Transient conditions for biogenesis on low-mass exoplanets with escaping hydrogen atmospheres

TL;DR

This paper explores the transient habitable conditions on low-mass exoplanets with hydrogen atmospheres, highlighting potential windows for life emergence due to atmospheric cooling and ocean formation.

Contribution

It introduces a model for transient ocean formation on hydrogen-rich exoplanets and discusses implications for prebiotic chemistry and habitability.

Findings

Transient oceans can form on hydrogen-rich exoplanets.

Duration of habitable conditions varies with planet and star type.

Hydrogen atmospheres can provide greenhouse warming conducive to life.

Abstract

Exoplanets with lower equilibrium temperatures than Earth and primordial hydrogen atmospheres that evaporate after formation should pass through transient periods where oceans can form on their surfaces, as liquid water can form below a few thousand bar pressure and H2-H2 collision-induced absorption provides significant greenhouse warming. The duration of the transient period depends on the planet size, starting H2 inventory and star type, with the longest periods typically occurring for planets around M-class stars. As pre-biotic compounds readily form in the reducing chemistry of hydrogen-rich atmospheres, conditions on these planets could be favourable to the emergence of life. The ultimate fate of any emergent organisms under such conditions would depend on their ability to adapt to (or modify) their gradually cooling environment.