2023-05-11 12:20:30
A very long journey in the Solar System brought them from the Ryugu asteroid to Earth, inside the collection capsule of the Hayabusa2 probe which collected them from the surface of the celestial body in 2019. Two small grains of the asteroid, less than two millimeters long and weighing a total of three milligrams, part of Hayabusa2’s cargo, have arrived from the Sagamihara Campus of JAXA in Japan to the laboratories of the National Institute of Astrophysics in Rome, where a research team will analyze them with the ambitious goal of reconstructing the history of evolution of Ryugu in its four billion year life. In homage to Japanese culture, INAF researchers have renamed the two grains Kiki and Totoro, after the characters of as many animated films by the master Hayao Miyazaki.
The Japanese space agency JAXA’s Hayabusa2 mission explored the one-kilometre-wide asteroid Ryugu, obtaining detailed images of the surface. Hayabusa2 hurled a small projectile at the asteroid in order to excavate a small portion of its outer layer and expose the material underneath, which has been preserved for billions of years. The spacecraft then collected fragments of the surface at two different sites on Ryugu, one of them in the vicinity of the crater. In two collection chambers, called A and C, both superficial and sub-surface fragments were therefore recovered, the latter protected by the deep vacuum of space until the moment of impact. The reentry capsule with the collected material was recovered in Woomera, Australia on December 6, 2020. It is the first collected sample belonging to a class of very primitive asteroids, whose composition gives us a snapshot of the material that gave origin to the early Solar System and the Earth.
The amount of material that has been collected in total is about 5 grams. After completing a first inspection, the Ryugu particles were individually removed from the small sapphire glass containers with vacuum tweezers and a microscopic analysis was performed on these grains. “Thanks to my contribution in the characterization of the asteroid Ryugu, as Co-Investigator of the Hayabusa 2 mission, I was called to be part of the small international team which, before the opening of the public tenders, dealt with the first analyzes in exclusive”, recalls Ernesto Palomba, INAF researcher in Rome.
As part of the second international public tender for the analysis of Ryugu samples, JAXA assigned the INAF research group coordinated by Ernesto Palomba two grains called C0242 (weighing 0.7 milligrams and 1.712 millimeters long) and A0226 (1.9 milligrams heavy and 2.288 millimeters long). Each grain is placed inside a particular steel container filled with nitrogen, the purpose of which is both to preserve the grain by avoiding contamination due to dust and water vapor present in the environment, and to allow safe transport. To honor Japanese culture, the Italian team decided to name the two grains by drawing on the tradition of Anime, in particular the works of studio Ghibli with its creator Hayao Miyazaki. The names were chosen by looking at both the shape (A0226-Totoro) from the film “My Neighbor Totoro”, and Hayabusa2’s task of sending extraterrestrial samples to Earth (C0242-Kiki) from the film “Kiki’s Delivery Service”.
“Of all the 38 analysis proposals accepted by JAXA for the second international tender, ours is the only Italian one” comments Palomba and continues: “The team is made up of a dozen people from the INAF offices in Rome, Naples, Catania and from the University of Florence, of which almost half are fellows, doctoral students and postdocs. To prepare ourselves for the analysis and manipulation of millimeter grains, we started training with fragments of a carbonaceous meteorite, the Tagish Lake, which can be considered very similar to the Ryugu fragments. We have designed and produced sample holders capable of keeping the grains still during transport and analysis. And now about ten days ago JAXA has contacted us asking for the address to ship the samples. Actually in less than a week, to our great excitement, Kiki and Totoro have arrived.
“For this project, we also had a Large Grant from INAF in support” underlines Palomba. “Our goal will be to understand how this asteroid evolved during its 4 billion year life. In particular, we will study the transformations caused by the interaction with the space environment, which, contrary to what one might believe, is far from being completely inert. A continuous rain of micrometeorites, galactic and cosmic particles, as well as the constant flow of the solar wind (the so-called space weathering) bombards the surfaces of planetary bodies incessantly for billions of years, also causing substantial transformations. To better understand these transformations, in our project we requested two grains, one coming from chamber A and another from chamber C, so that it will be possible to understand how much the space weathering has modified the surface of the asteroid”, concludes Palomba.
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