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uni'wissen 02-2013_ENG

Prof. Dr. Thomas Kenkmann has served as professor of general geology and struc- tural geology at the Univer- sity of Freiburg since 2010 and as assistant dean of the Faculty of Environment and Natural Resources since 2013. After studying geology and paleontology in Cologne, he earned his PhD at the Free University of Berlin in 1997 and com- pleted his habilitation in 2003. He then worked as a scientist and curator at the German Research Center for Geosciences in Pots- dam and later at the Mu- seum für Naturkunde in Berlin. From 2007 to 2010 he also served as director of the Center for Ries Cra- ter and Impact Research in Nördlingen. Since 2009 he has headed the research group “Multidisciplinary Experimental and Modeling Impact Research Network,” funded by the German Research Foundation. In addition to meteorite cra- ters, his research interests include rockslides and slower deformations of the Earth’s crust. Photo: Thomas Kunz Further Reading Kenkmann, T./Deutsch, A./Thoma, K./Poelchau, M. H. (2013): The MEMIN research unit: Experimental impact cratering. In: Meteoritics & Planetary Science 48/1 (MEMIN special issue), pp. 1–2. doi: 10.1111/maps.12035 Kenkmann, T./Wünnemann, K./Deutsch, A./ Poelchau, M. H./Schäfer, F./Thoma, K. (2011): Impact cratering in sandstone: The MEMIN pilot study on the effect of pore water. In: Meteoritics & Planetary Science 46/6, pp. 890–902. Poelchau, M. H./Kenkmann, T./Thoma, K./ Hoerth, T./Dufresne, A./Schäfer, F. (2013): The MEMIN research unit: Scaling impact cratering experiments in porous sandstones. In: Meteorit- ics & Planetary Science 48/1 (MEMIN special issue), pp. 8–22. doi: 10.1111/maps.12016 Prof. Dr. Thomas Kenkmann also simulates meteorite impact events in his lab at the University of Freiburg. Visit our research portal for a video clip and an article on the research facility: A contraption made of floral foam and Vaseline catches the tiny shards, drips, and fragments blasted out of the rock in the simulations of impact events. A look at the foam under the microscope reveals that more large fragments are caught when there is a lot of water in the rock (below). When the rock is dry, the fragments are smaller and all of roughly the same size. Photos: MEMIN will be to study the first nanoseconds following impact, in which an enormous amount of heat is generated and plasma is formed. Moreover, the researchers want to try out other rocks, like mar- ble and gneiss. Protection from Meteorites Can the findings help to protect the Earth from meteorite impacts? Like many other scientists, Kenkmann was surprised when a meteorite en- tered the Earth’s atmosphere over Russia on 15 February 2013. Luckily it broke up into thousands of tiny fragments, slowed down by the atmo- sphere. There was thus no impact crater. The 1500 injuries it caused were due to the atmo- spheric shock wave created by the meteorite. “Had the rock been only a little bit larger than 15 meters, it would have caused a crater,” explains Kenkmann. The city of Chelyabinsk would likely have been completely destroyed. The MEMIN project makes precise calculations like this pos- sible and shows how dangers can be averted: “According to the principle of billiard balls colliding with one another, projectiles can be used to divert celestial objects on a collision course with Earth from their course. The experiments conducted within the context of MEMIN have also yielded ini- tial findings concerning this mechanism,” says Dr. Frank Schäfer from the Ernst Mach Institute. The experiments help the scientists to under- stand the history of meteorite impacts on the Earth. One of the largest craters on Earth, with a diameter of 200 kilometers, is the Chicxulub cra- ter in Mexico. The meteorite that created it 65 mil- lion years ago triggered global mass extinctions, including dinosaurs. Like at the Nördlinger Ries, scientists have only succeeded in reconstructing the impact event in Chicxulub by analyzing rocks found at the site and making calculations, be- cause it is no longer possible to discern the origi- nal form of the crater itself due to erosion. There are 184 known impact craters on the Earth’s surface, and new ones are being discov- ered every year – also by geologists at the Uni- versity of Freiburg. “We’re something of a global impact crater taskforce,” says Kenkmann. When a meteorite hit the ground near Lake Titicaca in South America on 15 September 2007, the re- searcher flew there with his team to measure the crater and take samples. “You could say it has be- come a passion.” Kenkmann would love to experi- ence a real meteorite impact sometime – from a safe distance and in an uninhabited area. Until then, he’ll have to make do with shooting stars. 7