Shaping Galactic Habitability: the impact of stellar migration and gas giants

TL;DR

This study uses chemical evolution models to examine how stellar migration and gas giants influence the Galactic Habitable Zone, revealing significant effects on the distribution of potentially habitable planets across the galaxy.

Contribution

It is the first to incorporate detailed chemical evolution models to assess stellar migration's impact on the GHZ and explores how gas giants affect terrestrial planet formation.

Findings

Stellar migration increases habitable star count up to fivefold in outer galaxy regions.

Presence of gas giants raises terrestrial planet formation probability, especially in the inner galaxy.

Stellar migration and gas giants together significantly influence the distribution of habitable planets.

Abstract

In exoplanet research, the focus is increasingly on identifying Earth analogs, planets similar in density and habitability potential. As the number of rocky exoplanets grows, parallel discussions have emerged on system architectures and Galactic environments that may support life, drawing comparisons to our own Earth. This has brought renewed attention to the concept of the Galactic Habitable Zone (GHZ) as a broader context for interpreting the diversity of planetary environments. This study is the first to use detailed chemical evolution models to investigate the impact of stellar migration, modeled through a parametric approach, on the GHZ. Our findings reveal that stellar migration significantly enhances the number of stars capable of hosting habitable planets in the outer Galactic regions, with an increase of up to a factor of five at 18 kpc relative to a baseline value of unity at 6 kpc. Furthermore, we explore a novel scenario where the presence of gas giant planets increases the probability for the formation of terrestrial ones. We find that this increased probability is higher in the inner Galactic disc, but is also mitigated by stellar migration. In particular, at the present time, the number of FGK stars hosting terrestrial planets with minimum habitability conditions in the ring centered at 4 kpc is approximately 1.4 times higher than in scenarios where gas giants are assumed to hinder the formation and evolution of Earth-like planets. Without stellar migration, this factor increases to 1.5. Even larger ratios are predicted for terrestrial planets orbiting retired A stars, reaching 2.8 in models with stellar migration and 3.3 in models without it.