Aujourd’hui, le climat de la planète Mars et celui de la Terre diffèrent profondément . L’un est globalement froid et sec, l’autre est chaud et humide. Il y a 3 milliards d’années, selon un modèle scientifique récent dont nous publions ci-dessous les références, ils étaient très proches.
Le modèle tient compte de la présence sur Mars à cette date d’un océan circulaire qui restait liquide même si sur ses bords il était temporairement ou durablement glacé. Le cycle hydrologique (cycle des pluies) et celui de formation des glaciers d’altitude étaient très voisins.
Reste à comprendre sous quelle influence le climat martien s’est transformé pour devenir ce qu’il est aujourd’hui, quasiment sans atmosphère, dépourvu d’eau et brûlant. Avec l’actuel réchauffement climatique, un tel sort menace-il la Terre ?
Référence
Circumpolar ocean stability on Mars 3 Gy ago
119 (4) e2112930118
The current Martian climate is not habitable and far from Earth’s climate. At the same time that life spread on Earth (3 Gy ago), the Red Planet was possibly more similar to our Blue Planet. Our model includes a coupled model with dynamic ocean and atmosphere including a hydrological cycle and a simplified glacier mass flux scheme. We show that an ocean is stable in agreement with interpretations of the surface geological records.
Abstract
What was the nature of the Late Hesperian climate, warm and wet or cold and dry? Formulated this way the question leads to an apparent paradox since both options seem implausible. A warm and wet climate would have produced extensive fluvial erosion but few valley networks have been observed at the age of the Late Hesperian. A too cold climate would have kept any northern ocean frozen most of the time. A moderate cold climate would have transferred the water from the ocean to the land in the form of snow and ice. But this would prevent tsunami formation, for which there is some evidence. Here, we provide insights from numerical climate simulations in agreement with surface geological features to demonstrate that the Martian climate could have been both cold and wet. Using an advanced general circulation model (GCM), we demonstrate that an ocean can be stable, even if the Martian mean surface temperature is lower than 0 ∘°C. Rainfall is moderate near the shorelines and in the ocean. The southern plateau is mostly covered by ice with a mean temperature below 0 ∘°C and a glacier return flow back to the ocean. This climate is achieved with a 1-bar CO2-dominated atmosphere with 10% H2. Under this scenario of 3 Ga, the geologic evidence of a shoreline and tsunami deposits along the ocean/land dichotomy are compatible with ice sheets and glacial valleys in the southern highlands.
Europe Solidaire 