| Summary: | International audience Introduction: Ultracarbonaceous Antarctic Micrometeorites (UCAMMs) are dominated by a polyaromatic organic matter globally N-enriched showing bulk D enrichments, with heterogeneous distributions of the D/H and 15 N/ 14 N isotopic ratios [1-6]. The abundant organic matter of UCAMMs contains amorphous and crystalline mineral components [7-9]. This high abundance of organic matter is reminiscent of the CHON particles detected in comet 1P/Halley [10, 11], although the size of CHONs was estimated to be on the micrometer to sub-micrometer size, while UCAMMs from the Concordia collection range in size from ~ 30 µm to ~ 200 µm [12]. They most probably originate from the outer regions of the protoplanetary disk, from the cometary reservoir [1, 3, 4], thus we aim at comparing their composition with that of dust particles from comet 67P/Churyumov-Gerasimenko (hereafter 67P) measured by Ro-setta/COSIMA [13-15]. A recent summary of the general UCAMM characteristics can be found in [12]. Methods: UCAMMs from the Concordia collection were identified by SEM/EDX, and complementary UCAMM fragments were analyzed by synchrotron-based Fourier transform infrared (FTIR) microscopy at SOLEIL/SMIS, electron microprobe analysis (EMPA) at the CAMPARIS facility (Paris), transmission electron microscopy (TEM) at UMET (Lille), STXM-XANES analyses at synchrotron facilities (ALS Berkeley and SOLEIL/HERMES), NanoSIMS at MNHN Paris and Institut Curie Orsay [1, 3-6, 12, 16, 17]. Recent STXM-XANES analyses were performed at the SOLEIL/HERMES beamline on 4 additional UCAMMs. Results and discussion: The additional STXM-XANES measurements of 4 UCAMM fragments in FIB-sections confirmed the presence of 3 organic phases in UCAMMs : i) an extended (up to tens of µm) smooth N-rich organic phase with a low O content, which is devoid of crystalline phases but can occasionnaly contain Glass Embedded with Metal and Sulfides (GEMS) inclusions; ii) an organic phase similar to the insoluble organic matter (IOM) extracted from ...
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