Ceres is a key object in understanding the evolution of small bodies and is the only dwarf planet to have been orbited by a spacecraft, NASA’s Dawn mission. Dawn data paint an inconclusive picture of Ceres’ internal structure, composition and evolutionary pathway: crater morphology and gravity inversions suggest an ice-rich interior, while a lack of extensive crater relaxation argues for low ice content. Here we resolve this discrepancy by applying an ice rheology that includes effects of impurities on grain boundary sliding to finite element method simulations of Cerean craters. We show that Ceres can maintain its cratered topography while also having an ice-rich crust. Our simulations show that a crust with ~90% ice near the surface, which gradually decreases to 0% at 117 km depth, simultaneously matches the observed lack of crater relaxation, observed crater morphology and gravity inversions. This crustal structure results from a frozen ocean that became more impurity rich as it solidified top-down. Therefore, the Dawn data are consistent with an icy Ceres that evolved through freezing of an ancient, impure ocean.

谷神星是了解小天体演化的关键天体，也是唯一一颗由美国宇航局黎明任务航天器绕轨道运行的矮行星。黎明数据描绘了谷神星内部结构、组成和进化途径的不确定图景：陨石坑形态和重力倒转表明其内部富含冰，而缺乏广泛的陨石坑松弛则表明冰含量较低。在这里，我们通过将冰流变学（包括杂质对晶界滑动的影响）应用于谷神陨石坑的有限元方法模拟来解决这一差异。我们证明谷神星可以保持其坑坑洼洼的地形，同时也拥有富含冰的地壳。我们的模拟表明，地表附近有约 90% 的冰，在 117 公里深度处逐渐减少到 0%，同时与观察到的缺乏陨石坑弛豫、观测到的陨石坑形态和重力反演相匹配。这种地壳结构是由冰冻海洋产生的，当它自上而下凝固时，杂质变得更加丰富。因此，黎明数据与冰冷的谷神星是一致的，谷神星是通过古老的、不纯净的海洋冻结而演变而来的。