Three-dimensional modeling of Mercury's bow shock shape and position as functions of Alfven Mach number

Details Three-dimensional modeling of Mercury's bow shock shape and position as functions of Alfven Mach number Three-dimensional modeling of Mercury's bow shock shape and position as functions of Alfven Mach number

Sep 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008epsc.conf..306b&link_type=abstract

European Planetary Science Congress 2008, Proceedings of the conference held 21-25 September, 2008 in Münster, Germany. Online a

Physics

Scientific paper

Abstract Mercury's bow shock forms as a result of the interaction of the planet's magnetopause with the supersonic solar wind. The shape and position of this bow shock vary in response to changes in the solar wind ram pressure, flow velocity, interplanetary magnetic field (IMF) vector, and the alfvenic and sonic Mach numbers. In particular, the shock nose moves towards the planet for flows having high Mach number (Ma) and away from it for low Ma. Data from the Helios spacecraft indicate that around its perihelion, Mercury is immersed in solar wind flows having Ma ~ 2 or less [2]. This is markedly different from conditions at Earth, where typical values of Ma ~ 8 are expected. Thus, Mercury provides opportunities to study the response of a reconnecting magnetosphere to plasma parameters that affect the Earth only rarely during major interplanetary coronal mass ejections. In this paper we present an analysis of the shock location and shape using global three-dimensional magnetohydrodynamic (MHD) simulations [1]. In these MHD simulations, only solar wind protons are taken into consideration, and the effect of mass loading due to pick-up ions of magnetospheric origin is neglected. The internal magnetic field of Mercury is modelled as an eccentric tilted dipole. This study was conducted for a set of IMF orientations ranging from 0 to 90° and for Alfven Mach number ranging from 1.5 to 8. The bow shock spatial dimension was normalized by the solar wind ram pressure. Using these simulations, we derived an analytical model that describes the three-dimensional shape and the location of Mercury's magnetosphere in function of the IMF orientation and Alfven Mach number. The shock positions derived from this analytical model are compared with those derived from the inbound and outbound data of the Mariner 10 encounters and the first MESSENGER flyby of Mercury [3]. Fig. 1 The magnetic field magnitude profile derived from the MHD simulation serves to identify the position and the shape of the bow shock. References [1] Benna M. et al. (2008) 37th COSPAR Scientific Assembly, Montreal, Canada. [2] Sarantos M and Slavin J. A. (2008), Geophys. Res. Lett., submitted. [3] Slavin J. A. et al. (2008) Science, in press.

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