Characterization of carbon dioxide on Ganymede and Europa supported by experiments: Effects of temperature, porosity, and mixing with water
Abstract
The surfaces of icy moons are primarily composed of water ice that can be mixed with other compounds, such as carbon dioxide. The carbon dioxide (CO2) stretching fundamental band observed on Europa and Ganymede appears to be a combination of several bands that are shifting location from one moon to another. We investigate the cause of the observed shift in the CO2 stretching absorption band experimentally. We also explore the spectral behaviour of CO2 ice by varying the temperature and concentration. %H2O:CO2 deposition ratios. We analyzed pure CO2 ice and ice mixtures deposited at 10 K under ultra-high vacuum conditions using Fourier-transform infrared (FTIR) spectroscopy and temperature programmed desorption (TPD) experiments. Laboratory ice spectra were compared to JWST observation of Europa's and Ganymede's leading hemispheres. The simulated IR spectra were calculated using density functional theory (DFT) methods, exploring the effect of porosity in CO2 ice. Pure CO2 and CO2-water ice show distinct spectral changes and desorption behaviours at different temperatures, revealing intricate CO2 and H2O interactions. The number of discernible peaks increases from two in pure CO2 to three in CO2-water mixtures.
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