Solar-powered balloons soaring into the Earth’s stratosphere have captured an enigma – mysterious rumblings that baffle scientists in their origin. The infrasound signals, detected at 70,000 feet, are so low-pitched that they elude human hearing. Amidst a cacophony of concealed low-frequency sounds, including thunder, ocean waves, and human activities like rocket launches and transportation, these peculiar infrasounds remain unexplained.
Daniel Bowman, the lead investigator and a senior scientist at Sandia National Laboratories, expressed uncertainty about the source of these signals, which intermittently manifest a few times per hour during certain flights in the stratosphere. The stratosphere, extending from approximately 9 miles to 31 miles above the Earth, is a serene layer above the atmosphere, characterized by ultraviolet-blocking ozone and minimal turbulence. Most sounds in this region originate from ultra low-frequency reverberations from the Earth’s surface.
Since the 1890s, scientists and enthusiasts have launched balloons into the stratosphere. The recent study, employing 23-foot-wide plastic balloons equipped with infrasound sensors and charcoal powder for passive solar elevation, commenced in 2016. Initially focused on recording sounds from volcanic eruptions, the project unintentionally detected the unexplained low rumbles during their flights, defying precise identification.
The researchers have proposed hypotheses, ranging from undiscovered atmospheric turbulence to distorted echoes from below. The balloons, propelled by solar power, facilitated extensive tracking across hundreds of miles using GPS. Despite having some conjectures, the scientists remain uncertain about the exact nature of these mysterious stratospheric sounds. The investigation continues, aiming to unravel the origins, variability across seasons, and patterns in different global regions.