Hyper-spectral acquisitions of ice mixtures with Martian simulant at low temperatures

The remote sensing observation of ices and cryospheres in planets and satellites in our Solar System have been accompanied by studies on field analogs (e.g., Antarctica Cianfarra et al. 2022; Svalbard, Preston et Dartnell 2024;) and spectroscopy analysis of dusty ice mixtures in laboratory (e.g., Stephan et al. 2021, Yoldi et al. 2021).

In this project, we used the Mars Global (MGS-1) High-Fidelity Martian Dirt Simulant (Cannon et al. 2019) to create artificial ice mixtures similar to the layer of the North Polar Cap on Mars and we acquired their spectra at low temperature. The spectral acquisitions were performed with the aim to compare the synthetic ice spectra with the ones collected by the NASA Compact Reconnaissance Imaging Spectrometer for Mars (CRISM; Zurek and Smrekar 2007) in the polar regions in order to quantify the content and understand the composition of the dust entrapped in the North polar deposits.

The finest part (0-32 µm) of the simulant MGS-1 (Cannon et al. 2019) is spectrally representative of the atmospheric dust included in the polar strata.

We mixed the simulant with deionized water in different ice/dust ratio to obtain mixtures from 0% to 35% dust. We cooled the mixtures at 193 K in a refrigerator or using liquid nitrogen and varying the freezing time from 1.30 h to 1 minute. Then, using Headwall Photonics Nano/Micro-Hyperspec cameras we acquired the reflectance spectra of different mixtures in a nitrogen controlled environment to avoid moisture and using a cooled sample-holder and a thermocouple to monitor the temperature increase during the acquisitions.

Both the slabs created with slow and fast cooling show absorptions at 1500 and 2000 nm due to water ice and at 500 nm due to the iron content. However, the fast cooling slabs has well-defined absorption bands and shoulders whereas the slow cooling slabs show shallower bands. As expected with the increase of the simulant amount in the mixtures, the 500 nm-band deepens while the 1500 and 2000 nm-bands get shallower. The rise of the sample temperature resultes in an increase of the whole reflectance. The overall results are consistent with previous works on the granular icy mixtures (e.g., Stephan et al. 2021, Yoldi et al. 2021) although some relevant differences are recorded such as the shapes of the absorption bands and the reflectance.

In conclusion, we developed a new set-up to acquire hyperspectral cubes of icy slabs that better represent the condition of exposed ice along Martian polar rupes as well as cuts, cliffs and walls of icy crust of planetary and small bodies of the outer Solar System.

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