Unidentified flying object

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An unidentified flying object (UFO), or unidentified anomalous phenomenon^[a] (UAP), is any perceived airborne, submerged or transmedium phenomenon that cannot be immediately identified or explained.^[2] Upon investigation, most UFOs are identified as known objects or atmospheric phenomena, while a small number remain unexplained.

While unusual sightings have been reported in the sky throughout history, UFOs became culturally prominent after World War II, escalating during the Space Age. Studies and investigations into UFO reports conducted by governments (such as Project Blue Book in the United States and Project Condign in the United Kingdom), as well as by organisations and individuals have occurred over the years without confirmation of the fantastical claims of small but vocal groups of ufologists who favour unconventional or pseudoscientific hypotheses, often claiming that UFOs are evidence of extraterrestrial intelligence, technologically advanced cryptids, demons, interdimensional contact or future time travelers. After decades of promotion of such ideas by believers and in popular media, the kind of evidence required to solidly support such claims has not been forthcoming. Scientists and skeptic organizations such as the Committee for Skeptical Inquiry have provided prosaic explanations for UFOs, namely that they are caused by natural phenomena, human technology, delusions, and hoaxes. Beliefs surrounding UFOs have inspired parts of new religions even as social scientists have identified the ongoing interest and storytelling surrounding UFOs as a modern example of folklore and mythology understandable with psychosocial explanations.

The U.S. government currently has two entities dedicated to UFO data collection and analysis: NASA's UAP independent study team and the All-domain Anomaly Resolution Office.

UFOs and ufology
Notable sightings and hoaxes
Kenneth Arnold sighting 1947 wave Roswell Mantell crash Chiles-Whitted Gorman dogfight McMinnville photos Mariana film 1952 flap Sightings in outer space Flatwoods monster Barney and Betty Hill Travis Walton Rendlesham Forest Belgian wave Alien autopsy hoax Phoenix Lights Pentagon UFO videos
Government investigations
Operação Prato - Brazil Project Magnet - Canada GEIPAN - France Institute 22 - Soviet Union Flying Saucer Working Party - UK Project Condign - UK History of government investigations - US All-domain Anomaly Resolution Office - US NASA's UAP independent study team - US Condon Committee - US Project Blue Book - US
Conspiracy theories
Area 51 Bob Lazar Majestic 12 Men in black Serpo
Religions
Aetherius Society Church of the SubGenius Heaven's Gate Nation of Islam Raëlism Scientology Unarius Academy of Science
Lists of organizations, sightings, studies, etc.
UFO organizations Reported UFO sightings Sightings by country Investigations of UFOs by governments Identification studies of UFOs Ufologists Alleged extraterrestrial beings
v t e

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People have always observed the sky and have sometimes seen what, to some, appeared to be unusual sights including phenomena as varied as comets, bright meteors, one or more of the five planets that can be readily seen with the naked eye, planetary conjunctions, and atmospheric optical phenomena such as parhelia and lenticular clouds.^{[citation needed]} One particularly famous example is Halley's Comet: first recorded by Chinese astronomers in 240 BC and possibly as early as 467 BC as a strange and unknown "guest light" in the sky.^[3] As a bright comet that visits the inner solar system every 76 years, it was often identified as a unique isolated event in ancient historical documents whose authors were unaware that it was a repeating phenomenon.^{[citation needed]} Such accounts in history often were treated as supernatural portents, angels, or other religious omens.^{[citation needed]} While UFO enthusiasts have sometimes commented on the narrative similarities between certain religious symbols in medieval paintings and UFO reports,^[4] the canonical and symbolic character of such images is documented by art historians placing more conventional religious interpretations on such images.^[5]

Some examples of pre-contemporary reports about unusual aerial phenomena include:

• Julius Obsequens was a Roman writer who is believed to have lived in the middle of the fourth century AD. The only work associated with his name is the Liber de prodigiis (Book of Prodigies), completely extracted from an epitome, or abridgment, written by Livy; De prodigiis was constructed as an account of the wonders and portents that occurred in Rome between 249 and 12 BCE. An aspect of Obsequens' work that has inspired excitement in some UFO enthusiasts is that he makes reference to things moving through the sky. The descriptions provided bear resemblance to observations of meteor showers. Obsequens was also writing some 400 years after the events he described, thus the text is not an eyewitness account. No corroboration with those amazing sights of old with contemporary observations was mentioned in that work.^[6][7]
• Shen Kuo (1031–1095), a Song Chinese government scholar-official and prolific polymath inventor, wrote a vivid passage in his Dream Pool Essays (1088) about an unidentified flying object. He recorded the testimony of eyewitnesses in 11th-century Anhui and Jiangsu (especially in the city of Yangzhou), who stated that a flying object with opening doors would shine a blinding light from its interior (from an object shaped like a pearl) that would cast shadows from trees for ten miles in radius, and was able to take off at tremendous speeds.^[8]

  

• A woodcut by Hans Glaser that appeared in a broadsheet in 1561 has been featured in popular culture as the "celestial phenomenon over Nuremberg" and connected to various ancient astronaut claims.^[9] Skeptic and debunker Jason Colavito argues that the woodcut is "a secondhand depiction of a particularly gaudy sundog", a known atmospheric optical phenomenon.^[10] A similar report comes from 1566 over Basel and, indeed, in the 15th and 16th centuries, many leaflets wrote of "miracles" and "sky spectacles" which bear resemblance to natural phenomena which were only more fully characterized after the scientific revolution.^[11]
• On January 25, 1878, the Denison Daily News printed an article in which John Martin, a local farmer, had reported seeing a large, dark, circular object resembling a balloon flying "at wonderful speed". Martin, according to the newspaper account, said it appeared to be about the size of a saucer from his perspective, one of the first uses of the word "saucer" in association with a UFO. At the time, ballooning was becoming an increasingly popular and sophisticated endeavor, and the first controlled-flights of such devices were occurring around that time.^[12]

UFO-like alleged sightings before the 20th century

1561 celestial phenomenon over Nuremberg as printed in an illustrated news notice.

November 22, 1896 illustration of a "mystery airship" published in The San Francisco Call

November 29, 1896 illustration of another "mystery airship" published in The San Francisco Call

"Mystery airship" illustrated in The St. Paul Globe, April 13, 1897

• From November 1896 to April 1897, United States newspapers carried numerous reports of "mystery airships" that are reminiscent of modern UFO waves.^[13] Scores of people even reported talking to the pilots. Some people feared that Thomas Edison had created an artificial star that could fly around the country. On April 16, 1897, a letter was found that purported to be an enciphered communication between an airship operator and Edison.^[14] When asked his opinion of such reports, Edison said, "You can take it from me that it is a pure fake."^[15] The coverage of Edison's denial marked the end of major newspaper coverage of the airships in this period.^[16]

In the Pacific and European theatres during World War II, round, glowing fireballs known as "foo fighters" were reported by Allied and Axis pilots. Some explanations for these sightings included St. Elmo's fire, the planet Venus, hallucinations from oxygen deprivation, and German secret weapons (specifically rockets).^[17] In 1946, more than 2,000 reports were collected, primarily by the Swedish military, of unidentified aerial objects over the Scandinavian nations, along with isolated reports from France, Portugal, Spain, Italy, and Greece. The objects were referred to as "Russian hail" (and later as "ghost rockets") because it was thought the mysterious objects were possibly Russian tests of captured German V1 or V2 rockets, but most were identified as natural phenomena as meteors.^[18]

Science fiction depictions of spacecraft similar to flying saucers before the first widely-reported UFO sighting in 1947

Illustration from 1903 by Henrique Alvim Corrêa showing the first Martian emerging from a cylinder that had fallen from the sky for an edition of The War of the Worlds by H. G. Wells.

