The Tarda Meteorite: A Window into the Formation of D-type Asteroids

• Published in: The Astrophysical Journal Letters
• Main Authors: Marrocchi, Yves, Avice, Guillaume, Barrat, Jean-alix
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Astronomical Society 2021
• Subjects: Tagish; Tagish Lake
• Online Access: https://archimer.ifremer.fr/doc/00697/80884/84618.pdf; https://doi.org/10.3847/2041-8213/abfaa3; https://archimer.ifremer.fr/doc/00697/80884/

Dynamic models of solar system evolution suggest that D-type asteroids formed beyond Saturn's orbit and represent invaluable witnesses of the prevailing conditions in the outer solar system. Here, we report a comprehensive petrographic and isotopic characterization of the carbonaceous chondrite Tarda, a recent fall recovered in the Moroccan Sahara. We show that Tarda shares strong similarities with the D-type-derived chondrite Tagish Lake, implying that Tarda represents a rare sample of D-type asteroids. Both Tarda and Tagish Lake are characterized by the presence of rare 16O-rich chondrules and chondrule fragments, high C/H ratios, and enrichments in deuterium, 15N, and 13C. By combining our results with literature data on carbonaceous chondrites related to C-type asteroids, we show that the outer solar system 4.56 Gy ago was characterized by large-scale oxygen isotopic homogeneities in (i) the water–ice grains accreted by asteroids and (ii) the gas controlling the formation of FeO-poor chondrules. Conversely, the zone in which D-type asteroids accreted was significantly enriched in deuterium relative to the formation regions of C-type asteroids, features likely inherited from unprocessed, D-rich, molecular-cloud materials.