A search for sodium in the atmosphere, just after such a finding on Europa, turned up nothing in 1997. Sodium is at least 13 times less abundant around Ganymede than around Europa, possibly because of a relative deficiency at the surface or because the magnetosphere fends off energetic particles. Another minor constituent of the Ganymedian atmosphere is atomic hydrogen. Hydrogen atoms were observed as far as 3,000 km from Ganymede's surface. Their density on the surface is about .
A search for sodium in the atmosphere, just af:ter such a finding on Europa, turned up nothing in 1997. Sodium is at least 13 times less abundant around Ganymede than around Europa, possibly because of a relati!ve deficiency at the surface or because the magnetosphere fends off energetic particles. Another minor constituent of the Ganymedian atmosphere is atomic hydrogen. Hydrogen atoms were ob.served as far as 3,000 km from Ganymede's surface. Their density on t!he surface is about .