ta2.21 – Europlanet Society

20-EPN2-011: Water abundances and hydrogen isotopic ratios of pyroxenes in achondrite meteorites

June 5, 2023

20-EPN-008: Characterisation of a new type of extraterrestrial material through the study of Cumulate Porphyritic Olivine cosmic spherules

Virtual visit by Alice Stephant, Istituto di Astrofisica e Planetologia Spaziale (Italy) to TA2 Facility 21 – OU NanoSIMS 50L (UK).
Dates of visit: 24 March – 25 August 2022

One of the major unresolved questions in the field of cosmochemistry is to understand the source(s) and timing of volatile delivery in the inner Solar System. The goal of this project was to examine primitive achondrites which volatile inventory has not yet been investigated, in order to determine what portion of these volatiles was incorporated in the early stages of the Solar System history, relative to late-veneer delivery. In this regard, primitive achondrite acapulcoites and lodranites were selected as they sample a common parent body, hence allowing to also investigate the effect of various degrees of planetary differentiation on volatile abundances and isotopic compositions.

Using the NanoSIMS 50L at the Open University, we analysed chlorine and water content, as well as their associated isotopic composition in phosphates from three acapulcoites and two lodranites. Our results suggest that the acapulcoite-lodranite parent body incorporated a similar source of volatiles than ordinary chondrites, which chemical composition is similar to the chondritic precursor of acapulcoites and lodranites, arguing for a common reservoir of both Cl and H in the inner Solar System.

Read the full scientific report, with kind permission from Alice Stephant.

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20-EPN2-052: Water in silica-bearing iron meteorites – implications for early Solar System dichotomy

Visit by Ana Černok, Freie Universität Berlin (Germany)/University of Trieste (Italy) to TA2 Facility 21 – OU NanoSIMS 50L (UK).
Dates of visit: 14-21 November 2022 and virtual visit from 28 November – 20 December 2022

Understanding the volatile inventory of the earliest Solar System is inseparable from understanding which sources contributed to the volatiles of the oldest and relatively dry non-carbonaceous (NC) objects formed in the inner Solar System, and if they were different from wet carbonaceous (CC) materials, formed in the outer Solar System.

Two questions remain largely unanswered in this respect: (i) What are the abundances and isotopic composition of volatiles in the oldest NC objects and (ii) What were their sources? These questions can be answered by investigating some of the oldest objects in the Solar System, namely, the NC iron meteorites.

This Europlanet visit to the NanoSIMS facility was focused on trying to determine the content and isotopic composition of H or H₂O inside minerals within iron meteorites. The iron meteorites are some of the oldest formed materials in the Solar System and hold key evidence if there has been any water available when they formed, and if there was: where did this water originate from?

Here we focused on understanding water abundance and its isotopic composition in some of the oldest NC silica bearing iron meteorites (IVA type): Muonionalusta, Gibeon and Steinbach. Other investigated irons did not contain any silica. The lowest water content was measured in Gibeon (< 10 ppm) and Muonionlusta (15–20 ppm), while minerals in Steinbach contained significantly more water (40–120 ppm). The δD values for Gibeon show a large range and greater uncertainties, due to low measured water contents. The δD values in Muonionalusta and Steinbach cluster between ~0–300 ‰. In fact, silica phases in both minerals cluster between ~0–200 ‰, while low-water cpx in Steinbach shows the highest δD values (200–300 ‰). The difference in δD values between mineral phases in Steinbach likely reflects the difference in their crystallisation history, where opx may have lost H resulting in increased D/H ratio (higher δD) due to degassing. Overall, the source of water in these NC irons is very similar to that of the Earth and the chondrites, while low-D reservoirs have not been detected.

TESCAN Clara Electron Microscope used for analyses of meteorite composition and structure prior to isotopic analyses with NanoSIMS. Credit: A Cernok.

NanoSIMS instrument at the Open university used for isotopic analyses. — TESCAN Clara Electron Microscope used for analyses of meteorite composition and structure prior to isotopic analyses with NanoSIMS. Credit: A Cernok.

Read the full scientific report, with kind permission from Ana Černok.

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20-EPN-008: Characterisation of a new type of extraterrestrial material through the study of Cumulate Porphyritic Olivine cosmic spherules

October 8, 2022

20-EPN-008: Characterisation of a new type of extraterrestrial material through the study of Cumulate Porphyritic Olivine cosmic spherules

Virtual visit by Steven Goderis, Vrije Universiteit Brussels (Belgium) to TA2 Facility 21 – OU NanoSIMS 50L (UK).
Dates of visit: 4-25 October 2021

Oxygen isotopes are a powerful tool to determine the parent bodies of cosmic spherules, which are the entirely melted endmember of micrometeorites. After considering the fractionation processes affecting their original oxygen isotope signatures, >90% of cosmic spherules larger than 200 μm appear to be related to chondrite clans established studying chondritic meteorites.

About 10% of cosmic spherules that show clear chondritic major element compositions display unusual ¹⁶O-poor oxygen isotopic compositions that are not linked to chondritic material present in present-day meteorite collections. Simultaneously, a subset of porphyritic (Po) cosmic spherules labelled Cumulate Porphyritic Olivine (CumPo) particles exhibits textures testifying to the settling of olivine crystals during atmospheric deceleration. This unusual texture suggests these particles entered the Earth’s atmosphere at velocity of ⁓16 km s^-1 , which corresponds to orbital eccentricities >0.3 and is considered higher than most asteroidal dust bands.

By establishing a potential link between the CumPo particles and a subset of the ¹⁶O-poor spherules and characterising relict mineral grains in a selection of particles from the Sør Rondane Mountains and Larkman Nunatak micrometeorite collections using the Open University NanoSIMS, a parentage with the newly defined CY carbonaceous chondrite group is proposed. This implies that about 10% of the cosmic spherules reaching the Earth’s surface have a near-Earth origin. As such connection is rare in the meteorite collection, demonstrating the importance of fully characterising the flux of micrometeorites to understand the composition of the Solar System.

Read the full scientific report, with kind permission from Steven Goderis.

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20-EPN2-030: The O-isotope signatures of aqueously altered micrometeorites – probing the CO-CM gap and the diversity of C-type asteroids

Virtual visit by Jacopo Nava, University of Padova (Italy) to TA2 Facility 21 – OU NanoSIMS 50L (UK).
Dates of visit: 6-26 July 2022

Report Summary: The flux of extraterrestrial material falling to Earth is dominated by micrometeorites. They originate from asteroids and comets and their analysis provides a complementary perspective to the insights obtained from the study of larger meteorites and from space mission sample returns. Oxygen isotope compositions can be used to match micrometeorites to parent body sources based on distinctive δ¹⁷O and δ¹⁸O ratios.

We studied a population of seven giant Antarctic micrometeorites using high-precision, spatially resolved oxygen isotope analyses to measure the composition of fine-grained matrix in hydrated and dehydrated micrometeorites.

A characteristic feature of all micrometeorites was large intrasample isotopic variation (>15‰ in δ¹⁸O). In addition, most particles could be matched to known meteorite groups, including identification of CM, CV, CR and, potentially CY parentage. This is consistent with petrographic studies which conclude that the micrometeorite flux is dominated by material from hydrated carbonaceous chondrite asteroids. One particle (TAM5-30) has petrographic characteristics intermediate between the CO and CM chondrite groups. Oxygen isotope analyses of its fine-grained matrix plot either in the CO or CM chondrite fields. This particle is interpreted as a CO-like C2 ungrouped chondrite and may represent material from an otherwise unsampled parent body.

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