Cover of French pulp magazine Le Chevalier Illusion from December 29, 1912 portraying a flying machine spreading a toxic gas among the passengers and crew of a ship below

A "space flyer" depicted on the February 1912 cover of Modern Electrics as an illustration for the science fiction story Ralph 124C 41+ by Hugo Gernsback

Illustration by Frank R. Paul from February 1922 in Science and Invention showing Nikola Tesla's vision of warfare in the future with sea and air craft "controlled and directed" by radio waves

Illustration for a story by Hugo Gernsback in pulp science fiction magazine Amazing Stories from April 1928 (originally published on 1915 with similar illustrations in The Electrical Experimenter)

Depiction of a flying saucer by illustrator Frank R. Paul on the October 1929 issue of Hugo Gernsback's pulp science fiction magazine Science Wonder Stories

Cover of Amazing Stories winter 1930 issue depicting a disc-shaped spacecraft

Back cover of Amazing Stories illustrated by Frank R. Paul in August 1946 featuring many disc-shaped spacecraft (published about a year before the flying disc wave of 1947)

Many scholars, especially those arguing for the psychosocial UFO hypothesis, have noted that UFO characteristics reported after the first widely publicized modern sighting by Kenneth Arnold in 1947 resembled a host of science fiction tropes from earlier in the century.^{[19][20][21][22][23][24][25]}

By most accounts, the popular UFO craze in the US began with a media frenzy surrounding the reports on June 24, 1947, of a civilian pilot named Kenneth Arnold who described seeing "a group of bat-like aircraft flying in formation at high speeds" near Mount Rainier that he said were "moving like a saucer would if skipped across water" which led to headlines about "flying saucers" and "flying discs".^{[26][27][28][29]} Only weeks after Arnold's story was reported in 1947, Gallup published a poll asking people in the United States what the "flying saucers" might be. Already, 90% had heard of the new term. However, as reported by historian Greg Eghanian, "a majority either had no idea what they could be or thought that witnesses were mistaken" while "visitors from space were not initially among the options that anyone had in mind, and Gallup didn't even mention if anyone surveyed brought up aliens.^[27][30][31] Within weeks, reports of flying saucer sightings became a daily occurrence^[32] with one particularly famous example being the Roswell incident in 1947 where remnants of a downed observation balloon were recovered by a farmer and confiscated by military personnel.^[33] UFO enthusiasts in the early 1950s started to organize local "saucer clubs" modeled after science fiction fan clubs of the 1930s and 1940s, with some growing to national and international prominence within a decade.^[27] In 1950, three influential books were published—Donald Keyhoe's The Flying Saucers Are Real, Frank Scully's Behind the Flying Saucers, and Gerald Heard's The Riddle of the Flying Saucers. Each guilelessly proposed that the extraterrestrial UFO hypothesis was the correct explanation and that the visits were in response to detonations of atomic weapons. These books also introduced Americans to, as Eghanian puts it, "the crusading whistleblower dedicated to breaking the silence over the alien origins of unidentified flying objects".^[27] Media accounts and speculation ran rampant in the U.S., especially in connection to the 1952 UFO scare in Washington, D.C. so that, by 1953, the intelligence officials (Robertson Panel) worried that "genuine incursions" by enemy aircraft "over U.S. territory could be lost in a maelstrom of kooky hallucination" of UFO reports.^[34] A Trendex survey in August 1957, ten years after the Arnold incident, reported that over 25% of the U.S. public "believed unidentified flying objects could be from outer space".^[27] The cultural phenomenon showed up within some intellectual works such as the 1959 publication of Flying Saucers: A Modern Myth of Things Seen in the Sky by Carl Jung, a Swiss psychiatrist and psychoanalyst who founded analytical psychology.^[35]

Starting in 1947, the U.S. Air Force began to record and investigated UFO reports with Project Sign looking into "more than 250 cases" from 1947 to 1949. It was replaced by Project Grudge up through 1951.^[36] In the third U.S. Air Force program, from March 1952 to its termination in December 1969,^[37] "the U.S. Air Force cataloged 12,618 sightings of UFOs as part of what is now known as Project Blue Book".^[38] In the late 1950s, public pressure mounted for a full declassification of all UFO records, but the CIA played an role in refusing to allow this.^[39] This sense was not universal in the CIA, however, as fellow NICAP official Donald E. Keyhoe wrote that Vice Admiral Roscoe Hillenkoetter, the first director of the CIA, "wanted public disclosure of UFO evidence".^[40] Official U.S. Air Force interest in UFO reports went on hiatus in 1969 after a study by the University of Colorado led by Edward U. Condon and known as the Condon Report concluded "that nothing has come from the study of UFOs in the past 21 years that has added to scientific knowledge" and that further time investigating UFO reports "cannot be justified".^[38]

From the 1960s to 1990s, UFOs were part of American popular culture's obsession with the supernatural and paranormal. In 1961, the first alien abduction account was sensationalized when Barney and Betty Hill underwent hypnosis after seeing a UFO and reported recovered memories of their experience that became ever more elaborate as the years went by.^[41] In 1966, 5% of Americans reported to Gallup that "they had at some time seen something they thought was a 'flying saucer'", 96% said "they had heard or read about flying saucers", and 46% of these "thought they were 'something real' rather than just people's imagination".^[42] Responding to UFO enthusiasm, there have always been consistent yet less popular efforts made at debunking many of the claims,^[27] and at times the media was enlisted including a 1966 TV special, "UFO: Friend, Foe or Fantasy?", in which Walter Cronkite "patiently" explained to viewers that UFOs were fantasy.^[34] Cronkite enlisted Carl Sagan and J. Allen Hynek, who told Cronkite, "To this time, there is no valid scientific proof that we have been visited by spaceships".^[43]

Such attempts to disenchant the zeitgeist were not very successful at tamping down the mania. Keith Kloor notes that the "allure of flying saucers" remained popular with the public into the 1970s, spurring production of such sci-fi films, as Close Encounters of the Third Kind and Alien, which "continued to stoke public fascination". Meanwhile, Leonard Nimoy narrated a popular occult and mystery TV series In Search of... while daytime talk shows of Mike Douglas, Merv Griffin, and Phil Donahue featured interviews with alien abductees and people who credulously reported stories about UFOs .^[27] In the 1980s and 1990s, UFO stories featured in such pulp "true crime" serials as Unsolved Mysteries^[44] while the 33 Volume Time-Life series Mysteries of the Unknown which featured UFO stories sold some 700,000 copies.^[45] Kloor writes that by the late 1990s, "other big UFO subthemes had been prominently introduced into pop culture, such as the abduction phenomenon and government conspiracy narrative, via best-selling books and, of course, The X-Files".^[43]

Eghigian notes that, by this point, the UFO problem had become "far more interesting to ponder than to actually solve."^[27] Interest was particularly fevered in the 1990s with the publicity surrounding the television broadcast of an Alien autopsy video marketed as "real footage" but later admitted to be a staged "re-enactment".^[46] Eghigian writes that "there had always been outlier abduction reports dating back to the '50s and '60s" but that in the '80s and '90s "the floodgates opened, and with them a new generation of UFO advocates". Leaders among them were the artist Budd Hopkins, horror writer Whitley Strieber, historian David Jacobs, and Harvard psychiatrist John Mack. They all defended the "veracity of those claiming to have been kidnapped, examined, and experimented upon by beings from another world", writes Eghigian, as "new missionaries who simultaneously played the role of investigator, therapist, and advocate to their vulnerable charges".^[27] Eghigian says that Mack "signaled both the culmination and end of the headiest days of alien abduction". When Mack began working with and publishing accounts of abductees—or "experiencers", as he called them—in the early 1990s, he brought a sense of legitimacy to "the study of extraterrestrial captivity". By the late 1990s, however, the Harvard Medical School initiated a review of his position which allowed him to retain tenure. However, after this review, as the review board chairman Arnold Relman later put it, Mack was "not taken seriously by his colleagues anymore". Claims of alien abduction have continued, but no other clinicians would continue to speak of them as real in any sense.^[27] Nonetheless, these ideas persisted in popular opinion. According to a 1996 poll by Newsweek, 20% of Americans believed that UFOs were more likely to be proof of alien life than to have a natural scientific explanation.^[47]

