PRESSURE ISLE AFB MAINE, October 1952October 1952

On the night of October 10, 1952, weather observers at Presque Isle Air Force Base in Maine spotted something unusual in the sky. They saw a circular orange object with four green lights nearby, visible for five hours starting around 10 p.m. The observers set up a theodolite (a surveying instrument used to measure angles and altitude) to track the object carefully. When they called the nearby Limestone Air Force Base, about 20 miles away, observers there could see it too. Both teams recorded precise measurements of the object's position.

The two sets of measurements seemed to tell a dramatic story. When Air Force scientists plotted the numbers, the data appeared to show something hovering about 100 miles above Earth, more than 50 miles off the coast. The object seemed huge and was moving at high speed. This finding created real concern at the Air Force Technical Intelligence Center, or ATIC. Some officials worried the sighting might represent a Soviet orbiting vehicle or something from space.

However, ATIC's science consultant, Dr. J. Allen Hynek, looked at the same data and reached a very different conclusion. He identified the object as the planet Jupiter, which had risen in the eastern sky earlier that evening. Hynek noted that the four green lights were actually Jupiter's four bright moons, twinkling as their light passed through Earth's atmosphere. The file records that the observers at Limestone had made a mistake in determining true north when using the theodolite. This error in calibration threw off their bearing measurements. When that error was corrected, the lines of sight from both stations pointed directly at Jupiter.

The file concludes that the measurements likely pointed to Jupiter at infinity, rather than to any object within Earth's atmosphere. The full case file is reproduced below as held by the National Archives across 31 pages.