Characterization of Carbon Dioxide on Icy Moons: Laboratory Ice Analogues and JWST Observations

Abstract

Mixed ices of carbon dioxide (CO2) and water (H2O), prevalent in cometary nuclei, solar system satellites, and interstellar dust particles, have posed a persistent challenge in understanding the fundamental behaviors of carbon dioxide in these icy environments. Specifically, the intriguing shift in the CO2 stretching fundamental band observed on icy moons like Europa and Ganymede has remained enigmatic. In this study, we undertake a comprehensive investigation to elucidate this phenomenon by characterizing carbon dioxide on Ganymede and Europa through temperature-dependent spectral analyses.

Laboratory experiments involve the study of pure CO2 ice and its mixtures with water at varying concentrations, mimicking astrophysical conditions. Utilizing temperature-programmed desorption (TPD) and Fourier-transform infrared spectroscopy (FTIR) techniques, coupled with Gaussian deconvolution of obtained spectra, we explore the molecular interactions underlying the observed spectral shifts. Our experiments at 10 K under ultra-high vacuum conditions replicate interstellar medium conditions, providing crucial insights into CO2 behavior in icy environments.

In the discussion, a detailed overview is presented of the positions and behaviors of the fitted Gaussians for the asymmetric stretching bands of CO2 in pure form and when co-deposited with water. The temperature-dependent evolution of these bands reveals intricate dynamics, emphasizing the influence of CO2 concentration on the shifting positions and shapes of the spectral features.

The conclusions highlight key findings, including the complex nature of CO2 interactions within water ice, manifested in the emergence of multiple peaks at different concentrations. The thermal desorption analyses unveil distinct desorption behaviors, shedding light on the interactions during ice phase transitions. Importantly, our laboratory results align with observations from the James Webb Space Telescope (JWST), providing a synergistic approach to understanding CO2 behavior on icy worlds. The variations observed in Ganymede’s spectra across latitudes and longitudes further corroborate the influence of temperature and UV irradiation on CO2 dynamics within the ice.

This study contributes valuable insights into the molecular intricacies of CO2 in mixed ices, bridging laboratory experiments with observational data. The synergy between these approaches promises a more profound understanding of CO2 behavior in diverse astrophysical environments, advancing our knowledge of icy worlds in our Solar System and beyond.