The formation of planetesimals is expected to occur via particle-gas instabilities that concentrate dust into self-gravitating clumps^1,2,3. Triggering these instabilities requires the prior pile-up of dust in the protoplanetary disk^4,5. This has been successfully modelled exclusively at the disk’s snowline^6,7,8,9, whereas rocky planetesimals in the inner disk were only obtained by assuming either unrealistically large particle sizes^10,11 or an enhanced global disk metallicity¹². However, planetesimal formation solely at the snowline is difficult to reconcile with the early and contemporaneous formation of iron meteorite parent bodies with distinct oxidation states^13,14 and isotopic compositions¹⁵, indicating formation at different radial locations in the disk. Here, by modelling the evolution of a disk with ongoing accretion of material from the collapsing molecular cloud^16,17,18, we show that planetesimal formation may have been triggered within the first 0.5 million years by dust pile-up at both the snowline (at ~5 au) and the silicate sublimation line (at ~1 au), provided turbulent diffusion was low. Particle concentration at ~1 au is due to the early outward radial motion of gas¹⁹ and is assisted by the sublimation and recondensation of silicates^20,21. Our results indicate that, although the planetesimals at the two locations formed about contemporaneously, those at the snowline accreted a large fraction of their mass (~60%) from materials delivered to the disk in the first few tens of thousands of years, whereas this fraction is only 30% for the planetesimals formed at the silicate line. Thus, provided that the isotopic composition of the delivered material changed with time²², these two planetesimal populations should have distinct isotopic compositions, consistent with observations¹⁵.

预计小行星的形成将通过粒子气体的不稳定性发生，这些不稳定性将尘埃集中成自引力团^1,2,3。^{触发这些不稳定性需要事先在原行星盘4,5}中堆积灰尘。这已经成功地仅在圆盘的雪线^6,7,8,9处建模，而内盘中的岩石小行星仅通过假设不切实际的大颗粒尺寸^10,11或增强的全球圆盘金属丰度¹²获得。然而，仅在雪线上的星子形成很难与具有不同氧化态的铁陨石母体的早期和同期形成相协调^13,14和同位素组成¹⁵，表明在盘中不同径向位置的形成。^{在这里，通过模拟从坍缩分子云16、17、18}中不断吸积物质的圆盘的演化，我们表明，在最初的 50 万年内，两个雪线处的尘埃堆积可能触发了小行星的形成（在~5  au处）和硅酸盐升华线（在~1  au处），前提是湍流扩散很低。~1 au的颗粒浓度 是由于气体¹⁹的早期向外径向运动，并由硅酸盐的升华和再冷凝^20,21辅助. 我们的研究结果表明，尽管这两个位置的小行星大约同时形成，但雪线处的小行星质量的很大一部分（~60%）来自最初几万年传递到圆盘的物质，而这在硅酸盐线形成的小行星的比例仅为 30%。因此，假设所交付材料的同位素组成随时间而变化²²，这两个小行星群应该具有不同的同位素组成，与观察结果¹⁵一致。