[ music ]
The Sound of Earthsong -- Presented by Science@NASA
In space, they say, no one can hear you scream.
Nobody ever said anything about singing, though.
A NASA spacecraft has just beamed back a beautiful song sung by our own planet.
'It's called chorus,' explains Craig Kletzing of the University of Iowa.
'This is one of the clearest examples we've ever heard.'
[ SHORT AUDIO SNIPPET ]
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.
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.
[ LONGER AUDIO SNIPPET ]
'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 built the 'EMFISIS'
(Electric and Magnetic Field Instrument Suite and Integrated Science) receiver
used to pick up the signals.
He's careful to point out that these are not acoustic waves
of the kind that travel through the air of our planet.
Chorus is made of radio waves
that oscillate at acoustic frequencies,
between 0 and 10 kHz.
The long antennas of the Radiation Belt Storm Probes
are perfect for detecting 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.'
In particular, chorus might be responsible for so-called 'killer electrons,'
high-energy particles that can endanger both satellites and astronauts.
Most 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 rising a wave on Earth-
and gain enough energy to become dangerous.
The Radiation Belt Storm Probes are on a mission to find out for sure.
'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 in August 2012,
the two probes 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.
At the moment, the spacecraft are still undergoing their 60-day checkout phase
before the main mission begins.
So far, things are checking out very well.
'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.'
Eventually, Kletzing hopes to release
unprecedented stereo recordings of Earth's chorus.
'We have two spacecraft with two receivers,' he says,
'so a stereo recording is possible.'
Such a recording would not only sound wonderful,
but 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.
With a two-year mission planned for the Storm Probes,
the Earthsong is just getting started.
For more weird and wonderful sounds from space, stay tuned to science.nasa.gov