The Effect of a Strong Pressure Bump in the Sun's Natal Disk: Terrestrial Planet Formation via Planetesimal Accretion Rather than Pebble Accretion

Mass-independent isotopic anomalies of carbonaceous and noncarbonaceous meteorites show a clear dichotomy suggesting an efficient separation of the inner and outer solar system. Observations show that ring-like structures in the distribution of millimeter-sized pebbles in protoplanetary disks are common. These structures are often associated with drifting pebbles being trapped by local pressure maxima in the gas disk. Similar structures may also have existed in the Sun's natal disk, which could naturally explain the meteorite/planetary isotopic dichotomy. Here, we test the effects of a strong pressure bump in the outer disk (e.g., similar to 5 au) on the formation of the inner solar system. We model dust coagulation and evolution, planetesimal formation, as well as embryo growth via planetesimal and pebble accretion. Our results show that terrestrial embryos formed via planetesimal accretion rather than pebble accretion. In our model, the radial drift of pebbles fosters planetesimal formation. However, once a pressure bump forms, pebbles in the inner disk are lost via drift before they can be efficiently accreted by embryos growing at greater than or similar to 1 au. Embryos inside similar to 0.5-1.0 au grow relatively faster and can accrete pebbles more efficiently. However, these same embryos grow to larger masses so they should migrate inwards substantially, which is inconsistent with the current solar system. Therefore, terrestrial planets most likely accreted from giant impacts of Moon to roughly Mars-mass planetary embryos formed around greater than or similar to 1.0 au. Finally, our simulations produce a steep radial mass distribution of planetesimals in the terrestrial region, which is qualitatively aligned with formation models suggesting that the asteroid belt was born low mass.

Automated summary

The study reveals a clear separation between the inner and outer solar system, with ring-like structures in protoplanetary disks potentially explaining isotopic differences among meteorites and planets. Simulations show that a strong pressure bump in the outer disk can affect the formation of the inner solar system, leading to the conclusion that terrestrial embryos likely formed through planetesimal accretion rather than pebble accretion.