Periodic Reporting for period 2 - Mars through time (Modeling the past climates of planet Mars to understand its geology, its habitability and its evolution)
Berichtszeitraum: 2021-04-01 bis 2022-09-30
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.
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.
With a team of experienced scientists, PhD students, and experts in algorithms and high performance computing, we have made great progress in improving our Planetary Climate Model (PCM, to simulate the Martian climate over ~10 years) and creating a first version of the Planetary Evolution Model (PEM, to simulate Mars environment ’evolution over up to millions of years).
For the PCM, a new-generation “dynamical core’ (to resolve the “atmospheric dynamical equations”) has been implemented and tested. Thanks to this effort we are now be ready to carry out climate simulations with only a few kilometer resolution. In parallel, as part of a PhD research project, the modeling of the water cycle has been greatly improved by including new relevant physical processes. We can now start to accurately simulate the very “wet” climate experienced by Mars at higher obliquity than today.
The novel Planetary Evolution Model has been created from scratch and it is now able to calculate the evolution of H2O and CO2 ice deposits over many thousands of years. In parallel we have achieved most of the developments necessary to calculate the micro-climate on various slopes on Mars, in both the PCM and the PEM. These tools are now used to explore the possible climates that existed when Mars experienced a lower obliquity than today. We show that CO2 ice then condensed on poleward facing slopes and near the pole in such quantities that the atmospheric composition strongly changed, with CO2 concentration dropping from 95% today down to 40% (at 5° obliquity). Because glaciers were then litteraly made of “frozen atmosphere”, the atmospheric pressure was then and order of magnitude lower than today. We found that in our model, CO2 glaciers form in locations where weird-looking moraines had been discovered and tentatively attributed to past CO2 glaciers.
The evolution of the atmospheric pressure due to the sublimation of the currently-observed perennial CO2 glaciers may still occur today. This has been hypothesized on the basis of CO2 ice cap imaging from orbit. To test that, the Mars Through Time team have had the opportunity to access a unique dataset : more than one martian year of pressure measurements obtained by the NASA Insight Lander in 2018-2021. It could be compared to the pressure recorded by the Viking Landers, 40 Earth years before. We carefully compared the two datasets to look for a possible evolution of the average pressure that could reveal a current evolution of the Martian CO2 glaciers. In practice, This was not easy. We first had to recalibrate the InSight data because of their unexpected sensitivity to the sensor temperature. The conclusion of this work (published in an article led by a PhD student- is that no significant changes in the CO2 reservoir can be detected in the recent period (Lange et al., 2022)..
Our climate model is also used to investigate on the environment of Mars 4 billions years ago when the climate was warm enough to allow water lakes and rivers to form on the surface. No one know for sure how this could have happened. We used our existing climate model (including a simplified hydrological model to represent water lakes and possibly seas) to simulate Early Mars with an atmosphere composed of CO2 and H2 that induced a significant greenhouse effect. We showed that the presence of high amount of H2 could explain most of the geological features that are left from this era. However how Mars could have accumulated such large amount of H2 in the atmosphere remain mysterious. Alternatively we have speculated that the strong greenhouse effect on early Mars could have simply resulted from the very large amount of water vapor that could have been present in the atmosphere assuming that it could be highly super-saturated (in the absence of enough nuclei to condense ice clouds, for instance). We found that such a supersaturation could have warmed Early Mars, but only with unrealistic supersaturation ratios and if supersaturation occured in the lower atmosphere.
For the PCM, a new-generation “dynamical core’ (to resolve the “atmospheric dynamical equations”) has been implemented and tested. Thanks to this effort we are now be ready to carry out climate simulations with only a few kilometer resolution. In parallel, as part of a PhD research project, the modeling of the water cycle has been greatly improved by including new relevant physical processes. We can now start to accurately simulate the very “wet” climate experienced by Mars at higher obliquity than today.
