Scientists baffled: potentially deadly "oscillations" detected in an unexpected place

Scientists have detected strange "chirping" waves - like birdsong - thousands of kilometres from Earth. They are thought to pose a serious problem for future space flight plans.

Waves detected 3 times further away than normal

Chorus waves are disturbances in the Earth's electromagnetic field that produce signals, converted into sound, that resemble birdsong.

These waves can accelerate particles to speeds that can be deadly for spacecraft and astronauts. They appear as bursts of energy, lasting only a few tenths of a second, that ripple through the Earth's magnetosphere.

These mysterious waves have been observed emanating from Earth and other planets since the 1960s. But until now, scientists thought they only occurred close to our planet.

A new team of researchers from the US, China and Sweden has detected chorus waves 165 000 kilometres from Earth. That's about three times farther than they have been recorded before.

The most popular theory of choir waves

Scientists are still debating what causes choir waves. The most popular theory is that they are caused by an effect known as plasma instability.

In curved dipoles, such as conventional bar magnets and planetary magnetic fields, electrons emitted by the Sun are usually trapped along the magnetic field lines. Normally, the particles move along these lines in an orderly, spiral pattern.

However, sometimes field disturbances interfere with this movement, causing chorus waves. These waves begin to resonate with the electrons and accelerate them to the near-lethal speed of light.

According to this theory, the curvature of these dipoles allows the chorus waves to travel from one pole to the other, creating their characteristic "chirp".

Significance of the study

However, in the new study, the chorus waves were found in a relatively flat region of the Earth's magnetosphere. This means that they are caused by frequency changes across the magnetosphere.

To better study the waves and what might be causing them, the authors of the study suggested better monitoring of plasma flares coming from the Sun and their interaction with the Earth's magnetosphere. 

This could provide answers that could be key to ensuring that future satellites, astronauts and deep space missions to Mars and beyond are not fatally affected by high-speed electrons.

"This discovery does not invalidate existing theory, as plausible magnetic field gradients may still exist," wrote Richard Horne, head of the space weather division at the British Antarctic Survey, who was not involved in the study.

He stressed that the scientists' new discovery is unexpected and encourages further research into waves in regions where the Earth's magnetic field deviates significantly from dipoles.