Meteorite craters in the lab
Meteorite impacts have been shaping the surfaces of planets, moons, asteroids and comets for billions of years. How exactly meteorite craters are formed is being analysed by the MEMIN research network, one of the leading institutes in this field worldwide. This group, which also includes the working group headed by Prof. Alexander Deutsch from the Institute of Planetology at Münster University, has been receiving funding for three years from the German Research Foundation (DFG). Now the DFG has approved € 1.6 million of funding for another three years. Those benefiting from this in addition to the Münster researchers are the University of Freiburg, which is leading the project, the Universities of Jena and Munich, the Fraunhofer Institute of High-Speed Dynamics in Freiburg, research institutes in Berlin and Hamburg, and cooperation partners in Beauvais (France) and Stony Brook (USA). MEMIN stands for Multidisciplinary Experimental and Modeling Impact Research Network.
Meteorite impacts have left a large number of traces. Scientists attribute the formation of the moon to an enormous collision with the earth at an early stage. The extinction of the dinosaurs at the end of the Cretaceous period was also caused by a meteorite hitting the Earth. Even today, cosmic impacts present a danger for the Earth. "We were reminded of this in spectacular fashion on February 15 this year," says planetologist Alexander Deutsch, "when a meteor about 15 metres in size exploded upon entering the atmosphere over the Siberian city of Chelyabinsk."
The MEMIN researchers generate experimental meteor impacts in the lab and, using high-speed cameras and pressure sensors, researchers record a multitude of processes in real time. In these experiments a so-called light gas accelerator speeds up steel balls up to 1.2 cm in size, or real meteorites, to a speed of more than 25,000 kilometres per hour. In less than one millisecond, craters with a diameter of up to 40 centimetres are formed as a result of the energy released by the impact. Specially developed particle collectors capture the material thrown out of the crater for the purpose of mineralogical and geochemical analyses. The data thus acquired serve as a basis for numerical models which simulate the crater formation and allow new insights into the highly dynamic processes.
"We want to use the funding to build on the success we had in the first phase," explains Alexander Deutsch. "What's particularly interesting is the question of how the material properties of typical rocks found in the Earth's surface can influence crater formation." The focus of the scientists' interest is also turning to those processes which take place immediately upon impact. When the projectile makes contact with a body of rock there are, for just a short time, extreme pressures and temperatures which can lead to the impacted rocks melting and vaporizing, or even to the formation of plasma.
The physical conditions which arise during these processes are to be recorded using ultramodern high-speed measuring technology. "Such data are necessary to check and improve the accuracy of the numerical simulations," says Alexander Deutsch. A precise understanding of the highly dynamic, complex conditions found in a meteorite impact is an important basis, he says, for the meteorite defence strategies which have been undergoing development for more than ten years now.
Alexander Deutsch, co-spokesman of the MEMIN research network and co-publisher of a special volume – produced by the internationally renowned journal "Meteoritics and Planetary Science" – on the results of the first period of funding, shares responsibility for the success of 'impact research'.