Listen to space “singing”: NASA captures the chirps and chorus of the cosmos
Space is not the silent, desolate vacuum it may appear. The universe is overrun with charged particles that whistle and “sing” as they interact with each other.
These particles are thrown back and forth by the motion of electromagnetic waves known as plasma waves that surround our planet. In particular, these waves occur where fluctuating electric and magnetic fields meet clumps of ions and electrons that make up the plasma. This interaction controls the balance of highly energetic particles around Earth and keeps the fields in this constant state of flux.
And, like the rolling ocean waves, these plasma waves create what NASA has now described as a “rhythmic cacophony” of interstellar sound. There are three types of sound: whistle-mode waves, chorus waves, and plasmapheric hiss.
Whistler-mode waves create distinct sounds dependent on the type plasma they travel through. Around Earth, for example, in a region known as the plasmasphere, the plasma is cold and relatively dense. As waves travel through this dense plasma, they sound different to those that travel outside of it.
Out beyond the plasmasphere, where the plasma is said to be relatively warm, whistler-mode waves create “chirps”, like a flock of noisy birds, which sound remarkably like the noises made by the Clangers in the 1970s show. Given its similarity to birds, this creates the chorus type of wave and occurs when electrons are pushed towards the night side of Earth – which in some cases, may be caused by magnetic reconnection, a dynamic explosion of tangled magnetic field lines on the dark side of Earth.
The sounds made my whistler-mode waves inside the plasmasphere are called plasmaspheric hiss and sound similar to radio static. Some scientists think this hiss is caused by lightning strikes, while others believe it could be caused by chorus waves leaking inside the plasmasphere.
When lighting strikes the ground on Earth it creates an electrical discharge that can trigger whistler-mode plasma waves. Some of these waves escape beyond the atmosphere to bounce “like bumper cars” along Earth’s magnetic field lines between the north and south poles. Since the lightning creates a range of frequencies, and since higher frequencies travel faster, the wave howls a falling pitch, giving the wave its name.
Both chorus and hiss waves play a role in the behaviour of the Van Allen radiation belts, doughnut-shaped rings of high-energy particles encircling the planet.
To capture the sounds these waves make, NASA’s two Van Allen Probe spacecraft use an instrument called EMFISIS, short for Electric and Magnetic Field Instrument Suite and Integrated Science, to measure electric and magnetic waves as they circle Earth. As the spacecraft encounter waves, sensors record the changes in the frequency. The scientists then shift the frequencies to the audible range so that we can listen to the sounds of space.
NASA is using the sounds captured by the Van Allen Probes mission in an attempt to understand more about plasma waves. This will help the agency improve predictions of space weather, which can cause damage to our satellites, and boost the effectiveness of such satellites and telecommunication devices.