Bridging the Gap <scp>III</scp>: Impact cratering in nature, experiment, and modeling

In order to understand the highly dynamic and complex details of the process of impact cratering and further the state of knowledge in this subject, multidisciplinary approaches are becoming more and more of a necessity for impact cratering research. The exchange between scientific results in modeling, experiments, field work, and remote sensing was the goal of the third Bridging the Gap conference, held in September 20–26, 2015 at the foothills of the scenic Black Forest at the Albert-Ludwigs University Freiburg (ALU), Germany. The conference continues in the tradition of the two previous Bridging the Gap conferences held in 2003 at the LPI in Houston and 2007 in Montreal, Canada. Thomas Kenkmann and Michael Poelchau (both University of Freiburg), Stefan Hiermaier (Fraunhofer Ernst-Mach-Institute, Freiburg, EMI), Alex Deutsch (University of Münster), and Fred Hörz (NASA JSC) invited researchers to Germany to participate in the week-long meeting. Over 120 scientists from five continents and 22 countries gathered together to discuss latest findings in the field of impact cratering and beyond. Topics at the conference spanned the full spectrum of impact cratering, from shock-induced nanoscale phenomena to giant multiring impact basins over 1000 km in diameter. The inter- and multidisciplinary aspect of the conference was accentuated by several “excursions” that were offered alongside the presentations. Guided tours of the experimental facilities hosted by the EMI and the Institute of Geosciences ALU were given, showing participants (Fig. 1) the excitements and dangers of working in dynamic, experimental basement laboratories. A 3-day fieldtrip to the Nördlinger Ries and Steinheim craters was led by Thomas Kenkmann, forcing experimentalists and modelers to face the rain as well as the ground truths of field work in terrestrial impact craters and discuss the intricacies of how these craters were formed. Numerical modelers repaid the favor by offering a novel session format to present the capabilities and limitations of numerical simulations to nonmodelers. For this “virtual field trip,” modelers set up several computer stations at the Institute of Geosciences, each with a designated “pilot” as an expert in a specific modeling topic. Participants were then invited to wander between stations and view the models (Fig. 2). This led to numerous fruitful discussions and was an eye-opener for quite a number of researchers. There was an overwhelmingly positive response to the virtual field trip, and this concept will hopefully become a regular part of workshops and conferences of this size. A further, pleasant surprise was the large and somewhat unexpected turnout of ~120 researchers interested in the conference. Nearly half of the participants were graduate and PhD students, which we see as an important and promising signal for the future of the field of impact cratering research. Financial contributions and logistical support from several institutions were of immense importance for this conference, which greatly enhanced the quality of the event, and enabled numerous researchers to participate through travel grants as well as low conference fees. We gratefully acknowledge the German Science Foundation DFG, NASA, the Lunar and Planetary Institute LPI Houston, Nature Geoscience, the Barringer Crater Company, EMI Freiburg, and ALU Freiburg for their support. We were pleased to see a general interest in the continuation of the tradition of Bridging the Gap special issues. This MAPS special issue presents 14 conference contributions that cover a wide range of impact cratering topics. The issue begins with several studies based on field work in terrestrial impact structures. Dence discusses new constraints from Canadian impact structures on the simple to complex crater transition. Thompson and Spray present a new model for the formation of sub–melt sheet suevite based on observations from the Manicouagan impact structure. Rae et al. combine shock barometry measurements with numerical models to estimate acoustic fluidization parameters and erosion depths at West Clearwater Lake. Kenkmann et al. report the outcome of a comprehensive study of the rim structure of the complex crater Jebel Waqf as Suwwan. Three remote sensing studies include a paper by Barlow et al. comparing central pit craters on rocky bodies throughout the solar system, a modeling study by Martellato et al. investigating effects of lunar stratigraphy on the morphology of the Linné crater, and a review by Gottwald et al. of the latest results from the TANDEM-X mission yielding digital elevation models for terrestrial impact structures. This issue also presents several papers focusing on microanalytical and experimental studies of impactites. Fritzke et al. present new data on cathodoluminescence of moldavites, which can be used for the visualization of internal textures and inclusions. Fazio et al. focus on formation mechanisms of coesite during and after the shock wave, while Mansfeld et al. look at stishovite formation in low-pressure shock experiments of sandstone. Carl et al. deformed quartz in membrane-driven diamond anvil cells under nonhydrostatic dynamic conditions, creating stishovite. Ebert et al. simulated short-term high-temperature impact processes with a Nd:YAG-laser, creating melts, and Reznik et al. used shock-recovery experiments to study how shock waves affect the magnetic susceptibility and microstructure of magnetite-bearing ores. Finally, Harris and Burchell show that experimental crater diameters in layered ice targets depend on the composition of underlying materials. We would like to thank all the reviewers for their time and effort to improve the quality of the manuscripts in this issue, and Natalia Artemieva for her contribution to the Mansfeld et al. paper as an associate editor. We gratefully acknowledge Executive Editor Tim Jull, Managing Editor Agnieszka Baier, and the MAPS staff for making this issue possible.

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