VIS-NIR/SWIR Spectral Properties of H2O Ice Depending on Particle Size and Surface Temperature

Abstract

Laboratory measurements were performed to study the spectral signature of H2O ice between 0.4 and 4.2 µm depending on varying temperatures between 70 and 220 K. Spectral parameters of samples with particle sizes up to ~1360 µm, particle size mixtures, and different particle shapes were analyzed. The band depth (BD) of the major H2O-ice absorptions at 1.04, 1.25, 1.5, and 2 µm offers an excellent indicator for varying particle sizes in pure H2O ice. The spectral changes due to temperature rather, but not exclusively, affect the H2O-ice absorptions located at 1.31, 1.57, and 1.65 µm and the Fresnel reflection peaks at 3.1 and 3.2 µm, which strongly weaken with increasing temperature. As the BDs of the H2O-ice absorptions at 1.31, 1.57, and 1.65 µm increase, the band centers (BCs) of the H2O-ice absorptions at 1.25 and 1.5 µm slightly shift to shorter wavelengths. However, the BCs of the strong H2O-ice absorptions can also be affected by saturation in the case of large particles. The collected spectra provide a useful spectral library for future investigations of icy satellites such as Ganymede and Callisto, the major targets of ESA’s JUICE mission.

Hydrogen peroxide at the poles of Ganymede

“…As the best available proxy for water ice in the JWST cubes, we measure the strength of the double ~3.1 μm Fresnel H 2 O reflectance peak, which is visible to varying degrees in the spectra of Fig. 1, although it is characteristically stronger and more structured in crystalline ice than in amorphous ice and can change with temperature (30)(31)(32). The resulting distributions are also shown in Fig.…”

“…However, the trailing-hemisphere geography of the Fresnel peak is curious, as it shows slight enhancements at the poles, but the strongest signatures on the morning limb. Understanding this phenomenon is beyond the scope of this paper, but it is possible that temperature effects on peak strength ( 32 ) or potential day/night sublimation/condensation effects with Ganymede’s atmosphere ( 35 ) should be considered.…”

Cohesive properties of ice powders analogous to fresh plume deposits on Enceladus and Europa

“…As an analogy to these jets processes on Enceladus, one of the most common ways to produce ice powders mimicking possible fresh surface deposits on icy moons is to inject very small water droplets into a liquid nitrogen bath at -195.79°C (Gundlach et al, 2011;Yoldi, Pommerol, Jost, Poch, Gouman and Thomas, 2015;Jost, Pommerol, Poch, Gundlach, Leboeuf, Dadras, Blum and Thomas, 2016;Poch, Pommerol, Jost, Carrasco, Szopa and Thomas, 2016;Poch, Cerubini, Pommerol, Jost and Thomas, 2018;Choukroun et al, 2020;Stephan, Ciarniello, Poch, Schmitt, Haack and Raponi, 2021). This allows the droplets to freeze in a few seconds at cooling rates allowing the ice to be crystalline (water droplets may not freeze instantly due to Leidenfrost effect, see Cerubini, Pommerol, Yoldi and Thomas (2022), but may freeze on very short timescales, depending on particle size), producing spherical ice grains which size is determined by the pressurised device used to produce the droplets.…”