The extraterrestrial hypothesis (ETH) proposes that some

unidentified flying object An unidentified flying object (UFO), more recently renamed by US officials as a UAP (unidentified aerial phenomenon), is any perceived aerial phenomenon that cannot be immediately identified or explained. On investigation, most UFOs are ide ...

s (UFOs) are best explained as being physical

spacecraft A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, p ...

occupied by extraterrestrial life or non-human aliens, or non-occupied alien probes from other planets visiting

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

Etymology

Origins of the term ''extraterrestrial hypothesis'' are unknown, but use in printed material on UFOs seems to date to at least the latter half of the 1960s. French

ufologist Ufology ( ) is the investigation of unidentified flying objects (UFOs) by people who believe that they may be of extraordinary origins (most frequently of extraterrestrial alien visitors). While there are instances of government, private, and ...

Jacques Vallée Jacques Fabrice Vallée (; born September 24, 1939) is an Internet pioneer, computer scientist, venture capitalist, author, ufologist and astronomer currently residing in San Francisco, California and Paris, France. His scientific career began ...

used it in his 1966 book ''Challenge to science: the UFO enigma''. It was used in a publication by French engineer Aimé Michel in 1967, by James E. McDonald in a symposium in March 1968 and again by McDonald and James Harder while testifying before the Congressional Committee on Science and Astronautics, in July 1968. Skeptic Philip J. Klass used it in his 1968 book ''UFOs--Identified.'' In 1969 physicist

Edward Condon Edward Uhler Condon (March 2, 1902 – March 26, 1974) was an American nuclear physicist, a pioneer in quantum mechanics, and a participant during World War II in the development of radar and, very briefly, of nuclear weapons as part of the ...

defined the "extraterrestrial hypothesis" or "ETH" as the "idea that ''some'' UFOs may be spacecraft sent to Earth from another civilization or space other than Earth, or on a planet associated with a more distant star," while presenting the findings of the much debated

Condon Report The Condon Committee was the informal name of the University of Colorado UFO Project, a group funded by the United States Air Force from 1966 to 1968 at the University of Colorado at Boulder, University of Colorado to study unidentified flying o ...

. Some UFO historians credit Condon with popularizing the term and its abbreviation "ETH."

Chronology

Although the extraterrestrial hypothesis (ETH) as a phrase is a comparatively new concept, one which owes much to the flying saucer sightings of the 1940s–1960s, its origins can be traced back to a number of earlier events, such as the now-discredited

Martian canals During the late 19th and early 20th centuries, it was erroneously believed that there were "canals" on the planet Mars. These were a network of long straight lines in the equatorial regions from 60° north to 60° south latitude on Mars, observed ...

and ancient Martian civilization promoted by astronomer

Percival Lowell Percival Lowell (; March 13, 1855 – November 12, 1916) was an American businessman, author, mathematician, and astronomer who fueled speculation that there were canals on Mars, and furthered theories of a ninth planet within the Solar System. ...

, popular culture including the writings of

H. G. Wells Herbert George Wells"Wells, H. G."
Revised 18 May 2015. ''

Edgar Rice Burroughs, who likewise wrote of Martian civilizations, and even to the works of figures such as the Swedish philosopher, mystic and scientist

Emanuel Swedenborg Emanuel Swedenborg (, ; born Emanuel Swedberg; 29 March 1772) was a Swedish pluralistic-Christian theologian, scientist, philosopher and mystic. He became best known for his book on the afterlife, ''Heaven and Hell'' (1758). Swedenborg had a ...

, who promoted a variety of unconventional views that linked other worlds to the afterlife.Swedenborg, Emanuel (1758) ''Concerning the Earths in Our Solar System ...'' In the early part of the 20th century,

Charles Fort Charles Hoy Fort (August 6, 1874 – May 3, 1932) was an American writer and researcher who specialized in anomalous phenomena. The terms "Fortean" and "Forteana" are sometimes used to characterize various such phenomena. Fort's books sold ...

collected accounts of anomalous physical phenomena from newspapers and scientific journals, including many reports of extraordinary aerial objects. These were published in 1919 in ''The Book of the Damned''. In this and two subsequent books, ''New Lands'' (1923) and ''Lo!'' (1931), Fort theorized that visitors from other worlds were observing Earth. Fort's reports of aerial phenomena were frequently cited in American newspapers when the UFO phenomenon first attracted widespread media attention in June and July 1947. The modern ETH—specifically, the implicit linking of unidentified aircraft and lights in the sky to alien life—took root during the late 1940s and took its current form during the 1950s. It drew on

pseudoscience Pseudoscience consists of statements, beliefs, or practices that claim to be both scientific and factual but are incompatible with the scientific method. Pseudoscience is often characterized by contradictory, exaggerated or unfalsifiable clai ...

, as well as popular culture. Unlike earlier speculation of extraterrestrial life, interest in the ETH was also bolstered by many unexplained sightings investigated by the U.S. government and governments of other countries, as well as private civilian groups, such as

NICAP The National Investigations Committee On Aerial Phenomena (NICAP) is an unidentified flying object (UFO) research group most active in the United States from the 1950s to the 1980s. It remains active primarily as an informational depository on th ...

and APRO.

