Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p44a..05k&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P44A-05
Physics
[5440] Planetary Sciences: Solid Surface Planets / Magnetic Fields And Magnetism, [5443] Planetary Sciences: Solid Surface Planets / Magnetospheres, [6235] Planetary Sciences: Solar System Objects / Mercury
Scientific paper
Since insertion of the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft into orbit around Mercury on 18 March 2011, the Magnetometer (MAG) has routinely observed localized reductions of the magnetic field magnitude below the level predicted by a planetary dipole model corrected for magnetospheric magnetic fields. These magnetic depressions are observed on almost every orbit, and the latitude at which they are observed is local-time dependent. The depression signatures are indicators for the presence of enhanced plasma populations, which inflate the magnetic field locally to maintain pressure balance, thus lowering the magnetic flux density. Mapping the magnetic depressions in local time and latitude, the MAG observations provide comprehensive insight into the plasma distribution near the planet, which is complementary to that provided by MESSENGER's Fast Imaging Plasma Spectrometer (FIPS). The spatial distribution shows that magnetic depressions are concentrated in two distinct regions. First, there is a population in the nightside equatorial region extending from dusk to dawn, which is offset northward from the planetary geographic equator by about 10°, commensurate with the offset of the planetary dipole. The extent of this population is indicative of the plasma sheet located in the equatorial magnetotail. A second concentration of magnetic depressions is found at high latitudes, predominantly on the dayside, and is associated with the magnetospheric cusp. The magnitude of the pressures associated with the depressions ranges from 0.1 to 3 nPa in the equatorial region, shows a systematic gradient from dusk to dawn, and reaches 10 nPa at high latitudes. We discuss the MAG observations and interpret the dusk-to-dawn gradient in the derived pressure distribution with a simple paradigm of particle drifts within Mercury's magnetosphere.
Anderson Benjamin J.
Johnson Clifton L.
Korth Haje
McNutt Ralph L.
Purucker Michael E.
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