My Ph.D. has been devoted to the study of Mercury’s magnetic field environment through observations from the MESSENGER mission, to reveal the nature of the interaction between a weak planetary magnetic field and the interplanetary medium. I have characterized the bow shock, magnetopause, and magnetic cusp regions of Mercury’s magnetosphere using magnetic field observations, and obtained the first measurements of the surface magnetic field through the technique of proton reflection magnetometry.
The bow shock and magnetopause define the boundary regions of the planet’s magnetosphere, and thus they represent the initial interaction of the planetary field with the solar wind. I have characterized these boundaries using MESSENGER Magnetometer (MAG) observations and established their time-averaged shapes and locations. By investigating the influence of the solar wind and interplanetary magnetic field (IMF) on the boundaries, I found that they move as the solar wind ram pressure and the Alfvén Mach number vary, but their shapes remain unchanged.
The cusp region is where solar wind plasma can gain access to the planet’s magnetosphere, and in Mercury’s case, the surface. As such, this area is expected to experience higher than average space weathering and be a source for the exosphere. I have made the first systematic observations of Mercury’s northern cusp region using MESSENGER magnetic field data, and mapped out for the first time its latitudinal and longitudinal extent, average plasma pressure and observed its variation with the solar wind and IMF. Using our derived plasma pressure estimate from the magnetic field depressions, I calculated the flux of plasma to the surface.
Mercury’s internally generated dipole field, which is the dominant magnetic field component of the magnetosphere, is not centered on the planet’s geographic equator but has a significant northward offset. I have conducted the first-ever study using proton reflectometry, a novel adaptation of electron reflectometry, to acquire the first measurements of Mercury’s surface field strength, with the goal of providing independent verification of the long-wavelength planetary magnetic field structure. Our results confirm the offset dipole structure at the surface and demonstrate that proton reflectometry is a viable indirect method for surface magnetic field measurements at Mercury.
I am very interested in studying the response of planetary magnetospheres to extreme events, for example, when the planet is “hit” by coronal mass ejections (CMEs). CMEs are typically associated with low Alfvén Mach number conditions and high solar wind dynamic pressure, which are expected to have significant effects on the bow shock, magnetopause, and cusp regions. At Mercury, studying how the boundary regions of the magnetosphere react to these extreme events can reveal more information not just about the magnetosphere–solar wind interaction, but also about the planet’s internal field as well.
I am also very interested in the magnetic field environment of other planets. Due to its weak magnetic field, proximity to the Sun, and lack of atmosphere, Mercury and its highly dynamic magnetosphere are interesting end-member analogs for terrestrial planets / moons in general. Thus, the knowledge and expertise I gained from the MESSENGER mission are directly transferable to other planetary / space physics studies in the solar system as well as in exoplanetary systems.