The novel Planetary Evolution Model has been created from scratch and it is now able to calculate the evolution of H2O and CO2 ice deposits over many thousands of years. In parallel we have achieved most of the developments necessary to calculate the micro-climate on various slopes on Mars, in both the PCM and the PEM. These tools are now used to explore the possible climates that existed when Mars experienced a lower obliquity than today. We show that CO2 ice then condensed on poleward facing slopes and near the pole in such quantities that the atmospheric composition strongly changed, with CO2 concentration dropping from 95% today down to 40% (at 5° obliquity). Because glaciers were then litteraly made of “frozen atmosphere”, the atmospheric pressure was then and order of magnitude lower than today. We found that in our model, CO2 glaciers form in locations where weird-looking moraines had been discovered and tentatively attributed to past CO2 glaciers.
The evolution of the atmospheric pressure due to the sublimation of the currently-observed perennial CO2 glaciers may still occur today. This has been hypothesized on the basis of CO2 ice cap imaging from orbit. To test that, the Mars Through Time team have had the opportunity to access a unique dataset : more than one martian year of pressure measurements obtained by the NASA Insight Lander in 2018-2021. It could be compared to the pressure recorded by the Viking Landers, 40 Earth years before. We carefully compared the two datasets to look for a possible evolution of the average pressure that could reveal a current evolution of the Martian CO2 glaciers. In practice, This was not easy. We first had to recalibrate the InSight data because of their unexpected sensitivity to the sensor temperature. The conclusion of this work (published in an article led by a PhD student- is that no significant changes in the CO2 reservoir can be detected in the recent period (Lange et al., 2022)..
Our climate model is also used to investigate on the environment of Mars 4 billions years ago when the climate was warm enough to allow water lakes and rivers to form on the surface. No one know for sure how this could have happened. We used our existing climate model (including a simplified hydrological model to represent water lakes and possibly seas) to simulate Early Mars with an atmosphere composed of CO2 and H2 that induced a significant greenhouse effect. We showed that the presence of high amount of H2 could explain most of the geological features that are left from this era. However how Mars could have accumulated such large amount of H2 in the atmosphere remain mysterious. Alternatively we have speculated that the strong greenhouse effect on early Mars could have simply resulted from the very large amount of water vapor that could have been present in the atmosphere assuming that it could be highly super-saturated (in the absence of enough nuclei to condense ice clouds, for instance). We found that such a supersaturation could have warmed Early Mars, but only with unrealistic supersaturation ratios and if supersaturation occured in the lower atmosphere.
With the end of the Covid-19 crisis, in the coming years, the Mars Through Time project will take on another dimension in the coming years thanks to the recruitment of three new postdocs and an additional doctoral student at the end of 2022. Along with the existing team, these scientists will contribute to develop the Mars Planetary Evolution Model and use it to simulate in details the hydrology and cryology (i.e the formation and flows of glaciers) during the Mars’past. With such tools we will model at high resolution the possible environment on Mars billions of years ago when water was flowing on the surface, to interpret the observed geology. We will also simulate recent high-obliquity ice ages on Mars as well as periods with a collapsed atmospheres. Once again, we will compare our simulation results with the available geological records. Ultimately, we will perform simulations for the last 10 million years, for which we precisely know the evolution of the orbital parameters and of the obliquity. This will allow us to simulate the details of the development of the Northern polar layered deposits, the history of the observed “latitude-dependant ice mantle”, or the formation of the multi-layered CO2 ice reservoir detected by Radar near the South Pole..
In all these configurations, we plan to simulate the evolution of the atmospheric composition and the detailed photochemistry to address questions like : Did Mars experience periods of oxidizing conditions that destroyed possible subsurface bio-signatures? What was the chemical environment on Mars at other obliquities? Could photochemistry form greenhouse gases? In addition, a PhD student will be dedicated to the complete modeling of the dust cycle (lifting by winds, transport, sedimentation) on present-day Mars and at other epochs.
In all these configurations, we plan to simulate the evolution of the atmospheric composition and the detailed photochemistry to address questions like : Did Mars experience periods of oxidizing conditions that destroyed possible subsurface bio-signatures? What was the chemical environment on Mars at other obliquities? Could photochemistry form greenhouse gases? In addition, a PhD student will be dedicated to the complete modeling of the dust cycle (lifting by winds, transport, sedimentation) on present-day Mars and at other epochs.