Zero Age Planetary Orbit of Gas Giant Planets Revisited: Reinforcement of the Link with Stellar Metallicity

TL;DR

This paper revisits the Zero Age Planetary Orbit hypothesis, confirming its validity with expanded data, and emphasizes the link between stellar metallicity and the formation and characteristics of gas giant planets.

Contribution

It extends previous analysis of the ZAPO hypothesis using new exoplanet data, reinforcing the link between stellar metallicity and planet formation location.

Findings

Metal-rich stars tend to host gas giants with larger orbits.

Metal-poor stars are more likely to have planets formed closer to the star.

The ZAPO hypothesis remains valid with expanded exoplanet data.

Abstract

In 2005 we suggested a relation between the optimal locus of gas giant planet formation, prior to migration, and the metallicity of the host star, based on the core accretion model and radial profiles of dust surface density and gas temperature. At that time, less than two hundred extrasolar planets were known, limiting the scope of our analysis. Here we take into account the expanded statistics allowed by new discoveries, in order to check the validity of some premises. We compare predictions with the present available data and results for different stellar mass ranges. We find that the Zero Age Planetary Orbit (ZAPO) hypothesis continues to hold after a one order of magnitude increase in discovered planets. In particular, the prediction that metal poor stars harbor planets with an average radius distinctively lower than metal rich ones is still evident in the statistics, and cannot be explained away by chaotic planetary formation mechanisms involving migration and gravitational interaction between planets. The ZAPO hypothesis predicts that in metal poor stars the planets are formed nearer their host stars; as a consequence, they are more frequently engulfed by the stars during the migration process or stripped of their gaseous envelops. The depleted number of gas giant planets around metal poor stars would then be the result of the synergy between low formation probability, as predicted by the core accretion model, and high destruction probability, for the ones that are formed.