You can hear it here.
“It’s called chorus,” explains Craig Kletzing of the University of Iowa. “This is one of the clearest examples we’ve ever heard.”
“Chorus is an electromagnetic phenomenon caused by plasma waves in Earth’s radiation belts. For years, ham radio operators on Earth have been listening to them from afar,” a NASA nes release states. “Now, NASA’s twin Radiation Belt Storm Probes are traveling through the region of space where chorus actually comes from–and the recordings are out of this world.”
“This is what the radiation belts would sound like to a human being if we had radio antennas for ears,” says Kletzing, whose team at the University of Iowa created the “EMFISIS” (Electric and Magnetic Field Instrument Suite and Integrated Science) receiver that is used to pick up the signals.
He makes it a point to clarify, though, that these are not the kinds of acoustic waves that travel through the air of our planet that we can hear. “Chorus is made of radio waves that oscillate at acoustic frequencies, between 0 and 10 kHz.” The Radiation Belt Storm Probes possess magnetic search coil antennas that are able to detect and pick up these kinds of waves.
“Chorus emissions are front and center for the Storm Probe mission,” says Kletzing. “They are thought to be one of the most important waves for energizing the electrons that make up the outer radiation belt.”
The NASA press release adds:
“In particular, chorus might be responsible for so-called ‘killer electrons,’ high-energy particles that can endanger both satellites and astronauts. Many electrons in the radiation belts are harmless, with too little energy to do damage to human or electronic systems. But, sometimes, these electrons can catch a chorus wave, like a surfer riding a wave on Earth, and gain enough energy to become dangerous—or so researchers think.”
Currently, the Radiation Belt Storm Probes are investigating that as part of their mission.
“The production of killer electrons is a matter of much debate, and chorus waves are only one possibility,” notes the Storm Probes’ mission scientist Dave Sibeck.
Launched just a few months ago in August 2012, the two probes currently “are orbiting inside the radiation belts, sampling electromagnetic fields, counting the number of energetic particles, and listening to plasma waves of many frequencies. ”
“We hope to gather enough data to solve the mystery once and for all,” says Sibeck.
Presently, the spacecraft are undergoing a 60-day checkout phase before they begin their primary mission. Everything has checked up well so far.
“One of things we noticed right away is how clear the chorus sounds in the recording,” notes Kletzing. “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.”
Kletzing eventually plans to gather and release “unprecedented” stereo recordings of the Earth’s chorus.
“We have two spacecraft with two receivers,” he says, “so a stereo recording is possible.”
According to Kletzing, a recording of the chorus would have real scientific value. “One of the things we don’t know is how broad the region is over which chorus occurs. The widely-separated ‘stereo capability’ of the Storm Probes will give us the ability to figure this out,” he explains.