Six years ago, Joseph Dwyer, an atmospheric physicist, flew a jet plane into the heart of a thundercloud. The plane’s trajectory was no accident — Dwyer is a lightning expert. He’s known for sending small rockets tethered to the ground by copper wire directly into storms in order to attract bolts of lightning. But despite years of work, mysteries about lightning and the storms that produce it abound. "The insides of thunderstorms are like bizarre landscapes that we have barely begun to explore," he told Davide Castelvecchi for Nature.
And during that particular flight six years ago, Dwyer discovered something he still can’t fully explain. After what he calls "a wrong turn" the airplane entered into a strange cloud of antimatter.
Scientists already know that thunderstorms are breeding grounds for a particular kind of antimatter called positrons. These particles are the opposite of electrons. They carry a positive charge (hence the name) where electrons carry a negative charge. When the two meet, they annihilate each other, an event researchers can see because it throws off a flash of gamma rays. NASA’s Fermi Gamma-ray Space Telescope was able to spot these gamma ray flashes sparkling through thunderstorms soon after its launch in 2008. Each flash gives a distinct amount of energy — the signature of an electron and positron meeting.
Dwyer’s mission was therefore to look for those gamma ray flashes. He was then at the Florida Institute of Technology and was able to get a plane — the type usually flown by business executives, Castelvecchi reports — and fly off the Georgia coast in search of those gamma rays. At a fateful point the the pilots thought they had turned back towards the coast. Castelvecchi writes:
“Instead, it was a line of thunderstorms — and we were flying right through it,” Dwyer says. The plane rolled violently back and forth and plunged suddenly downwards. “I really thought I was going to die.”
During that time however, some of the gamma ray signatures Dwyer recorded didn’t come in at the right energy level. They were slightly lower energy than he expected. In the years since the flight, they’ve tried to figure out why. Dwyer and his colleagues suspect that the rays lost energy as they traveled through the air and reached the plane. They estimate that the plane flew through a small cloud of antimatter about one to two kilometers across.
The antimatter is still likely to be positrons, but where they were coming from is still up for debate. Instead of being created by the thunderstorm, they could have streamed in from space in the form of cosmic rays. Or, as another physicist, Aleksandr Gurevich, who was not on the team, suggests, the airplane’s wings could have gathered a charge, produced extremely intense electric fields that generated positrons.
The only way to answer all these lingering questions about the antimatter cloud is to go back to the scene of the crime — Dwyer wants to send weather balloons into the center of violent storms. Also, the U.S. National Science Foundation hopes to fly a detector that can measure gamma rays into a storm once again, this time on an armored anti-tank plane that won’t be tossed around as easily, Castelvecchi reports. "It’s very difficult to make measurements inside the thunderstorm," Dwyer told Ira Flatow on NPR’s Science Friday in 2010. "They're big dangerous places." But not dangerous enough to stymie curiosity.