Formation of terrestrial planet cores inside giant planet embryos

TL;DR

This paper models how terrestrial planet cores can form inside giant planet embryos through dust sedimentation and gravitational collapse, potentially leading to new planet formation pathways.

Contribution

It introduces a numerical study of solid core formation inside giant planet embryos, detailing the sequence from grain enrichment to core accretion and gas capture.

Findings

Solid cores form via rapid grain collapse within embryos.

Cores can reach several Earth masses before gas accretion begins.

This process may produce terrestrial planets or metal-rich giant planets.

Abstract

Giant planet embryos are believed to be spawned by gravitational instability in massive extended (R ~ 100 AU) protostellar discs. In a recent paper we have shown that dust can sediment inside the embryos, as argued earlier by Boss (1998) in a slightly different model. Here we study numerically the next stage of this process -- the formation of a solid core. If conditions are conducive to solid core formation, the centre of the gas cloud goes through the following sequence of phases: (i) becomes grain (and metal) rich; (ii) forms a terrestrial mass solid core via a rapid collapse driven by self-gravity of the grains; (iii) starts to accrete a gaseous atmosphere when the solid core reaches mass of a few to 10 Earth masses. This sequence of events may build either terrestrial planet cores or metal rich giant planets inside the larger gas reservoir of the giant planet embryo. In a companion Letter we argue that tidal and irradiation effects from the parent star should disrupt the outer metal poor layers of the embryo, releasing nearly "ready to use" planets. We propose this as an alternative way to build planets.