Talking to my co workers about things they have seen flying they can’t explain, and NASA footage of UFOs. My theory: about a hundred years ago people couldn’t get to the bottom of the ocean, but once they did they found all sorts of strange fish that could only live under that high pressure environment. The fish had lights to adapt to the darkness. They glowed and were unlike any fish in the shallower waters. So our advances in technology made it possible to see them for the first time.
Outer space is a different environment. Our eyes and instrument are made to detect our known realm of understanding. What if there are animals living in the outer strata that are so sparse and transparent they only show up part of the time. Space is infinite so for an animal to adapt to that environment it could be as large as a mile or two long and never run into anything. The air is so thin it would have to be lighter than air to stay up there. The movements of some of these UFOs appear to be animal like as well. Moving quick and darting back and forth. Maybe in a hundred years we will develop instruments sensitive enough to see them.