Historical reports of extraterrestrial visits

An early example of speculation over extraterrestrial visitors can be found in the French newspaper ''Le Pays'', which on June 17, 1864, published a story about two American geologists who had allegedly discovered an alien-like creature, a mummified three-foot-tall hairless humanoid with a trunk-like appendage on its forehead, inside a hollow

egg-shaped An oval () is a closed curve in a plane which resembles the outline of an egg. The term is not very specific, but in some areas (projective geometry, technical drawing, etc.) it is given a more precise definition, which may include either one ...

structure.

H. G. Wells Herbert George Wells"Wells, H. G."
Revised 18 May 2015. ''

The War of the Worlds ''The War of the Worlds'' is a science fiction novel by English author H. G. Wells, first serialised in 1897 by ''Pearson's Magazine'' in the UK and by ''Cosmopolitan (magazine), Cosmopolitan'' magazine in the US. The novel's first appear ...

, popularized the idea of Martian visitation and invasion. Even before Wells, there was a sudden upsurge in reports in "

Mystery airship Mystery airships or phantom airships are a class of unidentified flying objects best known from a series of newspaper reports originating in the western United States and spreading east during late 1896 and early 1897.. According to researcher ...

s" in the United States. For example, ''The Washington Times'' in 1897 speculated that the airships were "a reconnoitering party from Mars", and the ''Saint Louis Post-Dispatch'' wrote: "these may be visitors from Mars, fearful, at the last, of invading the planet they have been seeking." Later, there was a more international airship wave from 1909-1912. An example of an extraterrestrial explanation at the time was a 1909 letter to a New Zealand newspaper suggesting "atomic powered spaceships from Mars." From the 1920s, the idea of alien visitation in space ships was commonplace in popular comic strips and radio and movie serials, such as

Buck Rogers Buck Rogers is a science fiction adventure hero and feature comic strip created by Philip Francis Nowlan first appearing in daily US newspapers on January 7, 1929, and subsequently appearing in Sunday newspapers, international newspapers, books ...

and Flash Gordon. In particular, the Flash Gordon serials have the Earth being attacked from space by alien meteors, ray beams, and biological weapons. In 1938, a radio broadcast version of ''

'' by

Orson Welles George Orson Welles (May 6, 1915 – October 10, 1985) was an American actor, director, producer, and screenwriter, known for his innovative work in film, radio and theatre. He is considered to be among the greatest and most influential f ...

, using a contemporary setting for H. G. Wells' Martian invasion, created some public panic in the United States.

The 1947 flying saucer wave in America

On June 24, 1947, at about 3:00 p.m. local time, pilot

Kenneth Arnold Kenneth Albert Arnold (March 29, 1915 – January 16, 1984) was an American aviator, businessman, and politician. He is best known for making what is generally considered the first widely reported modern unidentified flying object sighting in ...

reported seeing nine unidentified disk-shaped aircraft flying near Mount Rainier. When no aircraft emerged that seemed to account for what he had seen, Arnold quickly considered the possibility of the objects being extraterrestrial. On July 7, 1947, two stories came out where Arnold was raising the topic of possible extraterrestrial origins, both as his opinion and those who had written to him. In an Associated Press story, Arnold said he had received quantities of

fan mail Fan mail is mail sent to a public figure, especially a celebrity, by their admirers or " fans". In return for a fan's support and admiration, public figures may send an autographed poster, photo, reply letter or note thanking their fans for th ...

eager to help solve the mystery. Some of them "suggested the discs were visitations from another planet." When the 1947 flying saucer wave hit the United States, there was much speculation in the newspapers about what they might be in news stories, columns, editorials, and letters to the editor. For example, on July 10, U.S. Senator

Glen Taylor Glen Allen Taylor (born April 20, 1941) is an American billionaire business magnate and politician from Minnesota. A self-made businessman, Taylor made his fortune from being the founder and owner of Minnesota-based Taylor Corporation, one of th ...

of Idaho commented, "I almost wish the flying saucers would turn out to be space ships from another planet," because the possibility of hostility "would unify the people of the earth as nothing else could." On July 8, R. DeWitt Miller was quoted by UP saying that the saucers had been seen since the early nineteenth century. If the present discs weren't secret Army weapons, he suggested they could be vehicles from Mars, or other planets, or maybe even "things out of other dimensions of time and space." Other articles brought up the work of

, who earlier in the 20th Century had documented numerous reports of unidentified flying objects that had been written up in newspapers and scientific journals. Even if people thought the saucers were real, most were generally unwilling to leap to the conclusion that they were extraterrestrial in origin. Various popular theories began to quickly proliferate in press articles, such as secret military projects, Russian spy devices, hoaxes,

optical illusions Within visual perception, an optical illusion (also called a visual illusion) is an illusion caused by the visual system and characterized by a visual percept that arguably appears to differ from reality. Illusions come in a wide variety; the ...

, and

mass hysteria Mass psychogenic illness (MPI), also called mass sociogenic illness, mass psychogenic disorder, epidemic hysteria, or mass hysteria, involves the spread of illness symptoms through a population where there is no infectious agent responsible for c ...

