Mysterious sounds in stratosphere can’t be traced to any known source

Solar-powered balloons floating within the stratosphere have recorded low-frequency sounds of mysterious origin.

“When we started flying balloons years ago, we didn’t really know what we’d hear,” says Daniel Bowman at Sandia National Laboratories in New Mexico. “We learned how to identify sounds from explosions, meteor crashes, aircraft, thunderstorms and cities. But virtually every time we send balloons up, we find sounds that we cannot identify.”

Bowman and his colleagues measured infrasound alerts – sounds with a frequency so low they’re inaudible to human ears – utilizing solar-powered balloons floating 20 kilometres excessive.

The researchers constructed balloons about 7 metres extensive and made from skinny plastic. They stuffed the balloons with charcoal powder, which heats up in shiny daylight and makes the balloon float. Unlike climate balloons, which rise till they pop, these DIY solar-powered balloons coasted within the stratosphere for hours, carrying infrasound sensors over a whole lot of kilometres. The researchers deployed greater than 50 balloons over the course of seven years beginning in 2016.

The knowledge they collected confirmed that the stratosphere sounds fairly completely different than the floor of Earth. On the bottom, infrasound sensors choose up alerts which were deflected by winds on their method down, however the balloons floated above these winds – they recorded signatures of turbulence in different elements of the environment, and infrasonic sounds of marine storms. However, Bowman says that many infrasound alerts from the stratosphere didn’t have an apparent origin. He offered the work at a gathering of the Acoustical Society of America in Chicago, Illinois, on 11 May.

These mysterious alerts could possibly be associated to forms of atmospheric turbulence which have by no means been recorded earlier than, however infrasounds within the stratosphere have solely not often been explored earlier than so it’s exhausting to make educated guesses, says Bowman.

He says one of many first balloon research of this type was a US Army Air Forces experiment code-named Project Mogul, which sought to detect infrasound alerts of nuclear weapons exams within the Soviet Union within the Forties. One of Project Mogul’s balloons crashed in Roswell, New Mexico, which introduced the highest secret programme into the general public eye. The cover-up to hide the balloon’s objective sparked UFO conspiracies, and many of the knowledge from consequent balloon flights, ending within the Nineteen Sixties, had been saved labeled, says Bowman.

Roger Waxler on the University of Mississippi says he isn’t shocked by enigmatic infrasound alerts showing in recordings of the stratosphere. “On the ground you can put sensors into arrays and know exactly where they are relative to each other, which helps calculate where an infrasound came from. With balloons, they just go where they go,” he says.

Bowman is collaborating with NASA to develop comparable balloon expertise for an excellent much less explored place: the clouds of Venus. He and his colleagues wish to adapt their solar-powered balloons to file infrasound above the floor of Venus, which might assist chronicle the planet’s seismic exercise.