It seems as if no one knows. Modern Science is supposed to have all the answers, but the answer it gives us, Gravity and The Vacuum of Space, seems like Magic and Make Believe. Flat Earth apparently doesn't have an answer to this question. Although, there are theories, but nothing convincing. Our World seems very different from what we think.
We don't know all the answers. Modern Science tells us we have almost all the answers and the few we don't, are on the way! If Modern Science is a fraud, then our World is much more mysterious, than we thought.