A NASA spacecraft has captured a beautiful song "sung" by our own planet.
The noise - which sounds similar to whale song - is called a "chorus", Craig Kletzing of the University of Iowa explained.
"This is one of the clearest examples we've ever heard," he told NASA Science.
Chorus is an electromagnetic phenomenon caused by plasma waves in Earth's radiation belts. Ham radio operators have been able to listen to the sounds from Earth for years, but now NASA's two Radiation Belt Storm Probes have transmitted the sound back to Earth, from where it is emitted.
Kletzing's team built the Electric and Magnetic Field Instrument Suite and Integrated Science receiver which picked up the signal.
"This is what the radiation belts would sound like to a human being if we had radio antennas for ears," Kletzing said.
Chorus is made of radio waves that oscillate at acoustic frequencies, between 0 and 10 kHz, which can be picked up by magnetic search coil antennas on the Radiation Belt Storm Probes.
"One of things we noticed right away is how clear the chorus sounds in the recording," Kletzing said. "That's because our data is sampled at 16 bits, the same as a CD, which has not been done before in the radiation belts. This makes the data very high quality and shows that our instrument is very, very healthy."
As there are two spacecraft with two receivers, Kletzing hopes to eventually record the Earth's chorus in stereo.
Chorus may be responsible for so-called killer electrons, high energy particles which can threaten satellites and astronauts. The Radiation Belt Storm Probes mission, which was launched in August and lasts two years, is to find out for sure what produces these electrons.