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Possible Connections Between the Unusual Micrometeorite TAM19B-7 and Dwarf Planet Ceres

Presentation #204.05 in the session “Dust, Meteoroids, Meteors”.

Published onOct 03, 2021
Possible Connections Between the Unusual Micrometeorite TAM19B-7 and Dwarf Planet Ceres

TAM19B-7 is the largest (~1.7 mm) fine-grained, unmelted micrometeorite found and analyzed to date [1]. Although no meteorite in our collection has ever been linked to dwarf planet Ceres, we hypothesize that TAM19B-7 may have originated from Ceres. This interpretation is based on TAM19B-7’s petrologic, textural, mineralogic, and isotopic data, all of which indicate severe aqueous processing compatible with the regolith chemistry of Ceres. Ceres is a volatile-rich asteroid with a partially differentiated interior, carbonate-rich crust, and evidence of advanced aqueous alteration on a global scale [2]. Ceres’ surface mineralogy is consistent with highly aqueously altered CI or CM carbonaceous chondrites [3]. If some micrometeorites in our collections indeed originated from Ceres-like objects, additional laboratory studies can provide ground truth data on organic preservation in icy asteroid regolith, while also providing new perspectives on prebiotic chemical pathways available in large-icy asteroids. TAM19B-7 was retrieved from sedimentary traps on the summit of Miller Butte in the Transantarctic Mountains in 2006 by the Programma Nazionale di Ricerche in Antartide expeditions. Petrographically TAM19B-7 is dominated by fine-grained matrix with no surviving unaltered anhydrous silicates. Pseudomorphic chondrules are identifiable and have small average diameters with oblate “crushed” shapes and evidence of aligned phyllosilicates attesting to a pervasive petrofabric [4]. TAM19B-7 possesses a unique oxygen isotope composition: 0.508‰ for ∆17O and 1.126‰ for δ18O that does not match any known chondrite groups [1]. Although this composition is affected by partial equilibration with Antarctic water, its inferred pre-atmospheric composition would have plotted above the TFL at 16O-poor values. This oxygen isotope space is populated by materials from intensely aqueously altered carbonaceous chondrites [1]. Despite low organic abundances (due to thermal decomposition during atmospheric entry), weak G and D Raman bands corresponding to aromatic macromolecules and aliphatic IR-bands associated with CH2 and CH3 molecules have been identified in TAM19B-7. The average δ13C value of TAM19B-7 is 3±8‰; however, multiple 13C enrichments (δ13C<35‰) are consistent with carbonate phases in carbonaceous chondrite meteorites [5] are observed (Figure 1). Although carbonate minerals were decomposed by flash-heating during atmospheric entry, the isotopic data support a carbonate-dominated carbon budget for TAM19B-7’s parent body. To summarize, the inferred carbon budget of TAM19B-7’s parent body is likely carbonate-rich with a minor organic component. Alongside existing data this supports an origin in Ceres-like asteroid body. Thus, we advocate for a dedicated sample-return mission to the dwarf planet Ceres [3] to look for associations with micrometeorites already available in our inventory. [1] Suttle, M et al. (2020) EPSL 546, 116444. [2] Castillo-Rogez J., et al. (2018) MAPS 53, 1820. [3] McSween Jr., H. Y. et al. (2017) MAPS 53, 1793. [4] Suttle, M.D., et al. (2019) GCA 245, 352. [5] Alexander, C. O. D., et al. (2015) MAPS 50, 810.

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