![HAADF image and quantified EDX map (at%) of a GEMS-like assemblage in UCAMM DC06- 18, which is located at the top of the FIB section, probably close to the external surface of the UCAMM. - [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/08/STXM-XANES.png?fit=1200%2C668&ssl=1)
[astro-ph.EP] The Concordia micrometeorite collection contains UltraCarbonaceous Antarctic MicroMeteorites (UCAMMs) of probable cometary origin. Eight FIB sections of UCAMMs were studied by Scanning Transmission X-ray Microscopy – X-ray Absorption Near Edge Structure and (Scanning)Transmission Electronic Microscopy.
Three different phases of organic matter (OM) exist in UCAMMs and small mineral aggregates are distributed in the OM. Two OMs share spectral features with those of insoluble organic matter (IOM) of carbonaceous chondrites and of cometary grains returned by the Stardust mission.
The third OM is N-rich (N/C at. ratios up to 0.22) and has only a few equivalents in extraterrestrial OM analyzed so far, such as in cometary particles collected during the Stardust mission, Interplanetary Dust Particles (IDPs) and UCAMMs collected near the Dome Fuji Station. This N-rich OM could have formed by irradiation of N-rich ices in the outer regions of the protoplanetary disk. UCAMMs contain variable amounts of minerals, consisting of crystalline Mg-rich silicates, Fe(Ni) sulfides and Fe oxides, which can be cemented in a Si-rich groundmass.
Hypocrystalline mineral assemblages are also observed. Glassy phases showing morphological resemblance to GEMS are also found in some UCAMMs. This mineralogy is mainly consistent with that of previous UCAMM analyses, and is close to what is observed in Chondritic Porous IDPs, which are also considered as cometary dust particles. A mineral exhibiting a phyllosilicate texture has been observed in this work, and raises the question of the possibility of aqueous alteration on comets.
Overall, UCAMMs’ mineralogical and organic characterization implies a complex formation history of UCAMMs, and the presence of large-scale radial mixing in the early solar system, to transport their mineral components to the outer parts of the protoplanetary disk.
(left) High angle annular dark field (HAADF) images and (right) colored images corresponding to the map of the different phases identified by Principal Component Analysis of the EDX hyperspectral maps. (A) Phyllosilicate-like phase (fibrous phase) decorated with a mineral assemblage. (B) Mineral assemblage located at the border of a vesicle. Both assemblages are embedded in the organic matter. — astro-ph.EP
B. Guérin, C. Engrand, C. Le Guillou, H. Leroux, E. Dartois, J. Duprat, S. Bernard, K. Benzerara, L. Delauche, D. Troadec
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2608.25795 [astro-ph.EP] (or arXiv:2608.25795v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2608.25795
Focus to learn more
Submission history
From: Cecile Engrand
[v1] Wed, 26 Aug 2026 13:46:49 UTC (16,593 KB)
https://arxiv.org/abs/2608.25795
Astrobiology, Astrochemistry, Astrogeology,
