Mars is an active planet. Thanks to high spatial resolution images, many active processes have been observed.
In the polar regions, mysterious dark patches appear and disappear with the seasons. They are probably related to cold gas jets. Unfortunately, these jets have so far nevery been observed in activity.
This process seems to be associated with the presence of CO2 ice which sublimes from below.
Much previous work has suggested that the transparency of the ice plays a key role, in particular for the creation of gas jets, so enabling the ice to sublime from below the layer via a solid state greenhouse effect.
The transparency of the CO2 ice on Mars, as well as its degree of contamination by water ice or dust plays a major role in the creation of numerous active processes on the surface during the Martian spring.
These processes, being so numerous, could play a major role for the regional martian climate. Nevertheless, this transparency is highly controversial, and had nevery been shown to exist.
Spectroscopic proof for the presence of transparent ice
The demonstration is based on data furnished by the spectro-imageur CRISM in the Richardson region, and radiation transfer modeling.
To start with, this study establishes the transparency of the CO2 ice through a comparison of simulation and observation, via a model of transparent ice and one of granular ice.
Only the transparent ice model is compatible with a layer thickness which decreases seasonally, in agreement with climatic models.
Furthermore, the exact surface composition has been studied in order to define locally the volatile and dust exchanges between the surface and the atmosphere.
This study has enabled one, for the first time, to show that water ice is injected into the southern martian atmosphere, right through spring.
The micro-physical mechanisms responsible for these exchanges are summarized in the figure below :
If this process takes place over the entire southern seasonal pole cap, the atmosphere can become significantly enriched in water. This prediction should soon be tested by the ExoMars TGO probe, which has just begun its scientific operations.
Collaborations :
The French laboratories involved in this work are the Laboratoire d’études spatiales et d’instrumentation en astrophysique (LESIA, Observatoire de Paris - PSL / CNRS / Sorbonne Université / Université Paris-Diderot), the Laboratoire Geosciences Paris Sud (GEOPS, Université Paris-Sud / CNRS )and the Institut de planétologie et d’astrophysique de Grenoble (IPAG, LAOG / LPG)
Reference :
Andrieu, François and Schmidt, Frédéric and Douté, Sylvain and Chassefière, Eric (2018) Ice state evolution during spring in Richardson crater, Mars, Icarus, doi:10.1016/j.icarus.2018.06.019