Mars, often considered a frozen desert, is an active planet shaped by CO₂ and water frosts today. However, traces of surface glaciers and the presence of massive buried water ice sheets in the mid-latitudes suggest that Mars experienced a very different climate in its recent past. Global Climate Models predict that when the planet’s obliquity is higher than its present-day values, the atmosphere becomes much wetter, leading to the formation of a snow mantle at mid- and high latitudes. These glaciers then sublimate as the obliquity decreases and become buried beneath the surface, where they can persist over time.
This buried subsurface water ice is thus a relic of these past climates and holds the key to understanding the different faces of Mars during its recent history. However, no current models can fully explain the geographical distribution and depth of this subsurface ice.
In this talk, I will first review the discoveries of subsurface water ice on Mars. I will then quantify where and at what depth these reservoirs are in equilibrium with the present-day climate and show that the subsurface ice detected at mid-latitudes is not in equilibrium with the current climate. Next, I will explore the limitations of the physical theories used to study this phenomenon, drawing on measurements from analogous sites in Antarctica. Finally, I will demonstrate that the subsurface ice observed on Mars is a remnant of the planet’s last ice age, which occurred approximately 630,000 years ago.
