Mysterious, Ghostly Blue Lights Called Will-o-the-Wisp May Just be Methane Bubbles
For centuries, Will-O’-the-Wisp has intrigued scientists and travelers. According to folklore, it is the product of fairies, demons and spirits. More recently, scientists have attributed Will-o’-the-Wisp, otherwise known as ignis Fatuus, meaning “stupid flame” in Latin, to more earthly origins. However, questions remain about how these ghostly blue lights occur intermittently.
Now, researchers writing in the Proceedings of the National Academy of Sciences (PNA) offered a more evidence-based solution to this age-old conundrum – methane bubbles spontaneously igniting in a process called microlightning.
Flaming Blue Will-O’-the-Wisp or Methane Bubbles?
Although previous generations moved toward supernatural explanations, there is now a strong consensus within the scientific community that links flickering blue light to methane released by organic matter as it decays. Methane is thought to ignite when it interacts with oxygen in the air, producing a “cool flame.”
However, it is not fully understood how exactly methane ignites in the first place, as the energy required to trigger this process is too high to occur naturally. Previous attempts to explain this have turned to phosphine or static electricity, but these are unproven.
Instead, the researchers, writing in PNA, turned to a phenomenon studied in an earlier study (published in Science Advances), which shows that tiny water droplets can accumulate charges which are then released spontaneously – a process called Microlightning.
“Micro-microbubbles between methane microbubbles provide a natural ignition mechanism for methane oxidation under ambient conditions,” the researchers explained in the PNA study.
“This finding supports a long-suspected link between electrified interfaces and spontaneous cool flames, and it provides a physically grounded explanation for the occurrence of Ignis Fatuus,” the study authors continued.
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Methane microbubble manufacturers
To test the hypothesis, the researchers built a microbubble generator that generated methane-air bubbles and exploded them in a pot of water. Using high-speed imaging, the team observed “brief, localized flashes” of less than a millisecond, which they explain are “consistent with electrical discharges.”
The reason the microbubbles were able to accumulate charges is because of the curved boundary that exists between the gas and liquid – the larger the curve, the greater the electric field at the boundary or “interface.” A discharge occurs when two microbubbles with opposite charges approach each other, which, in turn, can prompt the gas to ignite a “cool flame” (the faint blue luminescence characteristic of Will-o’-the-Wisp).
“These discharges trigger nonthermal oxidation of methane, producing luminescence and measurable heat under ambient conditions,” the researchers explained in the study.
The team tested how regular old air bubbles react and found that they also trigger flashes.
This, they say, suggests that the reaction is the result of interactions between two oppositely charged particles and is not due to the gas itself, although methane appears to enhance the intensity of the reactions and increase the frequency.
According to the researchers, these results could be the missing piece of the puzzle and help explain how methane in marshes and wetlands is able to produce blue luminescence spontaneously.
“For centuries, faint blue flames known as Fatuus ignis or Will-o’-the-wisps danced above marshes, graveyards, and wetlands,” they explained in the study.
Adding: “Our results provide a scientific basis for Ignis Fatuus and reveal a general mechanism by which electrified interfaces can drive redox reactions in natural environments without the need for external ignition sources.”
Other Explanations for Will-o’-the-wisp
But this is not the only explanation recently proposed. Researchers writing in Brazilian peer-reviewed journal Quim Nova Argue that Will-o’-the-wisp may be “extinct”, highlighting the fact that there are few or no reliable sightings in modern times.
Instead, the journal states that the old-fashioned torches carried by the travelers could have acted as an ignition source and “the abandonment of fire in favor of night lightning may hold the secret of this mystery of the extinction of Ignis Fatuus.”
Learn more: Old wives’ tales for predicting the weather: what is based in science and what is folklore?
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