Paraboloid model of Mercury's magnetosphere

Abstract

[1] A new ''Paraboloidal'' model of Mercury's magnetospheric magnetic field based upon the earlier terrestrial model and using similar techniques is developed. The model describes the field of Mercury's dipole, which is considered to be offset from the planet's center; the magnetopause currents driven by the solar wind; and the tail current system including the cross-tail currents and their closure currents at the magnetopause. The effect of the interplanetary magnetic field (IMF) is modeled as a partial penetration of the IMF into the magnetosphere. The goals of the present work are (1) to develop an easily usable, yet robust model of Mercury's magnetospheric magnetic field and (2) to produce an improved ''unified'' determination of Mercury's magnetic dipole moment which fits the measurements taken during both Mariner 10's first and third flybys. This new model of Mercury's magnetosphere is described and used to determine a best Mercury magnetic dipole moment of 192 nT R M 3 , from the two Mariner 10 flybys, a value which is intermediate between the various estimates produced by previous models. The best fit to the Mariner 10 measurements gives the dipole offset 0.18 R M above the equatorial plane. The new Paraboloidal model is used to predict the configuration of this miniature magnetosphere under average and extreme solar wind conditions.

The Magnetic Field of Mercury

“…Mariner 10 flyby data suggest that the tail current is sufficiently intense close to the planet to reduce the net field to less than one-third of the internal field as close as 700 km from the surface (Ness et al 1975). For this reason the tail current is one of the key features of magnetosphere magnetic field models customized for Mercury (Giampieri and Balogh 2001;Alexeev et al 2008).…”

“…The first is to use those portions of Earth models that we have confidence apply to Mercury, namely the magnetopause and tail currents, and scale the models to Mercury (e.g., Luhmann et al 1998;Korth et al 2004). The second alternative is to develop analytical and empirical models unique to Mercury (Giampieri and Balogh 2001;Alexeev et al 2008). Further development of these Mercury models is essential to take full advantage of data to be obtained from orbit around Mercury, first by MESSENGER ) and then by BepiColombo (Balogh et al 2007).…”

“…To the extent that the assumed boundary conditions are at variance with the natural system, the currents and hence the external field of the simulations will be in error. Empirical models for the magnetospheric magnetic field analogous to those developed for Earth and other magnetized planets (Khurana 1997;Alexeev and Belenkaya 2005;Arridge et al 2006;Alexeev et al 2008) customized for Mercury will therefore remain an important tool. They offer the advantages that they are tied primarily to the observations, employ only specified known distributions of current, and can be evaluated rapidly for application to all of the observational data.…”

Separation of the Magnetic Field into External and Internal Parts

“…Jackson and Beard (1977) and Whang (1977) with significant recent improvements reached by Giampieri and Balogh (2001), Korth et al (2004), Grosser et al (2004), Scuffham and Balogh (2006), and Alexeev et al (2008). The model used by Jackson and Beard (1977) is a scaled version of the terrestrial magnetic field model of Bearda (1974a, 1974b).…”

Intense solar near‐relativistic electron events at 0.3 AU

“…In particular, the compressed medium formed in the region downstream of the shocks clearly affects the properties of the planet's magnetosphere [e.g., Alexeev et al, 2008]. Hence, the entry of the spacecraft into the magnetosphere after the passage of the IP shocks reveals larger magnetic field magnitudes and magnetic field orientations somewhat different from those usually observed during orbits without the presence of IP shocks.…”