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Low-degree Structure in Mercury's Planetary Magnetic FieldThe structure of Mercury's internal magnetic field has been determined from analysis of orbital Magnetometer measurements by the MESSENGER spacecraft. We identified the magnetic equator on 531 low-altitude and 120 high-altitude equator crossings from the zero in the radial cylindrical magnetic field component, Beta (sub rho). The low-altitude crossings are offset 479 +/- 6 km northward, indicating an offset of the planetary dipole. The tilt of the magnetic pole relative to the planetary spin axis is less than 0.8 deg.. The high-altitude crossings yield a northward offset of the magnetic equator of 486 +/- 74 km. A field with only nonzero dipole and octupole coefficients also matches the low-altitude observations but cannot yield off-equatorial Beta (sub rho) = 0 at radial distances greater than 3520 km. We compared offset dipole and other descriptions of the field with vector field observations below 600 km for 13 longitudinally distributed, magnetically quiet orbits. An offset dipole with southward directed moment of 190 nT-R-cube (sub M) yields root-mean-square (RMS) residuals below 14 nT, whereas a field with only dipole and octupole terms tuned to match the polar field and the low-altitude magnetic equator crossings yields RMS residuals up to 68 nT. Attributing the residuals from the offset-dipole field to axial degree 3 and 4 contributions we estimate that the Gauss coefficient magnitudes for the additional terms are less than 4% and 7%, respectively, relative to the dipole. The axial alignment and prominent quadrupole are consistent with a non-convecting layer above a deep dynamo in Mercury's fluid outer core.
Document ID
20140010848
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
External Source(s)
doi:10.1029/2012JE004159
Authors
Anderson, Brian J. (Johns Hopkins Univ. Laurel, MD, United States)
Johnson, Catherine L. (British Columbia Univ. Vancouver, British Columbia, Canada)
Korth, Haje (Johns Hopkins Univ. Laurel, MD, United States)
Winslow, Reka M. (British Columbia Univ. Vancouver, British Columbia, Canada)
Borovsky, Joseph E. (Space Science Inst. Boulder, CO, United States)
Purucker, Michael E. (Stinger Ghaffarian Technologies, Inc. (SGT, Inc.) Greenbelt, MD, United States)
Slavin, James A. (Michigan Univ. Ann Arbor, MI, United States)
Solomon, Sean C. (Carnegie Institution of Washington Washington, DC, United States)
Zuber, Maria T. (Massachusetts Inst. of Tech. Cambridge, MA, United States)
McNutt, Ralph L. Jr. (Johns Hopkins Univ. Laurel, MD, United States)
Date Acquired
August 19, 2014
Publication Date
December 1, 2012
Publication Information
Publication: Journal of Geophysical Research Planets
Publisher: American Geophysical Union
Volume: 117
Issue: E12
ISSN: 0148-0227
Subject Category
Lunar And Planetary Science And Exploration
Report/Patent Number
GSFC-E-DAA-TN9344
Funding Number(s)
CONTRACT_GRANT: NAS5-97271
CONTRACT_GRANT: NNX13AJ86G
CONTRACT_GRANT: NASW-00002
CONTRACT_GRANT: NNG11HP14C
CONTRACT_GRANT: NNH08CC05C
CONTRACT_GRANT: NNX11AB84G
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
magnetometer
mercury
low-degree

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