Research Article

Bifurcation of planetary building blocks during Solar System formation

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Science  22 Jan 2021:
Vol. 371, Issue 6527, pp. 365-370
DOI: 10.1126/science.abb3091

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Two-part formation of the Solar System

Measurements of meteorites have shown that the inner and outer Solar System formed from two distinct reservoirs of material. Existing models have proposed that these were split by Jupiter forming first, which would open a gap in the protoplanetary disc. Lichtenberg et al. instead argue that the snow line, the boundary between regions containing water vapor and solid ice, migrated first outward and then inward, forming two separate populations of planetesimals. Those planetesimals then grew through collisions to form the planets. Their simulation of this model explains the meteorite data and is consistent with astronomical observations of protoplanetary disks around other stars.

Science, this issue p. 365


Geochemical and astronomical evidence demonstrates that planet formation occurred in two spatially and temporally separated reservoirs. The origin of this dichotomy is unknown. We use numerical models to investigate how the evolution of the solar protoplanetary disk influenced the timing of protoplanet formation and their internal evolution. Migration of the water snow line can generate two distinct bursts of planetesimal formation that sample different source regions. These reservoirs evolve in divergent geophysical modes and develop distinct volatile contents, consistent with constraints from accretion chronology, thermochemistry, and the mass divergence of inner and outer Solar System. Our simulations suggest that the compositional fractionation and isotopic dichotomy of the Solar System was initiated by the interplay between disk dynamics, heterogeneous accretion, and internal evolution of forming protoplanets.

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