In December 2017, a new round of media attention started when The New York Times broke the story of the secret Advanced Aviation Threat Identification Program that was funded from 2007 to 2012 with $22 million spent on the program.^[48][49] Following this story, along with a serious of sensationalized Pentagon UFO videos leaked by members of the program who became convinced that UFOs were genuine mysteries worth investigating, there was an increase in mainstream attention to UFO stories. In July 2021, Harvard astronomer Avi Loeb announced the creation of his Galileo Project which intended to use high-tech astronomical equipment to seek evidence of extraterrestrial artifacts in space and possibly within Earth's atmosphere. This was followed closely by the publication of Loeb's book Extraterrestrial, in which he argued that the first interstellar comet ever observed, 'Oumuamua, might be an artificial light sail made by an alien civilization.^[27] Two government sponsored programs, NASA's UAP independent study team and the All-domain Anomaly Resolution Office were charged in part by Congressional fiat to investigate UFO claims more fully,^[50][51][52] adopting the new moniker "unexplained aerial phenomenon" (UAP) to avoid associations with past sensationalism.^[53] On 17 May 2022, members of the United States House Intelligence Subcommittee on Counterterrorism, Counterintelligence and Counterproliferation held congressional hearings with top military officials to discuss military reports of UAPs.^[54] It was the first public congressional hearing into UFO sightings in the US in over 50 years. Another Congressional hearing took place on July 26, 2023, featuring the whistleblower claims of former U.S. Air Force (USAF) officer and intelligence official David Grusch.^[55][56][57]

A Harris Poll in 2009 found that 32% of Americans "believe in UFOs".^[58] A National Geographic study in June 2012 found that 36% of Americans believe UFOs exist and that 10% thought that they had spotted one.^[59] In June 2021 a Pew research poll found that 51% in the United States thought that UFOs reported by people in the military were likely to be evidence of intelligent life from beyond the Earth.^[60] In August 2021, Gallup, with a question not specific to military reports, only found that 41% of adults believed some UFOs involve alien spacecraft from other planets. This Gallup poll showed 44% of men and 38% of women believed this. This average of 41% in 2021 was up from 33% in a 2019 Gallup poll with the same question. Gallup further found that college graduates went in 2019 from being the least likely educational group to believe this to being on par in 2021 with adults who have no college education.^[61] An October 2022 poll by YouGov only found that 34% of Americans believe that UFOs are likely to involve alien life forms.^[62]

Historian Greg Eghigian wrote in August 2021 that "over the last fifty years, the mutual antagonism between paranormal believers and skeptics has largely framed discussion about unidentified flying objects" and that "it often gets personal" with those taking seriously the prospect that UFOs are extraterrestrial in origin dismissing those who consider UFOs to be worth studying as "narrow-minded, biased, obstinate, and cruel" while the skeptics brushed off "devotees" as "naïve, ignorant, gullible, and downright dangerous". Such "mudslinging over convictions is certainly familiar to historians of religion, a domain of human existence marked by deep divisions over interpretations of belief", and science too has found itself engaged increasing amounts of "boundary work" (which is "asserting and reasserting the borders between legitimate and illegitimate scientific research and ideas, between what may and what may not refer to itself as science") with regard to UFO questions. Eghigian points out our current "stark divide did not happen overnight, and its roots lie in the postwar decades, in a series of events that—with their news coverage, grainy images, celebrity crusaders, exasperated skeptics, unsatisfying military statements, and accusations of a government cover-up—foreshadow our present moment".^[27]

UFOs have been taken up by religious studies scholars in various scholarly books.^[63][64][65] Jeffrey Kripal, chair of the Department of Religion at Rice University, has said that "both the material and the mental dimensions [of UFOs] are incredibly important to get a sense of the full picture".^[66] As Adrian Horton writes "from The X-Files to Men in Black, Close Encounters of the Third Kind to Star Wars to Marvel, Hollywood has for decades provided an engrossing feedback loop for interest in the extraterrestrial: a reflection of our fears and capaciousness, whose ubiquitous popularity has in turn fueled more interest in UFOs as perennially compelling entertainment tropes not to be taken seriously". Horton observes that these "alien movies have generally reflected shifting cultural anxieties, from the existential terror of nuclear war to foreign enslavement to loss of bodily control". American entertainment has explored both "hostile aliens" as well as the "benevolent, world-expanding encounters" seen in films such as Steven Spielberg's Close Encounters of the Third Kind and E.T. the Extra-Terrestrial.^[67] In her research on the relationship of media to UFO beliefs, Diana Walsh Pasulka, a professor of philosophy and religion at the University of North Carolina, says that what is seen on a screen, "if it conforms to certain criteria, is interpreted as real, even if it is not real and even if one knows it is not real" and that "screen images embed themselves in one's brain and memories" in ways that "can determine how one views one's past and even determine one's future behaviors".^[68]

• The Rendlesham Forest incident was a series of reported sightings of unexplained lights near Rendlesham Forest in Suffolk, England in late December 1980 which became linked with claims of UFO landings.

The most notable cases of UFO sightings in France include:

• the Valensole UFO incident in 1965.
• the Trans-en-Provence Case in 1981.

• In the Kecksburg UFO incident, Pennsylvania (1965), residents reported seeing an object crash in the area.
• In 1975, Travis Walton claimed to be abducted by aliens. The movie Fire in the Sky (1993) was based on this event, but greatly embellished the original account.
• The "Phoenix Lights" on March 13, 1997

The USAF's Project Blue Book files indicate that approximately 1% of all unknown reports^[69] came from amateur and professional astronomers or other telescope users (such as missile trackers or surveyors). In 1952, astronomer J. Allen Hynek, then a consultant to Blue Book, conducted a small survey of 45 fellow professional astronomers. Five reported UFO sightings (about 11%). In the 1970s, astrophysicist Peter A. Sturrock conducted two large surveys of the AIAA and American Astronomical Society (AAS). About 5% of the members polled indicated that they had had UFO sightings.

Astronomer Clyde Tombaugh, who saw six UFOs, including three green fireballs, supported the extraterrestrial hypothesis for UFOs and said scientists who dismissed it without study were "unscientific". Another astronomer, Lincoln LaPaz, headed the United States Air Force's investigation into green fireballs and other UFO phenomena in New Mexico. LaPaz reported two personal sightings, of a green fireball and a disc. (Both Tombaugh and LaPaz were part of Hynek's 1952 survey.) Hynek took two photos through the window of a commercial airliner of a disc that seemed to keep pace with his aircraft.^[70]

Astronomer Andrew Fraknoi rejected the hypothesis that UFOs are extraterrestrial spacecraft and responded to the "onslaught of credulous coverage" in books, films and entertainment by teaching his students to apply critical thinking to such claims, advising them that "being a good scientist is not unlike being a good detective". According to Fraknoi, UFO reports "might at first seem mysterious", but "the more you investigate, the more likely you are to find that there is LESS to these stories than meets the eye".^[71]

In a 1980 survey of 1800 members of amateur astronomer associations by Gert Helb and Hynek for CUFOS, 24% responded "yes" to the question "Have you ever observed an object which resisted your most exhaustive efforts at identification?"^[72]

• The Maury Island incident
• George Adamski, over the space of two decades, made various claims about his meetings with telepathic aliens from nearby planets. He claimed photographs of the far side of the Moon taken by the Soviet lunar probe Luna 3 in 1959 were fake, and that there were cities, trees and snow-capped mountains on the far side of the Moon. Among copycats was a shadowy British figure named Cedric Allingham.
• Ed Walters, a building contractor, in 1987 allegedly perpetrated a hoax in Gulf Breeze, Florida. Walters claimed at first having seen a small UFO flying near his home and took some photographs of the craft. Walters reported and documented a series of UFO sightings over a period of three weeks and took several photographs. These sightings became famous, and are collectively referred to as the Gulf Breeze UFO incident. Three years later, in 1990, after the Walters family had moved, the new residents discovered a model of a UFO poorly hidden in the attic that bore an undeniable resemblance to the craft in Walters' photographs. Most investigators, like the forensic photo expert William G. Hyzer,^[73] now consider the sightings to be a hoax.

