Volatile and organic-rich C-type asteroids may have been one of the main sources of Earth’s water. Our best insight into their chemistry is currently provided by carbonaceous chondritic meteorites, but the meteorite record is biased: only the strongest types survive atmospheric entry and are then modified by interaction with the terrestrial environment. Here we present the results of a detailed bulk and microanalytical study of pristine Ryugu particles, brought to Earth by the Hayabusa2 spacecraft. Ryugu particles display a close compositional match with the chemically unfractionated, but aqueously altered, CI (Ivuna-type) chondrites, which are widely used as a proxy for the bulk Solar System composition. The sample shows an intricate spatial relationship between aliphatic-rich organics and phyllosilicates and indicates maximum temperatures of ~30 °C during aqueous alteration. We find that heavy hydrogen and nitrogen abundances are consistent with an outer Solar System origin. Ryugu particles are the most uncontaminated and unfractionated extraterrestrial materials studied so far, and provide the best available match to the bulk Solar System composition.

挥发性和富含有机物的 C 型小行星可能是地球水的主要来源之一。目前，我们对其化学性质的最佳了解是由碳质球粒陨石提供的，但陨石记录是有偏差的：只有最强的类型才能在进入大气层后幸存下来，然后通过与陆地环境的相互作用进行修改。在这里，我们展示了由隼鸟 2 号宇宙飞船带到地球的原始 Ryugu 粒子的详细体积和微分析研究结果。Ryugu 粒子显示出与化学未分级但水相改变的 CI（Ivuna 型）球粒陨石的紧密成分匹配，后者被广泛用作太阳系整体成分的代表。该样品显示了富含脂肪族有机物和层状硅酸盐之间复杂的空间关系，并表明在水蚀过程中的最高温度约为 30 °C。我们发现重氢和重氮的丰度与太阳系外的起源一致。Ryugu 粒子是迄今为止研究过的最未受污染和未分离的外星材料，并为太阳系的整体组成提供了最佳匹配。