Development with MESSENGER Data of a Model of Mercury's Magnetospheric Magnetic Field Confined within the Average Observed Magnetopause

Tuesday, 16 December 2014
Haje Korth1, Nikolai A Tsyganenko2, Catherine L Johnson3,4, Lydia C Philpott3, Brian J Anderson1, Manar Al Asad3,5, Sean C Solomon6,7 and Ralph L McNutt Jr1, (1)The Johns Hopkins University Applied Physics Laboratory, Laurel, MD, United States, (2)Saint Petersburg State University, St. Petersburg, Russia, (3)University of British Columbia, Department of Earth, Ocean and Atmospheric Sciences, Vancouver, BC, Canada, (4)Planetary Science Institute Tucson, Tucson, AZ, United States, (5)Saudi Aramco, Dhahran, Saudi Arabia, (6)Carnegie Institution of Washington, Department of Terrestrial Magnetism, Washington, DC, United States, (7)Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, United States
Accurate knowledge of Mercury’s magnetospheric magnetic field is required to understand the sources of the planet’s internal field. We present the first model of Mercury’s magnetospheric magnetic field that is confined within a magnetopause shape derived from Magnetometer observations by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. The model consists of individual modules for magnetic fields of internal origin, approximated by a dipole of magnitude 190 nT RM3, where RM is Mercury’s radius, offset northward by 479 km along the spin axis, and of external origin resulting from currents flowing on the magnetopause boundary and in the cross-tail current sheet. The cross-tail current is prescribed having a disk shape near the planet and extending into a Harris sheet at larger distances. The magnitude of the tail current is fit to minimize the root mean square residual between the magnetic field within the magnetosphere observed by MESSENGER and the model field. The magnetic field contribution from each module is shielded individually by a scalar potential function consisting of Cartesian harmonic expansions with linear and non-linear coefficients, which are fit to minimize the root-mean-square normal magnetic field component at the magnetopause. The resulting model resembles the observed magnetic field better than the previously developed paraboloid model in regions that are close to the magnetopause, i.e., at northern high latitudes and on the dayside. It will allow more accurate characterization of crustal magnetization, which may be observed during low-altitude orbits in the final months of the MESSENGER mission.