CE31 - Physique Subatomique, Sciences de l'Univers, Structure et Histoire de la Terre

Chronology and origin of Ancient Solids Sampling the Young Solar System – CASSYSS

Chronology and origin of ancient solids in the young solar system

Understanding the origin of our planet Earth as well as other planetary bodies in the solar system is a long standing question for mankind. Ancient solids like refractory inclusions and chondrules found in primitive meteorites are key witnesses of the protoplanetary disk evolution from the formation of tiny condensates to the accretion of planetary embryos and therefore of the earlier stages of the solar system formation.

Deciphering the formation mechanisms of ancient solids towards a better understanding of the solar system evolution

In spite of numerous studies and significant improvements during the last decades, the message carried out by the first solids formed in the accretion disk is still not clearly understood, limiting our understanding of the solar system early evolution. This project aims at establishing comprehensive and accurate constraints on the chronology and the mechanisms of formation and accretion of earliest solids in the protoplanetary disk. The CASSYSS project will thus allow addressing long lasting fundamental scientific questions regarding the early stages of the Solar System evolution.<br />The main scientific objectives of the CASSYSS project are: <br />1 – Acquiring a comprehensive understanding of relict minerals inherited from precursors in primordial solids – especially chondrules – and thus hints on the nature and origin of the precursors. <br />2 – Quantifying the importance of precursors recycling during earliest solids formation and exploring possible implications for the relationship between CAIs, AOAs and chondrules.<br />3 – Characterizing compositions of the nebular gas chondrules interact with during melting events and the extent of such interactions.<br />4 – Constraining thermal history of chondrules by studying the diffusion of minor elements in relict olivine grains and in experimental assemblages.<br />5 – Establishing an accurate and exhaustive chronology of thermal events experienced by earliest solids (condensation, precursors formation, last melting events, minor thermal events, parent bodies processes) in connection with our understanding of the complexity of these objects.<br />6 – Compiling data acquired during previous tasks in order to provide a comprehensive formation scenario and constraints for the earliest solids dynamic (formation mechanisms, transport, and preservation) in the PPD and the evolution of the PPD.

In order to tackle CASSYSS's objectives, we have performed pioneering analytical developments allowing to overthrow technical limitations and to study most ancient solids. With CASSYSS we propose an innovative and ambitious multidisciplinary project mixing petrological, cosmochemical, experimental and astrophysical approaches.
Petrographic, microstructural, chemical and isotopic characterization of refractory inclusions and chondrules from carbonaceous, ordinary and enstatite chondrites will be performed by combining high-level complementary techniques: Scanning Electron Microscopy (SEM), Field Emission Gun Scanning Electron Microscopy (FEG-SEM), Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA ICPMS), Cathodoluminescence (CL), Focused Ion Beam (FIB) coupled with Transmission Electron Microscopy (TEM), Electron Probe Microanalysis (EPMA), X-ray diffraction (X-ray), and MC-SIMS.
The complexity of extraterrestrial materials requires a careful selection of samples in order to address specific scientific questions. In view of the issues considered in the CASSYSS project, our researches will focus on emblematic CO, CR, CM and CV carbonaceous chondrites, H, L and LL ordinary chondrites and EH and EL enstatite chondrites. Most chondrites fall within one of these three groups. Therefore, by choosing relevant chondrites samples within these groups we ensure a representative selection of the diversity of refractory inclusions and chondrules. We already have at our disposal many chondrites samples that will be used for this project and additional samples will be obtained in a near future from collections of Paris and Vienna National Museums of Natural History.

The CASSYSS project has already resulted in the publication of major results concerning the understanding of the formation of the first solids in the accretion disc.
- Measurements of isotopic Si compositions in AOAs (high temperature condensates in the protoplanetary disk) indicate extremely rapid condensation rates, of the order of a few weeks, involving formation during brief and localized high temperature episodes in a dynamic and thermally heterogeneous accretion disk (Marrocchi et al., PNAS 2019)
- Isotopic measurements of Si in chondrules of carbonaceous meteorites show significant variations requiring rapid formation at high temperature of these objects in an open system by interaction between solid precursors, including AOAs type condensates, and a gas enriched in SiO characteristic of a strong enrichment in dust compared to the canonical conditions of the protosolar nebula (Villeneuve et al., EPSL 2020).

Petrographic, chemical and isotopic characterization of the samples of refractory inclusions and chondrules chosen for this project is progressing very well, in accordance with the forecasts. Results obtained have already been the subject of 3 publications in rank A journals (Marrocchi et al., 2019; Villeneuve et al., 2019, 2020) and 3 others are currently being written (Piralla et al., in prep .; Schnuriger et al., in prep). This work allowed us to identify several populations of objects in several families of primitive meteorites showing both different formation mechanisms and variable genetic links. Although less advanced, because based on the results and observations of the first part, the work of the tasks relating to the thermal history and the redox of the chonders and the chronology of formation are also well launched in accordance with the provisional schedule. These two strands concentrate most of the thesis work of the two students (M. Piralla and M. Schnuriger) who were recruited in October 2019. Over the next 18-month period, it is planned to finalize the work of the first part with characterization of target microstructures of our samples and publication of the latest results. At the same time, most of the analytical work will focus on the acquisition and processing of results on the thermal and redox conditions of chondrules formation and the chronology of the formation of the first solids.

1. Villeneuve, J., Marrocchi, Y., & Jacquet, E. (2020). Silicon isotopic compositions of chondrule silicates in carbonaceous chondrites and the formation of primordial solids in the accretion disk. Earth and Planetary Science Letters, 542, 116318.
2. Marrocchi, Y., Villeneuve, J., Jacquet, E., Piralla, M., & Chaussidon, M. (2019). Rapid condensation of the first Solar System solids. PNAS, 116(47), 23461–23466.
3. Villeneuve, J., Chaussidon, M., Marrocchi, Y., Deng, Z., & Watson, E. B. (2019). High-precision in situ silicon isotopic analyses by multicollector secondary ion mass spectrometry in olivine and lowcalcium pyroxene. Rapid Communications in Mass Spectrometry, 33, 1589–1597.

Refractory inclusions (Ca, Al-rich inclusions and amoeboid olivine aggregates) and chondrules found in primitive meteorites (chondrites) are ancient solids formed at high temperature during the first few millions years of the early Solar System. Because they are the buildings blocks of larger bodies, deciphering their origin, processes and timings of formation is of fundamental importance to understand the dynamical evolution of the young protoplanetary disk and the formation of planetary embryos. In spite of numerous studies and significant improvements during the last decades, the message carried by these solids is still not clearly understood and therefore the way these primordial solids and planetesimals formed remains very enigmatic and controversial. The CASSYSS project is an innovative and ambitious multidisciplinary project mixing petrological, cosmochemical, experimental and astrophysical approaches. Targeted object will be representative chondrules and refractory inclusions from least-altered chondrites from the carbonaceous, ordinary and enstatite groups. We have performed analytical developments allowing for the first time to study almost every kind of primordial objects, and thus to avoid sampling biases inherent to most studies. As a result, this project will provide the first accurate and unbiased chronology of formation coupled with a comprehensive petrographic, chemical and isotopic characterization of primordial solids. Thus we believe that the innovative and ambitious approach proposed in this project will produce results with first order implications in cosmochemistry, planetology and astrophysics.

Project coordinator

Monsieur Johan Villeneuve (Centre de recherches pétrographiques et géochimiques)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

CRPG Centre de recherches pétrographiques et géochimiques

Help of the ANR 269,671 euros
Beginning and duration of the scientific project: December 2018 - 48 Months

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