You know, that might not even be a UFO. That might actually be a rare species of plant/animal that somehow lives in upper atmosphere and just floats around. If it was UFO it would be moving, and these things just float. That's how animal life on Venus or Saturn would look like. Just float in atmosphere and feed on CO2 and energy from sun. There is a very long documentary about a small Italian town where they had some kind of biological substance raining from a similar object on the streets of the town.