Habitable Climate Scenarios for Proxima Centauri b With a Dynamic Ocean

TL;DR

This study uses 3D climate models with dynamic oceans to explore potential habitability of Proxima Centauri b, revealing broader liquid water areas at colder temperatures and implications for life and climate regimes.

Contribution

First 3D climate simulations of Proxima Centauri b with a dynamic ocean, showing different habitability conditions than static ocean models.

Findings

Broader surface liquid water area at colder temperatures.

Ocean heat transport and salinity depress freezing point.

Potential for habitable, saline, open ocean conditions.

Abstract

The nearby exoplanet Proxima Centauri b will be a prime future target for characterization, despite questions about its retention of water. Climate models with static oceans suggest that an Earth-like Proxima b could harbor a small dayside region of surface liquid water at fairly warm temperatures despite its weak instellation. We present the first 3-dimensional climate simulations of Proxima b with a dynamic ocean. We find that an ocean-covered Proxima b could have a much broader area of surface liquid water but at much colder temperatures than previously suggested, due to ocean heat transport and depression of the freezing point by salinity. Elevated greenhouse gas concentrations do not necessarily produce more open ocean area because of possible dynamic regime transitions. For an evolutionary path leading to a highly saline present ocean, Proxima b could conceivably be an inhabited, mostly open ocean planet dominated by halophilic life. For an ocean planet in 3:2 spin-orbit resonance, a permanent tropical waterbelt exists for moderate eccentricity. Simulations of Proxima Centauri b may also be a model for the habitability of planets receiving similar instellation from slightly cooler or warmer stars, e.g., in the TRAPPIST-1, LHS 1140, GJ 273, and GJ 3293 systems.