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.

太阳系演化的动力学模型表明，D 型小行星形成于土星轨道之外，代表了外太阳系普遍状况的宝贵见证。在这里，我们报告了碳质球粒陨石 Tarda 的综合岩相学和同位素特征，这是最近在摩洛哥撒哈拉沙漠中恢复的陨石。我们表明 Tarda 与 D 型衍生的球粒陨石 Tagish Lake 有很强的相似性，这意味着 Tarda 代表了 D 型小行星的罕见样本。Tarda 和 Tagish Lake 的特点是存在稀有的富含¹⁶ O 的球粒和球粒碎片、高 C/H 比以及富含氘、¹⁵ N 和¹³C. 通过将我们的结果与与 C 型小行星相关的碳质球粒陨石的文献数据相结合，我们表明 4.56 Gy 前的外太阳系的特征在于（i）小行星吸积的水冰粒中的大规模氧同位素同质性(ii) 控制贫铁球粒形成的气体。相反，相对于 C 型小行星的形成区域，D 型小行星吸积的区域明显富含氘，这些特征可能继承自未加工的、富含 D 的分子云材料。