Oh my word: Europa and its respective Jovian moons, are as I just said MOONS, and a moon is not something exclusive To earth that is just a term we give The natural satellites orbiting all planets, Our moon Is actually called Luna(look it Up its true), Jupiter and Saturn are Jovian planets meaning they are Both gas giants, meaning made ENTIRELY OF GAS, mostly hydrogen and helium, some neon and other trace gasses, they have no solid surface until thousands of Kilometres below the surface, And The pressure at those depths would Be enough to turn you into a small Star, Europa and triton, and titan however are very interesting places because it is possible That they could harbor life, and Europa is suspected to have water oceans and a molecular oxygen atmosphere!!!