The UFO That Wasn't Swamp Gas

by Brian Dunning
July 11, 2023

Anyone who's heard of UFOs — or, more specifically — anyone who's heard old UFO tales being scoffed at and dismissed, has probably heard the term swamp gas. Swamp gas is something of a hoary old nickname for a case that's not worth investigating. If there were lights in the sky, it was probably just swamp gas. But how many of us know the term's origin story, and how it first came to be associated with unconvincing UFOs?

To find out, we travel back to 1966, to a pair of small towns in Michigan, about an hour apart from one another. Over the course of two evenings, March 20th and 21st, each town had its own little UFO event. I say little because both cases were about as tame as UFO reports get; we'll talk about the details in a minute, but what mattered was the perversely disproportionate amount of media attention the cases got. This was at such a furor that the Air Force sent its civilian UFO expert, Dr. J. Allen Hynek, to investigate the cases for them. He later wrote:

My interrogations were made triply difficult because of the ubiquitous press, radio and TV men. It was impossible to talk quietly with anyone without having a microphone placed in front of your face. I was always importuned for "just a word" or, "will you answer just one question?" It is difficult to describe to one who wasn't there the general bedlam. Mr. Mannor, the chief protagonist in the Dexter case, reportedly complained that I had spent very little time with him. It was virtually impossible to do so; several times I was waiting and anxious to talk with him but he was occupied with several reporters. Here again is where some assistants would have come in handy; they could have diverted the reporters while I talked to Mannor. One needs some clever interference run for him in cases like this; it is virtually impossible to do it single handed.

J. Allen Hynek is one of the few truly interesting characters in the history of UFOlogy. A small man with a short, pointed beard, trifocal glasses, always with a pipe in his mouth — think of Vladimir Lenin with more hair. After World War II, Hynek carried a full load as a professor of physics and astronomy, and a research scientist, at a variety of institutions: Ohio State University, the Smithsonian Astrophysical Observatory, Northwestern University. Colleagues described him as agreeable, well-liked, humble, studious, curious, humane, energetic, and above all, rational in the extreme — all the qualities one would hope for in a scientist to lead a project as abstruse as the study of UFOs.

Hynek's connection with UFOlogy came quite by accident — he had no previous interest and had never dallied, until one day in 1948. At Wright-Patterson Air Force Base in Ohio, the Air Force was investigating some UFO case and they wanted an astronomer to suggest possible natural explanations, and so they simply called up the nearest one they could find — Dr. Hynek, then at Ohio State University. From that moment on, he was hooked; working with the Air Force at every opportunity offered, and putting in a considerable amount of his own time as well — all while never once letting up a bit on his actual astronomy work, which was both considerable and significant in the scope of his contributions.

Within the context of Hynek's role in the UFOlogy canon, he's probably best known for a general reversal of his opinion on UFOs. At first he saw them as individual minor mysteries that all had interesting explanations: misidentification of celestial phenomena, aerial clutter, optical illusions, what have you. But over the years, what grew in him was more and more respect for the eyewitnesses, and intrigue with a number of cases that he felt could not be easily explained. He'd long been frustrated by Project Blue Book and its process of simply filing reports away. Hynek's tipping point came with the 1968 publication of the Condon Report, prepared for the Air Force by a group led by Edward Condon, a physicist whom Hynek greatly respected. In short, the report found that there was basically nothing to the UFO phenomenon, and that further study was not justified. Hynek could not contain his disagreement. By then he was persuaded that a coordinated, ongoing investigation was more than warranted. This prompted him to become an author, and he then wrote what was to become the first of a number of books on UFOlogy: 1972's The UFO Experience: A Scientific Inquiry, which was really his version of what he felt the Condon Report should have been.

So when these Michigan cases came to him in March of 1966, he and an airman assigned to assist traveled to Michigan and set about interviewing the eyewitnesses. Here is what he learned.

The first of the two events took place in Dexter on the night of March 20. A father and teenage son observed a noisy object adorned with lights take off from a swamp, rise to a height of about 500 feet, and settle back down. Police were called. Some of them saw lights too, and the swamp was searched without result. More officers arrived. Over the space of about three hours, lights were reported around the swamp and over a nearby swamp area as well. In all, some 50 or so people saw something that night. From all of Hynek's interviews, he determined the only thing consistently reported was dim, visible lights; and although the newspaper accounts were full of much more dramatic apparitions, Hynek concluded dim lights visible at about a quarter mile distance, and no solid objects, were the only reliable reports.

