The effect of a strong pressure bump in the Sun's natal disk: Terrestrial planet formation via planetesimal accretion rather than pebble accretion

TL;DR

The study investigates how a pressure bump in the Sun's protoplanetary disk influences terrestrial planet formation, concluding that planetesimal accretion dominates over pebble accretion in forming Earth-like planets.

Contribution

It demonstrates that a strong pressure bump in the outer disk leads to terrestrial planets forming mainly through planetesimal accretion, not pebble accretion, aligning with observed solar system features.

Findings

Terrestrial embryos formed via planetesimal accretion rather than pebble accretion.

Pressure bumps cause pebbles to drift inward and be lost before accreting onto embryos.

Embryos inside 0.5-1.0 au grow faster but tend to migrate inward, inconsistent with current solar system.

Abstract

Mass-independent isotopic anomalies of carbonaceous and non-carbonaceous 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 mm-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. $\sim$5~au) on the formation of the inner solar system. We model dust coagulation and evolution, planetesimal formation, as well as embryo's 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 foster 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 $\gtrapprox$1~au. Embryos inside $\sim$0.5-1.0au 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 $\gtrapprox$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.