Solid celestial bodies (planets, asteroids, comets) undergo various kinds of stresses during their evolution. Their response to those stresses depends on their physical properties. In turn, those properties are modified as a result of the applied stresses. One of the main processes that contributed to the formation of planets and shaped their leftover building blocks (asteroids and comets) is the impact process. Meteorites collected on Earth are an indication of the collisional activity as they are the remnants of collisions that take place in the asteroid Main Belt between the orbits of Mars and Jupiter. The collisional process is therefore not a second-order problem in the understanding of the past, present and future history of our Solar System; it is actually at the heart of its formation and evolution. Although major advances have been performed by members of our team these recent years, on both the experimental and numerical sides, great efforts are still necessary to achieve a complete understanding that can be applied to the various properties of solid celestial bodies and allow better assessment of how these properties are influenced by this process. Moreover, such knowledge is crucial in the design of space mission tests of deflection in the framework of mitigation strategies.

Asteroids range in size from small (~10 m) boulders to bodies 1000 km across with consequently larger range in mass, from a few thousand tons to 1021 kg, which is still only a fraction of a percent of the mass of the Earth. As a result, from planets to asteroids, surface gravities vary by many orders of magnitude. The geology and geophysics of asteroids is a fascinating and constantly surprising field. Regolith, granular material covering the uppermost layer of solid planetary bodies, plays an important role in the surface geology of asteroids. The same can be stated, although to a lesser extent, for bodies like Mars and the Moon, whose surface gravities are also smaller than that of Earth’s. Thus, flows of granular materials driven by different gravitational conditions are particularly important in the understanding of the geology of small bodies and planets. The exploration of the Moon and Mars in the next two decades will require deployment of landing vehicles on surfaces of loose granular material. Space missions to small bodies also involve measurements by landers (e.g. the Rosetta mission) and sampling devices capable of coping with a wide range of surface properties. The proposed team and workshops at ISSI will bring together specialists in these two related processes (impacts and granular material dynamics) with the required expertise in modeling, laboratory experiments and space missions. The workshops will provide a stimulating environment for new ideas and for advancing existing and new projects.