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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