Periodic Reporting for period 1 - POSEIDON (Petrographic and vOlatile SignaturEs of prImitive and Differentiated achONdrites)
Période du rapport: 2020-09-01 au 2022-08-31
Project POSEIDON aims to determine the petrographic and volatile history of primitive and differentiated achondrites, through analyses of the water abundance and its hydrogen isotopic composition in nominally anhydrous minerals (NAMs), using a combination of three techniques, namely transmission infrared spectroscopy, reflectance spectroscopy and nano secondary ion mass spectrometry. Primitive and differentiated achondrites, which volatile inventory is not yet fully understood, were among the first planetesimals to form and thus are key witnesses for the origin of water and other volatiles in the inner Solar System. Moreover, NAMs, and in particular pyroxenes, are major constituents, early formed, of almost all achondrites and thus are likely to be more faithful recorders of the volatile history of their parent body. The leading goal of POSEIDON is thus to estimate bulk-parent body volatile abundances and isotopic composition of achondrites in order to develop a robust understanding of the distribution and source(s) of water in the inner Solar System.
To reach the objectives, the workload was divided into four tasks, using main analytical techniques such as Scanning Electron Microscopy (SEM), Electron Microprobe Analysis (EPMA), Secondary Ion Mass Spectrometry (NanoSIMS), Transmission and Reflectance Spectroscopy, Laser Fluorination and Thermodynamic Modeling. During the first task, the petrographic history of primitive achondrites was investigated in order to define new classification criteria amongst primitive achondrites and understand their parent body history. This work has led to the discovery of a new group of primitive achondrites, the tissemouminites. The second task was devoted to the reflectance and transmittance spectroscopy analyses of terrestrial standards and achondritic samples, so far without any substantial results. During the third task, hydrogen and chlorine abundances and isotopic composition have been carried out on NAMs and apatites in a range of achondritic samples, from primitive achondrite acapulcoites and lodranites, to lunar samples. Both these studies have led to the same main conclusion, that a water source was incorporated into various amount amongst the inner solar system planetesimals, and that this source of water must have incorporated some nebular hydrogen, as revealed by the low hydrogen isotopic composition measured in both acapulcoites-lodranites and lunar samples compared to the present-day Earth. Finally, the last task was to engage and disseminate the results to a diverse audience. Outreach events to raise awareness of planetary studies, in particular to promote woman in science, were conducted. Moreover, an educational trilingual website has been elaborated and is actively updated. This work opened and strengthened new and ongoing national and international collaboration with the University of Florence (Italy), the Open University (UK), Arizona State University (USA) and Bayreuth Geoinstitut (Germany). Results achieved in POSEIDON are of very high-quality and novelty, and were presented at many conferences, workshops, seminars, publications, media.
Several contributions from POSEIDON where made beyond the state of the art:
- In addition to the discovery of a new group of primitive achondrites that improve the current meteorite classification scheme, the redefinition of petrological, mineralogical, and geochemical classification criteria for primitive achondrites can be now use by the community for meteorite classification.
- As acapulcoites and lodranites record a range in planetary differentiation degree, from 1% up to 20% partial melting, their hydrogen and chlorine isotopic composition revealed that thermal metamorphism and partial melting (up to 20%) did not induce any significant hydrogen or chlorine fractionation and are thus good proxies to estimate their parent body volatile composition. This statement can be extended to any meteorite or terrestrial rocks that suffer from less than 20% partial melting.
- A unique source of hydrogen was present in the inner Solar System in the early stages, which was incorporated at various abundances amongst the inner Solar System planetesimals. This reservoir is also D-poor compared to the Earth and carbonaceous chondrites, implying some nebular contribution to the water inventory in the inner Solar System. This study will be of great interest to the cosmochemistry community, as our findings report original volatile data on a group of meteorites (acapulcoites and lodranites) never investigated before and have major implications for the origin of water in the early inner Solar System.
- This D-poor water source was also recorded by the early Moon, which in turn fingerprints the early Earth, highlighting that this reservoir was pervasive in the inner Solar System. These results make timely key contributions towards the ongoing debate of ‘wet’ vs. ‘dry’ scenario for accretion of volatiles in the inner Solar System as well as implications for the timing of water accretion into planetesimals, which is essential for developing dynamical models of Solar System formation. Indeed, comprehending the early stages of our Solar System evolution allow to understand other planetary systems in terms of habitability, as water is a key component for the emergence of life.
- In addition to the discovery of a new group of primitive achondrites that improve the current meteorite classification scheme, the redefinition of petrological, mineralogical, and geochemical classification criteria for primitive achondrites can be now use by the community for meteorite classification.
- As acapulcoites and lodranites record a range in planetary differentiation degree, from 1% up to 20% partial melting, their hydrogen and chlorine isotopic composition revealed that thermal metamorphism and partial melting (up to 20%) did not induce any significant hydrogen or chlorine fractionation and are thus good proxies to estimate their parent body volatile composition. This statement can be extended to any meteorite or terrestrial rocks that suffer from less than 20% partial melting.
- A unique source of hydrogen was present in the inner Solar System in the early stages, which was incorporated at various abundances amongst the inner Solar System planetesimals. This reservoir is also D-poor compared to the Earth and carbonaceous chondrites, implying some nebular contribution to the water inventory in the inner Solar System. This study will be of great interest to the cosmochemistry community, as our findings report original volatile data on a group of meteorites (acapulcoites and lodranites) never investigated before and have major implications for the origin of water in the early inner Solar System.
- This D-poor water source was also recorded by the early Moon, which in turn fingerprints the early Earth, highlighting that this reservoir was pervasive in the inner Solar System. These results make timely key contributions towards the ongoing debate of ‘wet’ vs. ‘dry’ scenario for accretion of volatiles in the inner Solar System as well as implications for the timing of water accretion into planetesimals, which is essential for developing dynamical models of Solar System formation. Indeed, comprehending the early stages of our Solar System evolution allow to understand other planetary systems in terms of habitability, as water is a key component for the emergence of life.