Current guesses include sound from a wind farm, the ocean, wind or vibrations from cables on the balloon, according to Live Science. 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.
“I was surprised by the sheer complexity of the signal,” Bowman told Live Science. “I expected to see a few little stripes.”
Bowman hopes that the recordings will be able to revive interest in infrasound recordings, which haven’t been made in the stratosphere for 50 years. Some scientists have proposed sending similar equipment to the moon and Mars, where it might be able to pick up information about weather and the environment.