The mystery line is very close to Fraunhofer B... which worries me. I assume Fraunhofer B is atmospheric O2
as is Fraunhofer A. The H2O band is visible in the spectra too.
The puzzle to me is that this Ganymede spectrum was the only one to show this band/line... it doesn't appear noticeably in the spectra for the other Galilean moons nor on the GamCru spectrum I used to check calibration...
. I'm not aware that Ganymede has O2...
...
Al.