Sparks between microscopic bubbles could explain the ghostly, glowing will-o’-the-wisps, study finds

By Mindy Weisberger, CNN

(CNN) — Hovering blue flames that flicker over bogs and marshes have inspired ghostly folktales for centuries. Known as “will-o’-the-wisp,” “jack-o’-lantern,” “corpse candle” and “ignis fatuus” (“foolish fire” in Latin), the global phenomenon has a spine-tingling history. But its origins could now have a scientific explanation: tiny flashes of lightning that ignite microscopic bubbles of methane.

Scientists have long suspected that the will-o’-the-wisp’s spectral glow came from a chemical reaction in gases released by decaying organic matter. Methane, which is odorless, colorless and highly flammable, is one such gas. Swamp gas is about two-thirds methane, and when methane reacts with oxygen, the oxidized methane glows blue-violet. However, methane does not spontaneously ignite in oxygen’s presence.

New research suggests that the elusive will-o’-the-wisp is triggered when flashes of “microlightning” arc between electrically charged bubbles of methane in water. As multiple bubbles of methane oxidize and combine, they produce the will-o’-the-wisp’s eerie light, according to the authors of a study published September 29 in the journal PNAS.

“There’s a paradox here: If you have a fire, you put it out with water. But little water droplets can make a fire,” said senior study author Dr. Richard Zare, the Marguerite Blake Wilbur Professor of Natural Science and professor of chemistry at Stanford University in California.

Using high-speed cameras recording video at 24,000 frames per second, the study authors captured flashes of electricity zipping between the surfaces of tiny charged bubbles. When oppositely charged bubbles came together, electrons jumped from a negatively charged surface to a positive one and generated a spark, Zare told CNN.

“That’s lightning,” he said. Though this lightning is at a minuscule scale, “it has enough energy to make all types of chemical reactions occur.” Future experiments with this mechanism could help researchers develop more sustainable methods for common chemical processes, Zare added.

Re-creating microlightning in a lab

Other explanations for glowing will-o’-the-wisp lights don’t hold up under scrutiny, Zare told CNN. Proposals that the lights were swarming insects or birds carrying glowing fungus were quickly debunked. Static electricity needs dry conditions to spark, which wouldn’t occur in swampy, water-logged ecosystems.

When the Italian chemist and physicist Alessandro Volta — who discovered methane in 1776 — suggested that lightning ignited methane in swamp gas to create will-o’-the-wisps, he was closer to the truth than he suspected.

“He thought it was lightning in the sky,” Zare said. “But no. It’s microlightning.”

In a prior study, Zare and other researchers showed that charged water droplets measuring between 1 micron and 20 microns in diameter — smaller than the width of a human hair — could generate microlightning powerful enough to form organic molecules. Billions of years ago, this process may have produced the building blocks of Earth’s earliest life.

The new experiments took place in a water-filled container. A microbubble generator pumped methane bubbles into the water through a nozzle. As the methane bubbles filled the water, the scientists observed microlightning flashes jumping between the surfaces of adjacent bubbles, resembling microlightning seen in earlier experiments with charged water droplets.

“The article puts forward a very interesting hypothesis and reports some evidence in support,” Dr. Alexei Khalizov, a physical chemist and a professor of chemistry and environmental science at the New Jersey Institute of Technology, told CNN in an email.

However, lingering questions accompany this explanation for the will-o’-the-wisp phenomenon, said Khalizov, who was not involved in the new research.

For example, the researchers’ experiments used pure, deionized water, while real swamp water is teeming with organic and inorganic compounds, Khalizov said. Among these compounds are salts called electrolytes, which could suppress charge separation between gas bubbles.

“Deionized water is a good insulator. Regular water is not,” he said. “Will the reported phenomenon even occur in non-deionized water?”

And while the experiments show the presence of microlightning between bubbles, the glow was not reproduced at a level that would be seen in a swamp. Nevertheless, Khalizov said that “the process is still very intriguing” and that further study of microlightning could reveal their role in oxidizing trace gases released at the sea surface — some of which play a role in global warming.

Beyond will-o-the-wisps

Harnessing microlightning could present more sustainable options for chemistry, according to Zare. “We’re doing this at room temperature without applying any external electric field and without necessarily having to add catalysts,” he explained.

One possible application for microlightning could be triggering chemical reactions that reduce atmospheric methane, the most abundant greenhouse gas after carbon dioxide. Methane makes up about 11% of greenhouse gas emissions globally and is about 28% more potent than carbon dioxide at trapping heat.

“The question is: Can we really scale it up and make it commercial and industrial?” Zare asked. “That’s what I’m working on.”

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