ganymede

In astronomy terms the difference between io and ganymede

is that io is short for 85 Io, a main belt asteroid; the asteroid shares its name with the Jovian moon while ganymede is a moon of Jupiter.

As proper nouns the difference between io and ganymede

is that io is the daughter of Inachus river god, and a lover of Zeus while Ganymede is a Trojan boy who was abducted (either by Zeus or Eos), and ultimately became immortal in order to be Zeus' cup-bearer and lover.

As a noun io

is a type of moth, the io moth.

As an interjection io

is an exclamation of joy or triumph.