No Snowball on Habitable Tidally Locked Planets with a Dynamic Ocean

TL;DR

This study uses a coupled ocean-atmosphere climate model to investigate whether tidally locked habitable planets can experience snowball events, finding that ocean heat transport prevents bifurcations and hysteresis in climate states.

Contribution

It demonstrates that including ocean heat transport in climate models prevents snowball bifurcations on tidally locked planets, challenging previous intermediate complexity model results.

Findings

Ocean heat transport does not cause snowball bifurcations.

Tidally locked habitable planets are unlikely to undergo long-term snowball states.

Coupled ocean-atmosphere models provide more accurate climate stability assessments.

Abstract

Terrestrial planets orbiting within the habitable zones of M-stars are likely to become tidally locked in a 1:1 spin:orbit configuration and are prime targets for future characterization efforts. An issue of importance for the potential habitability of terrestrial planets is whether they could experience snowball events (periods of global glaciation). Previous work using an intermediate complexity atmospheric Global Climate Model (GCM) with no ocean heat transport suggested that tidally locked planets would smoothly transition to a snowball, in contrast with Earth, which has bifurcations and hysteresis in climate state associated with global glaciation. In this paper, we use a coupled ocean-atmosphere GCM (ROCKE-3D) to model tidally locked planets with no continents. We chose this configuration in order to consider a case that we expect to have high ocean heat transport. We show that including ocean heat transport does not reintroduce the snowball bifurcation. An implication of this result is that a tidally locked planet in the habitable zone is unlikely to be found in a snowball state for a geologically significant period of time.