Curtis Peebles has written an interesting book, Watch the Skies! A Chronicle of the Flying Saucer Myth (1994). He chronicled in it how it developed over the decades, and it's rather interesting to compare the versions of it for each time period.
Prehistory: mysterious airships, foo fighters, and ghost rockets. They come and go.
1947: Strange disk-shaped air vehicles ("flying saucers") seen. They have flight performance far beyond what Earthling air vehicles are capable of. Over the next two or three years, flying-saucer believers come to believe that they are extraterrestrial spacecraft.
Over the years, large numbers of people see them, people including radar operators, airline pilots, and astronauts/cosmonauts, and they display additional capabilities like stopping cars and making such physical evidence of themselves as padprints.
1948-49: The US Air Force seems to know more about flying saucers than what it is stating in public. By 1950, this became a full-scale coverup, as advocated by Donald Keyhoe and others. In later years, the CIA got in on this coverup, a coverup that has including smearing reliable witnesses as liars and fools.
Mid 1950's: the "Men in Black" get involved in this coverup.
1950: Crashed flying saucers / UFO's. This notion lasted only until 1952, but it was revived in the 1980's. The Roswell case is the best-known one of them.
1980's: Some of our advanced technology was reverse-engineered from crashed UFO's.
1952: UFO contactees. They have close encounters of the friendly kind with benevolent human(oid) "Space Brothers" and "Space Sisters" who come from Star-Trek techno-utopian societies. They want the contactees to spread the word that nuclear-weapons development is recklessly risking self-destruction and that humanity can do better than what it is now doing.
The contactees do either physical contact (meeting the ET's in person), telepathic contact (spiritualist-medium channeling of the ET's), or both.
Contactism faded in the 1960's, but some contactees continue to be active, notably Billy Meier.
The contactees provoked a split in UFOlogy, with the more respectable of UFOlogists, like Donald Keyhoe, becoming completely skeptical of them.
1957: UFO abductees. Antonio Villas-Boas was the first, but it was the 1961 Betty and Barney Hill case that first got a lot of attention. Abductees' memories are often blocked, though hypnotists can undo that blocking. The abductions are for medical examinations and experiments and gamete extractions, making the abductors seem like wildlife biologists. It took some years for the more respectable UFOlogists to take abductee cases seriously, since they seemed too much like contactee cases.
1980's: Many of the abductors are the Grays, sort-of human-shaped ET's with gray skin, big heads, and small bodies and limbs.
1960's: UFO's involved with domestic-animal mutilations, notably cattle mutilations.
I don't know of any big twists in the UFO story since then, with the possible exception of the recent proliferation of camera-equipped smartphones.
So UFO's are a story that grew in the telling over the years. There are some questions that Curtis Peebles did not adequately address, or at least that's what it seems like to me.
Why did flying saucers succeed where their predecessors failed?
I think that there may be two reasons.
The first is magazine editor Ray Palmer. In the 1940's, he was editor of science-fiction magazine Amazing Stories, and he ran as nonfiction the Great Shaver Mystery. A certain Richard Shaver claimed that many of our misfortunes are caused by nasty "deros" tormenting up with their rays, and he even claimed to have visited their underground-cavern homes. It turned up later that he was a mental hospital the whole time, hospitalized for paranoid schizophrenia. His superiors eventually shut down the series, and Ray Palmer went on to start the paranormal magazine Fate. It covered flying saucers from its beginning, and in it, he kept the notion going after the fading of the first big wave of flying-saucer sightings. So as a sensation monger, he scored twice, first with deros and then with flying saucers.
The second is the US Air Force's involvement and the coverup conspiracy theory that many UFOlogists came to believe about it. The USAF was involved out of the possibility that flying saucers could be secret Russian airplanes or balloons. Some early USAF investigators apparently believed in the extraterrestrial-spacecraft hypothesis, though the USAF did not talk publicly about that. This was turned into the theory that the USAF knows that flying saucers are extraterrestrial spacecraft, but is covering it up.