. According to journalist Edward R. Murrow, the ETH as a serious explanation for "flying saucers" did not earn widespread attention until about 18 months after Arnold's sighting.

Edward R. Murrow Edward Roscoe Murrow (born Egbert Roscoe Murrow; April 25, 1908 – April 27, 1965) was an American broadcast journalist and war correspondent. He first gained prominence during World War II with a series of live radio broadcasts from Europe f ...

(April 7, 1950)
The Case of the Flying Saucer
', CBS News (Radio Documentary available in MP3/Real Media), (October 2006) These attitudes seem to be reflected in the results of the first U.S. poll of public UFO perceptions released by Gallup on August 14, 1947.Jacobs David M (2000), "UFOs and Abductions: Challenging the Borders of Knowledge", University Press of Kansas, (Compiled work: section sourced from Jerome Clark) The term "flying saucer" was familiar to 90% of the respondents. As to what people thought explained them, the poll further showed, that most people either held no opinion or refused to answer the question (33%), or generally believed that there was a mundane explanation. 29% thought they were optical illusions, mirages, or imagination; 15% a U.S. secret weapon; 10% a hoax; 3% a "weather forecasting device"; 1% of Soviet origin, and 9% had "other explanations," including fulfillment of Biblical

prophecy In religion, a prophecy is a message that has been communicated to a person (typically called a '' prophet'') by a supernatural entity. Prophecies are a feature of many cultures and belief systems and usually contain divine will or law, or pr ...

, secret commercial aircraft, or phenomena related to atomic testing.

U.S. military investigation and debunkery

On July 9, Army Air Forces Intelligence began a secret study of the best saucer reports, including that of Arnold's. A follow-up study by the

Air Materiel Command Air Materiel Command (AMC) was a United States Army Air Forces and United States Air Force command. Its headquarters was located at Wright-Patterson Air Force Base, Ohio. In 1961, the command was redesignated the Air Force Logistics Command wi ...

intelligence and engineering departments at

Wright Field Wilbur Wright Field was a military installation and an airfield used as a World War I pilot, mechanic, and armorer training facility and, under different designations, conducted United States Army Air Corps and Air Forces flight testing. Lo ...

, Ohio led to the formation of the U.S. Air Force's

Project Sign Project Sign (Project Saucer) was an official U.S. government study of unidentified flying objects (UFOs) undertaken by the United States Air Force (USAF) and active for most of 1948. It was the precursor to Project Grudge. History The project w ...

at the end of 1947, the first official U.S. military UFO study. In 1948, Project Sign concluded without endorsing any unified explanation for all UFO reports, and the ETH was rejected by USAF Chief of Staff General

Hoyt Vandenberg Hoyt Sanford Vandenberg (January 24, 1899 – April 2, 1954) was a United States Air Force general. He served as the second Chief of Staff of the Air Force, and the second Director of Central Intelligence. During World War II, Vandenberg was t ...

, citing a lack of physical evidence. Vandenberg dismantled Project Sign, and with this official policy in place, subsequent public Air Force reports concluded, that there was insufficient evidence to warrant further investigation of UFOs. Immediately following the great UFO wave of 1952 and the military debunking of radar and visual sightings, plus jet interceptions over Washington, D.C. in August, the CIA's Office of Scientific Investigation took particular interest in UFOs. Though the ETH was mentioned, it was generally given little credence. However, others within the CIA, such as the

Psychological Strategy Board The Psychological Strategy Board (PSB) was a committee of the United States executive formed to coordinate and plan for psychological operations. It was formed on April 4, 1951, during the Truman administration. The board was composed of the Un ...

, were more concerned about how an unfriendly power such as the Soviet Union might use UFOs for psychological warfare purposes, exploit the gullibility of the public for the sensational, and clog intelligence channels. Under a directive from the National Security Council to review the problem, in January 1953, the CIA organized the

Robertson Panel The Robertson Panel was a scientific committee which met in January 1953 headed by Howard P. Robertson. The Panel arose from a recommendation to the Intelligence Advisory Committee (IAC) in December 1952 from a Central Intelligence Agency (CIA) re ...

, a group of scientists who quickly reviewed the Blue Book's best evidence, including motion pictures and an engineering report that concluded that the performance characteristics were beyond that of earthly craft. After two days' review, all cases were claimed to have conventional explanations. An official policy of public debunkery was recommended using the mass media and authority figures in order to influence public opinion and reduce the number of UFO reports.

Evolution of public opinion

The early 1950s also saw a number of movies depicting flying saucers and aliens, including ''

The Day the Earth Stood Still ''The Day the Earth Stood Still'' (a.k.a. ''Farewell to the Master'' and ''Journey to the World'') is a 1951 American science fiction film from 20th Century Fox, produced by Julian Blaustein and directed by Robert Wise. It stars Michael Re ...

'' (1951), ''

'' (1953), '' Earth vs. the Flying Saucers'' (1956), and ''

Forbidden Planet ''Forbidden Planet'' is a 1956 American science fiction film from Metro-Goldwyn-Mayer, produced by Nicholas Nayfack, and directed by Fred M. Wilcox from a script by Cyril Hume that was based on an original film story by Allen Adler and Irvi ...

