Hurricanes on tidally locked terrestrial planets: Fixed surface temperature experiments

TL;DR

This study investigates the potential for hurricane formation on tidally locked exoplanets using high-resolution atmospheric models, revealing conditions under which hurricanes can or cannot form, impacting climate and habitability assessments.

Contribution

It provides the first detailed analysis of hurricane presence on tidally locked planets considering various atmospheric compositions and planetary parameters.

Findings

Hurricanes can form on tidally locked planets near the inner habitable zone edge.

Hurricanes are less likely or absent in middle and outer habitable zones.

Atmospheric composition similar to Earth's is crucial for hurricane formation.

Abstract

In this work, we study the presence of hurricanes on exoplanets. Tidally locked terrestrial planets around M dwarfs are the main targets of space missions looking to discover habitable exoplanets. The question of whether hurricanes can form on this kind of planet is important for determining their climate and habitability. Using a high-resolution global atmospheric circulation model, we investigated whether there are hurricanes on tidally locked terrestrial planets under fixed surface temperatures. The relevant effects of the planetary rotation rate, surface temperature, and bulk atmospheric compositions were examined. We find that hurricanes can form on the planets but not on all of them. For planets near the inner edge of the habitable zone of late M dwarfs, there are more numerous and stronger hurricanes on both day and night sides. For planets in the middle and outer ranges of the habitable zone, the possibility of hurricane formation is low or even close to zero, as has been suggested in recent studies. Earth-based hurricane theories are applicable to tidally locked planets only when the atmospheric compositions are similar to that of Earth. However, if the background atmosphere is lighter than H2O, hurricanes can hardly be produced because convection is always inhibited due to the effect of the mean molecular weight, similarly to the case of Saturn. These results have broad implications on the precipitation, ocean mixing, climate, and atmospheric characterization of tidally locked planets. Finally, A test with a coupled slab ocean and an Earth-like atmosphere in a tide-locked orbit of ten Earth days demonstrates that there are also hurricanes present in the experiment.