Sounds that were recorded on August 9, 2014 from the edge of space are special for a few reasons. First of all, no one knows the source. Second, it was the first time infrasounds had been captured from the edge of space in 50 years. On that August day in 2014, a balloon that was created by a university student for a NASA experiment traveled up to the edge of the stratosphere and picked up strange noises roughly 22 miles (36 kilometers) above Earth’s surface. The balloon was designed and built by Daniel Bowman, a graduate student at the University of North Carolina at Chapel Hill.These noises are only audible to the human ear after they are sped up, because the atmospheric infrasounds are sound waves at frequencies below 20 hertz. Once audible, the sounds are almost reminiscent of “The X Files” theme music — or maybe that’s just the imagination at work. Researchers have yet to nail down the exact source of these sounds, but there are theories as to what caused the noises captured above New Mexico. The sounds may be the result of a wind farm beneath the balloon’s flight path, ocean waves, wind turbulence, gravity waves, clear air turbulence, or vibrations from the balloon cable. Watch the video below to hear the sounds for yourself.