According to Merriam-Webster, "the term UAP first appeared in the late 1960s, while UFO has been around since 1947".^[74] The Oxford English Dictionary defines a UFO as "An unidentified flying object; a 'flying saucer'". The first published book to use the word was authored by Donald E. Keyhoe.^[75] The term "UFO" (or "UFOB") was adopted as a standard in 1953 by the United States Air Force (USAF) to serve as a catch-all for all such reports. In its initial definition, the USAF stated that a "UFOB" was "any airborne object which by performance, aerodynamic characteristics, or unusual features, does not conform to any presently known aircraft or missile type, or which cannot be positively identified as a familiar object". Accordingly, the term was initially restricted to that fraction of cases which remained unidentified after investigation, as the USAF was interested in potential national security reasons and "technical aspects" (see Air Force Regulation 200-2).

During the late 1940s and through the 1950s, UFOs were often referred to popularly as "flying saucers" or "flying discs" due to the term being introduced in the context of the Kenneth Arnold incident. The Avro Canada VZ-9AV Avrocar was a concept vehicle produced during the 1950s, which was a functional aircraft with a saucer shape.^[76] UFOs were commonly referred to colloquially, as a "Bogey" by Western military personnel and pilots during the cold war. The term "bogey" was originally used to report anomalies in radar blips, to indicate possible hostile forces that might be roaming in the area.^[77]

The term UFO became more widespread during the 1950s, at first in technical literature, but later in popular use. UFOs garnered considerable interest during the Cold War, an era associated with heightened concerns about national security, and, more recently, in the 2010s, for unexplained reasons.^[78][79] Nevertheless, various studies have concluded that the phenomenon does not represent a threat, and nor does it contain anything worthy of scientific pursuit (e.g., 1951 Flying Saucer Working Party, 1953 CIA Robertson Panel, USAF Project Blue Book, Condon Committee).

As an acronym, "UFO" was coined by Captain Edward J. Ruppelt, who headed Project Blue Book, then the USAF's official investigation of UFOs. He wrote, "Obviously the term 'flying saucer' is misleading when applied to objects of every conceivable shape and performance. For this reason the military prefers the more general, if less colorful, name: unidentified flying objects. UFO (pronounced yoo-foe) for short."^[80] Other phrases that were used officially and that predate the UFO acronym include "flying flapjack", "flying disc", "unexplained flying discs", and "unidentifiable object".^[81][82][83]

In popular usage, the term UFO came to be used to refer to claims of alien spacecraft,^[75] and because of the public and media ridicule associated with the topic, some ufologists and investigators prefer to use terms such as "unidentified aerial phenomenon" (UAP) or simply "anomalous phenomena", as in the name of the National Aviation Reporting Center on Anomalous Phenomena (NARCAP).^[84] "Anomalous aerial vehicle" (AAV) or "unidentified aerial system" (UAS) are also sometimes used in a military aviation context to describe unidentified targets.^[85]

More recently, U.S. officials have adopted the term "unidentified aerial phenomenon"^[86] (UAP), sometimes expanded as "unidentified anomalous phenomenon"^[87] (see below). As summarized in ETC: A Review of General Semantics, "aside from UAP's more encompassing description, this term avoids the heavy cultural baggage attached to UFO, whose initial association with extraterrestrial origins ...sets up a narrow and inflexible framework for honest scientific research."^[88] The term UFO now has decades of association with aliens across many areas of culture, popular entertainment, conspiracy theories, and religious movements as considered in American Cosmic by Diana Walsh Pasulka (published by Oxford in 2019).^[89] "Unidentified aerial phenomena (UAP), formerly referred to as UFOs, in theory, could include alien spacecraft, but the two aren't synonymous."^[90]

The National Defense Authorization Act for Fiscal Year 2023 (signed into law on December 23, 2022)^[91] defined "unidentified anomalous phenomena" in 50 U.S.C. § 3373(n)(8) to include not only "airborne objects" but also "submerged objects or devices" and "transmedium objects or devices" that are not immediately identifiable. In 2023, NASA's UAPIST study team changed the official meaning of the "A" in its name from "Aerial" to "Anomalous" to reflect their new mission as an "All-Anomaly" task force.^[91][87]

While technically a UFO refers to any unidentified flying object, in modern popular culture the term UFO has generally become synonymous with alien spacecraft;^[92] however, the term ETV (extra-terrestrial vehicle) is sometimes used to separate this explanation of UFOs from totally earthbound explanations,^[93] including the cryptoterrestrial hypothesis, or from other interpretations of the phenomenon such as the interdimensional hypothesis, the time-traveler hypothesis or the psychosocial hypothesis.

UFOs have been subject to investigations over the years that varied widely in scope and scientific rigor. Governments or independent academics in the United States, Canada, the United Kingdom, Japan, Peru, France, Belgium, Sweden, Brazil, Chile, Uruguay, Mexico, Spain, and the Soviet Union are known to have investigated UFO reports at various times. No official government investigation has ever publicly concluded that UFOs are indisputably real, physical objects, extraterrestrial in origin, or of concern to national defense.

Among the best known government studies are the ghost rockets investigation by the Swedish military (1946–1947), Project Blue Book, previously Project Sign and Project Grudge, conducted by the USAF from 1947 until 1969, the secret U.S. Army/Air Force Project Twinkle investigation into green fireballs (1948–1951), the secret USAF Project Blue Book Special Report No. 14^[94] by the Battelle Memorial Institute, and the Brazilian Air Force's 1977 Operação Prato (Operation Saucer). France has had an ongoing investigation (GEPAN/SEPRA/GEIPAN) within its space agency Centre national d'études spatiales (CNES) since 1977; the government of Uruguay has had a similar investigation since 1989.

Studies show that after careful investigation, the majority of UFOs can be identified as ordinary objects or phenomena. The most commonly found identified sources of UFO reports are:

• astronomical objects (bright stars, bolides, bright planets, and the Moon)
• aircraft (including military, civilian, and experimental aircraft as well as such peculiarities as aerial advertising, missile and other rocket launches, artificial satellites, re-entering spacecraft including space debris, kites, and various unmanned aerial vehicles often popularly termed "drones")
• balloons (surveillance balloons, toy balloons, weather balloons, large research balloons)
• other atmospheric objects and phenomena (birds, unusual clouds, flares, plasma)
• light phenomena (mirages, Fata Morgana, ball lightning, moon dogs, satellite flares, searchlights and other ground lights, etc.)
• psychological effects (pareidolia, suggestibility and false memories, mass psychogenic disorders, optical illusions, and hallucinations)
• hoaxes

A 1952–1955 study by the Battelle Memorial Institute for the USAF included these categories. An individual 1979 study by CUFOS researcher Allan Hendry found, as did other investigations, that fewer than one percent of cases he investigated were hoaxes and most sightings were actually honest misidentifications of prosaic phenomena. Hendry attributed most of these to inexperience or misperception.^[96]

On October 31, 2008, the National Archives of Brazil began receiving from the Aeronautical Documentation and History Center part of the documentation of the Brazilian Air Force regarding the investigation of the appearance of UFOs in Brazil. Currently, this collection gathers cases between 1952 and 2016.^[97]

In 1968, the SEFAA (previously CEFAA) began receiving case reports of the general public, civil aviators and the Chilean Air Force regarding the sightings or the appearance of UFOs in Chile, the initial work was an initiative of Sergio Bravo Flores who led the Chilean Committee for the Study of Unidentified Space Phenomena, supported even by the Chilean Scientific Society. Currently, the organization changed its denomination to SEFAA and its a department of the DGAC(Chile) which in turn depends on the Chilean Air Force.^[98]

In Canada, the Department of National Defence has dealt with reports, sightings and investigations of UFOs across Canada. In addition to conducting investigations into crop circles in Duhamel, Alberta, it still considers "unsolved" the Falcon Lake incident in Manitoba and the Shag Harbour UFO incident in Nova Scotia.^[99]

Early Canadian studies included Project Magnet (1950–1954) and Project Second Storey (1952–1954), supported by the Defence Research Board.

