Scientists just found more evidence that this mysterious water world might be able to support alien life "The cycling of oxygen and hydrogen in Europa's ocean will be a major driver for Europa's ocean chemistry and any life there, just as it is on Earth," NASA planetary geophysicist and lead author Steve Vance.
i can only conclude that the grays must be from a rogue world at odds with the galactic united federation of federations, as with all the billions of worlds on which life has evolved independently of each other, humans keep claiming to have seen so much of only this one sapient species not their own, messin with them. their violations of the prime directive would also seem to indicate this. yes it is not reasonable to assume that any large precentage of sapient life forms in this universe, could be portrayed by a human by means of makeup and costuming.