Seasonal thaws under mid-to-low pressure atmospheres on Early Mars

TL;DR

This study uses climate modeling to show that seasonal thaws on early Mars could occur under certain atmospheric and orbital conditions, explaining the presence of liquid water without requiring additional greenhouse gases.

Contribution

It demonstrates that 1.3-2.0 bar CO₂ atmospheres with specific orbital parameters can produce seasonal liquid water conditions on Mars without extra greenhouse gases.

Findings

Seasonal thaws occur with 1.3-2.0 bar CO₂ atmospheres and orbital eccentricity and obliquity variations.

Local thaw conditions persist for over 15% of the Martian year.

Methane presence broadens the conditions for seasonal thaw.

Abstract

Despite decades of scientific research on the subject, the climate of the first 1.5 Gyr of Mars history has not been fully understood yet. Especially challenging is the need to reconcile the presence of liquid water for extended periods of time on the martian surface with the comparatively low insolation received by the planet, a problem which is known as the Faint Young Sun (FYS) Paradox. In this paper we use ESTM, a latitudinal energy balance model with enhanced prescriptions for meridional heat diffusion, and the radiative transfer code EOS to investigate how seasonal variations of temperature can give rise to local conditions which are conductive to liquid water runoffs. We include the effects of the martian dichotomy, a northern ocean with either 150 or 550 m of Global Equivalent Layer (GEL) and simplified CO$_2$ or H$_2$O clouds. We find that 1.3-to-2.0 bar CO$_2$-dominated atmospheres can produce seasonal thaws due to inefficient heat redistribution, provided that the eccentricity and the obliquity of the planet are sufficiently different from zero. We also studied the impact of different values for the argument of perihelion. When local favorable conditions exist, they nearly always persist for $>15\%$ of the martian year. These results are obtained without the need for additional greenhouse gases (e.g. H$_2$, CH$_4$) or transient heat-injecting phenomena (e.g. asteroid impacts, volcanic eruptions). Moderate amounts (0.1 to 1\%) of CH$_4$ significantly widens the parameter space region in which seasonal thaws are possible.