Unveiling ignis fatuus: Microlightning between microbubbles.

Abstract

Will-o'-the-wisps, ghostly blue flames seen at night in marshlands and long attributed to methane cool flames, have remained scientifically unexplained, a mystery caused by the lack of a known ignition mechanism. Here, we demonstrate that spontaneous electrical discharges, termed "microlightning", can occur between rising methane-containing microbubbles in water. High-speed optical imaging reveals brief flashes between charged bubbles, arising from strong electric fields at curved gas-liquid interfaces. These discharges initiate nonthermal oxidation of methane, producing luminescence and measurable heat under ambient conditions. Our findings offer 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.