For centuries, will-o’-the-wisps—eerie, blue flames floating over marshes—spooked unassuming passersby. The strange aberrations inspired many supernatural interpretations, from fairies and ghosts to, of course, an adaptation as a Pokémon attack move. But as with many seemingly supernatural phenomena, there’s a very tangible, scientific explanation—one scientists long suspected but have only now confirmed.
In a Proceedings of the National Academy of Sciences paper published on September 29, researchers explain that tiny lightning sparks jumping between marshy bubbles create will-o’-the-wisps. Marshes and swamps are rich in flammable methane gas, and microscopic interactions between water droplets ignite the gas, according to the paper. In short, the ghostly flames are a product of chemical reactions occurring on a microscopic level.
“We continue to discover things about water that, once you understand them, they’re obvious, but before then, they seem completely bizarre,” Richard Zare, study senior author and a chemist at Stanford University, told New Scientist. “No one thinks of water related to fire. They think water puts out fire. They’re not telling you with water, I can get a spark and set something on fire. This is new.”
Spontaneous ‘microlightning’
The new study builds on Zare’s previous research, which introduced the idea of “microlightning.” This refers to a small flash of energy generated by electrically charged water droplets. Although water is typically neutral, exposure to the air can create positive or negative charges within the tiny droplets. The charge difference generates tiny electric fields that crackle into even tinier energy sparks—microlightning.
For the new paper, Zare and his colleagues focused on how microlightning could jump-start unintended chemical reactions. First, they designed a simplified version of the chemical conditions in a marsh, using a beaker of water with a nozzle to introduce methane and other gases. They captured the microscopic movement of the droplets by taking high-speed videos.
As expected, when the bubbles slammed against each other, tiny light flashes emerged within the beaker. By applying some analytical chemistry, the team confirmed that microlightning was indeed triggering the reaction between methane and oxygen. The power of these sparks is enough to ignite methane gas, according to the paper.
“This is really an interesting step forward,” James Anderson, a chemist at Harvard University not involved in the work, told Science. “It reveals a mechanism by which chemical reactions can be initiated.”
The origins of life?
In their first work on microlightning, Zare’s team hypothesized that the phenomenon could have “provided the sparks that gave rise to biomolecules necessary for life,” Zare explained to Science. The new work “strongly suggests” that microlightning indeed helped shape natural processes, in this case will-o’-wisps, Wei Min, a chemist at Columbia University not involved in the work, told Scientific American.
Then again, it’s important to remember that the experiment, while commendable, was strictly conducted inside a controlled laboratory. The dynamics of a real-life swamp are undoubtedly more complex. What’s more, the absence of modern will-o’-the-wisp sightings suggests as much, according to Antonio Pavão, a chemist at Brazil’s Federal University of Pernambuco in Recife who wasn’t involved in the study, speaking to Science News.
Regardless, the results offer fascinating insights into a neglected natural chemical process. If anything, it’s a phenomenon that warrants a closer look—even if there aren’t any ghosts involved.