The second event was the following night in Hillsdale, at Hillsdale College. A principal witness was the local county Civil Defense director, Mr. Van Horn, and Hynek considered him highly reliable and knowledgeable. The Van Horns received a phone call from the girls' dormitory at the college, where some 50 girls had been watching some colored lights above a swamp about a half mile away. Van Horn went to the dorm and saw the lights himself. Over several hours, the lights made four ascents to a few hundred feet in the air, each time settling back down. Same as the night before, Hynek found that lights alone were the only thing consistently reported.

Dismissing the inconsistent evidence from both events — things like solid craft and lights streaking rapidly through the sky — Hynek was struck by the similarity between the two events.

In both cases a distinctive reddish yellow, and green lights were reported, plus a general yellow glow. The spectacular lights, when reported, were stated to be of limited area... The similarity between the Dexter lights and the Hillsdale lights was striking. Not only as to color and intensity, but motion as well. The motion was described In both cases as smooth and slow, with a tendency to disappear rather suddenly and reappear elsewhere.

Hynek saw two photographs during his investigation. The first he immediately recognized as a blimp, and the second he recognized as a timed exposure of the crescent moon and Venus rising over the horizon.

And so it was in the heat of the media feeding frenzy that Hynek collected these stories, and he wrote up, at the request of the Air Force, a nineteen page Report on the Dexter-Hillsdale, Michigan UFO Sightings of 20-21 March 1966. In that paper, he told what happened next:

…Since the interest and excitement generated in these cases was mounting to fever pitch, it seemed expedient, in fact mandatory, to hold a press conference and make a progress report. Until the evening before I was to make such a statement, I was still puzzled as to a natural explanation for even the consistent sightings. Fortunately, I have a number of friends in the academic world in Ann Arbor and whose invaluable aid I enlisted. I would like to give credit to the scientists I talked with until very late into the night but they prefer to remain anonymous. I am sure, however, that should their testimony be officially required, rather than for the press, their cooperation could very easily be obtained.

It was from these academic gentlemen that I obtained the information on marsh gas and the lights frequently associated with it. To summarize, it appears that rotting vegetation In the swamps produces methane, CH₄, and hydrogen sulfide, H₂S, in ample quantities under certain conditions… In addition, phosphine PH₃ is produced by the reduction of phosphorous compounds In the marsh material. These three gases ordinarily do not spontaneously ignite, but I am told, a small impurity in the PH₃, namely P₂H₄ [diphosphane], is highly flammable and when exposed to air spontaneously ignites. This then apparently can serve to ignite the other gases. The phenomenon of swamp lights is apparently quite well known, and references to it are ample in the literature.

Hynek gave his press conference the next day in which he announced his hypothesis, and suffice it to say that it did not go over well. The eyewitnesses remained convinced they'd seen something extraordinary, a spacecraft or a secret military craft. Really, nobody was on Hynek's side here. He wrote:

I wish that a press conference had not been necessary, or, if necessary that it had been handled more expertly and adroitly. I have little to say that is complimentary about the public relations office at Selfridge Field. It was amateurish in the extreme, and displayed no knowledge of how a press conference should be handled.

I would say that it was equally amateurish of Hynek to convene a press conference without an adequate explanation and then work through the night with his colleagues to come up with something to announce — and Hynek was no stranger to press conferences, so it's a mystery why he felt pressured to announce the swamp gas explanation. He'd had such a short time to conduct his interviews and had arrived at no supported conclusions about anything. He would have done much better to simply say he had collected a lot of eyewitness reports and may have more to say later if a solid explanation suggested itself.

Now it bears mentioning that swamp gas is absolutely not an acceptable explanation for lights in the sky. The spontaneous ignition he mentioned is a real thing, but it has never been observed in nature, only in controlled laboratory conditions. And when it does burn, it flashes instantaneously with a loud pop. There is no mechanism by which it might burn in a sustained manner, or to burn at all anywhere except at the very surface where it is injected into the air. No theory — and certainly no evidence — supports the ability of swamp gas to simulate a light in the sky.

Hynek rued his choice in his 1972 book:

…Swamp gas became a household word and a standard humorous synonym for UFOs. UFOs, swamp gas, and I were lampooned in the press and were the subjects of many a delightful cartoon (of which I have quite a collection).

And so swamp gas entered the lexicon as a tongue-in-cheek explanation for UFOs, and it formed no small part of Hynek's undeserved reputation as a crackpot. He was not that. From his books, one gets the impression that Hynek never strayed much farther from solid objectivity than giving perhaps too much credence to the folly of eyewitness testimony. Overwhelming, a study of his long association with the Air Force shows that they were lucky to have him.

And no, nobody ever did solve the Dexter-Hillsdale lights.

By Brian Dunning
Follow @BrianDunning