¹Victoria Froh,¹Maitrayee Bose,^2,3Martin D.Suttle,⁴Jacopo Nava,^2,5Luigi Folco,¹Lynda B.Williams,⁶JulieCastillo-Rogez
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2022.115300]
¹School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA
²School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
³Dipartimento di Scienze della Terra, Università di Pisa, 56126 Pisa, Italy
⁴University of Padova, Department of Geosciences, Via G.Gradenigo 6, 35131 Padova, Italy
⁵CISUP, Centro per l’Integrazione della Strumentazione dell’Università di Pisa, Lungarno Pacinotti 43, 56126 Pisa, Italy
⁶Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
Copyright: Elsevier

Micrometeorites represent a major potential source of volatiles for the early Earth, although often overlooked due to their small sizes and the effects of atmospheric entry. In this study we explore an unusual ~2000 μm, fine-grained unmelted micrometeorite TAM19B-7 derived from a water-rich C-type asteroid. Previous analysis revealed a unique O-isotope composition and intensely aqueously altered geological history. We investigated its carbon isotopic composition using the NanoSIMS and characterized the carbon-bearing carriers using Raman and Near-Infrared spectroscopy. We found that TAM19B-7 has a 13C enriched bulk composition (δ13C = +3 ± 8 ‰), including a domain with 13C depletion (δ13C = −27.1 ‰). Furthermore, a few micro-scale domains show 13C enrichments (δ13C from +12.9 ‰ to +32.7 ‰) suggesting much of the particle’s carbon content was reprocessed into fine-grained carbonates, likely calcite. The heavy bulk C-isotope composition of TAM19B-7 indicates either open system gas loss during aqueous alteration or carbonate formation from isotopically heavy soluble organics. Carbonates have been detected on small body surfaces, including across dwarf planet Ceres, and on the C-type asteroids Bennu and Ryugu. The preservation of both carbonates with 13C enrichments and organic carbon with 13C depletion in TAM19B-7, despite having been flash heated to high temperatures (<1000 °C), demonstrates the importance of cosmic dust as a volatile reservoir.