U.S. investigations into UFOs include:

• Project Sign, by the Air Materiel Command (AMC) USAF, precursor to Project Grudge, 1948.
• Ghost rockets investigations by the Finnish, Swedish and British militaries, later the US and Greece, 1946–1947.
• Project Grudge, USAF from February 1949, succeeded by Project Blue Book, from March 1952.
• Project Twinkle investigation into green fireballs, by the U.S. Army/Air Force, briefly, from December 1949.
• The Central Intelligence Agency Directorate of Science & Technology (DS&T), study 1952–53.
• The Report on Unidentified Flying Objects, by USAF Cpt (rtd.), later director of Project Blue Book, 1956.
• The Project Blue Book Special Report No. 14 by the Battelle Memorial Institute for USAF, 1951–1954
• The Aerial Phenomena Research Organization (APRO), a private research group, 1952–1988.
• The Robertson Panel was a scientific committee which met in January 1953 to review the Project Blue Book report January 1953
• The Brookings Report, Proposed Studies on the Implications of Peaceful Space Activities for Human Affairs, in conjunction with NASA's Committee on Long-Range Studies, reported to Congress 1960
• The Condon Committee, an informal University of Colorado UFO Project funded by the USAF, 1966 to 1968.
• The RAND Corporation study, a private and internal study, 1968.^[100]
• The Mutual UFO Network (MUFON), is a US-based, civilian, non-profit, volunteer organization studying reported UFO sightings, May 1969 and continuing.
• The National Investigations Committee On Aerial Phenomena (NICAP) is a UFO research group most active in the United States from the 1950s to the 1980 and remains as an informational depository on UFO phenomena.
• The Center for UFO Studies (CUFOS), a privately funded UFO research group, 1973 and continuing.
• The Sturrock panel, private investigation arising from the Society for Scientific Exploration, 1982.
• The Advanced Aerospace Threat Identification Program which was funded from 2007 to 2012.^[48][49]
• The All-domain Anomaly Resolution Office, a continuing program within the United States Office of Naval Intelligence which was acknowledged in 2017.
• The Airborne Object Identification and Management Synchronization Group, the Pentagon, to investigate unidentified objects that may compromise the airspace of the United States, from November 24, 2021, ongoing.^[101]

In addition to these, thousands of documents released under FOIA also indicate that many U.S. intelligence agencies collected (and still collect) information on UFOs. These agencies include the Defense Intelligence Agency (DIA), FBI,^[83] CIA, National Security Agency (NSA), as well as military intelligence agencies of the Army and U.S. Navy, in addition to the Air Force.^{[note 1]}

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Following the large U.S. surge in sightings in June and early July 1947, on July 9, 1947, United States Army Air Forces (USAAF) intelligence, in cooperation with the FBI,^[83] began a formal investigation into selected sightings with characteristics that could not be immediately rationalized, such as Kenneth Arnold's. The USAAF used "all of its top scientists" to determine whether "such a phenomenon could, in fact, occur". The research was "being conducted with the thought that the flying objects might be a celestial phenomenon," or that "they might be a foreign body mechanically devised and controlled."^[102] Three weeks later in a preliminary defense estimate, the air force investigation decided that, "This 'flying saucer' situation is not all imaginary or seeing too much in some natural phenomenon. Something is really flying around."^[103]

A further review by the intelligence and technical divisions of the Air Materiel Command at Wright Field reached the same conclusion. It reported that "the phenomenon is something real and not visionary or fictitious," and there were disc-shaped objects, metallic in appearance, as big as man-made aircraft. They were characterized by "extreme rates of climb [and] maneuverability", general lack of noise, absence of a trail, occasional formation flying, and "evasive" behavior "when sighted or contacted by friendly aircraft and radar", suggesting a controlled craft. It was therefore recommended in late September 1947 that an official Air Force investigation be set up. It was also recommended that other government agencies should assist in the investigation.^{[note 2]}

Project Sign's final report, published in early 1949, stated that while some UFOs appeared to represent actual aircraft, there was not enough data to determine their origin.^[104]

The Air Force's Project Sign was created at the end of 1947, and was one of the earliest government studies to come to a secret extraterrestrial conclusion. In August 1948, Sign investigators wrote a top-secret intelligence estimate to that effect, but the Air Force Chief of Staff Hoyt Vandenberg ordered it destroyed. The existence of this suppressed report was revealed by several insiders who had read it, such as astronomer and USAF consultant J. Allen Hynek and Capt. Edward J. Ruppelt, the first head of the USAF's Project Blue Book.^[105]

Another highly classified U.S. study was conducted by the CIA's Office of Scientific Investigation (OS/I) in the latter half of 1952 in response to orders from the National Security Council (NSC). This study concluded UFOs were real physical objects of potential threat to national security. One OS/I memo to the CIA Director (DCI) in December read that "the reports of incidents convince us that there is something going on that must have immediate attention ... Sightings of unexplained objects at great altitudes and traveling at high speeds in the vicinity of major U.S. defense installations are of such a nature that they are not attributable to natural phenomena or any known types of aerial vehicles."^[106]

The matter was considered so urgent that OS/I drafted a memorandum from the DCI to the NSC proposing that the NSC establish an investigation of UFOs as a priority project throughout the intelligence and the defense research and development community. It also urged the DCI to establish an external research project of top-level scientists, now known as the Robertson Panel to analyze the problem of UFOs. The OS/I investigation was called off after the Robertson Panel's negative conclusions in January 1953.^[106]

Project Sign was dismantled and became Project Grudge at the end of 1948. Angered by the low quality of investigations by Grudge, the Air Force Director of Intelligence reorganized it as Project Blue Book in late 1951, placing Ruppelt in charge. J. Allen Hynek, a trained astronomer who served as a scientific advisor for Project Blue Book, was initially skeptical of UFO reports, but eventually came to the conclusion that many of them could not be satisfactorily explained and was highly critical of what he described as "the cavalier disregard by Project Blue Book of the principles of scientific investigation".^[107] Leaving government work, he founded the privately funded CUFOS, to whose work he devoted the rest of his life. Other private groups studying the phenomenon include the MUFON, a grassroots organization whose investigator's handbooks go into great detail on the documentation of alleged UFO sightings.

Air Force Regulation 200-2,^[108] issued in 1953 and 1954, defined an Unidentified Flying Object ("UFOB") as "any airborne object which by performance, aerodynamic characteristics, or unusual features, does not conform to any presently known aircraft or missile type, or which cannot be positively identified as a familiar object." The regulation also said UFOBs were to be investigated as a "possible threat to the security of the United States" and "to determine technical aspects involved." The regulation went on to say that "it is permissible to inform news media representatives on UFOB's when the object is positively identified as a familiar object" but added: "For those objects which are not explainable, only the fact that ATIC [Air Technical Intelligence Center] will analyze the data is worthy of release, due to many unknowns involved."^[108]

A public research effort conducted by the Condon Committee for the USAF and published as the Condon Report arrived at a negative conclusion in 1968.^[109] Blue Book closed down in 1970, using the Condon Committee's negative conclusion as a rationale, thus ending official Air Force UFO investigations. However, a 1969 USAF document, known as the Bolender memo, along with later government documents, revealed that non-public U.S. government UFO investigations continued after 1970. The Bolender memo first stated that "reports of unidentified flying objects that could affect national security ... are not part of the Blue Book system," indicating that more serious UFO incidents already were handled outside the public Blue Book investigation. The memo then added, "reports of UFOs which could affect national security would continue to be handled through the standard Air Force procedures designed for this purpose."^{[note 3]}

In the late 1960s, a chapter on UFOs in the Space Sciences course at the U.S. Air Force Academy gave serious consideration to possible extraterrestrial origins. When word of the curriculum became public, in 1970, the Air Force issued a statement to the effect that the book was outdated and cadets instead were being informed of the Condon Report's negative conclusion.^[110]

Controversy surrounded the report, both before and after its release. It has been observed that the report was "harshly criticized by numerous scientists, particularly at the powerful AIAA ... [which] recommended moderate, but continuous scientific work on UFOs."^[109] In an address to the AAAS, James E. McDonald said he believed science had failed to mount adequate studies of the problem and criticized the Condon Report and earlier studies by the USAF as scientifically deficient. He also questioned the basis for Condon's conclusions^[111] and argued that the reports of UFOs have been "laughed out of scientific court".^[112] J. Allen Hynek, an astronomer who worked as a USAF consultant from 1948, sharply criticized the Condon Committee Report and later wrote two nontechnical books that set forth the case for continuing to investigate UFO reports.

