A research team led by Professor Kentaro Terada of Osaka University conducted a dating analysis of fine particles collected from the asteroid Itokawa by the asteroid explorer "Hayabusa", crystallized about 46 billion years ago, and received shock transformation about 15 billion years ago. I discovered that it was.Other researchers from the University of Tokyo, Kyoto University, Tohoku University, Kyushu University, Wisconsin University, JAXA, and JASRI also participated in the research team.
The asteroid Itokawa is a near-Earth asteroid whose perihelion enters the inside of the earth's orbit.In 2010, the Japanese asteroid explorer "Hayabusa" succeeded in bringing back humanity's first asteroid fine particles from the asteroid Itokawa to the earth.
The research group focused on phosphate minerals with a size of several microns, which are rarely contained in Itokawa fine particles with a diameter of about 50 microns. Precise isotope analysis (U-Pb dating) of uranium and lead was performed using a secondary ion mass spectrometer.As a result, it was clarified that the phosphate mineral crystallized in the thermal transformation age of the asteroid Itokawa parent body about 2 billion years ago and received shock transformation (shock transformation) due to the impact of other celestial bodies about 46 billion years ago. ..
The shock age of the Itokawa particles obtained this time is different from the shock age of 42 billion years ago reported by the majority of LL chondrite meteorites that frequently fly to the earth, and LL chondrite on the asteroid Itokawa. It was found that there is an evolutionary history different from that of the meteorite mother celestial body.On the other hand, a shock metamorphism of the type of LL chondrite meteorite that fell to Chelyabinsk, Russia in 2013 was reported about 15 billion years ago, and its relationship with the asteroid Itokawa was clarified.
This achievement gives a chronological constraint to the sample taken from an asteroid for the first time by human beings, and is the world's first finding to give a concrete numerical value (absolute age) to the evolution of a near-Earth asteroid with a well-known orbit. Will be.
Paper information:[Scientific Reports] Thermal and impact histories of 25143 Itokawa recorded in Hayabusa particles