Strange sounds high in Earth's atmosphere baffle scientists

Sandia National Laboratories scientists have launched a solar-powered balloon into the stratosphere as part of a new study. It was equipped with a number of instruments for various measurements and microphones. Sounds that have been recorded about 50 km above the Earth's surface have baffled scientists.

The region of the atmosphere at this altitude is relatively calm and free from storms, turbulence and commercial air traffic. This means that microphones can recognize various sounds of our planet - natural and man-made.

In this particular study, the microphone picked up strange noises repeating several times an hour. Their source has not yet been identified. Sounds were recorded in the infrasonic range, that is, at frequencies of 20 Hz and below, which is well below the range of human hearing.

To collect acoustic data from the stratosphere, the team of researchers used devices originally designed for monitoring volcanoes - microbarometers that are capable of detecting low-frequency sounds. They rose in balloons with a diameter of 6 to 7 meters.

A group study describing these unidentified sources of infrasound was presented at the 184th meeting of the American Acoustic Society in Chicago. So far, it has not been possible to recognize the source, but scientists notethat the technology of such wiretapping has already proven itself well.

Now such devices are undergoing a number of other tests. If successful, they could be sent along with an orbiter to Venus to observe the planet's seismic and volcanic activity. Robotic balloons could well drift in the upper atmosphere, high above its hellishly hot and high-pressure surface.