A patchy CO$_2$ exosphere on Ganymede revealed by the James Webb Space Telescope
Abstract
Jupiter's icy moon Ganymede has a tenuous exosphere produced by sputtering and possibly sublimation of water ice. To date, only atomic hydrogen and oxygen have been directly detected in this exosphere. Here, we present observations of Ganymede's CO exosphere obtained with the James Webb Space Telescope. CO gas is observed over different terrain types, mainly over those exposed to intense Jovian plasma irradiation, as well as over some bright or dark terrains. Despite warm surface temperatures, the CO abundance over equatorial subsolar regions is low. CO vapor has the highest abundance over the north polar cap of the leading hemisphere, reaching a surface pressure of 1 pbar. From modeling we show that the local enhancement observed near 12 h local time in this region can be explained by the presence of cold traps enabling CO adsorption. However, whether the release mechanism in this high-latitude region is sputtering or sublimation remains unclear. The north polar cap of the leading hemisphere also has unique surface-ice properties, probably linked to the presence of the large atmospheric CO2 excess over this region. These CO2 molecules might have been initially released in the atmosphere after the radiolysis of CO precursors, or from the sputtering of CO embedded in the HO ice bedrock. Dark terrains (regiones), more widespread on the north versus south polar regions, possibly harbor CO precursors. CO molecules would then be redistributed via cold trapping on ice-rich terrains of the polar cap and be diurnally released and redeposited on these terrains. Ganymede's CO exosphere highlights the complexity of surface-atmosphere interactions on Jupiter's icy Galilean moons.
Keywords
Cite
@article{arxiv.2409.13364,
title = {A patchy CO$_2$ exosphere on Ganymede revealed by the James Webb Space Telescope},
author = {Dominique Bockelée-Morvan and Olivier Poch and Françcois Leblanc and Vladimir Zakharov and Emmanuel Lellouch and Eric Quirico and Imke de Pater and Thierry Fouchet and Pablo Rodriguez-Ovalle and Lorenz Roth and Frédéric Merlin and Stefan Duling and Joachim Saur and Adrien Masson and Patrick Fry and Samantha Trumbo and Michael Brown and Richard Cartwright and Stéphanie Cazaux and Katherine de Kleer and Leigh N. Fletcher and Zachariah Milby and Audrey Moingeon and Alessandro Mura and Glenn S. Orton and Bernard Schmitt and Federico Tosi and Michael H. Wong},
journal= {arXiv preprint arXiv:2409.13364},
year = {2024}
}
Comments
21 pages, 21 figures, Accepted as a Letter in Astronomy and Astrophysics