Radiatively Active Dust Controls Climate on Mars-like, Land Exoplanets

Land planets or planets with limited available water may be common. However, to date, there has been limited research to investigate the diverse climatologies and potential habitability of these planetary types, particularly in comparison to Earth-twin or ocean worlds. The goal of this work is to more fully understand the unique factors that control land planet climate. We utilize decades of research focused on the land planet in our own solar system, Mars, to motivate and act as a foundation for the parameter space chosen for investigation. The dust cycle is the most significant source of climate variability on present-day Mars. We therefore choose in this study to investigate the impact of radiatively active dust on land planet climate at different planetary orbits or stellar heating rates. We utilize a state-of-the-art Mars general circulation model (GCM) to simulate land planet climate at present-day Mars and Earth orbits with radiatively passive and active dust. We find that dust represents the controlling factor that determines the dynamics, surface conditions and spectral signature of simulated planets. As atmospheric dust accumulates, land planets rapidly diverge from a Mars-like climate to a new and dramatically different climate regime. Deeply mixed dust traps outgoing infrared radiation acting as greenhouse agent and raising surface temperatures above the freezing point of water even as the surface solar flux is reduced to near zero. Tides dominate the planetary dynamics and shift the distribution and dominant mechanism of surface dust lifting from the summer hemisphere to the winter hemisphere midlatitudes. Simulated spectra in this regime are relatively flat and may complicate interpretation, specifically when assessing surface temperature. We find that atmospheric dust is a critical component of land planet climatology and should be carefully considered in simulations, spectral interpretation, or assessments of potential land planet habitability.