The habitable zone of Earth-like planets with different levels of atmospheric pressure

TL;DR

This study uses a 1-D Energy Balance Model to explore how varying atmospheric pressure influences the size and habitability of the habitable zone around Sun-like stars, revealing that higher pressure broadens the zone.

Contribution

It introduces a pressure-dependent habitable zone model using a simplified climate approach, extending previous models to include atmospheric pressure effects.

Findings

Higher atmospheric pressure broadens the habitable zone by about 0.25 AU.

Habitability increases with pressure, becoming more uniform within the zone at high pressure.

The results are applicable to planets with different orbital eccentricities and around various star types.

Abstract

As a contribution to the study of the habitability of extrasolar planets, we implemented a 1-D Energy Balance Model (EBM), the simplest seasonal model of planetary climate, with new prescriptions for most physical quantities. Here we apply our EBM to investigate the surface habitability of planets with an Earth-like atmospheric composition but different levels of surface pressure. The habitability, defined as the mean fraction of the planet's surface on which liquid water could exist, is estimated from the pressure-dependent liquid water temperature range, taking into account seasonal and latitudinal variations of surface temperature. By running several thousands of EBM simulations we generated a map of the habitable zone (HZ) in the plane of the orbital semi-major axis, a, and surface pressure, p, for planets in circular orbits around a Sun-like star. As pressure increases, the HZ becomes broader, with an increase of 0.25 AU in its radial extent from p=1/3 bar to p=3 bar. At low pressure, the habitability is low and varies with a; at high pressure, the habitability is high and relatively constant inside the HZ. We interpret these results in terms of the pressure dependence of the greenhouse effect, the effciency of horizontal heat transport, and the extent of the liquid water temperature range. Within the limits discussed in the paper, the results can be extended to planets in eccentric orbits around non-solar type stars. The main characteristics of the pressure-dependent HZ are modestly affected by variations of planetary properties, particularly at high pressure.