You can keep it for as long as you want; you're the boss of your fridge.
But anyway, an open beer bottle can stay good in the fridge for up to 96 hours, probably more.
We use a spectrometer to help us determine what stars and planets are made of by passing a light through various chemical elements, different spectral patterns are created. By matching those patterns up to patterns generated in a laboratory environment we can tell what the composition of a distant star or planet is.
Answer; they are larger and made of rocky material
