The Bavarian Research Institute of Experimental Geochemistry and Geophysics (BGI) on the Campus of the University of Bayreuth. Photo: UBT.
Prof. Dr. Audrey Bouvier, University of Bayreuth. Photo: UBT / Christian Wißler.
The Hayabusa2 spacecraft of the Japanese space agency JAXA collected samples from the 0.9 km diameter asteroid in 2019 and sent them back to Earth in a capsule. The research results will contribute new insights into the formation of the solar system and the chemical composition of terrestrial planets. Under Bouvier's leadership, space rock research will be further intensified at BGI. In addition to asteroids, rock samples from Mars and the Moon will also be studied here in the coming years.
Prof. Dr. Audrey Bouvier is a member of the international research team that was involved in the first chemical analyses of Ryugu rock samples which were carried out in Japan. Unlike the large number of meteorites that have impacted the Earth's surface, the samples taken from the asteroid have a significant advantage: They are guaranteed not to have been chemically altered by entering the Earth's atmosphere or spending time on the ground. They were formed as they are, in space. The rock samples sent to Earth by Hayabusa2 had a total weight of just over 5.4 grams. "This was an amazing surprise when the containers were finally opened in Japan as it was far more materials than we originally expected," Bouvier says. "The samples in the containers looked like dark pebbles. Most were only a few millimeters in size, with a few larger, up to a one centimetre, which is close to the maximum obtainable size from the sampling site."
Ryugu shows traces of solar system history
In their study of Ryugu, the researchers discovered that its minerals were modified in contact with an aqueous fluid at a temperature of about 37 degrees Celsius, but never experienced temperatures above degrees Celsius. Chronological studies indicate that this period of aqueous alteration took place about five million years after the condensation of the first minerals in the solar system. These changes occurred in one of the countless solid bodies (planetesimals) from which the planets of the solar system later developed by accretion. On this planetesimal, from which Ryugu was blasted out, there might have been abundant water, which would have been an important condition for the emergence of life.
Another striking feature concerns the abundance of chemical elements contained in the rock samples: Ryugu is similar to CI (Ivuna) carbonaceous chondrites, and best resembles the composition of the solar photosphere. The photosphere is the outer shell of a star from which light is emitted into space, so that one can derive its composition.
The analyses of Ryugu samples further indicate that the asteroid stems from a planetesimal which was formed at the very edge of the solar system. Later, Ryugu migrated into the interior of the solar system and entered its present near-Earth orbit around the Sun. In current research, the hypothesis is that materials formed at the outermost edge of the solar system could have contributed in building the Earth. Carbonaceous materials could have been an important source of the so-called volatile elements on Earth. Volatile elements like hydrogen, oxygen, and carbon are essential components of the Earth's atmosphere and the oceans, therefore they have a decisive share in the formation of life.
In search of life in space: in the future also at the University of Bayreuth
A few days before the new "Science" article was published, another international research team announced that 20 different amino acids had been identified in rock samples from Ryugu. Amino acids are the building blocks of life on Earth. "This is the first time amino acids have now been discovered that clearly did not originate or were not modified on Earth. Against this background, too, the asteroid Ryugu is an exciting object of research that promises to provide revealing insights into the origins of life. That's why we at the University of Bayreuth want to get more involved in the analyses of extra-terrestrial rock samples in the future," says Prof. Dr. Audrey Bouvier. Together with Dr. Nobuyoshi Miyajima, mineralogist at the Bavarian Geoinstitute, she will apply to the Japanese space agency for Ryugu samples to be loaned to the BGI for further mineralogical and chemical analyses. In September 2022, new laboratories for isotope geochemistry and cosmochemistry will open at BGI. High-precision isotope studies of trace metals in a Ryugu and other planetary samples are intended here.
It is anticipated that samples of Martian rocks will also be studied at the University of Bayreuth, as meteorites or samples brought back from on-going and future missions. The National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) recently selected Prof. Dr. Audrey Bouvier as a member of the Mars Sample Return Campaign Science Group. This international body is currently planning the return of rock samples from Mars. It defines the scientific objectives of the ongoing sample collection by the Perseverance rover and eventually the preservation and distribution of the samples for scientific analysis.
About the Hayabusa2 mission
The Hayabusa2 spacecraft launched on December 3, 2014, and explored the asteroid Ryugu for 17 months (June 2018 to November 2019). The mission included two landing operations to collect asteroid samples. During the second landing, a crater was created by firing a 5-gram tantalum projectile so that not only surface material but also rock samples from deeper layers could be collected. The sample capsule was recovered in Australia on December 6, 2020, and brought to Japan under strict quarantine conditions during the COVID-19 pandemic. The international team that has analyzed the Ryugu samples to date consists of a total of six research groups led by scientists in Japan. Prof. Dr. Audrey Bouvier is a member of the working group that studies the chemical elements and their isotopes contained in the samples. Meanwhile, the Hayabusa2 spacecraft is en route to another asteroid.
Contact for scientific information:
Prof. Dr. Audrey Bouvier
Experimental Planetology
Bavarian Research Institute of Experimental Geochemistry and Geophysics (BGI)
University of Bayreuth
Phone: +49 (0) 921 55-3792
E-mail: audrey.bouvier@uni-bayreuth.de
Original publication:
Tetsuya Yokoyama et al: Samples returned from the asteroid Ryugu are similar to Ivuna-type carbonaceous meteorites. Science 2022, DOI: https://dx.doi.org/10.1126/science.abn7850
