The magnetic field of Mercury, 1

Abstract

An updated analysis and interpretation are presented of the magnetic field observations obtained during the Mariner 10 encounter with the planet Mercury on March 29, 1974. The combination of data relating to position of the detached bow shock wave and magnetopause and the geometry and magnitude of the magnetic field within the magnetospherelike region surrounding Mercury lead to the conclusion that an internal planetary field exists with dipole moment approximately 5.1 X 10 22 G cm a. The limited data set precludes quantitative determination of an intrinsic field more complex than a centered dipole. The dipole axis has a polarity sense similar to that of earth and is tilted 7 ø from the normal to Mercury's orbital plane. The magnetic field observations reveal a significant distortion of the modest Hermean field (350 ? at the equator) by the solar wind flow and the formation of a magnetic tail and neutral sheet which begins close to the planet on the night side. Presently, an active dynamo mechanism in the planetary interior appears to be favored in the interpretation of the field origih, although fossil reinanent magnetization cannot be excluded. The composite data set is not consistent with a complex induction process driven by the solar wind flow.

Do Inner Planets Modulate the Solar Wind Velocity at 1 AU from the Sun?

“…If the planet ever had a dynamo it would have ceased to work when the rapid cooling of the comparatively small planet led to a completely frozen core. During the flyby of the Mariner 10 the magnetic field peaked at about 400 nT and it clearly displayed its intrinsic character (Ness et al 1975). Although the magnetosphere of Mercury is qualitatively similar to the Earth's magnetosphere, its much smaller size obviously results in many quantitative differences.…”

Some aspects of core formation in Mercury

“…only a thin outer shell, perhaps 50 to 80 km thick ( Figs. 1 and 2), is cur..rently below the Curie temperature in models in which core differentiation has proceeded to completion, and the magnetization required of such a shell would be very high (Ness et al, 1975b). …”

“…5, 1) Mercury has an internal magnetic field (Ness et al, -1974(Ness et al, - , 1975a, and a cinvective dynamo in a fluid conductin g Y g core is the preferred mechanism for field generation (Ness et al, 1975b;Stevenson, 1974Stevenson, , 1975.…”

Some unsolved problems in evolutionary dynamics in the solar system

“…Higher spins which are half-integer multiples of the orbital mean motion arc also likely to be stable against further tidal reduction, and occupancy of the existing state is understood in terms of an increasing probability of capture into a resonance as the order of the resonance is reduced (Goldreich and Peale, 1965). However, Mercury apparently has an intrinsic magnetic field (Ness et al, 1974(Ness et al, , 1975, which by a process of elimination seems to require generation by an internal dynamo action in a liquid, conducting core. If we have the possibility of a liquid core at …”