Knowledge of the processes occurring in the early history of the solar system is critical to understanding the formation and evolution of planetesimals and planetary bodies. We propose to combine…

This $105,999.99 grant award from the National Aeronautics and Space Administration (NASA) was made to the California Institute of Technology (Caltech) to conduct observational and theoretical investigations into the formation of igneous rims around chondrules. The research aims to improve understanding of the processes that occurred in the early history of the solar system, with a focus on the formation and evolution of planetesimals and planetary bodies. The grant supports a highly interdisciplinary study incorporating petrographic studies, astrophysical modeling, and isotopic studies. The results will provide insight into the evaporation experienced by igneous rims during their formation and place constraints on conditions in the early solar nebula. This work is particularly relevant to NASA's Emerging Worlds program, which supports investigations related to the formation and early evolution of the solar system. The grant does not have a set-aside designation.

Knowledge of the processes occurring in the early history of the solar system is critical to understanding the formation and evolution of planetesimals and planetary bodies. We propose to combine petrographic studies, astrophysical modeling, and isotopic studies to investigate the formation of igneous rims around chondrules. This highly interdisciplinary study, conducted jointly by researchers at arizona state university (ASU) and the california institute of technology (CALTECH), will incorporate observed properties of chondrules into theoretical models of processes occurring in the chondrule forming regions. The results of our study will provide insight into the evaporation experienced by igneous rims during their formation, and will result in testable predictions and will place constraints on conditions in the early solar nebula. IT has long been presumed that igneous rims (IRS) around chondrules are indicative of a second heating event, occurring after a dust-rich mantle was acquired. The textures of IRS suggest they were formed by the same type of heating event as the majority of chondrules. Shocks in the solar nebula are the most generally accepted chondrule-forming mechanism. Rigorous shock models demonstrate that solids will experience significant evaporation in the pre-shock region. IT is therefore expected that the dust mantles from which IRS are formed will experience a reduction in volume due to loss of porosity, concomitant with evaporation. We seek to understand how this evaporation affects the final thickness and isotopic properties of the resulting igneous rim. Our previous observations of chondrules with accretionary rims found a 1:1 relationship between the size of the core and the dusty rim, through the examination of disaggregated chondrules. Modeling of the mass of dust swept up by a particle supports such a relationship. However, previous studies were conducted only on the carbonaceous chondrite allende. We propose to extend this work to a much larger sample set, in order to determine the core/rim size relationship to higher precision. Using this relationship, we propose to model the melting and evaporation of the precursor accretionary rim to predict the thickness of the resulting igneous rim. We will use our state-of-the-art shock code for chondrule-formation to perform extensive parameter studies of a variety of nebular conditions and precursor particle size. At the same time, we will fully develop our detailed evaporation model to incorporate the results of the parameter studies. The subsequent results from the integrated evaporation model will be used to make testable predictions of igneous rim thickness. The pre-shock evaporation experienced by rims would be expected to result in isotopic fractionation. Experimentally, we can gain insight into the evaporation history of igneous rims through investigation of isotopic fractionation of highly volatile to moderately volatile elements. We propose to conduct high-precision sims measurements of MG and SI isotopes on primitive and unequilibrated ordinary chondrites of low petrologic type in order to determine the extentof evaporation of IRS. Our research is particularly relevant to NASA's emerging worlds program, which supports investigations "related to understanding the formation and early evolution of our solar system", and addresses several of the specific examples listed under the scope of the program (e.g., chemical and physical processing of gas, dust, and ICE). The combination of observational data on disaggregated chondrules with theoretical investigations provides a unique opportunity to further understand the formation and evolution of our solar system. Studies of the isotopes will allow US to test the robustness of the constraints provided by experimental and theoretical results, and allow further refinements of models of transient thermal heating events in the early solar nebula.