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${}_2$ exosphere obtained with the James Webb Space Telescope. CO${}_2$ 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${}_2$ abundance over equatorial subsolar regions is low. CO${}_2$ 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${}_2$ 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${}_2$ precursors, or from the sputtering of CO${}_2$ embedded in the H${}_2$O ice bedrock. Dark terrains (regiones), more widespread on the north versus south polar regions, possibly harbor CO${}_2$ precursors. CO${}_2$ 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${}_2$ exosphere highlights the complexity of surface-atmosphere interactions on Jupiter's icy Galilean moons.

21 pages, 21 figures, Accepted as a Letter in Astronomy and Astrophysics

References in corpus (11)

• Surface composition and properties of Ganymede: Updates from ground-based observations with the near-infrared imaging spectrometer SINFONI/VLT/ESO
• A sublimated water atmosphere on Ganymede detected from Hubble Space Telescope observations
• Ganymede MHD Model: Magnetospheric Context for Juno's PJ34 Flyby
• Composition and thermal properties of Ganymede's surface from JWST/NIRSpec and MIRI observations
• The Optical Aurorae of Europa, Ganymede and Callisto
• Implications of Surface Roughness in Models of Water Desorption on the Moon
• Global Modelling of Ganymede's Surface Composition: Near-IR Mapping from VLT/SPHERE
• Simulated performance of the molecular mapping for young giant exoplanets with the Medium Resolution Spectrometer of JWST/MIRI
• Exosphere-Mediated Migration of Volatile Species On Airless Bodies Across the Solar System
• Alternating north-south brightness ratio of Ganymede's auroral ovals: Hubble Space Telescope observations around the Juno PJ34 flyby
• Short-Timescale Spatial Variability of Ganymede's Optical Aurora

Cited by in corpus (2)

• Plasma and Thermal Processing Leading to Spatial and Temporal Variability of the Trapped O2 at Europa and Ganymede
• Formation and Trapping of CO2 from Cryogenic Irradiation of Carbonate