From gas to dust: searching for the reactions at the origin of the first solids in the solar system

Astrophysical observations of young stellar objects and their disks, as well as studies of the components of primitive meteorites, concur to demonstrate that many of the mineralogical, chemical and isotopic characteristics of the first planetesimals to form in the protosolar nebula (PSN) were established during the first few hundreds of thousands of years of the solar system. However, the chemical and physical processes that transformed the dust and gas of the parent molecular cloud into the dust that formed the bodies of the solar system remain largely unknown. This is exemplified by the fact that all the rocks that are known in the Solar system exhibit, from the micrometer to the bulk scales, isotopic compositions for the major element oxygen that cannot result from the “classical” evaporation, condensation, melting crystallization processes observed in terrestrial rocks and in experiments.The aim of the DUST proposal is to make decisive advances in our understanding of the origin of dust in the PSN by discovering, from experiments in plasmas simulating the PSN, the gas-solid reactions that produced the oxygen isotope anomalies in solids and transferred them to all the precursors of primitive meteorites. This work will be complemented by the development of a new analytical technique to explore the mineralogical and chemical composition of hundreds of thousands of sub-micrometer-sized grains in the matrix of the most primitive chondrites, in search of preserved PSN dust. In addition, systematic isotopic studies of silicon in this matrix will be developed to better constrain the extent of kinetic processes during the so-called condensation sequence of the hot PSN gas. Finally, a condensation code including, for the first time, the various isotopic fractionations and the non-equilibrium effects due to variations in condensation rates, will be developed and used to predict the expected relationships between the mineralogy and isotopic composition of condensed dust.