Scientists have detected sounds high in Earth’s atmosphere that can’t be identified.
A solar-powered balloon mission launched by researchers from Sandia National Laboratories carried a microphone to a region of Earth’s atmosphere found around 31 miles (50 km) above the planet called the stratosphere. This region is relatively calm and free of storms, turbulence and commercial air traffic, meaning microphones in this layer of the atmosphere can eavesdrop on the sounds of our planet, both natural and human-made.
However, the microphone in this particular study also heard strange sounds that repeat a few times per hour. Their source has yet to be identified. The sounds were recorded in the infrasound range, meaning they were at frequencies of 20 hertz (Hz) and lower, well below the range of the human ear. “There are mysterious infrasound signals that occur a few times per hour on some flights, but the source of these is completely unknown,” Daniel Bowman of Sandia National Laboratories said in a statement.
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