Other
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p41a1571p&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P41A-1571
Other
[5430] Planetary Sciences: Solid Surface Planets / Interiors, [5440] Planetary Sciences: Solid Surface Planets / Magnetic Fields And Magnetism, [5455] Planetary Sciences: Solid Surface Planets / Origin And Evolution, [5480] Planetary Sciences: Solid Surface Planets / Volcanism
Scientific paper
Spatial variations in insolation on Mercury could give rise to long-wavelength variations in the depth to the Curie isotherm for a given magnetic mineral. Global-scale magnetic fields can result from remanent crustal magnetization in such an environment. Magnetic field data from previous flybys and from the first MESSENGER orbits around Mercury indicate that most of the signal can be explained by a dipole field of core origin and an external field associated with magnetospheric currents, rather than by a long-wavelength crustal field. Here we examine residual fields that remain after the removal of the main core and external fields and we test for signatures of remanent crustal magnetization tied to variations of insolation with latitude and longitude. Large-scale longitudinal variations in near-surface temperatures arise from the combination of Mercury's high eccentricity with its 3:2 spin-orbit resonance while invariant latitudinal temperature variations result from a stable near-zero obliquity. We calculate near-surface thermal boundary conditions for models of Mercury's crust. These boundary conditions, coupled with an assumed vertical thermal gradient, predict large-scale variations in the thickness of the layer capable of carrying a magnetic signature, either induced or remanent. The presence of a substantial dipole term led to the suggestion that this process might explain Mercury's small global magnetic field. We have previously shown, on the basis of flyby data, that Mercury's global magnetic field is inconsistent with such a mechanism. We confirm this earlier result with magnetic field observations collected through the first 120 days of MESSENGER's orbital phase, which now covers Mercury's entire northern hemisphere. However, we find residuals with respect to a model that describes the large-scale internal and external magnetic fields associated with Mercury, and those residuals indicate the presence of systematic, unmodeled magnetic fields of internal origin. The character of these residuals is stable with respect to moderate changes in model parameters. Repeated coverage of the northern hemisphere at all local times will be achieved after six months of orbital operations and will test the robustness of the solutions.
Alexeev Igor I.
Anderson Benjamin J.
Johnson Clifton L.
Korth Haje
Paige David
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