Diurnal and Seasonal Mapping of Martian Ices with EMM/EMIRS

Condensation and sublimation of ices at the surface of the planet is a key part of both the Martian H₂O and CO₂ cycles, either from a seasonal or diurnal aspect. If most of the ices are located within the polar caps, surface frost is known to be formed during nighttime down to equatorial latitudes. The Emirate Mars InfraRed Spectrometer (EMIRS) instrument onboard the Emirates Mars Mission (EMM) "Hope" probe is a Fourier Transform Infrared spectrometer that is observing the Martian surface and atmosphere between 6 and 100 μm from February 2022. The unique orbit of EMM allows EMIRS to observe the entire Martian disk at each observation, covering all the surface of the planet across all local times in ~ 4 orbits, which corresponds to ~ 5° of L_s.

Here we use the surface temperature data retrieved from the EMIRS spectra (Smith et al. 2022) to detect and map the ice at the surface of the Red Planet. We compute the amplitude of the diurnal temperature variations to derive maps of the presence of ices (either H₂O or CO₂) at the surface of the planet over the day, which allows us to monitor the seasonal evolution of the polar caps. And, based on the methodology used in Piqueux et al. (2016), we also compute for each EMIRS pixel the corresponding freezing temperature of CO₂, according to Clapeyron’s law, and we consider that CO2 ice is present at the surface if the retrieved temperature is below T_{CO2, ice}. This allows us to monitor the timing of the formation and disappearance of the surface CO₂ frost under midlatitudes over the Martian night, and its seasonal evolution.