'' (1956). Despite this, public belief in ETH seems to have remained low during the early 1950s, even among those reporting UFOs. A poll published in '' Popular Science'' magazine in August 1951 showed, that of the respondents who self-reported as UFO witnesses, 52% believed that they had seen a man-made aircraft, while only 4% believed that they had seen an alien craft. However, an additional 28% were uncertain, with more than half of these stating they believed they were either man-made aircraft, or "visitors from afar." Thus the total number of UFO witnesses who considered the ETH viable, was approximately 20%. Within a few years, belief in ETH had increased due to the activities of people such as retired U.S. Marine Corps officer Maj. Donald E. Keyhoe, who campaigned to raise public awareness of the UFO phenomenon. By 1957, 25% of Americans responded that they either believed, or were willing to believe in he existence ofETH, while 53% responded that they were not (though a majority of these respondents indicated they thought UFOs to be real, but of earthly origin). 22% said that they were uncertain.Trendex Poll, St. Louis Globe Democrat (August 24, 1957) During this time, the ETH proponents fragmented into distinct camps, each believing slightly different variations of the hypothesis. The "

contactee Contactees are persons who claim to have experienced contact with extraterrestrials. Some claimed ongoing encounters, while others claimed to have had as few as a single encounter. Evidence is anecdotal in all cases. As a cultural phenomenon, c ...

s" of the early 1950s said that the " space brothers" they met were peaceful and benevolent, but by the mid-1960s, a number of alleged

alien abduction Alien abduction (also called abduction phenomenon, alien abduction syndrome, or UFO abduction) refers to the phenomenon of people reporting their experience of being kidnapped by extraterrestrial beings and subjected to physical and psychologica ...

s; including that of

Betty and Barney Hill Barney and Betty Hill were an American couple who claimed they were abducted by extraterrestrials in a rural portion of the state of New Hampshire from September 19 to 20, 1961. The incident came to be called the "Hill Abduction" and the "Zeta R ...

, and of the apparent mutilation of cattle cast the ETH in more sinister terms. Opinion polls indicate that public belief in the ETH has continued to rise since then. For example, a 1997 Gallup poll of the U.S. public indicated that 87% knew about UFOs, 48% believed them to be real (vs. 33% who thought them to be imaginary), and 45% believed UFOs had visited Earth. Similarly, a Roper poll from 2002 found, that 56% thought UFOs to be real, and 48% thought UFOs had visited Earth. Polls also indicate that the public believes even more strongly, that the government is suppressing evidence about UFOs. For example, in both the cited Gallup and Roper polls, the figure was about 80%.

Religion

Fewer sightings despite camera phone technology

As the proliferation of smartphone camera technology across the population has not led to a significant increase in recorded UFO sightings, the claimed ''phenomenology'' of UFOs has been called into question. This goes counter to the predictions of supporters of the extraterrestrial hypothesis, even causing a crisis of confidence among some within the informal UFO research community.

Involvement of scientists

The

scientific community The scientific community is a diverse network of interacting scientists. It includes many " sub-communities" working on particular scientific fields, and within particular institutions; interdisciplinary and cross-institutional activities are als ...

has shown very little support for the ETH, and has largely accepted the explanation that reports of UFOs are the result of people misinterpreting common objects or phenomena, or are the work of hoaxers. Professor Stephen Hawking has expressed skepticism about the ETH.Hawking Stephen
Space and Time Warps
In a 1969 lecture, U.S. astrophysicist Carl Sagan said: :"The idea of benign or hostile space aliens from other planets visiting the Earth s clearlyan emotional idea. There are two sorts of self-deception here: either accepting the idea of extraterrestrial visitation by space aliens in the face of very meager evidence because we want it to be true; or rejecting such an idea out of hand, in the absence of sufficient evidence, because we don't want it to be true. Each of these extremes is a serious impediment to the study of UFOs."Sagan Carl, Page Thornton (1972), "UFOs: A Scientific Debate". Cornell University Press, Similarly, British astrophysicist Peter A. Sturrock wrote :"for many years, discussions of the UFO issue have remained narrowly polarized between advocates and adversaries of a single theory, namely the extraterrestrial hypothesis ... this fixation on the ETH has narrowed and impoverished the debate, precluding an examination of other possible theories for the phenomenon."Sturrock Peter A (1999), "The UFO Enigma: A New Review of the Physical Evidence", Warner Books, An informal poll done by Sturrock in 1973 of

American Institute of Aeronautics and Astronautics The American Institute of Aeronautics and Astronautics (AIAA) is a professional society for the field of aerospace engineering. The AIAA is the U.S. representative on the International Astronautical Federation and the International Council of ...

members found that about 10% of them believed that UFOs were vehicles from outer space.John F. Schuessler (January 2000)
Public Opinion Surveys and Unidentified Flying Objects; 50+ years of Sampling Public Opinions
In another informal poll conducted in 1977 by astrophysicist Peter A. Sturrock, he surveyed members of the American Astronomical Society. Sturrock asked polled scientists to assign probabilities to eight possible explanations for UFOs. The results were: The primary scientific arguments against ETH were summarized by astronomer and UFO researcher J. Allen Hynek during a presentation at the 1983

MUFON The Mutual UFO Network (MUFON) is a US-based non-profit organization composed of civilian volunteers who study reported UFO sightings. It is one of the oldest and largest organizations of its kind, claiming more than 4,000 members worldwide wi ...

