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Laboratory investigation on ices analogs of the Galilean moons surfaces

Presentation #114.07 in the session Laboratory Investigations (Oral Presentation)

Published onOct 23, 2023
Laboratory investigation on ices analogs of the Galilean moons surfaces

Ultraviolet-visible spectroscopy has been extensively used to study ices in the Solar System. Ground-based observations revealed two features centered at 577.3 and 627.5 nm in Ganymede’s trailing hemisphere (Spencer et al. 1995) and on Europa and Callisto (Spencer and Calvin 2002), that were attributed to solid O2. The presence and maintenance of molecular oxygen in these icy surfaces are still debated.

In 2019 we obtained spectra of pure O2 ice layers and its mixtures with H2O, N2 and CO2 in the vis range at different temperatures and in different mixtures (Migliorini et al. 2022) using the AU-UV beam line of the ISA ASTRID2 ring storage, at the University of Aarhus.

In the pure O2 spectra, the two O2 bands at 577.3 and 627.5 nm can be seen, while for temperatures higher than 35 K the bands disappear because of O2 sublimation. We reported slight changes in the band shape and position with temperature, as well as differences in the relative intensities of the two bands. In the mixtures, we observed that the spectral profile, shape, relative intensities, and peak position of the two O2 bands vary as a function of the mixing ratios, ice composition, and temperature.

The mixtures we considered in our measurements allowed to improve the fit of the telescopic spectrum of Ganymede.

Further measurements of O2 and mixtures with different compounds are foreseen in October 2023 to further constrain the nature of the observed O2 bands in the icy surfaces of the Galilean satellites and other objects of the Solar System.

With these measurements, we aim to provide new insight on the characterization of molecular oxygen at low temperatures (20 to 40 K) to further constrain the nature of the observed features on the Galilean satellites. In addition, we contribute to build-up a background for the future interpretation of data acquired with the MAJIS instrument (Piccioni et al. 2019) on board the ESA JUICE mission.

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