Initially designed to monitor volcanoes on Earth, the balloons will be tested to see if they can contribute to the exploration of other planets.
Hot air balloons launched by scientists have recorded mysterious sounds of “unknown origin” high in the Earth’s atmosphere.
Researchers, including Daniel Bowman of Sandia National Laboratories in the US, sent large 6-7 meter-long balloons into the stratosphere, a relatively calm layer of the Earth’s atmosphere that is rarely affected by aircraft or turbulence.
In this layer of the Earth’s outer atmosphere, scientific instruments in balloons can detect a range of sounds not heard elsewhere, including the natural sounds of crashing ocean waves and thunder, as well as man-made sounds such as those emitted by wind turbines or explosions.
While the balloons can detect such human and environmental sounds, the researchers reported in a presentation at the 184th Meeting of the Acoustical Society of America that they were also able to record some strange unidentified sounds.
“There are mysterious low-frequency signals [in the stratosphere] that occur several times per hour on some flights, but their origin is completely unknown,” Dr. Bowman said in a statement.
Originally designed to monitor volcanoes on Earth, the balloons can collect data using micro-barometers and detect low-frequency beyond sound.
The researchers tracked their routes using GPS because the balloons can sometimes stay aloft for hundreds of kilometers and land in hard-to-reach places.
Dr. Bowman says:
Our balloons are basically giant plastic bags with some charcoal dust in them to make them dark. We create them using tarps from DIY stores, duct tape and charcoal dust from pyrotechnic shops.
When the sun hits the dark balloons, the air inside heats up and gains buoyancy. This passive solar energy is enough to lift the balloons from the surface to over 20 kilometers in the sky.
The scientists said their balloons could also help in the exploration of other planets.
They theorized that these balloons could be used to observe Venus’ seismic and volcanic activity through its thick atmosphere.
“A new generation of Venus balloons is being designed that can last for more than 100 days and can change their altitude to navigate through different layers of the Venusian atmosphere,” the scientists wrote in the study.
As part of the next phase of experiments, they hope to classify signals similar to those on Venus and develop instruments that can automatically identify signals of interest.
“Conducting this experiment from a balloon floating 50-60 kilometers above the surface of Venus provides a significantly extended observation period that exceeds the lifetime of any spacecraft landing on the surface with current technology,” the scientists said.