The “Mars Through Time” project primarily aims at modelling the past environments of Mars in order to interpret its geological records and understand its evolution and past habitability. Over the past decades, the robotic exploration of the planet Mars has produced a wealth of geological observations. They show that Mars has not always been the desert planet of today. It has seen eras conducive to rivers and lakes, ice ages, and even periods with a collapsed atmosphere. These different epochs are the reason why Mars remains the objective of many space agencies, as they evoke the possibility of past habitability and spectacular climate changes. Yet, in spite of all the data, the climatic processes that have shaped Mars’ surface through time remain largely unknown. What happened on Mars? Was the Red Planet suitable for life? What explains its evolution?
To address these questions, we develop numerical models to simulate the past environments of Mars. A completely new “Planetary Evolution Model” is beeing created to simulate in the computer the behavior of the water and CO2 reservoirs on the surface (glaciers, lakes, rivers and even seas) and in the subsurface (permafrost, formation of layers, aquifers). To predict the actual temperatures, precipitation or evaporation on the planet, this Planetary Evolution Model perform, when needed (e.g. every 1000 years), 2-years simulations with a separate 3D Global Climate Model (here called “Planetary Climate Model, or PCM) analogous to the weather and climate models used for the Earth, but adapted to Mars. It models the atmosphere minutes after minutes taking into account all relevant processes such as the atmospheric circulation (winds), the radiative transfer of solar and infrared light through the air, the condensation of ices in clouds and frost, the transport of tracers, the atmospheric photochemistry etc. This PCM had been developed for many years before the Mars Though Time project to interpret Mars satellite observations. However, we have updated it to model the different climates possibly experienced by Mars in the past, and better represent the interaction between the atmosphere and the surface. For instance, for the first time, we have introduced calculations to represent the micro-climates on various slopes everywhere on the planet. On poleward facing slope, it is usually colder, and ice tend to condense and form glaciers. On equatorward facing slope on the opposite, temperature are higher and ice may melt if present.
With these tools, we plan to explore how Mars has evolved because of the oscillations of its orbit and obliquity, because of changes in the atmospheric composition, or through events like meteoritic impacts or volcanic eruptions. These new tools can address numerous enigmas found in Mars sciences. They also offer a new platform to study specific processes such as the atmospheric escape through time or the chemical alteration of the soil. Furthermore, the project test our capacity to model planetary environments and climate changes, as well as provide lessons on the evolution of terrestrial planets and the possibility of life elsewhere.