Finally, UFO contact vs. UFO abduction cases. I think that the accounts of contactees provoked a lot of skepticism because to many people, they seemed too good to be true. UFO abductees' accounts don't have that quality.
Prehistory: mysterious airships, foo fighters, and ghost rockets. They come and go.
1947: Strange disk-shaped air vehicles ("flying saucers") seen. They have flight performance far beyond what Earthling air vehicles are capable of. Over the next two or three years, flying-saucer believers come to believe that they are extraterrestrial spacecraft.
Over the years, large numbers of people see them, people including radar operators, airline pilots, and astronauts/cosmonauts, and they display additional capabilities like stopping cars and making such physical evidence of themselves as padprints.
1948-49: The US Air Force seems to know more about flying saucers than what it is stating in public. By 1950, this became a full-scale coverup, as advocated by Donald Keyhoe and others. In later years, the CIA got in on this coverup, a coverup that has including smearing reliable witnesses as liars and fools.
Mid 1950's: the "Men in Black" get involved in this coverup.
1950: Crashed flying saucers / UFO's. This notion lasted only until 1952, but it was revived in the 1980's. The Roswell case is the best-known one of them.
1980's: Some of our advanced technology was reverse-engineered from crashed UFO's.
1952: UFO contactees. They have close encounters of the friendly kind with benevolent human(oid) "Space Brothers" and "Space Sisters" who come from Star-Trek techno-utopian societies. They want the contactees to spread the word that nuclear-weapons development is recklessly risking self-destruction and that humanity can do better than what it is now doing.
The contactees do either physical contact (meeting the ET's in person), telepathic contact (spiritualist-medium channeling of the ET's), or both.
Contactism faded in the 1960's, but some contactees continue to be active, notably Billy Meier.
The contactees provoked a split in UFOlogy, with the more respectable of UFOlogists, like Donald Keyhoe, becoming completely skeptical of them.
1957: UFO abductees. Antonio Villas-Boas was the first, but it was the 1961 Betty and Barney Hill case that first got a lot of attention. Abductees' memories are often blocked, though hypnotists can undo that blocking. The abductions are for medical examinations and experiments and gamete extractions, making the abductors seem like wildlife biologists. It took some years for the more respectable UFOlogists to take abductee cases seriously, since they seemed too much like contactee cases.
1980's: Many of the abductors are the Grays, sort-of human-shaped ET's with gray skin, big heads, and small bodies and limbs.
1960's: UFO's involved with domestic-animal mutilations, notably cattle mutilations.
I don't know of any big twists in the UFO story since then, with the possible exception of the recent proliferation of camera-equipped smartphones.
So UFO's are a story that grew in the telling over the years. There are some questions that Curtis Peebles did not adequately address, or at least that's what it seems like to me.
Why did flying saucers succeed where their predecessors failed?
I think that there may be two reasons.
The first is magazine editor Ray Palmer. In the 1940's, he was editor of science-fiction magazine Amazing Stories, and he ran as nonfiction the Great Shaver Mystery. A certain Richard Shaver claimed that many of our misfortunes are caused by nasty "deros" tormenting up with their rays, and he even claimed to have visited their underground-cavern homes. It turned up later that he was a mental hospital the whole time, hospitalized for paranoid schizophrenia. His superiors eventually shut down the series, and Ray Palmer went on to start the paranormal magazine Fate. It covered flying saucers from its beginning, and in it, he kept the notion going after the fading of the first big wave of flying-saucer sightings. So as a sensation monger, he scored twice, first with deros and then with flying saucers.
The second is the US Air Force's involvement and the coverup conspiracy theory that many UFOlogists came to believe about it. The USAF was involved out of the possibility that flying saucers could be secret Russian airplanes or balloons. Some early USAF investigators apparently believed in the extraterrestrial-spacecraft hypothesis, though the USAF did not talk publicly about that. This was turned into the theory that the USAF knows that flying saucers are extraterrestrial spacecraft, but is covering it up.
Finally, UFO contact vs. UFO abduction cases. I think that the accounts of contactees provoked a lot of skepticism because to many people, they seemed too good to be true. UFO abductees' accounts don't have that quality.
