Magnetopause reconnection is the primary mechanism responsible for coupling planetary fields to the interplanetary magnetic field (IMF), the RE-configuration of magnetospheric field topology and…

The National Aeronautics and Space Administration (NASA) awarded a $530,400 grant to the Regents of the University of Michigan (doing business as the University of Michigan) to conduct in-depth studies on magnetopause reconnection, flux transfer events, and region-1 field-aligned currents at Mercury using the full dataset from the MESSENGER mission. The research aims to understand the nature of magnetopause reconnection at Mercury, how solar wind conditions affect reconnection rate and related phenomena, and how reconnection rate impacts Mercury's region-1 field-aligned currents. This grant does not have a set-aside designation. The University of Michigan, a leading public research university, has extensive experience conducting R&D for federal agencies like NASA through both prime and subcontract awards.

Magnetopause reconnection is the primary mechanism responsible for coupling planetary fields to the interplanetary magnetic field (IMF), the RE-configuration of magnetospheric field topology and driving internal magnetospheric dynamics. Initial messenger studies suggest that at mercury, intense dayside reconnection occurs for all shear angles. This is different from earth's observations, where larger shears (e.g.>90 DEG) are required to support significant reconnection rates. However, these mercury studies have analyzed only a small fraction of messenger magnetopause (MP) crossings and conducted limited studies of the factors influencing reconnection occurrence and rate. Earlier surveys of flux transfer events (ftes) and cusp plasma filaments indicate that MP reconnection at mercury is highly episodic. In fact, "showers" of ftes and filaments have been reported with time separations of only ~8-10S. Ftes and cusp filaments are important because they channel magnetosheath plasma down to the surface. At earth, newly opened dayside magnetic field lines give rise to region-1 field-aligned currents (facs), which transmit electromagnetic energy derived from the solar wind down into the ionosphere and close across the polar cap. Similar currents have been derived from the low-altitude magnetic field measurements taken by messenger during dawn-dusk orbits. They appear to close radially through mercury's resistive regolith and then across the surface of its highly conductive iron core. However, the dependence of region-1 current intensity on upstream conditions and dayside reconnection rate has not yet been studied. We propose to conduct in-depth studies of MP reconnection, ftes, FTE shower events and cusp filament occurrence and region-1 currents at mercury using the entire 4 year messenger dataset and university of michigan global MHD simulation model of mercury's magnetosphere. Our research aims to answer the following science questions: 1. What is the nature of MP reconnection at mercury (symmetric or asymmetric) and how do magnetic shear angle, magnetosheath plasma beta and intensities of the magnetic field internal and external to the magnetopause affect its rate? 2. How are the occurrence and physical properties of ftes, FTE shower events and cusp plasma filaments and MP reconnection rate determined by solar wind condition? Does reconnection rate influence the flux of solar wind plasma to mercury's surface carried by cusp filaments? 3. Does the global MHD model with an electrically conducting mercury iron core confirm the current close path of region-1 facs at mercury? How does the rate of MP reconnection affect mercury's region-1 field-aligned current intensity? All of the messenger data required for this study have been archived in the planetary data system. Previous investigations of these important phenomena at mercury have used only a small fraction of the 4 year messenger dataset. Our approach is to conduct comprehensive studies using all of messenger's magnetic field and plasma measurements. Reconnection rate will be determined using the ratio of the magnetic field component normal to the MP to the total magnetic field. Ftes and cusp plasma filaments will be identified and modelled using techniques that were validated by the initial messenger studies. Correlation analysis will be performed to determine relationship between reconnection rate, shear angle and magnetosheath plasma beta. The BAT-r-US global MHD simulation for mercury, which includes a realistic fully coupled iron core, has already been developed and validated using messenger observation. IT will be used, for the first time, here to study mercury's region-1 facs closure and to determine how reconnection rate affects total current intensity. The proposed work will greatly enhance the science return from messenger in areas of magnetic reconnection and related dynamics at mercury's MP, and IT is highly relevant to the roses 2017 ddap objectives.