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

Abstract

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 16 O-rich chondrules and chondrule fragments, high C/H ratios, and enrichments in deuterium, 15 N, and 13 C. By combining our results with literature data on carbonaceous chondrites related to C-type asteroids, we show that the outer solar system at that time 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.

Origin of radiogenic 129Xe variations in carbonaceous chondrites

“…In addition, both chondrites show similar cosmic-ray exposure and radiogenic retention ages: 5-10 Ma and 2.4-2.7 Ga for Tarda, and 5-8 Ma and 2.0-2.8 Ga for Tagish Lake. Altogether, our results thus reinforce the genetic link between Tarda and Tagish Lake, which share similar isotopic signatures for elements having drastically different geochemical behaviour (Marrocchi et al, 2021).…”

“…Based on multiple isotopic systems (i.e. H, C, N and O), it has recently been proposed that Tarda and Tagish Lake could be genetically related (Marrocchi et al, 2021). This hypothesis can be tested in the light of noble gas measurements reported here.…”

“…As this large monoisotopic excess would require unlikely 129 I enrichment, it has been interpreted as originating from a specific nucleosynthetic process producing 129 Xe that was sampled by icy bodies formed in the outer solar system (Marty et al, 2017). Interestingly, the carbon-rich primitive chondrites Tagish Lake and Tarda are thought to originate from D-type asteroids (Hiroi et al, 2001;Marrocchi et al, 2021) considered to have formed at large heliocentric distances beyond the current orbit of Saturn, and potentially as far as the Kuiper Belt (i.e. 30-50 astronomical units = au; Levison et al, 2009).…”

Diversity of chondritic organic matter probed by ultra-high resolution mass spectrometry

“…3). Tarda has been proposed to derive from D-type asteroids with higher ice proportion than Ctype asteroids (Marrocchi et al, 2021) while CIs have shown resemblance to the Cb-asteroid Ryugu samples recovered during the Hayabusa2 mission (Watanabe et al, 2017). In both cases, the parent bodies originate from distant regions, possibly outside the CO 2 and H 2 O snowlines in the case of the Ryugu parent asteroid (Nakamura et al, 2022), whilst CI Orgueil possesses a volatile content of cometary origin (Gounelle and Zolenski, 2014).…”

Connecting Asteroids and Meteorites with visible and near-infrared spectroscopy

“…They may have slight concave curvature or be relatively flat. Tagish Lake was the earliest meteorite spectral match in the literature Barucci et al 2018), although they have also more recently been associated with the Tarda carbonaceous chondrite (Marrocchi et al 2021) and a primitive clast from the Zag ordinary chondrite meteorite (Kebukawa et al 2019). While the study of Tarda measures compositional similarity to the expected composition of D-types, it does not present data to prove spectral similarity.…”