Los Alamos, Las Vegas UFO Sighting (December 5, 1948) — FBI Files
FBI records detail a 1948 sighting of a wedge-shaped green fireball over New Mexico, part of a series of unidentified aerial phenomena in the region.
Background
On December 5, 1948, in Los Alamos, Las Vegas, U.S. government investigators recorded an unidentified-object incident later released to the public on May 8, 2026, as part of the Presidential Unsealing and Reporting System for UAP Encounters (PURSUE). This event occurred during a period of intense public and governmental scrutiny regarding aerial phenomena. The sighting was part of the first wave of “flying saucer” reports that swept the United States following the Kenneth Arnold sighting of June 1947 and the Roswell incident of July 1947. During this era, the emergence of high-altitude reconnaissance and the early stages of the Cold War created a climate of heightened vigilance regarding any unidentified movement in the upper atmosphere.
The case was filed with the Federal Bureau of Disquisition, and the FBI’s Knoxville, Albuquerque, and Los Angeles field offices followed established standing protocols for the protection of vital installations. Because Los Alamos served as a critical site for national security and nuclear research, any unexplained aerial activity was treated with significant administrative gravity. The Bureau’s internal procedures required that reports of unidentified objects near sensitive government sites be routed directly to headquarters to ensure that no breach of security or unauthorized surveillance was occurring.
The Incident and Reported Phenomena
The documentation released via the PURSUE program details a specific set of observations that occurred on the night of December 5, 1948. The witnesses involved described the object as being triangular or wedge-shaped in its physical geometry. The visual characteristics of the object were noted for their distinct color, specifically described as a green fireball. This specific visual signature was not an isolated occurrence in the region during this timeframe.
Since December 5, 1948, more than ten incidents involving a “green fireball” and approximately twenty others with minor variations were reported. These sightings were not randomly distributed across the country but were primarily confined to a specific geographic triangle encompassing Los Alamos, Las Vegas, and parts of Texas. The recurrence of these sightings within a localized corridor led military authorities to anticipate further sightings, suggesting a pattern of activity rather than a singular, random atmospheric event. While the released document provides a detailed account of the nature of the objects, the total number of witnesses involved in the December 5 incident is not specified in the official record.
Historical Context and Analysis
The late 1940s represented a transitional period in both aviation technology and atmospheric science. The period was characterized by the proliferation of experimental high-altitude platforms and the development of sophisticated radar systems. When investigating such reports, contemporary authorities often had to distinguish between genuine anomalies and the side effects of new military technologies. For example, the Project Mogul series of high-altitude balloons was active during this era, designed to detect Soviet nuclear tests via acoustic sensors, which often resulted in unidentified sightings by civilian and military observers alike.
In the broader context of unidentified aerial phenomena, the Los Alamos, Las Vegas sighting shares characteristics with other mid-century reports involving luminous, colored objects. Atmospheric optical phenomena, such as sundogs, lenticular clouds, or meteors appearing near the horizon, were frequently considered by investigators. Furthermore, the brightness of planets like Venus or the Moon could often be mistaken for moving objects during periods of low visibility.
Current Status
All records released under the PURSUE program are designated unresolved by the All-domain Anomaly Resolution Office (AARO) by default. The federal government has not concluded that the events described in the December 5, 1948, file were anomalous, nor has it concluded that they were conventional. The official position remains that the government has not ruled out either possibility. While conventional candidates for sightings of this period include experimental aircraft, weather balloons, and astronomical objects, the specific pattern of the green fireball sightings in the New Mexico-Texas triangle remains a subject of historical interest within the archives of unidentified aerial phenomena.