Some people who see a strange object in the sky wonder whether it is a visitor from another world. What do investigators find when they look into such reports? In 1947, a businessman named Kenneth Arnold said he saw nine fast things near Mount Rainier. They moved "like saucers skipping on water." A newspaper wrongly called them shaped like saucers, and that is how we got the term flying saucer. UFO stands for unidentified flying object. It means something the person who saw it could not identify at that moment. Bright planets such as Venus and Jupiter, and meteors, are sometimes reported as strange lights because they can look like they are hovering or moving.
The U.S. Air Force began Project Sign in 1948. Project Grudge came next, and then, in 1952, Project Blue Book. From 1947 to 1969, the Air Force investigated UFO reports, and Project Blue Book was based at Wright-Patterson Air Force Base. Of 12,618 sightings reported, 701 stayed a mystery. Each report was put into one group: identified with an astronomical, atmospheric or human-made cause, or not identified. The 701 cases included ones with too little information to match a known cause. The Condon Report of 1968 was written by 37 scientists. They studied 59 reports in detail. It found nothing other than plain things. With fewer reports, it led to the end of Blue Book on Dec. 17, 1969. Blue Book's own conclusions had three parts. First, no reported UFO was a threat to the nation. Second, nothing showed that those cases used technology beyond modern scientific knowledge. Third, nothing showed they were vehicles from another world.
In summer 1952, radar and visual reports near National Airport in Washington, D.C. were attributed to temperature inversions in the air, though not everyone was convinced by that explanation. In 1953, a panel led by physicist H.P. Robertson met. It decided that 90 percent of reports could be easily attributed to space or weather events or to everyday objects such as planes, balloons and birds. Parts of its report stayed classified until 1979, which fueled suspicions of a cover-up. Planes are a common cause of UFO reports: seen from odd positions or in poor light they can look strange. Secret high-flying planes in the 1950s and 1960s caused many reports. High-altitude balloons often lack markings and can look strange from certain angles. Weather and research balloons are also sometimes reported as UFOs.
Another case began in June 1947. Rancher W.W. Brazel found strange scraps of tinfoil, rubber strips and sticks near Roswell, New Mexico. The Army Air Field press release said a "flying disc" had been recovered. Almost immediately the military said the "saucer" was a weather balloon carrying a radar target made of foiled paper on a balsa wood frame, though Brazel did not believe the debris was from a weather balloon. In 1994 the Air Force reported that the debris came from Project Mogul, a secret Army Air Forces balloon project meant to detect Soviet nuclear tests. The 1997 Air Force report "The Roswell Report: Case Closed" proposed that stories of alien bodies came from other events, including a 1956 KC-97 aircraft accident that killed 11 airmen and a 1959 manned balloon mishap.
NASA announced in June 2022 that it would commission an independent study team to examine unidentified anomalous phenomena (UAP) with the tools of science. UAP is the term NASA uses, to be consistent with the National Defense Authorization Act. The team published its final report on September 14, 2023. NASA's study found no sign that UAPs are extraterrestrial. It says there are too few high-quality observations to draw scientific conclusions about what such events are. Most UAP reports produce very limited data, so the study focused on what data could be collected in the future. AARO says the most useful reports include recorded, time-stamped and geolocated data for both observer and object, so they can be checked against air traffic, balloon and satellite tracking databases.
Space science sets a similar bar for claims about life on other worlds. In 1976 NASA's two Viking landers tested Martian soil for signs of biological activity and found nothing definite, but later probes showed that water most likely once flowed on Mars. A potential biosignature is a substance or structure that might have a biological origin but needs more data or further study before scientists can reach a conclusion about life. NASA reported in 2025 that a Perseverance rock sample called Sapphire Canyon contains potential biosignatures: spots with two iron-rich minerals. The same minerals can also form without life, so as of November 2026 the finding is a question for further study, not a confirmed discovery.
The Pentagon's All-domain Anomaly Resolution Office, called AARO, says many reports are listed as not identified simply because sensors could not collect enough information to name what was seen. It lists causes. They include plastic bags and mylar balloons blown by the wind, birds, balloons, planes, drones, rocket launches, and sunlight glinting off satellites. Motion parallax can make a stationary or slow object look very fast. The observer's speed and a small field of view move the background behind the object, not the object itself. As of November 2026, AARO answers the question of whether it has found any evidence of extraterrestrial technology with "No," adding that examination of UAP reports is ongoing.
Words to know
- unidentified: not yet named
- biosignature: possible life sign
- inversions: layered air
- classified: kept secret
