Scientists hear mysterious sounds outside the Earth's atmosphere. Looks like a "giant sigh"

Scientists have spotted mysterious sounds via giant solar balloons equipped with sensitive microphones sent to 70,<> feet above the surface where they entered the heart of Earth's second layer of atmosphere known as the stratosphere.
NASA explained that the thin, dry air in the stratosphere, where jet planes and weather balloons reach their maximum altitude, is a relatively calm atmosphere, rarely affected by turbulence.

The "stratosphere", according to the US space agency (NASA), is the second layer of the Earth's atmosphere, and at its lowest level there is the ozone layer, which absorbs and dissipates the sun's ultraviolet rays, according to CNN.
Daniel Bowman, principal scientist at Sandia National Laboratory in New Mexico, is exploring the acoustic landscape of this layer of the atmosphere, inspired by his study of low-frequency sounds produced by volcanoes. This phenomenon is scientifically known as ultrasound, which the human ear cannot hear.

Baumann and his team previously installed cameras on weather balloons to capture images of the black sky at the top and the ground below, and then successfully created their own solar balloon.

He also proposed linking infrared recorders to balloons to record the sounds of volcanoes, in collaboration with his adviser, Jonathan Lis, of the University of North Carolina.

"We decided to go ahead and explore what this new platform can do, in collaboration with Earth, Ocean and Environmental Sciences specialist Jonathan Liss as well as his expertise in seismological and volcanological research.

According to Bowman, these balloons are equipped with sensors twice as fast as commercial aircraft.

"In our solar balloons we recorded chemical explosions, thunder, crashing ocean waves, helicopters, city sounds, additional rocket launches, earthquakes, freight trains and jets," Bowman said in an email, adding, "We have recorded other sounds, but their origin is unclear."
In a recording shared by Bowman from a NASA balloon orbiting Antarctica, the ultrasound of ocean waves crashing sounds like a constant sigh, or giant sigh, but explosions and other shocks are of unknown origin.

Bowman said Thursday during that participation that "within the stratosphere some aircraft had mysterious infrared signals a few times an hour, but their source is not fully known."
Bowman and his aides conducted the search using NASA balloons and other aviation service providers, but decided to build their own, each with a diameter of 6 to 7 meters. Bowman estimates he launched dozens of solar balloons to collect infrasound recordings from 2016 to April 2023.

The researchers tracked their balloons using GPS as they traveled hundreds of miles before landing far away.

The advantage of the high altitude reached by balloons is that the noise level is lower and the detection range increases, and the entire planet can be explored.
Balloons pose challenges for researchers, however, as the stratosphere is a harsh environment in which temperatures fluctuate between hot and cold.

Bowman said, according to "", "There are a lot of balloons that detect signals whose origin we do not understand. It's definitely normal or caused by air turbulence."

Sarah Albert, a geophysicist at Sandia National Laboratories, investigated a "sound channel" (a channel that transmits sounds over great distances across the atmosphere) located at altitudes determined by Bowman's research.

Sarah's recordings captured rocket launches and other unknown sounds.