Ruppelt recounted his experiences with Project Blue Book, a USAF investigation that preceded Condon's.^[113]

According to a 1979 New York Times report, "records from the C.I.A., the F.B.I. and other Federal agencies" ("about 900 documents—nearly 900 pages of memos, reports and correspondence") obtained in 1978 through the Freedom of Information Act request, indicate that "despite official pronouncements for decades that U.F.O.'s were nothing more than misidentified aerial objects and as such were no cause for alarm ... the phenomenon has aroused much serious behind‐the‐scenes concern" in the US government. In particular, officials were concerned over the "approximately 10%" of UFO sightings which remained unexplained, and whether they might be Soviet aircraft and a threat to national security.^[114] Officials were concerned about the "risk of false alerts", of "falsely identifying the real as phantom", and of mass hysteria caused by sightings. In 1947, Brigadier General George F. Schulgen of Army Air Corps Intelligence, warned "the first reported sightings might have been by individuals of Communist sympathies with the view to causing hysteria and fear of a secret Russian weapon."^[114]

In November 2011, the White House released an official response to two petitions asking the U.S. government to acknowledge formally that aliens have visited this planet and to disclose any intentional withholding of government interactions with extraterrestrial beings. According to the response:

The U.S. government has no evidence that any life exists outside our planet, or that an extraterrestrial presence has contacted or engaged any member of the human race...no credible information to suggest that any evidence is being hidden from the public's eye....

— Statement by the White House^[115][116]

The response further noted that efforts, like SETI and NASA's Kepler space telescope and Mars Science Laboratory, continue looking for signs of life. The response noted "odds are pretty high" that there may be life on other planets but "the odds of us making contact with any of them—especially any intelligent ones—are extremely small, given the distances involved."^[115][116]

On June 25, 2021, the Office of the Director of National Intelligence released a report on UAPs.^[117] The report found that the UAPTF was unable to identify 143 objects spotted between 2004 and 2021. The report said that 18 of these featured unusual movement patterns or flight characteristics, adding that more analysis was needed to determine if those sightings represented "breakthrough" technology. The report said that "some of these steps are resource-intensive and would require additional investment."^[118] The report did not link the sightings to extraterrestrial life.^[119][120]

The Uruguayan Air Force has conducted UFO investigations since 1989 and reportedly analyzed 2,100 cases of which they regard approximately 2% as lacking explanation.^[121]

In March 2007, the French space agency CNES published an archive of UFO sightings and other phenomena online.^[122]

French studies include GEPAN/SEPRA/GEIPAN within CNES (French space agency), the longest ongoing government-sponsored investigation. About 22% of the 6,000 cases studied remain unexplained.^[123] The official opinion of GEPAN/SEPRA/GEIPAN has been neutral, stating on their FAQ page that their mission is fact-finding for the scientific community, not rendering an opinion. They add they can neither prove nor disprove the Extraterrestrial Hypothesis (ETH), but their Steering Committee's clear position is that they cannot discard the possibility that some fraction of the very strange 22% of unexplained cases might be due to distant and advanced civilizations.^[124]

Possibly their bias may be indicated by their use of the terms "PAN" (French) or "UAP" (English equivalent) for "Unidentified Aerospace Phenomenon" (whereas "UAP" is normally used by English organizations stands for "Unidentified Aerial Phenomenon", a more neutral term). In addition, the three heads of the studies have gone on record in stating that UFOs were real physical flying machines beyond our knowledge or that the best explanation for the most inexplicable cases was an extraterrestrial one.^{[125][126][127]} In 2007, the CNES's own report stated that, at that time, 28% of sightings remained unidentified.^[128]

In 2008, Michel Scheller, president of the Association Aéronautique et Astronautique de France (3AF), created the Sigma Commission. Its purpose was to investigate UFO phenomena worldwide.^[129] A progress report published in May 2010 stated that the central hypothesis proposed by the COMETA report is perfectly credible.^[130] In December 2012, the final report of the Sigma Commission was submitted to Scheller. Following the submission of the final report, the Sigma2 Commission is to be formed with a mandate to continue the scientific investigation of UFO phenomena.^[131][132]

Alleged UFO sightings gradually increased since the war, peaking in 1978 and 2005. The total number of sightings since 1947 are 18,500, of which 90% are identifiable.^[133]

This section needs to be updated. Please help update this article to reflect recent events or newly available information. (December 2020)

The UK's Flying Saucer Working Party published its final report in June 1951, which remained secret for over fifty years. The Working Party concluded that all UFO sightings could be explained as misidentifications of ordinary objects or phenomena, optical illusions, psychological misperceptions/aberrations, or hoaxes. The report stated: "We accordingly recommend very strongly that no further investigation of reported mysterious aerial phenomena be undertaken, unless and until some material evidence becomes available."^[134]

Eight file collections on UFO sightings, dating from 1978 to 1987, were first released on May 14, 2008, to The National Archives by the Ministry of Defence (MoD).^[135] Although kept secret from the public for many years, most of the files have low levels of classification and none are classified Top Secret. 200 files are set to be made public by 2012. The files are correspondence from the public sent to the British government and officials, such as the MoD and Margaret Thatcher. The MoD released the files under the Freedom of Information Act due to requests from researchers.^[136] These files include, but are not limited to, UFOs over Liverpool and Waterloo Bridge in London.^[137]

On October 20, 2008, more UFO files were released. One case released detailed that in 1991 an Alitalia passenger aircraft was approaching London Heathrow Airport when the pilots saw what they described as a "cruise missile" fly extremely close to the cockpit. The pilots believed a collision was imminent. UFO expert David Clarke says this is one of the most convincing cases for a UFO he has come across.^[138]

A secret study of UFOs was undertaken for the Ministry of Defence between 1996 and 2000 and was code-named Project Condign. The resulting report, titled "Unidentified Aerial Phenomena in the UK Defence Region", was publicly released in 2006, but the identity and credentials of whoever constituted Project Condign remains classified. The report confirmed earlier findings that the main causes of UFO sightings are misidentification of man-made and natural objects. The report noted: "No artefacts of unknown or unexplained origin have been reported or handed to the UK authorities, despite thousands of Unidentified Aerial Phenomena reports. There are no SIGINT, ELINT or radiation measurements and little useful video or still IMINT."^[139]

It concluded: "There is no evidence that any UAP, seen in the UKADR [UK Air Defence Region], are incursions by air-objects of any intelligent (extraterrestrial or foreign) origin, or that they represent any hostile intent." A little-discussed conclusion of the report was that novel meteorological plasma phenomenon akin to ball lightning are responsible for "the majority, if not all" of otherwise inexplicable sightings, especially reports of black triangle UFOs.^[139]

On December 1, 2009, the Ministry of Defence quietly closed down its UFO investigations unit. The unit's hotline and email address were suspended by the MoD on that date. The MoD said there was no value in continuing to receive and investigate sightings in a release, stating that "in over fifty years, no UFO report has revealed any evidence of a potential threat to the United Kingdom. The MoD has no specific capability for identifying the nature of such sightings. There is no Defence benefit in such investigation and it would be an inappropriate use of defence resources. Furthermore, responding to reported UFO sightings diverts MoD resources from tasks that are relevant to Defence." The Guardian reported that the MoD claimed the closure would save the Ministry around £50,000 a year. The MoD said it would continue to release UFO files to the public through The National Archives.^[140]

UFO reports, Parliamentary questions, and letters from members of the public were released on August 5, 2010, to the UK National Archives. "In one letter included in the files, a man alleges Churchill ordered a coverup of a WW II-era UFO encounter involving the Royal Air Force".^[141][135]

Reports of UFO sightings continue. According to The Independent, there were 957 reported UFO sightings across the UK between January 2021 and May 2023, with Manchester, London, Liverpool, and Glasgow being hotspots.^[142]

