How do you make planets ? What happens to objects that did not accrete into larger bodies ? What is the source of our water and organic material ? Can you form Earth-like planetsĀ  in the habitable zone without having a disk of planetesimals at large distance ?

The processes leading to the formation of planetary systems leave behind a significant mass of small bodies orbiting at large heliocentric distance, up to 35 Earth masses depending on the models (Tsiganis et al., 2005), observed around 20% of Sun-like stars. It is established that those bodies play an important role in the migration of gas giants away from their stars and may be necessary for life to develop on the smaller planets. Yet, the conditions within these primitive populations are not well understood, especially their collisional environment.

In the last decade, space missions have brought fascinating new data which challenge our concepts of impacts in the Early Solar System. The mission Rosetta at comet 67P, for instance, has revealed a complex cometary world where collisions, from small to catastrophic, played a significant role. Recent work suggests that the topography of cometary nuclei and potential layering are shaped by processes which are primarily ancient. On a larger scale, dynamical simulations argue that objects like the Jupiter Family Comets may have been totally disrupted by catastrophic collisions. While models show that the high porosity and volatile content of cometary nuclei would survive such impacts, it is not clear whether the deeper structural features like layers can be preserved. From the same data set, different authors (Blum, Davidsson, Morbidelli, Rickman) come to different conclusions with respect to collisions in the early outer planetary system. Furthermore, different modeling approaches (de Niem, Jutzi, Schwartz) lead to distinct results.

The concept of this working group is to bring together for the first time European experts on collisions and cometary morphology. Over the last few years, modelers have developed new numerical simulations which are now able to properly treat cometary-like material. In parallel, thanks to Rosetta mission, small bodies morphologists have a much better understanding of the type of landform that can exist on comets, and measurements of the material physical properties. By combining our expertise, we aim to assess the role of impacts in the formation and evolution of comets, as well as properly benchmarking and comparing the different modeling approaches. This work will lead to a new understanding of impact processes in the Solar System history and provide very strong constraints on the formation and evolution of objects at large heliocentric distance, with applications beyond our own System.

Full proposal: JB_Vincent_ISSI_2018.pdf