Scientists constantly study planets within our cosmic neighborhood to unravel their mysteries and understand their unique characteristics. By examining these planets’ atmospheres, surfaces, and geological formations, scientists hope to grasp fundamental insights about our solar system’s origins, the potential for extraterrestrial life, and the dynamics of cosmic phenomena such as meteor showers and stellar winds.
One celestial body that has long intrigued astronomers is Mercury, a rocky planet with a non-existent atmosphere and situated very close to the Sun, which makes it susceptible to solar radiation and solar wind. Since the 1970s, scientists have been aware of Mercury’s magnetic field, which is influenced by solar wind and influences the X-ray aurorae that can occur on its surface.
A team led by Mitsunori Ozaki of Kanazawa University in Japan has revealed that tinkling, whistling plasma waves called chorus waves have been detected around Mercury. These are a type of electromagnetic wave commonly observed in planetary magnetospheres (the regions surrounding a planet influenced by its magnetic field) and have previously been recorded on Earth, Jupiter, and Saturn, as well as at Uranus and Neptune.
This is the first time that chorus waves have been observed on Mercury. The researchers analyzed data from the Mio instrument on board the BepiColombo spacecraft, scheduled to enter Mercury’s orbit in 2025, and from two flybys of Mercury by the spacecraft in 2021 and 2022. Using modeling and simulations, they found that the waves were present only in Mercury’s magnetosphere, the dawn sector. The team suspects some physical mechanism in this sector promotes the generation of chorus waves and suppresses them everywhere else.
The researchers also conducted modeling and simulations to determine that, in the dawn sector, energy transfer from electrons to electromagnetic waves is more efficient. This generates the chorus waves, which give off a whistle-like sound when the particles collide with Mercury’s magnetic field. The results of this first-time observation will allow the scientists to plan their investigations in detail ahead of MIO’s orbital insertion.
The scientists say that the discovery of chorus waves on Mercury is an essential step toward understanding how the planetary magnetic environment shapes a planet’s magnetic fields. It also provides clues about the underlying mechanisms that govern the dynamics of charged particles in a planetary magnetosphere and may contribute to understanding how solar wind shapes these magnetic fields. The findings are published this week in the journal Nature Astronomy.