Symposium, where he outlined seven key reasons why he could not accept the ETH. # Failure of sophisticated surveillance systems to detect incoming or outgoing UFOs # Gravitational and atmospheric considerations # Statistical considerations # Elusive, evasive and absurd behavior of UFOs and their occupants # Isolation of the UFO phenomenon in time and space: the

Cheshire Cat The Cheshire Cat ( or ) is a fictional cat popularised by Lewis Carroll in ''Alice's Adventures in Wonderland'' and known for its distinctive mischievous grin. While now most often used in ''Alice''-related contexts, the association of a "Ch ...

effect # The space unworthiness of UFOs # The problem of astronomical distances Hynek argued that: #Despite worldwide

radar Radar is a detection system that uses radio waves to determine the distance ('' ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, we ...

systems and Earth-orbiting satellites, UFOs are alleged to flit in and out of the atmosphere, leaving little to no evidence. #Space aliens are alleged to be overwhelmingly humanoid, and are allegedly able to exist on Earth without much difficulty often lacking "

space suit A space suit or spacesuit is a garment worn to keep a human alive in the harsh environment of outer space, vacuum and temperature extremes. Space suits are often worn inside spacecraft as a safety precaution in case of loss of cabin pressure, ...

s", even though

extra-solar planets An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

would likely have different atmospheres,

biosphere The biosphere (from Greek βίος ''bíos'' "life" and σφαῖρα ''sphaira'' "sphere"), also known as the ecosphere (from Greek οἶκος ''oîkos'' "environment" and σφαῖρα), is the worldwide sum of all ecosystems. It can also ...

gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...

and other factors, and extraterrestrial life would likely be very different from Earthly life. #The number of reported UFOs and of purported encounters with UFO-inhabitants outstrips the number of expeditions that an alien civilization (or civilizations) could statistically be expected to mount. #The behavior of extraterrestrials reported during alleged abductions is often inconsistent and irrational. #UFOs are isolated in time and space: like the

, they seem to appear and disappear at will, leaving only vague, ambiguous and mocking evidence of their presence #Reported UFOs are often far too small to support a crew traveling through space, and their reported flight behavior is often not representative of a craft under intelligent control (erratic flight patterns, sudden course changes). #The distance between planets makes interstellar travel impractical, particularly because of the amount of energy that would be required for

interstellar travel Interstellar travel is the hypothetical travel of spacecraft from one star system, solitary star, or planetary system to another. Interstellar travel is expected to prove much more difficult than interplanetary spaceflight due to the vast diffe ...

using conventional means, (According to a NASA estimate, it would take 7

joule The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applie ...

s of energy to send then-the current

Space Shuttle The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program ...

on a one-way 50-year journey to the nearest star, an enormous amount of energyWarp Drive, When?
A Look at the Scaling
(October 2006)) and because of the level of technology that would be required to ''circumvent'' conventional energy/fuel/speed limitations using exotic means, such as Einstein-Rosen Bridges as ways to shorten distances from point A to point B. (''see

Faster-than-light Faster-than-light (also FTL, superluminal or supercausal) travel and communication are the conjectural propagation of matter or information faster than the speed of light (). The special theory of relativity implies that only particles with zero ...

travel'').Clark Jerome (1998), "The UFO Book: Encyclopedia of the Extraterrestrial", Visible Ink, According to the personal assessment of Hynek at the time, points 1 through 6 could be argued, but point 7 represented an "insurmountable" barrier to the validity of the ETH.

Recent support

Others have argued that (unless mechanisms of repulse or dissolution and/or data-manipulation and/or cloaking technologies are and remain sufficiently deployed to prevent this),

self-replicating spacecraft The concept of Self-replicating spacecraft, as envisioned by mathematician John von Neumann, has been described by futurists including physicist Michio Kaku and discussed across a wide breadth of hard science fiction novels and stories. Self-rep ...

or their communications networks could potentially be detectable within our Solar system or in nearby star-based systems, if they are located there. Other research has since also addressed earlier arguments about the distance-related bottleneck with potential solutions other civilizations may have developed such as

embryo space colonization Embryo space colonization is a theoretical interstellar space colonization concept that involves sending a robotic mission to a habitable terrestrial planet, dwarf planet, minor planet or natural satellite transporting frozen early-stage human ...

and

Alcubierre drive The Alcubierre drive () is a speculative warp drive idea according to which a spacecraft could achieve apparent faster-than-light travel by contracting space in front of it and expanding space behind it, under the assumption that a configurable ...

s. A 2021

scientific review A review article is an article that summarizes the current state of understanding on a topic within a certain discipline. A review article is generally considered a secondary source since it may analyze and discuss the method and conclusions i ...

concluded there to be robust rationale for organizing missions for searching artifacts – including probes – within the Solar system. The sentiment in the scientific community about the extraterrestrial hypothesis in relation to UFO reports and data shifted substantially after serious news reports about the topic by large media outlets within the U.S. and Canada and a public debate including former and present public servants in anticipation of a report by the U.S. intelligence apparatus. During this change of attitude in early summer 2021, still small but increasing numbers of scientists first began to publicly discuss UFOs and systematic investigations of them in a sober manner on large platforms.

