Positive metallicity correlation for coreless giant planets

TL;DR

This paper demonstrates a positive correlation between host star metallicity and the survival of giant planets formed via gravitational instability, highlighting pebble accretion as a key factor in their formation and survival.

Contribution

It introduces pebble accretion into the gravitational instability model, showing how it explains the observed planet-metallicity correlation.

Findings

Survival fraction of planets increases with host star metallicity.

Pebble accretion accelerates GI fragment contraction.

Correlation supports GI model with pebble accretion.

Abstract

Frequency of detected giant planets is observed to increase rapidly with metallicity of the host star. This is usually interpreted as evidence in support of the Core Accretion (CA) theory, which assembles giant planets as a result of formation of a massive solid core. A strong positive planet-metallicity correlation for giant planets formed in the framework of Gravitational disc Instability (GI) model is found here. The key novelty of this work is "pebble accretion" onto GI fragments which has been recently demonstrated to accelerate contraction of GI fragments. Driven closer to the star by the inward migration, only the fragments that accrete metals rapidly enough collapse and survive the otherwise imminent tidal disruption. The survival fraction of simulated planets correlates strongly with the metallicity of the host star, as observed.