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Investigation of Mercury's magnetospheric and surface magnetic fields

University of British Columbia

This thesis is devoted to the study of Mercury’s magnetic field environment, to reveal the nature of the interaction between a weak planetary magnetic field and the interplanetary medium. Due to the lack of orbital spacecraft observations at Mercury prior to the MErcury Surface, Space Environment, GEochemistry, and Ranging (MESSENGER) mission, work in this thesis presents some of the first analysis and interpretation of observations in this unique and dynamic environment. The bow shock and magnetopause define the boundary regions of the planet’s magnetosphere, thereby representing the initial interaction of the planetary field with the solar wind. We established the time-averaged shapes and locations of these boundaries, and investigated their response to the solar wind and interplanetary magnetic field (IMF). We found that the solar wind parameters exert the dominant influence on the boundaries; we thus derived parameterized model shapes for the magnetopause and bow shock with solar wind ram pressure and Alfven Mach number, respectively. The cusp region is where solar wind plasma can gain access to the magnetosphere, and in Mercury’s unique case, the surface. As such, this area is expected to experience higher than average space weathering and be a source for the exosphere. Using magnetic field observations, we mapped the northern cusp’s latitudinal and longitudinal extent, average plasma pressure and observed its variation with the solar wind and IMF. From the derived plasma pressure estimates we calculated the flux of plasma to the surface. Mercury’s internal dipole field is not centered on the planet’s geographic equator but has a significant northward offset. We developed the technique of proton-reflection magnetometry to acquire the first measurements of Mercury’s surface field strength. Proton loss cones are evident in both the northern and southern hemispheres, providing confirmation of persistent proton precipitation to the surface in these regions. We used the size of the loss cones to estimate the surface magnetic field strength, which confirm the offset dipole structure of the planetary field. With additional proton-reflection magnetometry observations, we generated a global proton flux map to Mercury’s surface and searched for regional-scale surface magnetic fields in the northern hemisphere.

Text

2014-08-21

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/50100

Geophysics

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/