NASA

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...

frequently fields questions in regard to the ETH and UFOs. As of 2006, its official standpoint was that ETH has a lack of empirical evidence. :"no one has ever found a single artifact, or any other convincing evidence for such alien visits". David Morrison.Morrison David, Senior Scientist at the NASA Astrobiology Institute (June 2006),
Ask an Astrobiologist
, (October 2006) :"As far as I know, no claims of UFOs as being alien craft have any validity -- the claims are without substance, and certainly not proved". David MorrisonMorrison David, Senior Scientist at the NASA Astrobiology Institute (July 2006),
Ask an Astrobiologist
, (October 2006) Despite public interest, up until 2021, NASA had considered the study of ETH to be irrelevant to its work because of the number of false leads that a study would provide, and the limited amount of usable scientific data that it would yield. On the History Channel UFO Hunters episode "The NASA Files" (2008), Former NASA astronauts have commented;

Gordon Cooper Leroy Gordon "Gordo" Cooper Jr. (March 6, 1927 – October 4, 2004) was an American aerospace engineer, test pilot, United States Air Force pilot, and the youngest of the seven original astronauts in Project Mercury, the first human spa ...

wrote that NASA and the government "swept these and other sightings under the rug". Brian O'Leary stated "some of my fellow astronauts and scientists astronauts that did go up and who have observed things, very clearly, they were told - not to report it". In June of 2021, NASA Administrator Bill Nelson announced that he had directed NASA scientists to investigate Unidentified Aerial Phenomenon. Clarence William Nelson II, Administrator at NASA (June 2021), https://earthsky.org/human-world/nasa-and-ufos-bill-nelson/ During an interview at the University of Virginia, Bill Nelson explored the possibility that UAP could represent extraterrestrial technology. Clarence William Nelson II, Administrator at NASA (October 2022), https://news.virginia.edu/content/space-jam-former-senator-talks-aliens-asteroids-and-star-trek-larry-sabato NASA scientist Dr. Ravi Kopparapu advocates studying UAP. James E. McDonald, Professor of Atmospheric Sciences University of Arizona Tucson, Arizona, (December, 1969) http://noufors.com/Documents/scienceindefault.pdfstating from the American Association for the Advancement of Science, 134th Meeting General Symposium that supported ETH. Dr. Kopparapu stated he and his colleagues found the paper "perfectly credible". Ravi Kopparapu, Planetary Scientist at NASA Goddard, American Institute of Aeronautics and Aviation Propulsion and Energy Forum (August 2021), https://youtube.com/watch?v=HJiFhazryiA

Conspiracy theories

A frequent concept in ufology and popular culture is that the true extent of information about UFOs is being suppressed by some form of conspiracy of silence, or by an official

cover-up A cover-up is an attempt, whether successful or not, to conceal evidence of wrongdoing, error, incompetence, or other embarrassing information. Research has distinguished personal cover-ups (covering up one's own misdeeds) from relational co ...

that is acting to conceal information. In 1968, American engineer James Harder argued that significant evidence existed to prove UFOs "beyond reasonable doubt," but that the evidence had been suppressed and largely neglected by scientists and the general public, thus preventing sound conclusions from being reached on the ETH. :"Over the past 20 years a vast amount of evidence has been accumulating that bears on the existence of UFOs. Most of this is little known to the general public or to most scientists. But on the basis of the data and ordinary rules of evidence, as would be applied in civil or criminal courts, the physical reality of UFOs has been proved beyond a reasonable doubt." J A Harder A survey carried out by Industrial Research magazine in 1971 showed that more Americans believed the government was concealing information about UFOs (76%) than believed in the existence of UFOs (54%), or in ETH itself (32%). People have had a long-standing curiosity about extraterrestrial life. Aliens are the subject of numerous urban legends, including claims that they have long been present on earth or that they may be able to assist humans in resolving certain issues. Despite these myths, the truth is that there is no scientific proof to back up these assertions, hence we cannot declare with certainty whether or not aliens exist.

Documents and investigations regarding ETH

Other private or government studies, some secret, have concluded in favor of the ET hypothesis, or have had members who disagreed in contravention with official conclusions reached by the committees and agencies to which they belonged. The following are examples of sources that have focused specifically on the topic: *In 1967, Greek physicist Paul Santorini, a

Manhattan Project The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project w ...

scientist, publicly stated that a 1947 Greek government investigation into the European

Ghost rockets Ghost rockets ( sv, Spökraketer, also called Scandinavian ghost rockets) were rocket- or missile-shaped unidentified flying objects sighted in 1946, mostly in Sweden and nearby countries like Finland. The first reports of ghost rockets were ma ...

of 1946 under his lead quickly concluded that they were not missiles. Santorini claimed the investigation was then quashed by military officials from the U.S., who knew them to be extraterrestrial, because there was no defense against the advanced technology and they feared widespread panic should the results become public. 1948 Top Secret USAF UFO extraterrestrial document

1948 Top Secret USAF UFO extraterrestrial document

*A 1948 Top Secret USAF Europe document ( at right) states that Swedish air intelligence informed them that at least some of their investigators into the ghost rockets and flying saucers concluded they had extraterrestrial origins: "...

