Probing the Protosolar Cloud: Characterization of the Solar System’s circumstellar building blocks at the sub-micrometer scale

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All stars lose mass in the form of ionized atoms, either continuously as stellar winds, or in explosive scenarios like novae and supernovae. Around evolved stars, these atoms eventually condense into solid particles, which carry information about the condensation conditions, and the elemental and isotopic composition of the parent star itself. So-called “presolar” stardust that is found today in primitive Solar System materials (meteorites, interplanetary dust, cometary matter) was incorporated into the molecular dust and gas cloud from which the Sun and our planetary system formed some 4.57 billion years ago. Presolar grains can be distinguished from solids of Solar System origin by their highly anomalous isotopic compositions. The study of presolar dust offers not only a unique possibility for the laboratory-based investigation of material from – now extinct – stars other than the Sun; these stardust grains also represent initial building blocks of our Solar System.In this project, I will focus on the stellar origins and isotopic compositions of the rock-forming elements calcium, titanium, and iron, and how they are affected by Galactic Chemical Evolution. Investigation of the trace elements Sr, Zr, Mo, and Ba in presolar silicates and oxides will provide additional information on grain condensation, and will help to answer the question if these elements were introduced into the protosolar nebula by O-rich presolar grains, or if they were mainly provided by carbonaceous dust. Ultimately, all these studies will allow to better constrain the different types of stellar sources that contributed material to the nascent Solar System, e.g., low-mass asymptotic giant branch (AGB) stars, core-collapse supernovae, massive AGB stars, novae, other types of supernovae), and will provide a groundwork for a classification scheme for Ca and Ti isotopes. This might even provide hints for potential connections between the presolar carriers of Ca and Ti, and the isotopic compositions of calcium-aluminum-rich inclusions (CAIs), the first solids that formed in the Solar nebula.The isotopic and trace element measurements of presolar grains will be carried out by NanoSIMS ion imaging. They will be combined with resonance ionization mass spectrometry (RIMS) of Fe and trace element isotopes from suitable grains and studies by transmission electron microscopic (TEM) techniques of selected presolar silicates and oxides, to characterize their mineralogy and monitor the degree of alteration by monitoring the distribution and oxidation state of Fe. High-precision O-isotopic investigations of presolar silicate host sites will be carried out to determine their respective degrees of alteration. Samples will be characterized by scanning electron microscopy (SEM) and SEM-based energy-dispersive x-ray spectroscopy (SEM-EDS) prior to SIMS analysis to identify promising target areas.