The Japan Aerospace Exploration Agency (JAXA), together with Nagoya University, the University of Aizu, and the University of Tokyo, has published three papers summarizing the initial results based on the exploration activities of the asteroid Ryugu by the asteroid explorer "Hayabusa2". It was announced that it was published on the website of "(Science)" magazine (March 3, Japan time). "Hayabusa3" was launched in December 20 and arrived at Ryugu in June 2.
In the first paper, Ryugu has a low bulk density (mass divided by volume) and porosity (volume ratio of voids between particles) of 1% or more, so the fragments of the destroyed parent object are regenerated. It indicates that it is a rubble pile object formed by accumulating.In addition, Ryugu is a top (top) type with a remarkable circular equatorial ridge, and it is speculated that it was formed by high-speed rotation in the past.
In the second paper, observations by a near-infrared spectrometer (NIRS2) mounted on Hayabusa2 showed that water exists as a hydrous mineral on the surface of Ryugu.From the characteristics of the spectrum, it was found that the constituent materials experienced secondary metamorphism due to heating and impact, and that the composition was generally homogeneous by global observation by NIRS3.In addition, asteroids such as Ryugu are considered to be one of the leading candidates that brought water to the earth, and it is expected that analysis will clarify the origin of water on the earth.
According to the third paper, asteroids of about 3 km such as Ryugu were born by the collisional destruction of a large parent body formed in the early solar system, but it is highly possible that Ryugu was born from the asteroid Polana or Eulalia. I heard that I understood.In addition, it is highly possible that substances have been replaced in the surface layer of about 1 m in about 1 million years or less, and it is estimated that the surface rock mass has a breccia-like structure with many voids inside.
Paper information:[Science] Hayabusa2 arrives at the carbonaceous asteroid 162173 Ryugu — a spinning-top-shaped rubble pile
