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Earth song recorded by NASA spacecraft

Sarah Cruddas
Oct 4, 2012, 7:00 UTC

Sen—A NASA spacecraft has recorded the sounds sung from planet Earth. The phenomenon known as chorus is caused by plasma waves in Earth's radiation belt. 

The recordings were made by NASA's twin Radiation Belt Storm Probes. Launched in August 2012 they are travelling through the region of space where the electromagnetic phenomenon comes from. The probes are on a two-year mission to explore the Van Allen Belts which consist of highly energetic ionised particles trapped in the Earth's geomagnetic fields.

Professor Craig Kletzing from the University of Iowa, whose team built the receivers used to pick up the signals, said "This is one of the clearest examples we've ever heard."

However chorus is not to be confused with acoustic waves that you get here on planet Earth. It's caused by radio waves that oscillate at acoustic frequencies, between 0 and 10 kHz. According to Kletzing "This is what the radiation belts would sound like to a human being if we had radio antennas for ears".

The waves have been detected by the magnetic coil antennas of the Radiation Belt Storm Probes, which are currently orbiting inside the radiation belts. The two probes are listening to plasma waves of many frequencies, sampling electromagnetic fields and counting the number of energetic particles.

Researchers think that chorus may be the cause of 'killer electrons'. Most electrons in the radiation belt have too little energy to be a danger to astronauts or spacecraft. However these are high energy particles which can cause hazards for humans and objects in space.  

According to mission scientist Dr Dave Sibeck “The production of 'killer electrons' is a matter of much debate, and chorus waves are only one possibility". The Radiation Belt Storm Probes aim to find out if this is the case. 

As for the recording of the chorus, Professor Kletzing hopes to release unprecedented stereo recordings. For years, ham radio operators on Earth have been listening to them from afar, however the data from this mission is sampled in 16 bits the same as a CD - which has never been done before in the radiation belts. 

Professor Kletzing says “One of things we noticed right away is how clear the chorus sounds in the recording,” 

The main part of the mission for the spacecraft still hasn't begun. That will happen once the 60 day checkout phase has finished.

As well as sounding great, the recordings will bring real scientific value. At the moment scientists don't know how broad the region is over which chorus occurs. According to Kletzing "The widely-separated ‘stereo capability’ of the Storm Probes will give us the ability to figure this out".

The Radiation Belt Storm Probes are the second mission in NASA's Living With a Star program to explore aspects of the connected sun-Earth system that directly affect life and society.