לוח שנה משולב

The origin of Solar System satellites is actively debated. We know understand that, despite the morphological analogy between a satellite system and a planetary system, the formation processes of satellites may be significantly different from planetary formation processes. in addition, satellites evolve quickly under the effects of tides. Different scenarios seem to be required for different types of planets (terrestrial, giant or ice giant). In this talk I will quickly review our current understanding of satellite formation and the different constrains. Based on Cassini images and numerical simulation, I will show that there is today on-going accretion processes at the edge of Saturn's rings, pointing to a new satellite formation process. I will show that satellite formation may be deeply linked to the evolution of planetary rings, to the point that it is very probable that most of Solar System’s regular satellites may have born inside rings, either massive, like the protolunar disk,or light, like giant planet’s rings. I will illustrate this vividly in the case of Saturn using numerical simulations and CASSINI images. Case of Ice giants, Mars and Jupiter will be also discussed. Some extension to the case of exoplanets’ regular satellites will be attempted.

The actin cytoskeleton plays a major role during the initial stages of embryonic development. In particular, the actin cytoskeleton can switch, in a cell-cycle dependent manner, into a contractile state and exhibit large scale flows which are essential for the organization and the establishment of polarity in the early embryo. We developed a reconstituted model system to study cytoskeletal organization and emulate these processes in artificial cells. The actin machinery is encapsulated within water-in-oil emulsions, and actin nucleators are added to induce the formation of various cytoskeletal structures. By controlling the localization and concentration of these nucleators, we can tune the properties of the system, and induce cytoskeletal symmetry breaking which appears remarkably similar to the initial polarization of the embryo in many species, or bulk actin network contraction which can drive directional transport as observed during cell division. Overall, our reconstituted system provides a powerful platform to study important cytoskeletal phenomena in a simplified environment detached from the complexity of the living cell, and explore fundamental aspects of the properties of active matter.