How and where the first generation of inner Solar System planetesimals formed remains poorly understood. Potential formation regions are the silicate condensation line and water snowline of the solar protoplanetary disk. Whether the chemical compositions of these planetesimals align with accretion at the silicate condensation line (water-free and reduced) or water snowline (water-bearing and oxidized) is, however, unknown. Here we use the Fe/Ni and Fe/Co ratios of magmatic iron meteorites to quantify the oxidation states of the earliest planetesimals associated with non-carbonaceous (NC) and carbonaceous (CC) reservoirs, representing the inner and outer Solar System, respectively. Our results show that the earliest NC planetesimals contained substantial amounts of oxidized Fe in their mantles (3–19 wt% FeO). In turn, we argue that this required the accretion of water-bearing materials into these NC planetesimals. The presence of substantial quantities of moderately and highly volatile elements in their parent cores is also inconsistent with their accretion at the silicate condensation line and favours, instead, their formation at or beyond the water snowline. Similar oxidation states in the early formed parent bodies of NC iron meteorites and those of NC achondrites and chondrites with diverse accretion ages suggest that the formation of oxidized planetesimals from water-bearing materials was widespread in the early history of the inner Solar System.

第一代内太阳系星子是如何以及在哪里形成的仍然知之甚少。潜在的形成区域是太阳原行星盘的硅酸盐凝结线和水雪线。然而，这些星子的化学成分是否与硅酸盐凝结线（无水和还原）或水雪线（含水和氧化）处的吸积一致尚不清楚。在这里，我们使用岩浆铁陨石的 Fe/Ni 和 Fe/Co 比率来量化与非碳质 (NC) 和碳质 (CC) 储层相关的最早星子的氧化态，分别代表内太阳系和外太阳系。我们的结果表明，最早的北卡罗来纳星子的地幔中含有大量的氧化铁（3-19 wt% FeO）。反过来，我们认为这需要将含水物质吸积到这些北卡罗来纳星子中。其母核中存在大量的中等和高挥发性元素也与它们在硅酸盐凝结线处的积聚不一致，并且有利于它们在水雪线处或水雪线之外的形成。北卡罗来纳铁陨石的早期形成母体以及北卡罗来纳无球粒陨石和具有不同吸积年龄的球粒陨石的类似氧化态表明，在内太阳系的早期历史中，由含水物质形成氧化星子的情况很普遍。