Tag: ta2.21

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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