An introduction to impact research

Hypervelocity impact: a fundamental geological process

The collision of solid bodies has been and still is one of the fundamental geological processes in our solar system. Not only the heavily cratered lunar surface testies to the important role hypervelocity impacts have played in the evolution of Moon and Earth: The Moon itself was most probably formed by a giant impact less than 40 Ma after formation of the Earth. Later, impacts of comets and carbonaceous chondrites have delivered water and probably organic molecules, and large impacts have probably caused re-cycling of the early crust.

The formation of impact craters has produced and/or conserved some world-class economic deposits (e.g., NiCu ores at Sudbury, Canada, diamonds at Popigai, Russia, gold at Vredefort, South Africa, hydrocarbons in impact breccias, for example, the Ek oilfield at the Campeche bank, Gulf of Mexico). Finally, at least one collision, the Chicxulub impact event 65 Ma ago, caused a major mass extinction at the Cretaceous-Tertiary (K/T) boundary.

Constant re-shaping of the Earth’s surface by plate tectonics and erosion, however, has erased most of the evidence of the cratering record on Earth. Nevertheless, 176 impact structures have been identified on Earth by 2008 and this number is growing continuously (http://www.unb.ca/ passc/ImpactDatabase/ and new discoveries); in addition, a small number of ejecta layers is known – again, the K/T boundary is the most famous example.

There are currently 176 craters known on Earth

It has to be pointed out that hypervelocity impact poses a certain threat for civilization; therefore, systematic search programs for potentially dangerous projectiles (Near-Earth-Objects NEOs, http://neo.jpl.nasa.gov/ca/ ), and projects to evaluate mitigation techniques of Earth-targeted NEOs are currently pursued. The 15-m-sized meteorite impact crater, formed on September 15, 2007 at Carancas, Peru, documented quite plainly the persistent timeliness of impact events. Impact as a process and impact induced environmental effects are important research topics – for the named scientific reasons, but also under the aspect of technological achievements, as the extreme time and energy scales of hypervelocity collisions require specific techniques in experimentation and highly sophisticated codes for modeling.