Behaviors of Martian CO2-driven dry climate system and conditions for atmospheric collapses

Abstract

The present Martian climate is characterized by a cold and dry environment with a thin atmosphere of carbon dioxide (CO₂). In such conditions, the planetary climate is determined by the distribution of CO₂ between exchangeable reservoirs, that is, the atmosphere, ice caps, and regolith. This produces unique responses of the Martian CO₂-driven climate system to variations of astronomical forcings. Specifically, it has been shown that the phenomenon called an atmospheric collapse occurs when the axial obliquity is low, affecting the Martian climatic evolution. However, the long-term evolution of the behavior of the Martian climate system and the accompanying changes in climate and habitability remain ambiguous. Here we employed a latitudinally-resolved Martian energy balance model and assessed the possible climate on Mars for wider ranges of orbital parameters, solar irradiance, and total exchangeable CO₂ mass. We show that, among the orbital parameters, variations of axial obliquity have a strong impact on the carbon distribution on Mars, while variations of eccentricity and longitude of perihelion have a minor impact. We show that the threshold obliquity for atmospheric collapse under cold and dry conditions decreases from ∼20° at the end of Noachian to ∼14° at the present condition, indicating that the atmospheric collapse would have occurred repeatedly in the history of Mars. When the obliquity is over ∼20°, the atmospheric pCO₂ on Mars would be affected primarily by the changes in the total exchangeable CO₂ mass. We also show that the magnitude of the variation of atmospheric pCO₂ when atmospheric collapse occurs decreases during the Hesperian. Even considering the broad ranges of these parameters, the habitable conditions in the Martian CO₂-driven dry climate system would be limited to high-latitude summers if there are no warming mechanisms other than the greenhouse effect of CO₂ and H₂O.