In the 2000s, the MESSENGER spacecraft offered a detailed image of Mercurys magnetic field and magnetosphere, and exposed that Mercurys electromagnetic field center is moved northward from the planets center by roughly 0.2 RM (RM is Mercurys radius of 2,439.7 km).
The 3rd exploration of Mercury is presently being made by the BepiColombo International Mercury Exploration Project [1] thanks to the Mio spacecraft (Project Scientist, Dr. Murakami) and the Mercury Planetary Orbiter (MPO). In particular, unlike Mariner 10 and MESSENGER, the Mio spacecraft is geared up with a full suite of plasma wave instrument (PWI, Principal Investigator Prof. Kasaba) created specifically to investigate for the very first time the electro-magnetic environment around Mercury. Electromagnetic waves can efficiently accelerate plasma particles (electrons, protons, much heavier ions); as such, they play a crucial role in Mercurys magnetospheric dynamics.
Outcomes of Current Study
The current study was performed by a global joint research study group consisting of scientists from Kanazawa University, Tohoku University, Kyoto University, MagneDesign Corporation, Laboratoire de Physique des Plasmas, France with assistance from CNES (French Space Agency), and the Institute of Space and Astronautical Science, the Japan Aerospace Exploration Agency (JAXA).
The Mio spacecraft, launched on October 20, 2018, is currently on its way to Mercury, with a last insertion in orbit around the world scheduled for December 2025. Although getting Mio into Mercurys orbit is technically extremely difficult due to the strong gravity of the Sun as compared to that of Mercury, it is scheduled to enter into orbit around Mercury in 2025 after several flybys [ 2] of Earth, Venus, and Mercury for gravity help maneuvers.
During the Mercury flybys that occurred on October 1, 2021, and June 23, 2022, the Mio spacecraft approached the planet at an altitude of around 200 km. The stowed configuration of the spacecraft throughout the journey to Mercury is not ideal for determining electromagnetic waves since of the disturbance sound coming from the spacecraft itself. Nevertheless, the Mio spacecraft was established to decrease as much as possible its electromagnetic noise level, and hence has actually been certified as an electromagnetically tidy spacecraft through EMC tests. [3]
Alternating present magnetic field sensing units that can manage the scorching environment of Mercury have been established collectively by Japan and France and have actually permitted the first electro-magnetic wave observations around Mercury without being polluted by the noise from the spacecraft itself. This has exposed the local generation of chorus waves, such as those that are frequently spotted in the magnetosphere of Earth.
The existence of chorus waves in the magnetosphere of Mercury, which is now validated, was anticipated (frequency variety, intensity, and so on) since the 2000s when the plasma wave instrument (PWI) of the Mio spacecraft was designed. What most surprised the global joint research team, including Dr. Ozaki of Kanazawa University, was the “spatial region” of the chorus waves, which were identified just in a very minimal area in the dawn sector of the Mercurys magnetosphere during the two flybys. This indicates that there is a physical system that tends to generate chorus waves just in the dawn sector of the magnetosphere of Mercury.
In order to investigate the cause of the generation of chorus waves in the dawn sector, the global joint research study group utilized the nonlinear development theory of chorus waves developed by Prof. Omura, Kyoto University, to examine the result of curvature of the magnetic field of Mercury, which is highly misshaped by the solar wind. The magnetic field lines in the night sector are extended by the solar wind pressure, while the magnetic field lines in the dawn sector are less affected resulting in a smaller curvature.
Based on the characteristics of the magnetic field lines and the nonlinear development theory, it is exposed that in the dawn sector, energy is effectively transferred from electrons to electromagnetic waves along magnetic field lines, developing conditions that favor chorus wave generation. The effect is also confirmed in a mathematical simulation of the Mercury environment utilizing a high-performance computer system.
In this research study, the team has exposed the value of the planetary magnetic field lines, which are strongly impacted by the solar wind, on the region of chorus wave generation thanks to a strong synergy in between “spacecraft observation,” “theory,” and “simulation.”.
Future Prospects.
In the Mercury flyby observations, the group prepared for the extensive electro-magnetic environment study utilizing the prepared Mio spacecraft probe in orbit around Mercury. Chorus waves, which were anticipated to be discovered at the time of preparation, are observed in a rather regional manner, i.e. in the dawn sector of Mercury, which was not anticipated, and the results show various variations in the magnetosphere of Mercury.
