Something magical happens around planets with magnetospheres. If you listen with the right instruments, you can hear chirps and whistles at dawn and dusk that almost sound like birds chirping. These so-called chorus waves have been recorded on Earth, Jupiter, and Saturn, and observed on Uranus and Neptune.

Now, scientists from Japan and France, led by Kanazawa University astronomer Mitsunori Ozaki, have discovered that they are rapidly orbiting the barren and lonely Mercury as it orbits the Sun. This is interesting because other planets have a few things that Mercury does not: thick, fertile atmospheres and permanent radiation belts where solar particles are trapped by the planet’s magnetic field.

Scientists say the discovery could shed light on the magnetic environment around Mercury and how the planet’s magnetic fields are generally shaped by solar winds. Mercury does not have a large magnetic field. It’s a fairly bare piece of rock, has almost no atmosphere, and is too close to the Sun for comfort. It is constantly exposed to radiation and solar wind.

But this cruel, broken world holds secrets, oh yes. Just this year, scientists finally discovered that Mercury, despite its pitiful magnetic field and atmosphere, has its own kind of aurora.

But long before this discovery, scientists believed that Mercury might have chorus waves. This occurs when energetic electrons become trapped in the planet’s magnetosphere, spiraling along magnetic field lines and creating waves in the plasma.

These waves can be recorded and converted into sounds that vary depending on how and where the electrons move. For example, you can hear whistling waves recorded on Earth in the video below.

Studies of Mercury are scattered and rare; This means that our understanding of its cosmic environment is patchy. We have known about its magnetic field since Mariner 10 made observations in the 1970s. However, scientists are trying to fill this gap. Part of the Mercury BepiColombo mission, launched in 2018, is an instrument called MIO designed to study Mercury’s magnetosphere.

This instrument is not yet fully in orbit; The Sun’s gravity makes it difficult to enter orbit. However, the spacecraft passed by Mercury in 2021 and 2022 and recorded observations of Mercury’s magnetic field.

And there, in data collected by MIO, researchers found clear evidence of whistle-like waves in Mercury’s magnetosphere. But this being Mercury, there was something odd about them: They only appeared in a small part of Mercury’s magnetosphere, a slice known as the dawn sector.

This suggests that there is some physical mechanism that either promotes chorus waves in this region or suppresses them everywhere else. The team performed modeling and simulations and determined that energy transfer from electrons to electromagnetic waves is more efficient in the dawn sector, leading to the formation of whistles.

A better understanding and characterization of these chorus waves will require additional observations and analysis. These initial detections will allow researchers to plan their work in detail before MIO is launched into orbit in 2025.

“To date, we still do not know whether Earth and Mercury have similar spatiotemporal properties of their electron-driven choruses,” the researchers write.

“This work paves the way for challenging future studies to show how magnetized planetary environments in our Solar System are formed by the solar wind, with a possible prediction of exoplanets and their interactions with stellar winds.”