The cheerful trill of birdsong is typically a welcome sign of spring rather than a sound you'd expect to encounter in the vastness of space. Yet, bizarrely, scientists at Beihang University in China have just detected something similar over 100,000km (62,000 mi) away from Earth.
Analysing data from NASA's Magnetospheric Multiscale (MMS) satellites, the researchers identified a phenomenon known as a ‘chorus wave’ – bursts of electromagnetic radiation that travel along Earth’s magnetic field lines.
If you were to go into space, however, you wouldn’t hear it (not least because there’s no air to carry sound waves). That’s because this ‘chirping’ is actually the sound of the waves when converted into audio signals for analysis.
So, what's causing the electromagnetic chirps? Sadly, it's not some interstellar songbird. In fact, chorus waves actually quite normal. What’s strange is, however, how far they’ve been spotted away from Earth.
Chorus waves transfer energy to electrons, accelerating them to energies close to the speed of light. This is essential in forming Earth’s radiation belts (the regions around the planet that act as a protective shield against the Sun’s high-energy particles).
While creating breathtaking auroras like the Northern Lights, these high-speed particles are often referred to as 'killer electrons'. That's because they pose a significant threat due to their potential to damage satellites, astronauts, and vital communication systems.
Usually, the waves are found around 51,000km (32,000mi) away, where something called the ‘magnetic dipolar effect’ gives our magnetic field a north and south pole.
But this study, published in Nature, marks the first time these chorus waves have been observed as far as 165,000km (103,000mi) away. Here, Earth’s magnetic field is highly distorted and there is no magnetic dipolar effect.
What’s more: the waves share similar qualities to those found nearer Earth, lasting around only 0.1 seconds at rates close to 100Hz (a similar frequency to that of a rumbling car engine).
So why does all this matter? Well, it implies the waves don’t need Earth’s environmental conditions to form, as scientists previously thought they did.
“The discovery doesn’t rule out the existing theory … but it means that scientists need to take a closer look,” said Prof Richard Horne, head of space weather at the British Antarctic Survey, who was not involved in the study.
“It is a surprising result in a surprising region, and it prompts further investigation of chorus waves in regions in which Earth’s magnetic field deviates substantially from a dipole.”
While chorus waves play an important role in protecting Earth from solar storms, they can also cause a lot of damage. Knowing more about them could help us better protect against them.
According to Horne, this discovery could “enhance our understanding of these waves, which will go a long way towards improving our forecasting ability.”
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