Scientists discover 'space chorus' far from Earth

An international research team led by Chinese scientists has discovered chorus waves more than 160,000 km away from Earth – a space phenomena previously believed to occur only near Earth's dipole magnetic field regions, according to a study paper published in Nature Thursday.

"We observed chorus waves with frequencies below 100 Hz. When we converted the chorus waves into audio output, we obtained a piece of 'space chorus' that we can hear," said Liu Chengming at Beihang University, the paper's first author, describing the sound like "the chirping of birds."

The Earth's magnetic field extends into space. When charged particles in the cosmos pass the magnetic field, they can excite chorus waves, or the electromagnetic waves with frequency characteristic similar to bird songs in the morning. As one of the most intense electromagnetic fluctuations in space, chorus waves have been at the forefront of space physics research. It was widely believed that they only occurred near Earth's dipole magnetic field regions.

The team, which consists researchers from China, the United States and Sweden, has analyzed vast amounts of data collected by the Magnetospheric Multiscale Mission, a solar-terrestrial probe mission. They discovered chorus waves more than 160,000 km away from Earth, and provided a theoretical explanation that nonlinear wave-particle interactions are the cause.

Chorus waves play a crucial role in understanding fundamental questions in space and have wide practical implications. They are key to the acceleration of high-energy electrons in Earth's radiation belts and the generation of pulsating auroras in the polar regions. They can also influence space weather changes, endangering the stable operation of spacecraft and the health of astronauts.

These findings provide essential theoretical support for the precise modeling and forecasting of space weather, according to the study.