Comparison of "warm and wet" and "cold and icy" scenarios for early Mars in a 3D climate model

TL;DR

This study uses a 3D climate model to compare early Mars scenarios, revealing how different conditions affect water distribution, valley networks, and potential habitability, with implications for future geological research.

Contribution

It provides a detailed comparison of warm and cold early Mars climate scenarios using 3D modeling, highlighting water cycle variations and valley network correlations.

Findings

Warm scenario requires high solar flux or greenhouse warming.

Valley networks correlate with snow in cold scenario.

Snow transport depends on obliquity and surface pressure.

Abstract

We use a 3D general circulation model to compare the primitive Martian hydrological cycle in "warm and wet" and "cold and icy" scenarios. In the warm and wet scenario, an anomalously high solar flux or intense greenhouse warming artificially added to the climate model are required to maintain warm conditions and an ice-free northern ocean. Precipitation shows strong surface variations, with high rates around Hellas basin and west of Tharsis but low rates around Margaritifer Sinus (where the observed valley network drainage density is nonetheless high). In the cold and icy scenario, snow migration is a function of both obliquity and surface pressure, and limited episodic melting is possible through combinations of seasonal, volcanic and impact forcing. At surface pressures above those required to avoid atmospheric collapse (~0.5 bar) and moderate to high obliquity, snow is transported to the equatorial highland regions where the concentration of valley networks is highest. Snow accumulation in the Aeolis quadrangle is high, indicating an ice-free northern ocean is not required to supply water to Gale crater. At lower surface pressures and obliquities, both H2O and CO2 are trapped as ice at the poles and the equatorial regions become extremely dry. The valley network distribution is positively correlated with snow accumulation produced by the cold and icy simulation at 41.8 degrees obliquity but uncorrelated with precipitation produced by the warm and wet simulation. Because our simulations make specific predictions for precipitation patterns under different climate scenarios, they motivate future targeted geological studies.