A “strange” sound with a “completely unknown origin” has been heard coming from the stratosphere, which is Earth’s high atmosphere. Large solar balloons that were 6-7 metres long and included a microphone were sent by a group of US researchers from Sandia National Laboratories to record the sound. Around 50 kilometres (31 miles) above the surface of the globe, the stratospheric region is relatively peaceful and devoid of storms, turbulence, and commercial air activity.
But when the scientists heard through the microphone enigmatic noises that were allegedly repeated a few times per hour, they were perplexed.
The sounds were in the infrasound spectrum, which is significantly below the audible range of human hearing and occurs at frequencies of 20 hertz (Hz) and below. The source has not yet been located. “There are mysterious infrasound signals that occur a few times per hour on some flights, but the source of these is completely unknown,” Daniel Bowman of Sandia National Laboratories said in a statement.
Microbarometers, a type of sound-gathering apparatus that can pick up low-frequency sounds were utilised by the research team
Microbarometers, a type of sound-gathering apparatus that can pick up low-frequency sounds, were utilised by the research team. Initially, it was intended to keep an eye on volcanoes. These sensors were sent into the air by balloons that the researchers made out of accessible and affordable materials. These solar-powered balloons can soar to an altitude of around 70,000 feet (13.3 miles) above Earth and are propelled by sunlight. Since balloons can often soar for hundreds of kilometres and may land in unfavourable terrains on the earth, tracking them after launch required the use of GPS.
“Our balloons are basically giant plastic bags with some charcoal dust on the inside to make them dark,” Bowman was quoted as saying by CNN. “We build them using painter’s plastic from the hardware store, shipping tape, and charcoal powder from pyrotechnic supply stores. When the sun shines on the dark balloons, the air inside heats up and becomes buoyant.” Though solar balloons offer greater access to record noise levels at lower frequency ranges since the whole Earth is accessible, they also present challenges for researchers. The stratosphere is a harsh environment with wild temperature fluctuations between heat and cold. “Solar balloons are a bit sluggish, and we’ve wrecked a few on bushes when trying to launch them,” Bowman said. “We’ve had to hike down into canyons and across mountains to get our payloads. Once, our Oklahoma State colleagues actually had a balloon land in a field, spend the night, and launch itself back in the air to fly another whole day!”
