This April 17, 2014 image provided by NASA shows workmen unloading a saucer-shaped test vehicle for NASA's Low-Density Supersonic Decelerator (LDSD) project, at the U.S Navy's Pacific Missile Range Facility at Kekaha on the island of Kaua‘i in Hawaii. The engineering test flight of this vehicle is scheduled for June 3, 2014. The saucer will be boosted to high altitudes via balloon and rocket, before releasing an inflatable doughnut-shaped tube and an enormous supersonic parachute -- possible landing technologies for future Mars missions.(AP Photo/NASA) Photo: HOPD / NASA
-launched balloon

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For the first time in 50 years, microphones attached to a NASA-launched student balloon have captured strange hisses, crackling sounds and faint whistling.

Researchers aren’t sure what the sounds are but have some guesses: Signals from a wind farm under the balloon’s flight path, crashing ocean , wind turbulence, gravity and vibrations caused by the balloon cable, according to Live Science. 

The balloon, which flew above New and on Aug. 9, , was part of High Altitude Student Platform, conducted by NASA and the Space Consortium and designed to foster student excitement in aerospace careers.

Daniel Bowman, a graduate student at the University of North Carolina at Chapel Hill, designed and built the equipment, Live Science reported.

Bowman Live Science he was surprised at the complexity of the “infrasounds,” which are very low-frequency counds that cannot be heard by human ears but can be speeded up to make them audible.

Strange noises captured on audio

During its nine- flight, Bowman’s balloon reached a height of more than 123,000 feet (more than 23 miles), a altitude for infrasound experiments, according to Live Science. The region is “near space” — above where airplanes fly but below the 62-mile marker at the top of the stratosphere.

Bowman said he hoped the results would help revive interest in atmospheric infrasound, which peaked in the 1960s as a way to detect nuclear explosions. 

“There haven’t been acoustic recordings in the stratosphere for 50 years,” he told Live Science. “Surely, if we place instruments up there, we find things we haven’t seen before.”