Sep 23, 2022

Research results of asteroid samples collected by explorer Hayabusa2 published in ‘Science’ journal



Tohoku University, Rikkyo University and other research institutions have announced that a paper summarizing the research results of samples from the asteroid Ryugu, which were collected by Japan’s asteroid explorer Hayabusa2, has been published in the U.S. journal “Science” on September 22, 2022 (September 23, Japan time).

Hayabusa2 successfully delivered samples collected from Ryugu back to Earth on December 6, 2020. The samples were analyzed to investigate the history of Ryugu, which is believed to have been formed by the reassembly of fragments from the original asteroid (parent body), after it was destroyed in a collision event. Researchers of the Hayabusa2 Initial Analysis Stone Team studied a total of 17 particles ranging in size from 1 millimeter to 8 millimeters to learn details including:
  • how and where the parent body was formed in the solar system.
  • what substances it is composed of.
  • how it evolved due to subsequent chemical reactions.
  • how fragments of the parent body were released.

The researchers found that Ryugu’s parent body was formed about 2 million to 3 million years after the birth of the solar system and in the outer solar system where water and carbon dioxide were present as ice. In the outer solar system, virtually all materials formed at low temperatures.

Water ice in the parent body’s interior melted due to decay heat from radioactive elements about 3 million years after its formation. The composition of anhydrous minerals then gradually changed due to water-rock chemical reactions, making the parent body’s substances mostly hydrated minerals.

The study concluded that the subsequent collision with an impactor about 1 billion years ago destroyed the parent body and that Ryugu was formed through the reassembly of fragments in a region distant from the collision point.

The results, including those from this study by the Hayabusa2 Initial Analysis Stone Team (headed by Professor Tomoki Nakamura of Tohoku University), were published in the American Association for the Advancement of Science (AAAS) journal “Science” on September 22.

Rikkyo University participated in the development of the optical navigation camera system mounted on Hayabusa2, in addition to the landing operation for sample collection. The optical navigation camera system consists of one telescopic camera (ONC-T) and two wide-angle cameras (ONC-W1, 2). The university conducted performance tests of these cameras and studied plans to capture images in addition to image-capturing operations and exploration of satellites around the asteroid, among other projects.

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