Critics argue that all UFO evidence is anecdotal^[143] and can be explained as prosaic natural phenomena. Defenders of UFO research counter that knowledge of observational data, other than what is reported in the popular media, is limited in the scientific community and further study is needed.^[144][145] Studies have established that the majority of UFO observations are misidentified conventional objects or natural phenomena—most commonly aircraft, balloons including sky lanterns, satellites, and astronomical objects such as meteors, bright stars and planets. A small percentage are hoaxes.^{[note 4]}

Fewer than 10% of reported sightings remain unexplained after proper investigation and therefore can be classified as unidentified in the strictest sense. According to Steven Novella, proponents of the extraterrestrial hypothesis (ETH) suggest these unexplained reports are of alien spacecraft, however the null hypothesis cannot be excluded; that these reports are simply other more prosaic phenomena that cannot be identified due to lack of complete information or due to the necessary subjectivity of the reports. Novella says that instead of accepting the null hypothesis, UFO enthusiasts tend to engage in special pleading by offering outlandish, untested explanations for the validity of the ETH, which violate Occam's razor.^[146]

Historically, ufology has not been considered credible in mainstream science.^[147] The scientific community has generally deemed that UFO sightings are not worthy of serious investigation except as a cultural artifact.^{[148][112][109][149][150][151][152]}

Studies of UFOs rarely appear in mainstream scientific literature. When asked, some scientists and scientific organizations have pointed to the end of official governmental studies in the U.S. in December 1969, following the statement by the government scientist Edward Condon that further study of UFOs could not be justified on grounds of scientific advancement.^[109][153]

Nevertheless, on 14 September 2023, NASA reported the appointment, for the first time, of a Director of U.A.P. (known earlier as U.F.O.), identified as Mark McInerney, to scientifically, and transparently, study such occurrences.^[154]

Jacques Vallée, a scientist and ufologist, claimed there were deficiencies in most UFO research, including government studies. He criticized the mythology and cultism often associated with UFO sightings, but despite the challenges, Vallée contended that several hundred professional scientists—a group both he and Hynek termed "the invisible college"—continued to study UFOs quietly on their own time.^[144]

UFOs have become a prevalent theme in modern culture,^[144] and the social phenomena have been the subject of academic research in sociology and psychology.^[147]

Besides anecdotal visual sightings, reports sometimes include claims of other kinds of evidence, including cases studied by the military and various government agencies of different countries (such as Project Blue Book, the Condon Committee, the French GEPAN/SEPRA, and Uruguay's current Air Force study).

A comprehensive scientific review of cases where physical evidence was available was carried out by the 1998 Sturrock panel, with specific examples of many of the categories listed below.

• Radar contact and tracking, sometimes from multiple sites. These have included military personnel and control tower operators, simultaneous visual sightings, and aircraft intercepts. One such example was the mass sightings of large, silent, low-flying black triangles in 1989 and 1990 over Belgium, tracked by NATO radar and jet interceptors, and investigated by Belgium's military (included photographic evidence). Another famous case from 1986 was the Japan Air Lines flight 1628 incident over Alaska investigated by the Federal Aviation Administration (FAA).
• Photographic evidence, including still photos, movie film, and video.
• Claims of physical trace of landing UFOs, including ground impressions, burned or desiccated soil, burned and broken foliage, magnetic anomalies^[specify], increased radiation levels, and metallic traces. (See, e. g. Height 611 UFO incident or the 1964 Lonnie Zamora's Socorro, New Mexico encounter of the USAF Project Blue Book cases.) A well-known example from December 1980 was the USAF Rendlesham Forest incident in England. Another occurred in January 1981 in Trans-en-Provence and was investigated by GEPAN, then France's official government UFO-investigation agency. Project Blue Book head Edward J. Ruppelt described a classic 1952 CE2 case involving a patch of charred grass roots.
• Physiological effects on people and animals including temporary paralysis, skin burns and rashes, corneal burns, and symptoms superficially resembling radiation poisoning, such as the Cash-Landrum incident in 1980.
• Animal/cattle mutilation cases, which some feel are also part of the UFO phenomenon.
• Biological effects on plants such as increased or decreased growth, germination effects on seeds, and blown-out stem nodes (usually associated with physical trace cases or crop circles)
• Electromagnetic interference (EM) effects. A famous 1976 military case over Tehran, recorded in CIA and DIA classified documents, was associated with communication losses in multiple aircraft and weapons system failure in an F-4 Phantom II jet interceptor as it was about to fire a missile on one of the UFOs.^[184]
• Apparent remote radiation detection, some noted in FBI and CIA documents occurring over government nuclear installations at Los Alamos National Laboratory and Oak Ridge National Laboratory in 1950, also reported by Project Blue Book director Edward J. Ruppelt in his book.
• Claimed artifacts of UFOs themselves, such as 1957, Ubatuba, Brazil, magnesium fragments analyzed by the Brazilian government and in the Condon Report and by others. The 1964 Lonnie Zamora incident also left metal traces, analyzed by NASA.^[185][186] A more recent example involves a teardrop-shaped object recovered by Bob White and was featured in a television episode of UFO Hunters^[187] but was later found to be accumulated waste metal residue from a grinding machine.^[188]
• Angel hair and angel grass, possibly explained in some cases as nests from ballooning spiders or chaff.^[189]

A scientifically skeptical group that has for many years offered critical analyses of UFO claims is the Committee for Skeptical Inquiry (CSI). One example is the response to local beliefs that "extraterrestrial beings" in UFOs were responsible for crop circles appearing in Indonesia, which the government and the National Institute of Aeronautics and Space (LAPAN) described as "man-made". Thomas Djamaluddin, research professor of astronomy and astrophysics at LAPAN stated: "We have come to agree that this 'thing' cannot be scientifically proven. Scientists have put UFOs in the category of pseudoscience."^[190]

UFOs have been the subject of investigations by various governments that have provided extensive records related to the subject. Many of the most involved government-sponsored investigations ended after agencies concluded that there was no benefit to continued investigation.^[191][192] These same negative conclusions also have been found in studies that were highly classified for many years, such as the UK's Flying Saucer Working Party, Project Condign, the U.S. CIA-sponsored Robertson Panel, the U.S. military investigation into the green fireballs from 1948 to 1951, and the Battelle Memorial Institute study for the USAF from 1952 to 1955 (Project Blue Book Special Report No. 14).

Some public government reports have acknowledged the possibility of the physical reality of UFOs, but have stopped short of proposing extraterrestrial origins, though not dismissing the possibility entirely. Examples are the Belgian military investigation into large triangles over their airspace in 1989–1991 and the 2009 Uruguayan Air Force study conclusion (see below).

In 2007, former Arizona governor Fife Symington claimed he had seen "a massive, delta-shaped craft silently navigate over Squaw Peak, a mountain range in Phoenix, Arizona" in 1997.^[193] Apollo 14 astronaut Edgar Mitchell claimed he knew of senior government employees who had been involved in "close encounters", and because of this, he has no doubt that aliens have visited Earth.^[194]

In May 2019, The New York Times reported that American Navy fighter jets had several instances of unidentified instrumentation and tracking data while conducting exercises off the eastern seaboard of the United States from the summer of 2014 to March 2015. The Times published a cockpit instrument video that appeared to show an object moving at high speed near the ocean surface as it appeared to rotate, and objects that appeared capable of high acceleration, deceleration and maneuverability. In two separate incidents, a pilot reported his cockpit instruments locked onto and tracked objects but he was unable to see them through his helmet camera. In another encounter, flight instruments recorded an image described as a sphere encasing a cube between two jets as they flew about 100 feet apart.^[195] The Pentagon officially released these videos on April 27, 2020.^[196] The United States Navy has said there have been "a number of reports of unauthorized and/or unidentified aircraft entering various military-controlled ranges and designated air space in recent years".^[197]

In March 2021, news media announced a comprehensive report is to be compiled of UFO events accumulated by the United States over the years.^[198]

On April 12, 2021, the Pentagon confirmed the authenticity of pictures and videos gathered by the Unidentified Aerial Phenomena Task Force (UAPTF), purportedly showing "pyramid shaped objects" hovering above the USS Russell in 2019, off the coast of California, with spokeswoman Susan Gough saying "I can confirm that the referenced photos and videos were taken by Navy personnel. The UAPTF has included these incidents in their ongoing examinations."^{[199][200][201][197]}

In May 2021, military pilots recalled their related encounters, along with camera and radar support, including one pilot's account noting that such incidents occurred "every day for at least a couple of years", according to an interview broadcast on the news program, 60 Minutes (May 16, 2021).^[202][203] Science writer and skeptic Mick West suggested the image was the result of an optical effect called a bokeh which can make out of focus light sources appear triangular or pyramidal due to the shape of the aperture of some lenses.^[204][205] In August, 2022, an article by West provided his detailed analysis of the video.^[206]

On June 25, 2021, U.S. Defense and intelligence officials released the nine pages Pentagon UFO Report (Preliminary Assessment: Unidentified Aerial Phenomena) on what they know about a series of unidentified flying objects that have been seen by American military pilots in the skies between 2004 and 2021.^{[207] [208]} The document refers to UAP rather than UFO.

