Gravoturbulent Planetesimal Formation in the Early Solar System

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We investigate the formation of planetesimals from a gravitationally unstable cloud of chondrules and matrix material embedded in the early solar nebula. The planetesimal precursor material (chondrules or chondrule-sized grains plus matrix material) evolves due to coagulation, fragmentation, and drift in the early solar nebula. In our project we connect predictions on the abundance of precursor material to the composition of primitive chondrites in the framework of gravoturbulent formation scenario of planetesimals. In this scenario precursor material from a range of feeding zones gets concentrated in non-laminar gas structures of the solar nebula (zonal flows, vortices, and streaming instability) to gravitational unstable densities, e.g., exceeding the local Roche density. In the new funding period we will study the final collapse and possible fragmentation of these material concentrations to connect our models of precursor material evolution to the physical and chemical properties of primitive chondrites, asteroids, and cometesimals. Based on our simulations of gas and dust material evolution inside the solar nebula, we derive a time-dependent local abundance and size distribution of precursor material. We know from our magnetohydrodynamical simulations of zonal flows, vortices, and the streaming instability how strong this precursor material gets concentrated and what size segregation will occur in the overdensities. We use these overdense clouds and simulate their gravitational collapse in local high resolution hydro and dust simulations basically down to the solid density (which is only 2-3 orders of magnitude in spatial resolution), i.e., we can spatially resolve the forming planetesimals by up to 1000 grid cells in volume. Thus, we can measure, for instance, the fraction of chondrules vs. the mass fraction in matrix material. Chondrules will in this process be the most mobile particles, driving the dynamics of the collapse, whereas the matrix material is passively dragged along by the gas, and will only at a so far unpredicted level get incorporated into the planetesimal. By varying the initial mass, volume, and size distribution within the precursor cloud we can find the sweet spot that produces a certain kind of chondritic material. We can link the properties of a chondrite to its precursor properties and its formation time and location inside the nebula. One can already speculate that during the evolution of the nebula different locations and times will produce different sized chondrites with varying internal size distributions. By testing the properties of our artificial population of planetesimals to the observed data on size distributions of the material in chondrites, its chemical variations, and size distributions of asteroid belt and Kuiper belt objects and their observed binarity, we can improve our model of precursor evolution of planetesimal building material and also test the physical conditions for planetesimal formation.