Abstract: Hayabusa 2 and OSIRIS-REx space missions will give a unique access to study the composition of carbonaceous asteroids. A key issue will be the comparison of the organic and mineral compounds from these near-Earth active carbonaceous asteroids with that of carbonaceous chondrites, carbon-rich interplanetary dust particles and cometary samples (81P/Wild2 or in-situ analyses from 67P/CG). The comparison of Ryugu and Bennu samples with chondritic micrometeorites and with extremely carbon-rich interplanetary dust particles such as the Ultra-Carbonaceous MicroMeteorites (UCAMMs) will provide a unique tool to assess their possible links with cometary organics. Analytical methods applied to study micrometeorites from Concordia collection (Antarctica) and the most recent results obtained will be summarised. A particular emphasis will be put on the dedicated experimental protocols that we developed to analyse such micrometeorite fragments and study their mineral-organic association at scales relevant to their intimate association, ranging from tens of nanometers to a few microns.

Abstract: Introduction: Ultracarbonaceous Antarctic Micrometeorites (UCAMMS) are extraterrestrial dust particles containing large amount of carbonaceous material with elevated D/H ratios [1] and high N/C atomic ratio (up to 0.2)[2]. UCAMMS are rare (~ 1% of the particles in the Concordia meteorite collection) but they have been identified in several collection of interplanetary dust [3, 4]. They are most probably of cometary origin. Here, we studied the association of organic matter and minerals by scanning transmission X-ray microscopy (STXM-XANES) coupled with scanning transmission electronic microscopy (TEM/STEM). Samples and Methods: The UCAMMs studied here were collected in the Antarctic snow, close to the Concordia station at Dome C [3]. FIB sections of 8 UCAMMs (DC06-18, DC06-41, DC06-43, DC06-65, DC06-308, DC06-139, DC16-30, DC16-309) were analyzed using synchrotron based STXM-XANES at the carbon, nitrogen and oxygen K-edges. The FIB sections were subsequently analyzed with transmission electron microscopy (TEM/STEM) using a FEI Tecnai G2 20 and a FEI TITAN Themis 300 [5, 6]. Peak identification of STXM-XANES spectra are based on [7]. XANES spectra are processed and quantified using Quantorxs method [8] and quantification of STEM EDS spectra has been realized using Hyperspy software [9]. Here, we mainly present results obtained on two recently identified UCAMMs (DC06-308 and DC16-309) and compare them with previous observations [1, 5, 6]. Results: The STXM-XANES analysis reveals 3 types of organic matter (OM) characterized by different carbon speciation. Figure 1 shows type I OM in blue and type II OM in green, both having spectra close to that of chondritic insoluble organic matter (IOM). The main peaks of type I and II OMs are found around 284.8 eV (aromatic and olefinic groups (C=C)), 286.4 eV (ketone and phenol C=O) and 288.4 eV (carboxyl O=C-O). Type II OM exhibits similar functional groups as type I OM but the first peak position is shifted to 285 eV, indicating a stronger contribution of the aromatic groups. The atomic N/C ratio of types I/II OMs range between 0.01 and 0.05 (1?=0.02) similar to those of chondritic IOM. The type III, in red on Figure 1 exhibits larger differences. The main peak is at 286.4 eV (C?N nitrile), a small peak at 284.8 eV (alkene

Abstract: Introduction: The chemical composition of organic matter (OM) in interplanetary samples (meteorites and micrometeorites) is suitably characterized by the distribution of the different chemical bonds using infrared (IR) vibrational spectroscopy (see e.g. [1]). Classical IR microscopy provides a global view of the dust grain chemical structure content but remains limited by the diffraction, with typical spot sizes sampling a few micrometers in the mid-IR range. This spatial resolution limitation is well above that of complementary techniques such as isotopic imaging with NanoSIMS or transmission electron or X-ray microscopy techniques. These techniques reveal mineralogical, chemical and isotopic heterogeneities at the sub-micron scale but do not give full access to the distribution of the various chemical bonds. The IR diffraction limitation can be circumvented by using AFM-IR microscopy. This technique opens a new window for studies of OM at ten to tens of nanometer scales and will be of importance for studies of the samples from carbonaceous asteroid Ryugu, returned by the Hayabusa 2 space probe in December 2020. AFM-IR is now a well-established microscopy technique in the vibrational field. It combines an atomic force microscope (AFM) and a tunable IR source to detect photo-thermal effect and access chemical information down to a nanoscale resolution [2]. This technique is now applied in a wide diversity of scientific fields [3], and was recently used to analyze extraterrestrial OM [4, 5]. We report here on recent results obtained on imaging two UltraCarbonaceous Antarctic MicroMeteorites (UCAMMs) using AFM-IR [5]. A small fraction of the Antarctic micrometeorites from the Concordia collection consists in UCAMMs, particles with extreme concentrations in OM, most of them exhibiting large deuterium excesses [6]. UCAMMs are also found in Japanese interplanetary dust collections [7-9]. These UCAMMs most likely originate from the surface of small icy bodies in the outer regions of the solar system [1,6,7,10]. The large OM fraction of UCAMMs (considerably higher than in the most carbon-rich meteorites) enables direct analyses without the pre-treatment generally applied to extract the OM from other meteoritic samples, and give access to unaltered chemical maps of the intimate association of minerals and organics.