Mercury's Magnetic Field

at the instant God created the water molecules, the spins of the hydrogen nuclei were all pointing in a particular direction. By the ordinary laws of physics, the spins of the nuclei would lose their alignment within seconds, but the large magnetic field would preserve itself by causing an electric current to circulate in the interior of each planet. By the same laws, the currents and fields would preserve themselves with only minor losses, as God rapidly transformed the water into other materials. After that, the currents and fields would decay due to electrical resistance.

INTRINSIC MAGNETIC-FIELDS OF THE PLANETS - MERCURY TO NEPTUNENESS NFPHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY OF LONDON SERIES A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES 349 (1690): 249-260 NOV 15 1994Abstract: In the past three decades, studies of the magnetic fields of Earth's Moon and all the planets, except for Pluto, have been conducted by spacecraft of the U.S.A. and of Venus and Mars by the former U.S.S.R. Among the terrestrial planets, only Mercury (Mariner 10: 1974 and 1975) is globally magnetized while the Moon and Venus are unmagnetized. The situation at Mars is still unclear, but if any global field exists, it is quite small. In 1979, Pioneer 11 discovered a magnetic field and radiation belt at Saturn, further elaborated on by Voyagers 1 (1980) and 2 (1981). Pioneers 10 (1974) and 11 (1975) and Voyagers 1 (1979) and 2 (1979) examined in detail the magnetic field of Jupiter, which had been inferred initially and studied remotely due to its non-thermal radio emissions in the late 1950s. Jupiter's magnetic field is much stronger than Earth's and distinctly nondipolar close to the planet. Saturn has a much weaker field than Jupiter, and it is surprisingly axisymmetric (to degree n = 3) with respect to its rotation axis. The Voyager fly-bys of Uranus and Neptune in 1986 and 1989 discovered global magnetic fields and trapped energetic particle radiation belts. Both Uranus and Neptune display remarkably similar magnetic fields (quite different from Jupiter, Saturn and Earth). In an astrophysical sense, Uranus and Neptune are described as oblique rotators because of the large angular offset of their magnetic axes from their rotation axes (59 degrees and 47 degrees). Additionally, their magnetic 'centres' are displaced by substantial fractions of a planetary radius (0.31 R(U) and 0.55 R(N)) This paper summarizes our present knowledge of the quantitative characteristics of the magnetic fields of these planets.

MAGNETIC-FIELDS OF THE OUTER PLANETSCONNERNEY JEPJOURNAL OF GEOPHYSICAL RESEARCH-PLANETS 98 (E10): 18659-18679 OCT 25 1993
Abstract: It is difficult to imagine a group of planetary dynamos more diverse than those visited by the Pioneer and Voyager spacecraft. The magnetic field of Jupiter is large in magnitude and has a dipole axis within 10-degrees of its rotation axis, comfortably consistent with the paleomagnetic history of the geodynamo. Saturn's remarkable (zonal harmonic) magnetic field has an axis of symmetry that is indistinguishable from its rotation axis (<< 1-degrees angular separation); it is also highly antisymmetric with respect to the equator plane, According to one hypothesis, the spin symmetry may arise from the differential rotation of an electrically conducting and stably stratified layer above the dynamo. The magnetic fields of Uranus and Neptune are very much alike, and equally unlike those of the other known magnetized planets. These two planets are characterized by a large dipole tilts (59-degrees and 47-degrees, respectively) and quadrupole moments (Schmidt-normalized quadrupole/dipole ratio almost-equal-to 1.0). These properties may be characteristic of dynamo generation in the relatively poorly conducting ''ice'' interiors of Uranus and Neptune. Characteristics of these planetary magnetic fields are illustrated using contour maps of the field on the planet's surface and discussed in the context of planetary interiors and dynamo generation.

Mars doesn't have much of a magnetic field since its density is so low- its core must not be completely metal, or really small.