The formation of planetesimals is expected to occur via particle-gas instabilities that concentrate dust into self-gravitating clumps1,2,3. Triggering these instabilities requires the prior pile-up of dust in the protoplanetary disk4,5. This has been successfully modelled exclusively at the disk’s snowline6,7,8,9, whereas rocky planetesimals in the inner disk were only obtained by assuming either unrealistically large particle sizes10,11 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 states13,14 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 cloud16,17,18, 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 silicates20,21. 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.
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The compiled code, the input file and the ascii output files of our reference simulation including silicate condensation/sublimation (one file per output timestep (104 yr) for a total of 100 files) are provided at: lagrange.oca.eu/images/LAGRANGE/pages_perso/morby/forNature.tar.gz. A readme file describes the content of each file.
The code for the calculation of the disk evolution is available on request from the corresponding author.
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A.M. and S.C. acknowledge support from programme ANR-20-CE49-0006 (ANR DISKBUILD). The work presented here has been performed in preparation for the proposal HolyEarth by A.M. and T.K., which has been funded by the European Research Council (grant No. 101019380). The authors thank R. Deienno and C. Ormel for constructive and detailed comments.
The authors declare no competing interests.
Peer review information Nature Astronomy thanks Rogerio Dienno, Chris Ormel and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Surface density of the disk as a function of heliocentric distance at different times.
Turbulent parameter α, for the nominal simulation presented in the main text.
total masses of rocky and icy planetesimals for 4 values of αmin and two values of Qlim.
Relation between fraction of early material in CC and NC as given by Ti and Mo isotope anomalies in meteorites. The thick solid line assumes the average value for NC meteorites ε50TiNC = –1 while the thin line assumes ε50TiNC = – 2 (that is the extreme value observed in NC). Orange-shaded area indicates the predicted fractions of our model: 0.275-0.3 for NC planetesimals and 0.450.70 for CC planetesimals.
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Morbidelli, A., Baillié, K., Batygin, K. et al. Contemporary formation of early Solar System planetesimals at two distinct radial locations. Nat Astron 6, 72–79 (2022). https://doi.org/10.1038/s41550-021-01517-7
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