Unexplained Sounds Detected in Earth's Stratosphere.

Solar balloons were sent 70,000 feet up in the air to record sounds of Earth’s stratosphere, and the microphones picked up some unexpected sounds. The balloons can take sensors twice as high as commercial jets can fly. The researchers tracked their balloons using GPS, since they can travel for hundreds of miles and land in inconvenient locations. The advantage of the high altitude reached by the balloons means that noise levels are lower and the detection range is increased — and the whole Earth is accessible.