BEIJING — An
international research team led by Chinese scientists has discovered chorus
waves more than 160,000 km away from Earth -- a space phenomenon previously
believed to occur only near Earth's dipole magnetic field regions, according to
a study on 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, Xinhua news agency reported.
In the study, published in the journal Nature, Chengming
described the sound as "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 electromagnetic waves with frequency characteristics like birdsongs 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.
Researchers from China, the US, and Sweden analysed 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 modelling and forecasting
of space weather, according to the study.
