A recording instrument set by a graduate student has picked up 'infrasound', frequencies that cannot be heard by human ears. The experiment was conducted as a part of a NASA project to record sound from the edges of the atmosphere.

The Independent reported that the equipment set by the student picked up whistles and hisses that could be ascertained by speeding up the infrasound recordings.

The recordings were taken from a helium balloon in August last year, said researchers. The microphones that were hanged over New Mexico and Arizona were the key to get the first infrasound recordings ever taken at such altitudes, said Daniel Bowman, the University of North Carolina student who captured the sounds.

Bowman told Live science that the sound recorded was like 'The X-Files'.

According to the science news blog, current guesses as the origin of the noises include sound from a wind farm, the ocean, or vibrations from cables on the balloon.

NASA scientists will be sending some more devices later this year in the hope that they can learn something more.

Bowman, who has been constructing and launching his own high-altitude balloons since his high school, hopes that his experiment will revive the interest in atmospheric infrasound.

He further said that the sounds, picked up at frequencies below 20 hertz, the threshold for human sound detection, could only be heard by human ears after being sped up.

Bowman told Live Science, "There haven't been acoustic recordings in the stratosphere for 50 years. Surely, if we place instruments up there, we will find things we haven't seen before".

The Independent noted that some scientists have even proposed sending similar equipment to the moon and Mars, where they would be able to pick up transmit information about the extraterrestrial weather and the environment.