A graduate student from the University of North Carolina was able to record strange noise in the Earth's stratosphere using ultra-sensitive microphones fitted on a high altitude scientific balloon.

UNC's Daniel Bowman captured infra-sonic sounds with his balloon while conducting a scientific study for the National Aeronautics and Space Administration (NASA) and the Louisiana Space Consortium.

The project, called High Altitude Student Platform (HASP), is meant to spark student interest in learning about space.

Bowman's helium balloon was flying around 22 miles above Arizona and New Mexico when the mysterious sounds were recorded on Aug. 9, 2014. The event marked the first time sounds were recorded from space in 50 years using a NASA space balloon.

The balloon had traveled for nine hours across a total of 450 miles at an altitude of 123,000 feet.

In an interview with Live Science, Bowman said that the captured infra-sonic sounds were "kind of like The X-Files."

"I was surprised by the sheer complexity of the signal," Bowman said. "I expected to see a few little stripes."

The discovery of the strange noises has generated several theories as to what could have caused them.

Some pointed out that the sounds were signals coming from a wind farm below the flight path of the balloon. Others said that it could have been the sound of ocean waves crashing or wind turbulence the balloon might have encountered during its flight.

Turbulence from clear air, gravitational waves and even vibrations from the balloon's cable were also raised as possible explanations.

Another HASP research balloon is scheduled to launch this year, which scientists believe could help explain the mysterious infrasound further.

Infrasonic sounds are known to travel long distances, but they can only be heard at a frequencies below 20 hertz. Some sources of infrasound waves on Earth include avalanches, volcanoes, storms and earthquakes. They can also be produced during the passing of a meteor.

NASA's HASP project has launched around 70 experiments to the edge of space since it began in 2006. All of the balloons were designed by students from colleges all over the United States.

Photo: NASA Goddard Space Flight Center | Flickr