Retirement of Prof. Dr. Ulrich Christensen

The former MPS director has retired and now heads the Emeritus Group "Planetary Interiors".

March 17, 2020

Prof. Dr. Ulrich Christensen, who was director of the department "Planets and Comets" at the Max Planck Institute for Solar System Research (MPS) since 2002, has retired. Nevertheless he will continue his scientific work at the institute. Christensen will remain involved in scientific projects and international space missions and will now lead the Emeritus Group “Planetary Interiors”. An official farewell for Prof. Dr. Christensen is still pending. A symposium, which was planned for this purpose for 18 March, had to be cancelled due to the current corona situation, but will possibly be postponed to a later date.

Since the beginning of his scientific career, Prof. Dr. Ulrich Christensen's main research interests have been the dynamic processes in the Earth's mantle and core. He relies primarily on numerical calculations in order to simulate the gigantic material upheavals that take place there and thus better understand them. In recent years, he has focused his attention mainly on the Earth's core, where such high pressures and temperatures prevail that the main components iron and nickel are liquid and electrically conductive. These metals rise up, cool and sink down again in huge currents that are additionally swirled and twisted by the Earth's rotation. The interaction of these movements creates the Earth’s magnetic field in a kind of dynamo process. 

Besides Earth, other celestial bodies also have a global magnetic field. Among them are the planets Mercury, Jupiter, and Saturn as well as some of the ice giants’ moons. Christensen investigated the question why these magnetic fields are of such different strengths and was able to identify the energy flow in the planets’ liquid cores as the decisive variable. Such findings are also based on measurements from space missions, that study the magnetic fields of the planets and their moons from close up and in which Christensen and the MPS were and are involved. 

Under Christensen's leadership, numerous international space missions, to which the MPS department “Planets and Comets” contributed, experienced their active and therefore most exciting phase. These include the missions Mars Express, Venus Express, and Rosetta of the European Space Agency (ESA), the missions Phoenix and Dawn of the American National Aeronautics and Space Administration (NASA) and the joint ESA-NASA mission Cassini-Huygens. During this period, scientific instruments from MPS investigated, among other things, the planets Mars, Venus, and Saturn, as well as the asteroids Vesta and Ceres, and the comet Churyumov-Gerasimenko.

Not least because of ongoing missions, Christensen continues his research at MPS after his retirement. For example, NASA’s InSight mission, to which Christensen contributes, is currently the first mission to regularly provide meaningful seismic data from the surface of Mars. This can help answer the question, why our neighboring planet evolved so differently from Earth and today only shows the remains of a magnetic field. In addition, the European-Japanese space probe BepiColombo will not enter orbit around its target planet Mercury until 2025, and the European mission JUICE will be launched in 2022 to its destination Jupiter. Christensen is also involved in the evaluation of these data.

Prof. Dr. Ulrich Christensen studied physics at the Technical University of Braunschweig (Germany) where he received his doctorate. As part of his habilitation at the University of Mainz he turned to geophysics. This was followed by research positions in Tempe (Arizona, USA), Karlsruhe (Germany), and Utrecht (Netherlands). In 1992 Christensen accepted a call to the Institute of Geophysics at the University of Göttingen. Ten years later, he became director at the Max Planck Institute for Solar System Research, which at that time was still located in Katlenburg-Lindau under the name Max Planck Institute for Aeronomy. Among the many awards and honors bestowed on Christensen are the Gottfried-Wilhelm Leibniz Prize of the German Research Foundation, which he received in 1994, the August Love Medal of the European Geosciences Union and the Inge Lehmann Medal of the American Geophysical Union.

The symposium originally planned for March 18th, with which the MPS wanted to give Prof. Dr. Christensen a ceremonial farewell, unfortunately had to be cancelled. The reason is the current risk situation caused by the corona virus. The symposium will possibly be held at a later date.

The current projects of the former department "Planets and Comets" will be continued. Until a successor to Christensen takes up his work, MPS director Prof. Dr. Sami K. Solanki will be the acting head of these research groups.

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