The unusual readings gathered by the Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) mission in 2009 have been explained by theoretical physicists by using simulations.
Researchers have been baffled by the origin of energetic electrons observed in Mercury’s magnetic tail. This innovative research, which was reported in the Physics of Plasmas journal from AIP Publishing, offers a probable explanation for the formation of these energetic electrons.
The flow of a magnetic material inside a planet leads to the formation of a global magnetic field. In Mercury, as well as in Earth, the planets’ magnetic fields are induced by liquid metal currents flowing in the planetary cores. Although the size, shape, strength, and angle of these fields differ between planets, they have a vital role in protecting the planets from solar particles.
The planets are blasted with radiation by the solar wind, resulting in magnetic substorms, which is at times observed on Earth as the northern lights. Magnetic tails, or magnetotails, are formed when a planet’s magnetic fields are “pushed” by the intense radiation pressure from solar winds. These tails are formed on the nighttime face of the planet, away from the sun. In contrast to Earth, on Mercury, magnetic substorms in the tail are more rapid and bigger.
Since magnetic field of Mercury was 100 times weaker when compared to Earth’s magnetic field, physicists were puzzled when MESSENGER detected signs of energetic electrons in the magnetic tail on Mercury—the Hermean magnetotail. “We wanted to find out why the satellite found energetic particles,” stated Xiaowei Zhou, one of the authors of the study.
A probable cause for the existence of these energetic particles is magnetic reconnection, which occurs due to change in the arrangement of magnetic field lines, leading to the release of thermal and kinetic energy. Yet, there is no clear understanding of magnetic reconnection in the turbulent astrophysical environment. In this research, Chinese and German physicists analyzed magnetic reconnection within the framework of turbulence in the Hermean magnetotail.
When magnetohydrodynamic simulations and test particle calculations were carried out, it was found that plasmoids, or unique magnetic structures that contain plasma, are produced as a result of magnetic reconnection. The energetic electrons are accelerated by these plasmoids. The simulation outcomes are supported by measurements of plasmoid species by the MESSENGER and measurements of plasmoid reconnection in the Hermean magnetotail.
The team also used a mean-turbulence model to account for the turbulence of subgrid-scale physical processes. Acceleration processes were calibrated to parameters that emulate the attributive conditions observed in the Hermean magnetotail. The simulations demonstrated that under these conditions, electron acceleration could be caused due to turbulent plasmoid reconnection responsible. “We also showed that turbulence enhances reconnection by increasing the reconnection rate,” stated Zhou.
The model developed by the researchers estimates the upper limits for turbulent plasmoid reconnection and the analogous electron acceleration. The Bepi-Colombo mission, which will be launched in October 2018, will investigate these predictions. The Bepi-Colombo satellites, which were constructed to endure the harsh and hot environment near the sun, will be introduced into Mercury’s orbit in 2025 for one Earth year to communicate observations from the planet.
“Previous satellites could not test the high energies from electrons and one aim of this mission is to measure the energetic particles from the Hermean magnetotail with new detector technology,” stated Zhou. The scientists hope that this innovative technology will help in gaining a more elaborative subscale view of the impacts of turbulence.