CO2 in Ganymedes exosphere revealed by JWST

Jupiter's icy moon Ganymede has been seen to have a tenuous exosphere produced by sputtering and possibly sublimation of water ice. To date, only hydrogen and oxygen have been detected in this exosphere (Barth et al. , 1997; Hall et al. 1998; Roth et al. 2021). Here, we report on the first detection of CO2 in Ganymede's exosphere through observations of the 4. 3 microns band with the NIRSPec/IFU instrument of the James Webb Space Telescope. Maps of the CO2 gas distribution over the leading and trailing hemispheres reveal an unexpected patchy CO2 exosphere. CO2 gas is observed over different terrain types, principally those exposed to intense Jovian irradiation, but also over some bright or dark terrains. The highest CO2 column density is found over the north polar cap of the leading hemisphere, which also has unique surface ice properties. The distribution and production mechanisms of CO2 vapor will be discussed using simulations of Ganymede's exosphere (Leblanc et al. 2017) and through comparison with maps of surface ice properties obtained with JWST (Bockele-Morvan et al. 2024). References: *Barth, C. A. , Hord, C. W. , Stewart, A. I. F. , Pryor, W. R. , Simmons, K. E. , McClintock, W. E. , Ajello, J. M. , Naviaux, K. L. , Aiello, J. J.: Galileo ultraviolet spectrometer observations of atomic hydrogen in the atmosphere of Ganymede. GRL 24 (17), 21472150 (1997) *Bockele-Morvan, D. , Lellouch, E. , Poch, O. , Quirico, E. , Cazaux, S. , de Pater, I. , Fouchet, T. , Fry, P. M. , Rodriguez-Ovalle, P. , Tosi, F. , Wong, M. H. , Boshuizen, I. , de Kleer, K. , Fletcher, L. N. , Meunier, L. , Mura, A. , Roth, L. , Saur, J. , Schmitt, B. , Trumbo, S. K. , Brown, M. E. , ODonoghue, J. , Orton, G. S. , Showalter, M. R.: Composition and thermal properties of Ganymedes surface from JWST/NIRSpec and MIRI observations. A 681, 27 (2024) *Hall, D. T. , Feldman, P. D. , McGrath, M. A. , Strobel, D. F.: The Far-Ultraviolet Oxygen Airglow of Europa and Ganymede. The Astrophysics Journal 499 (1), 475481 (1998) https: //doi. org/10. 1086/ 305604 *Leblanc, F. , Oza, A. V. , Leclercq, L. , Schmidt, C. , Cassidy, T. , Modolo, R. , Chaufray, J. Y. , Johnson, R. E.: On the orbital variability of Ganymedes atmosphere. Icarus 293, 185198 (2017) *Roth, L. , Ivchenko, N. , Gladstone, G. R. , Saur, J. , Grodent, D. , Bonfond, B. , Molyneux, P. M. , Rether- ford, K. D.: A sublimated water atmosphere on Ganymede detected from Hubble Space Telescope observations. Nature Astronomy 5, 10431051 (2021)