International Comet Experiments

Over the past few decades, very successful space missions have significantly improved our knowledge of the origin and activity of comets. These space missions have been supported by a variety of different theoretical models and intensive observational campaigns. However, the support from ground-based laboratory experiments has been limited, although they can provide deeper insights into the physics of comets. The laboratory experiments performed so far were very useful to understand the nature of ice-dust samples under cometary-like conditions. However, since we have now data from several fly-by missions and from Rosetta more than two years of escorting a comet from the onset of activity throughout the perihelion (activity maximum) and beyond, the picture of gas and dust production has changed. These new insights have impact on the requirements needed to carry out state-of-the art comet simulation experiments with realistic sample materials. Thus, a new generation of ground-based laboratory experiments is mandatory to interpret the data gathered by previous space missions (especially by the Rosetta mission) and to support future space missions to comets, or to other icy bodies in the Solar System. These experiments require a broad spectrum of facilities and expertise to characterize the thermal, physical and optical properties of the analogue samples and their behavior during simulated cometary activity. As such they can only be addressed by a multi-national effort with contributions from several laboratories. The objective of this proposal is to better understand the fundamentals of cometary activity by performing state-of-the art laboratory experiments, accompanied by theoretical modeling, in an international framework. This will be done by designing, performing and evaluating a series of experiments to study the physical properties and activity behavior of comet analogue materials. The goal of these experiments is to design scientifically relevant and realistic test scenarios, which can be used to investigate the physical processes associated with comet activity (this project is not an attempt to perfectly reproduce a cometary nucleus in the laboratory). Additionally, this project aims at providing a guideline for state-of-the art cometary analogue sample preparation, which will be based on the expert knowledge of the proposers, extended in the framework of this project. In order to achieve these goals, scientists from Germany (D), Austria (A) and Switzerland (CH) will closely collaborate by joining together their expertise and laboratory equipment (D-A-CH group). This collaboration provides the possibility to perform a large variety of scientifically important, but small-scaled, experiments with the ultimate goal to construct a well-equipped simulation chamber (by bringing together the already available scientific equipment of the D-A-CH group), which will allow studying various aspects of comet activity. Lead agency (D): TU Braunschweig, Germany Dr. Bastian Gundlach Prof. Dr. Jürgen Blum International cooperation partner (A-CH): Dr. Günter Kargl, Österreichische Akademie der Wissenschaften Prof. Dr. Nicolas Thomas ,Universität Bern Dr. Holger Sierks, Max-Planck-Institut für Sonnensystemforschung, Göttingen

The DACH Lead Agency project "International Comet Experiment" (CoPhyLab), is dedicated to the investigation of recurring cometary activity. The project was a joint proposal of the TU-Braunschweig as lead agency, the University of Bern and the Space Research Institute of the Austrian Academy of Sciences. The consortium included also the German Centre for Air and Space (DLR) Berlin, the Max-Planck Institute for Solar System Research Göttingen and the University of Stirling. At a later stage the QIANXUESEN Laboratory off Space Technology in China, the Open University in UK and the Swedish Institute of Space Physics/IRF Kiruna also joined the consortium. All additional partner supported the project with their own budget, staff and devices. The planned experiments have been divided into three categories. S(mall)-experiments as fast implementable local measurements where usually only one or two partners were involved at their home institution. The medium or M-Class experiments where at least two project partners were involved. The last class of experiments were the L- experiments. These were exclusively located at the TU Braunschweig and required using the CoPhyLab facilities implemented during the project and was supported by the whole consortium with both equipment and staff presence at the laboratory site. The planning and execution of all experiments was coordinated with the whole CoPhyLab team during the regular video meetings. A main part of the work was to establish a joint experiment facility. In this facility not only, a set of vacuum chambers dedicated to cometary research was set up. Each partner provided instrumentation according to their special field of comet research. Which means the CoPhyLab L-Chamber was holding up to 21 different instruments which allowed a more comprehensive investigation and more interdisciplinary research than any individual laboratory alone could achieve. IWF Graz contributed substantially to the planning and design of the large thermal vacuum chamber in Braunschweig. This included technical expertise for designing the cooling system and the contribution of hardware equipment like a solar simulator and various measurement devices . Another major contribution from Graz was the design and construction of a sample manipulation robot for the L-Chamber which can transport various sensors and instruments around the sample mounted in the chamber in vacuum and ambient temperatures as low as 77 K. Tt is a worldwide unique piece of instrument which no other laboratory can use for comet experiments. Another focal point of research was the measurement of gas transport in granular media analogous to cometary surfaces. For this purpose, a dedicated measurement set-up was established in Graz which could measure this effect in both viscous and molecular (Knudsen) flow regimes. A review of previously used analogue materials was used to create a new standardised comet analogue material.