When you think of an alien world, you might think of a strange, stormy place with an inhospitable environment, frequent lightning strikes, and extreme radiation. But who needs an imagination when the storms here on Earth already beam radiation, including antimatter, down toward the ground?
Hurricane Patricia in 2015 was the second most intense tropical cyclone ever on record, travelling up the Pacific coast of Mexico with winds topping out at 346km-per-hour. Despite the fierce conditions, scientists still had science to do, and they flew in a plane through its eyewall on October 23, 2015. The plane's instruments measured gamma-rays blasted from lightning inside the hurricane, as well as what seemed to be beam of positrons, the antimatter opposite of electrons. Events like these are probably more common than you'd think.
"These terrestrial gamma-ray flashes can happen in any storm that makes lightning," David Smith, one of the study's authors from the University of California, Santa Cruz, told Gizmodo.
The detector onboard the plane measured a phenomenon that scientists have been interested in for decades: terrestrial gamma-ray flashes. It's unclear exactly how it happens, but lightning in storms seems to accelerate electrons to nearly light speed. These electrons collide with the particles in the atmosphere, resulting in high-energy x-rays and gamma rays that scientists have measured in satellites and on the ground. The rays could also result from collisions between electrons and their antimatter partners, positrons.
The team behind the newest paper had a tool called the Airborne Detector for Energetic Lightning Emissions (ADELE) on board a hurricane-hunting WP-3D plane, according to the paper published recently in the Journal of Geophysical Research: Atmospheres. It was a very simple radiation-detecting experiment: two pieces of plastic and one special kind of crystal, all called scintillators, that flash when a high-energy particle hits them. An instrument called a photomultiplier tube turns the flashes into signals that a computer or oscilloscope can read. There was also a radio-wave detector.
The scintillators flashed 184 times in the split-second following a lightning bolt in Hurricane Patricia's eyewall. Based on their modelling, the signal matched what a downward beam of positrons would look like — meaning they didn't measure positrons directly.
This is the first time such an effect has been measured in a hurricane's eyewall, though it's been known to happen in lots of different kinds of storms. And no, the positrons aren't anything to worry about, since you're probably already being struck by lightning. Positrons are a typical byproduct of certain radioactive sources, and their numbers drop off precipitously with distance. Still, said Smith, if you were in a plane at the exact unluckiest place at unluckiest time (higher than their experimental plane flew) you might receive a deadly dose of radiation.
Most interesting to Smith was the mystery of why these wild events happen when and how they do. "From a scientific perspective, this is an exotic phenomenon and there's a lot we don't understand, like why it is as bright as it is and why it happens sometimes but not others," he said. "We're trying to understand whatever phenomenon nature throws at us."