"We are extremely pleased that Thorsten Kleine, a leading international expert in the field of cosmochemistry, is joining the MPS," says Prof. Dr. Laurent Gizon, Managing Director of the MPS. “The scientific results of Thorsten Kleine are groundbreaking and have fundamentally changed our view of the formation of the Solar System," he adds. Thorsten Kleine takes over the leadership of the department from Prof. Dr. Ulrich Christensen, who retired at the beginning of 2020.
"For me, this appointment is a dream come true," says Thorsten Kleine, who most recently held a professorship in planetary science at the University of Münster in Germany. "Planetary research at MPS owes its international reputation, among other things, to its many significant participations in international space missions. I intend to continue this work while placing it in a new context," Kleine says. "Combining the data from space missions with laboratory studies holds huge potential," he adds.
Groundbreaking results
Thorsten Kleine's work takes us back to the beginnings of the Solar System. At that time, a disk of dust orbited the young Sun. The dust grains stuck together and grew to ever larger chunks, so-called planetesimals, that later merged to form planets. Contrary to a long-held view, Thorsten Kleine was able to show that these planetesimals emerged in two different places of the protoplanetary disk. The early formation of Jupiter may have been responsible for this separation. Initially, the two populations of planetesimals developed independently of each other. Only after several million years did the further growth of Jupiter lead to mixing of these two groups: Planetesimals from the region outside the gas giant's orbit were scattered into the inner Solar System, where they mixed with the “local” population in the asteroid belt. These results suggest that meteorites contain material that originally formed far beyond Jupiter's orbit in the outer Solar System.
Thorsten Kleine's work also sheds new light on the evolution of our own home, the Earth and its Moon. According to his findings, our planet likely collected water-rich material from the outer Solar System already in its main growth phase and thus earlier than thought. With an age of 4.425 billion years, the Moon is, as Thorsten Kleine's latest results show, relatively young. Researchers assume that it emerged from the violent collision of the Earth with a body about the size of Mars. How exactly this process took place is still unclear. However, the comparatively young age of the Moon and Thorsten Kleine’s further research provides decisive constraints that can help to further refine the model of the giant impact.
Metallic traces
For his investigations, Thorsten Kleine brings the Solar System into the laboratory - or at least fragments of it. His "tools" are primarily meteorites, i.e. pieces of rock that originate from asteroids and Mars and fell onto Earth. In addition, terrestrial rock samples play a role, as well as lunar material brought to Earth by astronauts during the Apollo missions. "Such rock samples are witnesses to the beginnings of the Solar System and the formation of the planets. In a way, they tell their own story and contain clues to their place of origin, evolution, and age," Kleine says.
Crucially, such rock samples contain small amounts of the isotopes of rare chemical elements such as tungsten, hafnium, ruthenium, and molybdenum. The term "isotopes" refers to varieties of the same chemical element that differ solely in the weight of their atomic nucleus. Thorsten Kleine was able to show that such rare metal isotopes were not evenly distributed in the early Solar System, but that the isotopic composition depended, among other things, on the distance from the Sun. Furthermore, the chemical composition of a body is influenced by its further evolution: impacts of other bodies, the formation of a metallic core, changes of location within the Solar System - all this leaves its traces and can be reconstructed by isotope analyses.
In addition, isotope analysis offers the possibility to date events and evolutionary steps of the early Solar System. This is because some of the isotopes under consideration are not stable, but decay radioactively. The age of a rock sample can thus be inferred from the quantitative ratio of certain isotopes.
Highly specialized laboratories
To avoid contamination of the extraterrestrial rock samples in the laboratory, the analyses have to take place under ultra-clean conditions in specially equipped clean rooms. There, the samples are first powdered and chemically prepared. Mass spectrometers can then be used to determine differences in the ratios of selected isotopes to within a few parts per million. To this end, laboratories with powerful multicollector plasma mass spectrometers and thermal ionization mass spectrometers are to be built at the MPS in the coming months. Until the construction work is completed, the researchers will conduct their work in specially equipped laboratory containers.
The highly specialized laboratories will also be able to examine samples taken by unmanned space probes from asteroids, comets, the Moon, or Mars, which will be brought back to Earth. Thorsten Kleine's future interest lies also in such sample return missions. He was part of an international group of researchers who explored the scientific potential of a sample return mission to Mars and he is a member of the team responsible for the initial analysis of the samples taken by the Japanese space probe Hayabusa 2 from the asteroid Ryugu.
Thorsten Kleine studied geology and paleontology as well as mineralogy at the University of Münster in Germany. After completing his PhD in Münster, he was awarded a Marie Curie Fellowship to work at the Institute of Geochemistry and Petrology at the Swiss Federal Institute of Technology (ETH) Zurich. In 2009, he became assistant professor of isotope geochemistry there. In the same year, he accepted a full professorship in the Institute of Planetology at the University of Münster, where he has worked ever since. Among Thorsten Kleine's numerous awards and honors are the F. W. Clarke Medal of the Geochemical Society, the Victor Moritz Goldschmidt Prize of the German Mineralogical Society, and the Nier Prize of the Meteoritical Society. Kleine is an elected member of the North Rhine-Westphalian Academy of Science, Humanities and the Arts and a Fellow of the Meteoritical Society.