It's a hot night out here in the Australian outback. We're about 40 miles east of the tiny village of Boulia, near the site of an old ghost town called Min Min that doesn't even exist anymore. They call this part of western Queensland the channel country, a flat expanse of flood plains and creeks and dry washes that almost never flow. Stand on a high point and you can see to the horizon in every direction. And if you're lucky, on a night like this, you might see the region's most infamous denizen: The Min Min Light.
Sometimes it's an orange speck, sometimes it's a big white ball. Sometimes it's close and sometimes it follows you, sometimes it just hovers away out in the distance. Some say it's just a tall tale, and others say they've seen it with their own eyes. It's been called a ghost light, a spirit orb, and in later years, all manner of scientific sounding natural phenomena. But it's real and it's there, and only a lucky few will see it, but see it they do, and have for the better part of two centuries. We can go all the way back to 1838 to find the earliest known written account of the Min Min Light. It comes from T. Horton James' book, Six Months in South Australia:
A group of explorers were camped in the Ovens River region of eastern Victoria, when they saw a fire a little way off. Some of them rode off to investigate, but it was about three hours before they returned, and had seen neither fire, bushrangers, nor travelers. They rode boldly up to the spot where the fire, as they thought, was burning, but it was as far off as when they started. In short, it turned out to be an ignis fatuus, or jack-a-lantern, and kept them upwards of an hour trotting on in the vain pursuit, 'till by some sudden flickering and paleness, it confirmed them in its unsubstantial nature, and they returned rather mortified to bed...
It was a full century before the best known Min Min Light encounter was published in a 1937 issue of Australia's late Walkabout magazine. Rancher Henry Lamond told of an adventure that happened to him 25 years earlier:
...I did not leave the head station until about 2 am, expecting to get to Slasher's well before daylight… 8 or 10 miles out on the downs I saw the headlight of a car coming straight for me. Cars, though they were not common, were not rare. I took note of the thing, singing and trotting as I rode, and I even estimated the strength of the approaching light by the way it picked out individual hairs in the mare's mane.
Suddenly I realized it was not a car light — it remained in one bulbous ball instead of dividing into the 2 headlights, which it should have done as it came closer; it was too green-glary for an acetylene light; it floated too high for any car; there was something eerie about it.
The light came on, floating as airily as a bubble, moving with comparative slowness ... I should estimate now that it was moving at about 10 mph and anything from 5 to 10 feet above the ground ... Its size, I would say, at an approximate guess, would be about that of a new-risen moon. That light and I passed each other, going in opposite directions. I kept an eye on it while it was passing, and I'd say it was about 200 yards off when suddenly it just faded and died away. It did not go out with a snap -its vanishing was more like the gradual fading of the wires in an electric bulb.
Misidentifications of natural phenomena such as wind-blown mists; phosphorescence in marshes; spontaneous neuronal discharges in the visual field; clusters of luminescent insects; light refraction effects; ball lightning or other electric discharge.
An unknown natural phenomenon involving low-level air oscillations; or ionization in geophysically-generated electrical fields.
Psychokinetic or poltergeist effects unconsciously produced by an individual.
Small, physical UFOs ("remote-control probes").
These nominations are all quite fanciful, and would be difficult to test. But they're not without historical basis. In a 1955 issue of Walkabout, writer Ernestine Hill found plausible cause for a ghost light in the history of Min Min:
So many were its crimes and murders of kerosene and brimstone, that in righteous anger they burnt it to the ground. The place was stories and desolation- but the dead men would not be forgotten on their stoney plain. Just as a rider was passing by, out of that graveyard came the biggest Jack-O'-Lantern in Australia!
Most intriguing to the scientific mind, though, are the suggestions that some interesting natural wonder is responsible for the lights. Regular Skeptoid listeners might remember our episode about The Marfa Lights in Texas, a similar phenomenon. Piezoelectric effects have been proposed as an explanation for each. The piezoelectric effect is observed in certain crystals that change shape when an electrical current is applied to them, making them useful for such applications as the tiny sound element in a beeping digital watch. The effect also works in reverse: Apply mechanical force to the crystal and it produces an electrical current. A few naturally occurring minerals exhibit this effect, namely some types of quartz, topaz, and tourmaline structures. The idea is that geologic forces within the rock, either tectonic or thermal, create these piezoelectric charges. But there have always been two problems with this hypothesis: First, the effect is a weak electrical voltage, not light; and second, the voltage is measurable only on the crystal itself, it is not projected up into the air in the form of a glowing orb. At least, no such effect has ever been observed or predicted by calculation.
However, an article published in the journal Nature in 2006 by authors Eddingsaas and Suslick described a newly discovered form of mechanoluminescence, light from mechanical force. Scientists have known about mechanoluminescence for centuries, since it was first observed as sparks when scraping lumps of sugar. Eddingsaas and Suslick found that shockwaves of acoustic cavitation in a mechanically aggravated crystal slurry produced light much brighter than mechanical crushing alone. Very cool, but also a poor explanation for the Min Min Light. Neither crystal slurries nor sufficient mechanical aggravation are present at the Min Min site, and even if they were, the light is produced immediately at the source of the acoustic cavitation, and not projected up into the air in the form of a floating ball.
Optical science has produced a far better candidate for our mystery ghost light, one that is reproducible and that fully accounts for the observations. Professor Jack Pettigrew, writing in the journal Clinical and Experimental Optometry, described The Min Min Light and the Fata Morgana. You may remember the Fata Morgana mirage from our discussion of the Marfa Lights. Named for King Arthur's sister Morgana, who was said to be able to levitate objects, a Fata Morgana mirage is one type of superior mirage. In a superior mirage, the object is seen above its actual position, for example above the horizon, when in fact the object is far away and hidden below the horizon. Fata Morgana mirages are caused by thermal inversion layers in the atmosphere. They are fairly common in the arctic regions where temperature inversions are endemic. Often the ocean water temperature, hovering right around freezing, is warmer than the air directly above it, which can be well below freezing. A line of sight stretching along this gradient toward the horizon can easily become distorted, bending light like a fiber optic cable. Arctic islands that are low lying and below the horizon are often seen floating in the air above the horizon, inverted or doubled or stretched into tall blocky mesas.
Pettigrew found that Australia's channel country naturally creates ideal conditions for superior mirages. All of the hollows and ravines trap warm air, and on a cool evening following a hot day, the conditions are virtually certain to take place. Pettigrew and six observers parked a car with its headlights on, drove ten kilometers away past intervening high ground and out of the line of sight, and presto, the headlights were visible as a Min Min Light. The following morning they took photographs of a distant mountain range distorted by the Fata Morgana, that gradually faded away to its actual position below the horizon as the conditions dispersed.
As long as there have been people around to observe the Min Min Light, there have been people around to build campfires or have lanterns in the window dozens and perhaps hundreds of kilometers away. What about Henry Lamond's account of the light passing him? Well, who knows. Our memories often exaggerate remarkable events. Perhaps his trail curved away and created that perception, perhaps the story was improved in the retelling, there's no way to know.
But whether you choose to regard the Min Min Light as an optical artifact, as the ghost of a cowboy shot in an outback saloon, as a piezoelectric light beacon or as a remote controlled alien probe, there's no doubt that stories like the channel country jack o' lantern make our world ever more intriguing.