October 1, 2012
The Song Of The Earth Captured And Sampled By Twin NASA Spacecraft
Earth is filled with many sounds and no matter where you go it is inescapable. From the roar of the city streets, to the ever-pleasing sounds of nature, and the endless commotion of human chatter. But there is one sound that most of us have never heard: the sound of the Earth itself.
The sound (or song) is called “chorus,” explains Craig Kletzing of the University of Iowa. This song has been captured by ham radio operators for as long as the devices have been used. The song stems from a region of space known as the Van Allen Belts, which envelop the Earth.
“This is one of the clearest examples we´ve ever heard,” adds Kletzing.
Chorus is an electromagnetic phenomenon caused by plasma waves in our planet´s radiation belts. And now, NASA´s twin Radiation Belt Storm Probes (RBSPs) are traveling through this region of space to track down the recordings that 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 UIowa team built the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) receiver used to pick up the signals.
Kletzing notes that the song doesn´t derive from acoustic waves that travel through the air of the planet. Chorus is the product of radio waves that oscillate at acoustic frequencies, between 0 and 10 kHz. The RBSP magnetic search coil antennas are designed to detect these very 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.”
One of the directives for the twin satellites, is to determine if chorus is responsible for the so-called “killer electrons” that pose significant dangers to orbiting satellites and spaceward astronauts. Most electrons in space are thought to be harmless, with too little energy to be a danger to humans or electronic systems. But those that intermingle with chorus waves can get a significant boost of energy and pose a threat, according to theory.
To be sure, the RBSPs will investigate.
“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. “We hope to gather enough data to solve the mystery once and for all.”
The twin probes, launched in August 2012, will sample electromagnetic fields and count the number of energetic particles, as well as listen to plasma waves of many frequencies. But for now, the RBSPs are undergoing a 60-day checkout phase to ensure all systems are working properly. So far, so good.
Kletzing said he and his team “noticed right away“¦how clear the chorus sounds in the recording” were. The probes sample data at 16 bits, the same as a CD, which has not been done before in the Van Allen Belts. “This makes the data very high quality and shows that our instrument is very, very healthy.”
Kletzing hopes that he and his team will be able to capture, produce and release unprecedented stereo recordings of Earth´s chorus.
As much as producing a stereo recording would be exhilarating, the results would also 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.
The RBSPs are on a two-year mission, so Kletzing and his team have plenty of time to produce--perhaps--a chorus symphony.