Absorption Coefficients of Condensed O2: Application to Ganymede
Year: 2025
Type: article
Abstract: Two absorption features in the visible reflectance spectra of the icy Galilean satellites are associated with dense phase molecular oxygen (O2). These were identified from ground-based and Hubble Space Telescope data on Ganymede, Europa, and Callisto. Molecular oxygen is the radiolytic product of energetic particle bombardment and breakdown of water ice. The oxygen features are strongest near the equator on the trailing hemisphere of Ganymede. We review previous laboratory measurements of high-pressure gas, liquid, and solid phases of O2, noting differences that arise with increased density and phase changes. We measure transmission spectra of condensed liquid and solid-γ phase O2 from 455 to 5000 nm (22,000–2000 cm−1) using a Fourier transform infrared spectrometer at 1 cm−1 spectral resolution. This spectral range includes the strongest visible and near-infrared absorption features. The measured absorption is dependent on both phase and temperature increasing with colder temperatures and in the solid form. We use these data to determine the absorption coefficients of the liquid and solid phases. These are then compared with absorption by water ice, the dominant constituent of Ganymede’s surface. O2 has an absorption coefficient that is ∼2 orders of magnitude stronger than water ice in the visible. Using simple reflectance models we estimate that a fractional abundance of 4%–5% over the path length in the surface is needed to create the observed visible absorptions, and this fraction does not contribute noticeable features in the infrared.
Source: The Planetary Science Journal
DOI: 10.3847/psj/adfc63
Author: Wendy M. Calvin
Language: English
Topic: Astro and Planetary Science
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,800
OpenAlex ID: W4414120136