Habitable Zones of Post-Main Sequence Stars

TL;DR

This study models the shifting habitable zones of stars after they leave the main sequence, assessing the potential for habitable planets during stellar evolution phases and their detectability.

Contribution

It introduces a comprehensive model of post-main sequence habitable zones across various stellar types and metallicities, including atmospheric loss during stellar evolution.

Findings

Post-MS habitable zones are comparable to known exoplanet distances.

Planets can remain habitable for hundreds of millions to billions of years.

Atmospheric erosion mainly affects close-in planets.

Abstract

Once a star leaves the main sequence and becomes a red giant, its Habitable Zone (HZ) moves outward, promoting detectable habitable conditions at larger orbital distances. We use a one-dimensional radiative-convective climate and stellar evolutionary models to calculate post-MS HZ distances for a grid of stars from 3,700K to 10,000K (~M1 to A5 stellar types) for different stellar metallicities. The post-MS HZ limits are comparable to the distances of known directly imaged planets. We model the stellar as well as planetary atmospheric mass loss during the Red Giant Branch (RGB) and Asymptotic Giant Branch (AGB) phases for super-Moons to super-Earths. A planet can stay between 200 million years up to 9 Gyr in the post-MS HZ for our hottest and coldest grid stars, respectively, assuming solar metallicity. These numbers increase for increased stellar metallicity. Total atmospheric erosion only occurs for planets in close-in orbits. The post-MS HZ orbital distances are within detection capabilities of direct imaging techniques.