In our Solar System, a bizarre, tinkling song of magnetic field sounding like a chime in the solar wind have been found in some planets. Known as "whistler-mode chorus waves", the strange chirping signals that can be converted to sounds have been previously detected at Earth, Neptune, Uranus, Saturn, and Jupiter.
Song of the Magnetic Field
Mercury recently joined the list of planets that experience these odd chorus waves. The discovery was made by the Mio spacecraft launched on October 20, 2018, and is currently on its way to orbit Mercury by December 2025. The occurrence of this phenomenon in Mercury was detected by astronomer Mitsunori Ozaki of Kanazawa University and other experts from Japan and France.
The chorus waves are triggered by energetic electrons that were trapped in the magnetosphere of a planet. These particles ripple along the magnetic field lines and generate plasma waves. When these waves are recorded, they can be converted into sounds that tinkle and chime, depending on the motion of the electrons.
In their research paper, the authors described the direct probing of chorus waves in the localized dawn sector during the first and second flybys of BepiColombo/Mio spacecraft in Mercury. The search coil magnetometers of Mio found the chorus events with tens of picotesla intensities located in the dawn sector. Meanwhile, no clear chorus activity was observed in the night sector.
READ ALSO: NASA's Voyager 1 Records Weird, Steady 'Hum' of Plasma in Interstellar Space
Understanding Mercury's Magnetosphere
The discovery was a surprise to scientists since Mercury does not have the same thick atmosphere and permanent radiation belt as the other planets. Mercury has a very thin atmosphere composed of potassium, helium, hydrogen, sodium, and oxygen. This is specifically known as an exosphere since these gases come from solar wind and meteoroids that blast atoms off the surface.
Compared to Earth, Mercury also has a much-weaker magnetic field, which was discovered only in the 1970s by the Mariner 10 expedition.
The chorus waves in Mercury were found to be unusual because they were discovered in only a small chunk of the planet's magnetosphere, also known as the dawn sector. The researchers suggest that this may be due to the waves that were either promoted in this region, or being suppressed elsewhere.
After modeling and simulating the magnetosphere of Mercury, the scientists found that it was likely that the planet's dawn sector was the most efficient site for the transfer of energy from electrons to the chorus waves.
According to the researchers, this observational evidence is important in understanding the energetic electron dynamics of the localized dawn sector of Mercury's magnetosphere. To date, astronomers still do not know if Mercury and Earth have the same spatiotemporal properties of their electron-driven chorus.
Experts are hopeful that these learnings can be used in understanding magnetic fields in general, including that of Earth. The findings can also challenge future studies on how magnetized planet environments can be shaped by the solar wind in our Solar System, with potential extrapolation to exoplanets and their interactions with stellar winds.
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