A sublimated water atmosphere on Ganymede detected from Hubble Space Telescope observations

Lorenz Roth; Nickolay Ivchenko; G. Randall Gladstone; Joachim Saur; Denis Grodent; Bertrand Bonfond; Philippa M. Molyneux; Kurt D. Retherford

doi:10.1038/s41550-021-01426-9

paper

A sublimated water atmosphere on Ganymede detected from Hubble Space Telescope observations

arXiv:2106.03570 · doi:10.1038/s41550-021-01426-9

Abstract

Ganymede's atmosphere is produced by charged particle sputtering and sublimation of its icy surface. Previous far-ultraviolet observations of the O{\small I\,}1356-Å and O{\small I\,}1304-Å oxygen emissions were used to infer sputtered molecular oxygen (O $_{2}$ ) as an atmospheric constituent, but an expected sublimated water (H $_{2}$ O) component remained undetected. Here we present an analysis of high-sensitivity spectra and spectral images acquired by the Hubble Space Telescope revealing H $_{2}$ O in Ganymede's atmosphere. The relative intensity of the oxygen emissions requires contributions from dissociative excitation of water vapor, indicating that H $_{2}$ O is more abundant than O $_{2}$ around the sub-solar point. Away from the sub-solar region, the emissions are consistent with a pure O $_{2}$ atmosphere. Eclipse observations constrain atomic oxygen to be at least two orders of magnitude less abundant than these other species. The higher H $_{2}$ O/O $_{2}$ ratio above the warmer trailing hemisphere compared to the colder leading hemisphere, the spatial concentration to the sub-solar region, and the estimated abundance of $\sim$ 10 $^{15}$ H $_{2}$ O/cm $^{2}$ are consistent with sublimation of the icy surface as source.

published in Nature Astronomy (2021) (reformatted for arXiv)

A sublimated water atmosphere on Ganymede detected from Hubble Space Telescope observations

Abstract

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