Which type of planets do we expect to observe in the Habitable Zone?

TL;DR

This study investigates the relationship between stellar metallicity and the orbital characteristics of super-Earth-like planets, revealing that habitable zone planets are more common around metal-poor stars, suggesting ancient galaxy origins.

Contribution

It provides new insights into how stellar metallicity influences the orbital placement and potential habitability of super-Earth planets, highlighting a correlation with host star type and composition.

Findings

Most habitable zone planets orbit metal-poor GK stars.

Super-Earths around metal-rich stars are closer and hotter.

HZ planets may be more common in the ancient Galaxy.

Abstract

We used a sample of super-Earth-like planets detected by the Doppler spectroscopy and transit techniques to explore the dependence of orbital parameters of the planets on the metallicity of their host stars. We confirm the previous results (although still based on small samples of planets) that super-Earths orbiting around metal-rich stars are not observed to be as distant from their host stars as we observe their metal-poor counterparts to be. The orbits of these super-Earths with metal-rich hosts usually do not reach into the Habitable Zone (HZ), keeping them very hot and inhabitable. We found that most of the known planets in the HZ are orbiting their GK-type hosts which are metal-poor. The metal-poor nature of planets in the HZ suggests a high Mg abundance relative to Si and high Si abundance relative to Fe. These results lead us to speculate that HZ planets might be more frequent in the ancient Galaxy and had compositions different from that of our Earth.