Flying saucers A flying saucer (also referred to as "a flying disc") is a descriptive term for a type of flying craft having a disc or saucer-shaped body, commonly used generically to refer to an anomalous flying object. The term was coined in 1947 but has g ...

have been reported by so many sources and from such a variety of places that we are convinced that they cannot be disregarded and must be explained on some basis which is perhaps slightly beyond the scope of our present intelligence thinking. When officers of this Directorate recently visited the Swedish Air Intelligence Service... their answer was that some reliable and fully technically qualified people have reached the conclusion that 'these phenomena are obviously the result of a high technical skill which cannot be credited to any presently known culture on earth.' They are therefore assuming that these objects originate from some previously unknown or unidentified technology, possibly outside the earth." *In 1948, the USAF

produced a Top Secret Estimate of the Situation, concluding that the ETH was the most likely explanation for the most perplexing unexplained cases. The study was ordered destroyed by USAF Chief of Staff General

, citing lack of proof. Knowledge of the existence of the Estimate has come from insiders who said they read a surviving copy, including the later USAF Project Blue Book head Edward J. Ruppelt, and astronomer and USAF consultant J. Allen Hynek. *West Germany, in conjunction with other European countries, conducted a secret study from 1951 to 1954, also concluding that UFOs were extraterrestrial. This study was revealed by German rocketry pioneer Hermann Oberth, who headed the study and who also made many public statements supporting the ETH in succeeding years. At the study's conclusion in 1954, Oberth declared: "These objects (UFOs) are conceived and directed by intelligent beings of a very high order. They do not originate in our solar system, perhaps not in our galaxy." Soon afterwards, in an October 24, 1954 article in ''The American Weekly'', Oberth wrote: "It is my thesis that flying saucers are real and that they are space ships from another solar system. I think that they possibly are manned by intelligent observers who are members of a race that may have been investigating our earth for centuries..." *The

CIA The Central Intelligence Agency (CIA ), known informally as the Agency and historically as the Company, is a civilian foreign intelligence service of the federal government of the United States, officially tasked with gathering, processing, ...

started their own internal scientific review the following day. Some CIA scientists were also seriously considering the ETH. An early memo from August was very skeptical, but also added: "...as long as a series of reports remains 'unexplainable' (interplanetary aspects and alien origin not being thoroughly excluded from consideration) caution requires that intelligence continue coverage of the subject." A report from later that month was similarly skeptical, but nevertheless concluded: "...sightings of UFOs reported at Los Alamos and Oak Ridge, at a time when the background radiation count had risen inexplicably. Here we run out of even 'blue yonder' explanations that might be tenable, and we still are left with numbers of incredible reports from credible observers." A December 1952 memo from the Assistant CIA Director of Scientific Intelligence (O/SI) was much more urgent: "...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 U.S. defense installation [''

sic The Latin adverb ''sic'' (; "thus", "just as"; in full: , "thus was it written") inserted after a quoted word or passage indicates that the quoted matter has been transcribed or translated exactly as found in the source text, complete with any e ...

''] are of such nature that they are not attributable to natural phenomena or known types of aerial vehicles." Some of the memos also made it clear, that CIA interest in the subject was not to be made public, partly in fear of possible public panic. (Good, 331–335) *The CIA organized the January 1953

of scientists to debunk the data collected by the Air Force's Project Blue Book. This included an engineering analysis of UFO maneuvers by Blue Book (including a motion picture film analysis by Naval scientists) that had concluded UFOs were under intelligent control and likely extraterrestrial. *Extraterrestrial "believers" within Project Blue Book included Major Dewey Fournet, in charge of the engineering analysis of UFO motion, who later became a board member on the civilian UFO organization

. Blue Book director Edward J. Ruppelt privately commented on other firm "pro-UFO" members in the USAF investigations, including some Pentagon generals, such as Charles P. Cabell, USAF Chief of Air Intelligence, who, angry at the inaction and debunkery of

Project Grudge Project Grudge was a short-lived project by the U.S. Air Force (USAF) to investigate unidentified flying objects (UFOs). Grudge succeeded Project Sign in February, 1949, and was then followed by Project Blue Book. The project formally ended in De ...

, dissolved it in 1951, established Project Blue Book in its place, and made Ruppelt director. In 1953, Cabell became deputy director of the CIA. Another defector from the official Air Force party line was consultant J. Allen Hynek, who started out as a staunch skeptic. After 20 years of investigation, he changed positions and generally supported the ETH. He became the most publicly known UFO advocate scientist in the 1970s and 1980s. *The first CIA Director, Vice Admiral

Roscoe H. Hillenkoetter Roscoe Henry Hillenkoetter (May 8, 1897 – June 18, 1982) was the third director of the post–World War II United States Central Intelligence Group (CIG), the third Director of Central Intelligence (DCI), and the first director of the Central In ...

