Reflectance study of ice and Mars soil simulant associations—II. CO 2 and H 2 O ice

We measure the visible and near-infrared reflectance of icy analogues of the Martian surface made of CO2 ice
associated in different ways with H2O ice and the regolith simulant JSC Mars-1. Such experimental results
obtained with well-controlled samples in the laboratory are precious to interpret quantitatively the imaging
and spectral data collected by various Mars orbiters, landers and rovers. Producing and maintaining well-
characterised icy samples while acquiring spectro-photometric measurements is however challenging and we
discuss some of the difficulties encountered in preparing and measuring our samples. We present the results
in the form of photometric and spectral criteria computed from the spectra and plotted as a function of
the composition and physical properties of the samples. Consistent with previous studies, we find that when
intimately mixed with other materials, including water ice, CO2 ice becomes rapidly undetectable due to its
low absorptivity. As low as 5 wt% of fine-grained H2O ice is enough to mask entirely the signatures of CO2.
Similarly, sublimation experiments performed with ternary mixtures of CO2 ice, H2O ice and JSC Mars-1 show
that water, even when present as a minor component (3 wt%), determines the texture and evolution of the
mixtures. We assess the ability of various combinations of spectral parameters to identify samples with H2O,
CO2, JSC Mars-1, or various mixtures from their reflectance and orient our study to helping interpret ice and
soil reflectance spectra from the Martian surface. From the laboratory spectra, we simulate the colour signal
generated by the CaSSIS instrument to allow for direct comparisons with results from this instrument and
provide to databases the necessary spectral data to perform the same operations with other instruments