Periodic Reporting for period 1 - Complementarity (A unifying model: bulk chondrite complementarity by individual chondrule-matrix mentality) Reporting period: 2018-08-01 to 2020-07-31 Summary of the context and overall objectives of the project Our Solar System consists of a central star, our Sun, and eight (confirmed) orbiting planets. The Earth, so far, is the only planet on which life is found. One of the fundamental questions to our existence is, therefore, how this life was formed and what the initial conditions were for life to start. To answer this, we must investigate how our Solar System and our planet formed and evolved over time. For life to evolve on Earth, critical starting materials were needed, such as water and complex organic molecules from which eventually RNA, DNA and cells were formed. We need to unravel what Earth’s building blocks are with respect to these prebiotic molecules to understand how life could initiate in exoplanetary systems and, finally, to answer: are we truly alone in the universe? The key building blocks of the rocky planets in our Solar System may be represented by chondrules, once molten silicate spherules that are the main constituents of chondritic meteorites. These in turn are fragments of asteroids, planetary bodies that did not make it into becoming planets. When studying these chondritic fragments, we are probing the very first solids that agglomerated in the Solar System and with that, the initial conditions that are key to Earth’s habitability. Chondrites mainly consist of volatile-depleted chondrules and volatile-rich matrix, which contains water and organics. Potential genetic links between the chondrules and matrix can provide important clues into how actively these components were transported throughout our Solar System before finally being accreted into planets and asteroids. For example, did Earth acquire a matrix-component only from the relatively dry inner Solar System or could this component have arrived from the wet outer Solar System, from regions were comets and icy planets accreted? Answering this question is critical to understand how and when prebiotic molecules arrived on Earth. Hence, the main objective of this project was to investigate the genetic links, or potential complementarity, between chondrules and matrix by probing their chemical and isotopic make-up. The current state of the art is undecided whether complementarity exists or not. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far To reach the COMPLEMENTARITY objectives, the research was divided into several task packages: 1) The first step towards this goal was identifying and obtaining appropriate meteorite samples, which included chondrites that experienced the least amount of secondary alteration. This alteration could be, for example, terrestrial weathering, during which chemical exchange between chondrules and matrix could overprint the original signatures. 2) The selected meteorites were prepared for detailed petrological characterization and chemical analyses of individual chondrules and surrounding matrix areas, to provide insights into potential complementary relationships between these components. 3) This hypothesis was further tested by Cr and Zn isotope analyses of chondrules and matrix, which can elucidate the heritage of materials from which these components are formed and the physical processes behind chondrule formation.4) A start has been made to date the chondrules using the Pb-Pb dating system and, thereby, combining all results, provide a spatiotemporal model of chondrule storage and transport dynamics to trace the evolution of planetary building blocks.5) The final step was to disseminate these results into publications, at conference and seminar meetings and to formulate new ideas from these results into grant proposals.The main scientific goal of this project was to address the issue of chondrule-matrix complementarity in chondrites. By approaching this issue from several angles, namely chemically and isotopically, using multiple isotope systems, it was possible to resolve that this proposed complementarity does not exist. In detail, the chemical and isotopic composition of different stages of chondrule formation and the primitive volatile-rich dust that surrounds these chondrules do not reflect a common genetic origin. This implies that they formed separate from each other and were transported together to their final accretion region onto their parent asteroids. This has fundamental implications for how we think planets formed and what types of materials they accreted. For Earth in particular, the results from this project indicate that our planets’ volatile inventory (e.g. water and organics) were delivered early in the first million years of Solar System formation. In contrast, the current paradigm favors a volatile delivery model in which comets or water-rich asteroids from the outer Solar System delivered water at some point in Earth’s history. Instead, the project results suggest that the delivery of volatiles occurred through chondrule accretion (e.g. the pebble accretion model), which progressively carried volatile-rich dust rims into Earth’s feeding zone.References: + Van Kooten EMME, Cavalcante L, Wielandt D, Bizzarro M (2020) MAPS 55, 575-590.+ Van Kooten EMME, Moynier F (2019) GCA 261, 248-268.+ Van Kooten EMME, Moynier F, Agranier A (2019) PNAS 116, 18860-18866.+ Van Kooten EMME (2019) Zenit, January 2019.+ Day J, van Kooten EMME, Moynier F (2019) EPSL 531, 115998. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) The fundamental research that drives our understanding of Solar System formation, its potential for life and by extension that of exoplanetary systems, is pillared by the fields of cosmochemistry, astrophysics, astronomy, and astrobiology. All these disciplines working together stand the best chance to unravel how our Solar System evolved and whether it takes a unique place in the universe. Cosmochemical data provide the basic parameters for numerical models of planetary evolution and are, therefore, crucial to oversee the bigger picture of spatiotemporal dynamics in the maturing protoplanetary disk. Moreover, advancing insights into the nature and origins of meteorites and their parent bodies, planets, and asteroids, can progress the aims of space exploration and provide guidance to its targets. For example, the comet 67P/C-G was targeted by the ESA Rosetta mission to increase our understanding of the nature of volatiles and prebiotic molecules that could have kickstarted life on Earth. At the same time, the Rosetta orbiter and its lander Philae represented incredible technological feats in space exploration, necessitated by the complex nature of the mission. Hence, fundamental insights into the origins of meteorites and their components are ripples in the proverbial pond of science and technology. When modelling an evolving protoplanetary disk and accreting planets, astrophysicists must make critical assumptions about the degree of mass transport in the disk and the feeding zones of planets. Earth’s feeding zone, for example, could have been from the dry inner Solar System, or, as this projects results predict, progressively from the wet outer Solar System. The main implication from the COMPLEMENTARITY project is in fact that meteorite components are not genetically related and, thus, formed in different regions of the protoplanetary disk. The solidity of this projects data and its implications, verified using different analytical approaches, will provide an anchor for future numerical and astrobiological models that tackle the formation of our Solar System and the potential habitability of exoplanets.
