10:15 AM - 10:30 AM
[PPS04-06] A Statistical Study on Current Structure of Magnetic Field Depressions in Mercury's Magnetosphere
Keywords:Mercury, Magnetosphere
It is widely known that Mercury’s magnetosphere is like Earth's. There may be many structures that are unique or like Earthe’s but are different in time scale and spatial scale since the strength of Mercury’s magnetic field and physical parameters such as solar wind are different. MESSENGER is the only satellite that orbited and observed Mercury’s magnetosphere for a long time. However, its details are still unknown because there were many constraints on the MESSENGER observation.
Focusing on the magnetic field observation of MESSENGER, we find a characteristic depression structure in the nightside magnetosphere. Even in a series of orbits where the satellites pass over almost the same region, this depression structure may or may not be observed. This observational feature suggests that this structure changes on a time scale of a few hours. The structure is observed over a wide region in the nightside magnetosphere. Several previous studies have concluded that this structure is due to the tail current sheet crossing, and no in-depth studies have been conducted. However, when we focus on the magnetic field components that create this depression structure, we find that the main components are different between those observed near Mercury and those observed on the magnetotail side of the magnetosphere. This suggests that the depression structure observed, especially near Mercury, is caused by some magnetospheric structure other than the tail current sheet.
In this study, we refer to this structure as a "depression" and conduct an analysis using both magnetic field and plasma data. Our results indicate that the depression is closely related to nightside currents, previously unresolved in detail, based on magnetic field-derived current calculations, plasma temperature and pitch angle anisotropy, and its dependence on solar wind dynamic pressure. These findings suggest that the ring current in Mercury’s nightside magnetosphere plays a crucial role.
In this presentation, I will report on the status of our research.
Focusing on the magnetic field observation of MESSENGER, we find a characteristic depression structure in the nightside magnetosphere. Even in a series of orbits where the satellites pass over almost the same region, this depression structure may or may not be observed. This observational feature suggests that this structure changes on a time scale of a few hours. The structure is observed over a wide region in the nightside magnetosphere. Several previous studies have concluded that this structure is due to the tail current sheet crossing, and no in-depth studies have been conducted. However, when we focus on the magnetic field components that create this depression structure, we find that the main components are different between those observed near Mercury and those observed on the magnetotail side of the magnetosphere. This suggests that the depression structure observed, especially near Mercury, is caused by some magnetospheric structure other than the tail current sheet.
In this study, we refer to this structure as a "depression" and conduct an analysis using both magnetic field and plasma data. Our results indicate that the depression is closely related to nightside currents, previously unresolved in detail, based on magnetic field-derived current calculations, plasma temperature and pitch angle anisotropy, and its dependence on solar wind dynamic pressure. These findings suggest that the ring current in Mercury’s nightside magnetosphere plays a crucial role.
In this presentation, I will report on the status of our research.