The report does not mentions extraterrestrials, but instead warns of the phenomenon's potential threat to national security, which was the primary motive for writing the study. It concludes that the objects found by the US military appear to be real in the majority of the 144 occurrences documented. Only one of the cases described in the study was identified as a balloon.^[208]

"Most of the UAP reported probably do represent physical objects given that a majority of UAP were registered across multiple sensors, to include radar, infrared, electro-optical, weapon seekers, and visual observation", according to the report.^[208] The report also stated that "UAP probably lack a single explanation", and proposed five possible categories of explanation: airborne clutter, natural atmospheric phenomena, US government or industry development technology, foreign craft, and an "Other" category.^[209]

Commenting on the document, NASA Administrator Bill Nelson said that he did not think we are alone, but the UFO sightings by pilots "may not be extraterrestrial."^[210]

In December 2021, further official governmental investigations into UAPs and related, along with annual unclassified reports presented to Congress, have been authorized and funded.^[211] Some have raised concerns about the new investigations.^[212]

UFOs are sometimes an element of conspiracy theories in which governments are allegedly intentionally "covering up" the existence of aliens by removing physical evidence of their presence or even collaborating with extraterrestrial beings. There are many versions of this story; some are exclusive, while others overlap with various other conspiracy theories.

In the U.S., an opinion poll conducted in 1997 suggested that 80% of Americans believed the U.S. government was withholding such information.^[213][214] Various notables have also expressed such views. Some examples are astronauts Gordon Cooper and Edgar Mitchell, Senator Barry Goldwater, Vice Admiral Roscoe H. Hillenkoetter (the first CIA director), Lord Hill-Norton (former British Chief of Defense Staff and NATO head), the 1999 French COMETA study by various French generals and aerospace experts, and Yves Sillard (former director of CNES, new director of French UFO research organization GEIPAN).^[122]

In June 2023, United States Air Force officer and former intelligence official David Grusch claimed that the U.S. federal government has maintained a highly secretive UFO retrieval program since the 1940s and that the government possesses multiple spacecraft of "non-human" origin.^{[215][216][217][218]}

In May 2001, a press conference was held at the National Press Club in Washington, D.C., by an organization called the Disclosure Project, featuring twenty persons including retired Air Force and FAA personnel, intelligence officers and an air traffic controller.^{[219][220][221][222][223][224][225]} They all gave a brief account of their claims that evidence of UFOs was being suppressed and said they would be willing to testify under oath to a Congressional committee. According to a 2002 report in the Oregon Daily Emerald, Disclosure Project founder Steven M. Greer is an "alien theorist" who claims "proof of government coverup" consisting of 120 hours of testimony from various government officials on the topic of UFOs, including astronaut Gordon Cooper.^[226]

In 2007, the German UFO conspiracy forum Disclose.tv was created. The website's name references the concept of disclosure.^[227]

On September 27, 2010, a group of six former USAF officers and one former enlisted Air Force man held a press conference at the National Press Club in Washington, D.C., on the theme "U.S. Nuclear Weapons Have Been Compromised by Unidentified Aerial Objects"^[228] in which they claimed they had witnessed UFOs hovering near missile sites and even disarming the missiles.

From April 29 to May 3, 2013, the Paradigm Research Group held the "Citizen Hearing on Disclosure" at the National Press Club. The group paid former U.S. Senator Mike Gravel and former Representatives Carolyn Cheeks Kilpatrick, Roscoe Bartlett, Merrill Cook, Darlene Hooley, and Lynn Woolsey $20,000 each to hear testimony from a panel of researchers which included witnesses from military, agency, and political backgrounds.^[229][230]

The void left by the lack of institutional or scientific study has given rise to independent researchers and fringe groups, including the National Investigations Committee on Aerial Phenomena (NICAP) in the mid-20th century and, more recently, the Mutual UFO Network (MUFON)^[231] and the Center for UFO Studies (CUFOS).^[232] The term "Ufology" is used to describe the collective efforts of those who study reports and associated evidence of unidentified flying objects.^[233]

Some private studies have been neutral in their conclusions but argued that the inexplicable core cases call for continued scientific study. Examples are the Sturrock panel study of 1998 and the 1970 AIAA review of the Condon Report.

UFOs have been interpreted by some groups in a religious way, often influenced by the Theosophical tradition. Some Christians have interpreted UFOs as demonic entities.^[234]

Ufology is a neologism describing the collective efforts of those who study UFO reports and associated evidence.

UFOs have constituted a widespread international cultural phenomenon since the 1950s. Gallup Polls rank UFOs near the top of lists for subjects of widespread recognition. In 1973, a survey found that 95 percent of the public reported having heard of UFOs, whereas only 92 percent had heard of U.S. President Gerald Ford in a 1977 poll taken just nine months after he left the White House.^[235][236]

A 1996 Gallup Poll reported that 71 percent of the United States population believed the U.S. government was covering up information regarding UFOs. A 2002 Roper Poll for the Sci-Fi Channel found similar results, but with more people believing UFOs are extraterrestrial craft. In that latest poll, 56 percent thought UFOs were real craft and 48 percent that aliens had visited the Earth. Again, about 70 percent felt the government was not sharing everything it knew about UFOs or extraterrestrial life.^[237][238]

Another effect of the flying saucer type of UFO sightings has been Earth-made flying saucer craft in space fiction, for example the United Planets Cruiser C57D in Forbidden Planet (1956), the Jupiter 2 in Lost in Space, and the saucer section of the USS Enterprise in Star Trek. UFOs and extraterrestrials have been featured in many movies.

The intense secrecy surrounding the secret Nevada base, known as Area 51, has made it the frequent subject of conspiracy theories and a central component of UFO folklore. In July 2019, more than 2 million people responded to a joke proposal to storm Area 51 which appeared in an anonymous Facebook post.^[239] Two music festivals in rural Nevada, "AlienStock" and "Storm Area 51 Basecamp", were subsequently organized to capitalize on the popularity of the original Facebook event.^[240]

• "Government Reports on UFOs" from the Government Information Library at the University of Colorado Boulder
• "CIA's Role in the Study of UFOs, 1947–90" Archived October 1, 2019, at the Wayback Machine by Gerald K. Haines, Central Intelligence Agency
• "UFOs: Fact or Fiction?" Declassified CIA documents from the 1940s through the early 1990s.
• "UFO Reports in the UK" from 1997 to 2009 by the Ministry of Defence
• "Newly released UFO files from the UK government" at The National Archives
• "Canada's UFOs: The Search for the Unknown", a virtual museum exhibition by the Library and Archives Canada
• Declassified files on UFOs from many countries
• Declassified video – Chilean UAP event of November 11, 2014 (official; video (9:59))
• An astrophysicist's view of UFOs (Adam Frank; NYT; May 30, 2021)
• A list of skeptical resources (astronomer Andrew Fraknoi)
• UFO Explanations (videos; scientist Mick West)
• Some UAPs may be laser-generated holograms? (WSJ; July 29, 2021).
• UAPs need a high-resolution image (Avi Loeb; Scientific American; August 2, 2021).
• Video (92:50): U.S. Congressional Hearing on UFO/UAP (May 17, 2022) on YouTube.