The information show the presence of energetic electrons on Mercury that can produce chorus waves, the possibility of creating active electrons efficiently sped up by chorus waves, and the generation of X-ray auroras by electrons forcibly precipitating from Mercurys magnetosphere to the surface area of Mercury driven by chorus waves. These observations will have a large effect on the scientific understanding of Mercurys environment.
The Mio spacecraft is on its way to carry out a detailed expedition of Mercury. Based upon flyby observations we have actually discovered that magnetic field distortion is accountable for the regional (i.e. dawn sector) generation of the chorus waves. The detailed expedition of the electro-magnetic environment by the Mio spacecraft in Mercurys orbit will contribute not only to comprehending the plasma environment of the entire Mercurys magnetosphere but also to a deep understanding of the magnetospheric characteristics in general.
The magnetosphere acts as a barrier avoiding deadly cosmic radiations on the worlds of the planetary system. Contrast of data from Mercury and Earth will enhance our understanding of this essential natural shielding of our home planet.
Glossary.
In specific, unlike Mariner 10 and MESSENGER, the Mio spacecraft is equipped with a full suite of plasma wave instrument (PWI, Principal Investigator Prof. Kasaba) created specifically to investigate for the first time the electromagnetic environment around Mercury. The stowed setup of the spacecraft during the journey to Mercury is not optimum for determining electromagnetic waves due to the fact that of the disturbance noise coming from the spacecraft itself. The presence of chorus waves in the magnetosphere of Mercury, which is now validated, was anticipated (frequency variety, intensity, etc) since the 2000s when the plasma wave instrument (PWI) of the Mio spacecraft was developed. What most surprised the global joint research team, including Dr. Ozaki of Kanazawa University, was the “spatial region” of the chorus waves, which were discovered only in a very minimal area in the dawn sector of the Mercurys magnetosphere during the two flybys. The extensive exploration of the electromagnetic environment by the Mio spacecraft in Mercurys orbit will contribute not just to comprehending the plasma environment of the entire Mercurys magnetosphere but likewise to a deep understanding of the magnetospheric characteristics in basic.
BepiColombo International Mercury Exploration Project: Comprehensive exploration project for Mercury using two spacecraft probes (Mio and MPO) by Japan-Europe cooperation. In particular, Japan is in charge of the Mercury magnetosphere probe Mio, geared up with electro-magnetic wave observation instruments, etc.
Flyby: With a spacecraft probe passing in distance to a world. The orbit of the spacecraft probe is to be changed in a preferred manner by utilizing the gravity of the planet.
EMC (electromagnetic compatibility) test: Evaluation test to examine whether unneeded electromagnetic sound is emitted and whether the devices is designed and made in such a method that it will not malfunction even if it gets unwanted electromagnetic noise.
Picture of chorus wave generation on Mercury. Credit: Image of Mercury: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Mercurys exploration by the Mio spacecraft revealed localized chorus waves in its magnetosphere. International research study utilized advanced theories and simulations to comprehend these waves, emphasizing the magnetospheres crucial function in protecting planets from cosmic radiation.
Considering that Mercury is the closest planet to the Sun amongst the solar system planets, it is strongly influenced by the solar wind, a high-speed (several hundred km/s) stream of plasma blowing from the Sun.
Explorations of Mercury were very first performed by the Mariner 10 spacecraft in 1974 and 1975, which exposed that Mercury has an electromagnetic field, and thus a magnetosphere, similar to that of Earth.
Evaluation test to examine whether unnecessary electromagnetic sound is released and whether the equipment is created and made in such a method that it will not malfunction even if it gets undesirable electro-magnetic sound.
Reference: “Whistler-mode waves in Mercurys magnetosphere observed by BepiColombo/Mio” by Mitsunori Ozaki, Satoshi Yagitani, Yasumasa Kasaba, Yoshiya Kasahara, Shoya Matsuda, Yoshiharu Omura, Mitsuru Hikishima, Fouad Sahraoui, Laurent Mirioni, Gérard Chanteur, Satoshi Kurita, Satoru Nakazawa and Go Murakami, 14 September 2023, Nature Astronomy.DOI: 10.1038/ s41550-023-02055-0.