, stated in a signed statement to Congress, also reported in ''

The New York Times ''The New York Times'' (''the Times'', ''NYT'', or the Gray Lady) is a daily newspaper based in New York City with a worldwide readership reported in 2020 to comprise a declining 840,000 paid print subscribers, and a growing 6 million paid d ...

'' (February 28, 1960): "It is time for the truth to be brought out... Behind the scenes high-ranking Air Force officers are soberly concerned about the UFOs. However, through official secrecy and ridicule, many citizens are led to believe the unknown flying objects are nonsense... I urge immediate Congressional action to reduce the dangers from secrecy about unidentified flying objects." In 1962, in his letter of resignation from

, he told director

Donald Keyhoe Donald Edward Keyhoe (June 20, 1897 – November 29, 1988) was an American Marine Corps naval aviator, Donald E(dward) Keyhoe. (April 30, 1998) Contemporary Authors Online, Gale, 2002. Reproduced in Biography Resource Center. Farmington Hills, M ...

, "I know the UFOs are not U.S. or Soviet devices. All we can do now is wait for some actions by the UFOs." *Although the 1968

came to a negative conclusion (written by Condon), it is known that many members of the study strongly disagreed with Condon's methods and biases. Most quit the project in disgust, or were fired for insubordination. A few became ETH supporters. Perhaps the best known example is David Saunders, who in his 1968 book ''UFOs? Yes'' lambasted Condon for extreme bias, and for ignoring or misrepresenting critical evidence. Saunders wrote: "It is clear... that the sightings have been going on for too long to explain in terms of straightforward terrestrial intelligence. It's in this sense that ETI (Extra Terrestrial Intelligence) stands as the 'least implausible' explanation of 'real UFOs'." *In 1999, the private French COMETA report (written primarily by military defense analysts) stated the conclusion regarding UFO phenomena, that a "single hypothesis sufficiently takes into account the facts and, for the most part, only calls for present-day science. It is the hypothesis of extraterrestrial visitors." The report noted issues with formulating the extraterrestrial hypothesis, likening its study to the study of meteorites, but concluded, that although it was far from the best scientific hypothesis, "strong presumptions exist in its favour". The report also concludes, that the studies it presents, "demonstrate the almost certain physical reality of completely unknown flying objects with remarkable flight performances and noiselessness, apparently operated by intelligent eings... Secret craft definitely of earthly origins (drones, stealth aircraft, etc.) can only explain a minority of cases. If we go back far enough in time, we clearly perceive the limits of this explanation." * Jean-Jacques Velasco, the head of the official French UFO investigation SEPRA, wrote a book in 2005, saying, that 14% of the 5800 cases studied by SEPRA were 'utterly inexplicable and extraterrestrial' in origin.

Yves Sillard Yves Sillard is a French scientist and High public servant who played a major role in the development of the French space program ( Ariane). He headed the CNES, IFREMER, and the Délégation générale pour l'armement (General Directorate for Armam ...

, the head of the new official French UFO investigation

GEIPAN GEIPAN (an acronym for ''Groupe d'Études et d'Informations sur les Phénomènes Aérospatiaux Non-identifiés'', or unidentified aerospace phenomenon research and information group). (), its name since September 2005. (The group was formerly know ...

and former head of French space agency

CNES The (CNES; French: ''Centre national d'études spatiales'') is the French government space agency (administratively, a "public administration with industrial and commercial purpose"). Its headquarters are located in central Paris and it is und ...

, echoes Velasco's comments and adds, that the United States 'is guilty of covering up this information.' However, this is not the official public posture of SEPRA, CNES, or the French government. (The CNES placed their 5,800 case files on the Internet starting March 2007.)

Official White House position

In November 2011, the

White House The White House is the official residence and workplace of the president of the United States. It is located at 1600 Pennsylvania Avenue NW in Washington, D.C., and has been the residence of every U.S. president since John Adams in ...

released an official response to two petitions asking the U.S. government to acknowledge formally that aliens have visited Earth 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." Also, according to the response, there is "no credible information to suggest that any evidence is being hidden from the public's eye." The response further noted that efforts, like

SETI The search for extraterrestrial intelligence (SETI) is a collective term for scientific searches for intelligent extraterrestrial life, for example, monitoring electromagnetic radiation for signs of transmissions from civilizations on other pl ...

, the

Kepler space telescope The Kepler space telescope is a disused space telescope launched by NASA in 2009 to discover Earth-sized Exoplanet, planets orbiting other stars. Named after astronomer Johannes Kepler, the spacecraft was launched into an Earth-trailing heliocen ...

and the

NASA Mars rover The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

, continue looking for signs of life. The response noted "the 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."

References

External links

{{DEFAULTSORT:Extraterrestrial hypothesis Pseudoscience Extraterrestrial life Ufology 20th-century neologisms