Twelve years ago, a U.S. military rescue mission in Afghanistan went horribly wrong. A Chinook helicopter carrying U.S. troops failed to receive a crucial radio message and was shot down over the snow-covered peak of Takur Ghar.
But the radio failure was not caused by malfunctioning equipment. Instead, a giant, 62-mile-long (100-kilometer-long) "plasma bubble" made up of clouds of electrically charged particles was responsible for the communication blackout, new research suggests.
Michael Kelly, a researcher at the Johns Hopkins University Applied Physics Lab (APL), in Laurel, Maryland, started to put the pieces together after reading a journalist's account of the Battle of Takur Ghar. He suspected the radio failure was caused by a little-known space weather effect caused by these mysterious plasma bubbles. (10 Surprising Ways Weather Has Changed History)
During daylight hours in the upper atmosphere, radiation beaming down from the sun rips electrons from their atoms. But once the sun sets, the electrons start recombining with their atoms. This recombination process happens faster in the lower atmosphere because there are heavier particles there, and electrons recombine faster with molecules than they do with single atoms. Since the plasma in this part of the atmosphere is less dense, it rises and burrows into the denser plasma above. This causes giant bubbles of charged particles to form, similar to the way air bubbles rise from a submerged diver.
The huge bubbles of charged particles can bend and warp radio waves. In 2002, the Chinook helicopter was flying over Afghanistan in the spring, which is the height of plasma bubble activity, Kelly said.
Military officers based in Bagram, Afghanistan, issued a fateful radio warning to the helicopter crew to stay away from al Qaeda forces on the mountaintop, but the message was scrambled and lost. The helicopter crash-landed, and seven individuals were killed.
To figure out what went wrong, Kelly and a team of researchers used data from a NASA satellite mission called TIMED, which launched in 2001 to study the composition of Earth's upper atmosphere. Their model showed that on March 4, 2002, a plasma bubble loomed above the unlucky helicopter. The mountainous terrain had likely already made the radio signals weak, and the presence of the plasma bubble could have interrupted this weakened signal, causing a complete radio blackout.