock masses are densely distributed, we proceeded with the work of selecting landing points for sampling from both aspects of landing safety and scientific evaluation.As a result, we selected the first candidate area on the equatorial ridge, aimed at the area with a radius of 3 m, and succeeded in pinpoint landing at 2019:2 (Japan time) on February 22, 7.

　The bullets fired by the collision device are likely to have successfully generated an artificial crater, and its diameter makes it possible to estimate the strength inside the object.The strength of asteroids is important in clarifying the process of mass transport from the asteroid belt to the earth.It is expected that further understanding will be further advanced from the analysis of the observation results of "Hayabusa2" and the analysis of the returned sample in the future.

reference:[Nagoya University] Scientific exploration of the asteroid Ryugu by "HayabusaXNUMX" (PDF)