NASA balloon experiment has captured atmospheric infrasound 22 miles above Earth.

The hisses and whistles heard in the recordings were captured by Daniel Bowman, University of North Carolina student, last year. The recordings were taken from a helium balloon in August last year. The microphones dangled over New Mexico and Arizona and were one of 10 sent out by NASA as part of the High Altitude Student Platform.

Like Us on Facebook

Infrasound, at frequencies below 20 hertz, is undetected to the human ear, but becomes audible when sound waves are sped up. Sensors on a helium balloon let loose above New Mexico and Arizona in August managed to record hours of audio, including stratospheric signals researchers say they've never heard before, at altitudes of up to 123,000 feet, never reached by such an experiment.

Bowman described the sounds as "like the X-Files", and scientists aren't sure where they came from.

Current guesses include sound from a wind farm, the ocean, wind or vibrations from cables on the balloon.

"I was surprised by the sheer complexity of the signal. I expected to see a few little stripes,” Bowman told in an interview.

Reports said that interest in atmospheric infrasound as a means of detecting nuclear explosions was high in the 1960s, before ground-based sensors became commonplace.

However, scientists have more recently explored the idea of sending infrasound sensors to Venus and Mars to monitor weather or earthquakes. The scientists will be sending more devices up as part of the 2015 run of the project, and hope that they can learn more then.

TagsStudent Capture Intriguing X-Files Sounds from Outer Space, NASA, Sound recording and reproduction, Alien, Universe, outer space, X-Files, extra-terrestrial, space exploration