Laboratory investigations of the physical state of CO 2 ice in a simulated Martian environment

We have experimentally investigated CO 2 ice condensation under conditions similar to those expected in the Martian polar areas using the Environmental Wind Tunnel of Aarhus University in the framework of Trans-National Access opportunities within the EuroPlanet Research Infrastructure. Our goal was to condense CO 2 directly from the chamber’s atmosphere onto a specially designed cooling plate. We inves- tigated ranges of temperatures and pressures similar to those in Martian polar areas, observed the texture of the created CO 2 ice layer, and measured its optical properties. Most importantly, we find that under conditions usual for Martian polar areas in fall and winter, CO 2 ice always deposits as a translucent slab. The maximum thickness of the ice that we have achieved approached 2 cm and this CO 2 slab ice layer was either transparent or highly translucent. Under significantly lower temperatures or in states away from equilibrium (for example, when CO 2 gas input into the chamber was fast and created over-pressure) CO 2 deposited as different crystalline structures. In this case, when a thick layer was created, it was not visually transparent. However, even in those cases it still retains some level of translucency. Our results will advance the analysis of remote-sensing data related to CO 2 ice, Mars’ seasonal cycles, and various models considering CO 2 ice condensation-sublimation related processes