9 Mi W of Benson, ArizonaOctober 1957

On the evening of October 18, 1957, a group of civilians set up cameras about 9 miles west of Benson, Arizona, hoping to photograph the newly launched Russian satellite Sputnik I. They never saw the satellite, but around 1827 (6:27 p.m.) local time, a bright object appeared over the southeast horizon and traveled rapidly across the sky, disappearing toward the north-northwest about six minutes later. The object was brighter than any star visible that night but dimmer than the planet Venus. It glowed with a yellowish hue that suggested reflected sunlight. The witnesses took three photographs of the object before it vanished.

The observers quickly concluded the object was not the Sputnik rocket they had been expecting. The rocket, they noted, was supposed to follow a southeast-to-northeast path, but this object traveled southeast to north-northwest, a different direction entirely. It also appeared fourteen minutes earlier than the rocket was predicted to show up, and it lacked the brightness variations associated with the satellite's third stage. Radio signals from Sputnik itself were heard later that night on schedule.

The mysterious object's brightness and light quality intrigued investigators from multiple agencies. Researchers at the Smithsonian Astrophysical Observatory analyzed the sighting carefully. They considered several possibilities: a meteor, the satellite's rocket booster, or an artificial meteor. Around that time, the U.S. Air Force was conducting experiments at Alamogordo, New Mexico, launching small aluminum pellets into the upper atmosphere at heights between 35 and 50 miles. At those altitudes, the pellets glowed brightly enough to be photographed. Air Force scientists determined that such an artificial meteor, fired from somewhere in Texas, could have achieved the brightness observed at Benson and traveled in roughly the right direction at the reported height.

The full case file is reproduced below as held by the National Archives, consisting of 16 pages.