The structure of Mercury's magnetic field from MESSENGER's first flyby

During its first flyby of Mercury, the MESSENGER spacecraft measured the planet's near- equatorial magnetic field. The field strength is consistent to within an estimated uncertainty of 10% with that observed near the equator by Mariner 10. Centered dipole solutions yield a southward planetary moment of 230 to 290 nanotesla R-M(3) ( where R-M is Mercury's mean radius) tilted between 5 and 12 from the rotation axis. Multipole solutions yield non- dipolar contributions of 22% to 52% of the dipole field magnitude. Magnetopause and tail currents account for part of the high- order field, and plasma pressure effects may explain the remainder, so that a pure centered dipole cannot be ruled out.