Shocks in the solar system: the role of thermal and collisional processes in the formation of the regolith on celestial minor bodies and other fine particles. – SHOCKS

Fine particles are ubiquitous in the Solar System throughout its whole history. They tell us about the formation of solid celestial bodies as well as their nature. However, how these particles form remains still enigmatic. The aim of this project is to make significant advances in our understanding of this fundamental question. In view of the interdisciplinary implications and the scientific complexity of this problem, two laboratories, one involved in astrophysics (Cassiopée, UMR 6202, Nice) and one in Earth Science (Centre de Recherches Pétrographiques et Géochimiques, UPR 2300, Nancy) decided to merge their resources and their competences to create a unique scientific initiative to tackle this issue.
Two kinds of fine particles that formed at different epochs of the evolution of the Solar System will be studied: i) the regolith observed on asteroid surfaces because of their link to the formation and evolution of the planetary bricks, and ii) the chondrules that are the main component of primitive meteorites, since they offer unique insights into processes that occurred during the early formation of the Solar System from its accretion disk. Both environments requiring highly energetic events, we will investigate the relative role of thermal and impact shocks in the formation of these particles. What is the efficiency of thermal fatigue resulting from the day/night temperature cycles to the shattering and comminution of rocks and boulders on asteroid surfaces? What is the efficiency of the impact cratering process in regolith production? Are the shocks produced by impacts between planetesimals during the early epoch of the Solar System relevant for chondrule formation? What are the proper impact conditions that lead to the formation of chondrules and are they consistent with the dynamics of the Solar System in its early phase? Finally, in general, what is the fundamental role of shock processes in fine particle production throughout the Solar System history?
These fundamental first order questions, among others, are now reachable because of all the analytical, experimental and numerical simulation developments that were carried out during the last years in the two laboratories participating to this proposal. The major breakthrough will be the coupling of observations at different scales (remote-sensing and space vs. meteorite observations) to new original experiments of thermal fatigue and highly energetic impacts, and their simulations with upgraded numerical codes. At its term, this project will provide a new understanding of formation processes and properties of fine particles over the Solar System history. This knowledge will also be of key importance in the preparation and data interpretation of space missions devoted to the visit and /or sampling of celestial body surfaces (e.g. Dawn, OSIRIS-Rex, Hayabusa, MarcoPolo-R, …). The funding of the ANR is essential to provide the necessary support to this innovative multi-disciplinarity approach characterized by the combination of expertises in primitive meteorites, laboratory experiments, geomechanics and numerical modeling. Thus, it can be anticipated that the present initiative will stimulate many new developments combining these different disciplines and fruitful interactions among the different involved communities.