Physics
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agusm.u31a..03k&link_type=abstract
American Geophysical Union, Spring Meeting 2008, abstract #U31A-03
Physics
1595 Planetary Magnetism: All Frequencies And Wavelengths, 2756 Planetary Magnetospheres (5443, 5737, 6033), 5440 Magnetic Fields And Magnetism
Scientific paper
The first MESSENGER encounter with Mercury provided observations near the planet's equatorial plane during quieter magnetospheric conditions than those of the Mariner 10 flyby I (M10-I), which had a comparable geometry. The new MESSENGER data complement Mariner 10 flyby III (M10-III) data obtained on a transit over the north pole. We combine data from all three flybys to: (1) assess whether there is a change in the planetary magnetic moment since 1974-75; (2) determine the planetary dipole strength; (3) assess the presence of higher-order terms in the intrinsic field. We use two approaches to correct for the external field: a scaled magnetospheric model based on the Tsyganenko-Sitnov 2004 (TS04) terrestrial magnetosphere magnetic field model, and a conventional spherical harmonic potential representation for external sources. Using only dipole inversions with the TS04 external field correction, we find no evidence for a significant change in the planetary dipole since 1974- 75. Solutions for the planetary dipole using data from all three flybys agree to within 20 percent regardless of the approach used to account for the external field. The presence of higher-order terms is assessed both using a degree-two internal field solution and using a regularized solution in which the power in the higher-order terms is allowed but constrained. Both approaches yield a significant quadrupole term. The quadrupole term is driven by the fact that the peak MESSENGER colatitudinal component (at the equator) is lower than one would expect from a centered dipole giving a field consistent with the M10-III radial component (at the pole). However, the magnetic field and plasma observations by MESSENGER imply a significant plasma pressure near Mercury within the magnetosphere at the equator, which may play a role in suppressing the field intensity measured at the equator and may contribute to the apparent quadrupole signature.
Acuña Mario Humberto
Anderson Benjamin J.
Gloeckler George
Gold Robert E.
Johnson Clifton L.
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