Contribution of surface magnetic recordings to planetary exploration

Details Contribution of surface magnetic recordings to planetary exploration Contribution of surface magnetic recordings to planetary exploration

Nov 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996p%26ss...44.1289m&link_type=abstract

Planetary and Space Science, v. 44, p. 1289-1302.

Computer Science

8

Scientific paper

The transient variations of the magnetic field at the surface of a planet have a primary external source, the interaction between the environment of the planet and solar radiation, and a secondary source, the electric currents induced in the conductive planet. The continuous recording of the time variations of the magnetic fields at the surface of Mars by means of three-component magnetometers installed on board landers would therefore allow study of both the internal structure of Mars and the dynamic of its ionized environment. The depth of penetration of an electromagnetic wave in a conductive medium depends on both the period of the wave and the electrical resistivity of the medium. The larger the period and the resistivity, the greater the depth of penetration (skin effect). The high frequency spectrum will therefore enable one to estimate the resistivity in the uppermost kilometres of the planet, and to give information about the presence (or absence) of liquid water under the permafrost. The low frequency spectrum of the transient variations will give information on the presence (or absence) of sharp variations in the resistivity in the uppermost hundreds of kilometres of Mars, and thus on the thermodynamic conditions within the upper mantle of this planet. Averages of the measurements made during ``quiet time measurements'' would provide a very good estimate of the field of internal origin at the locations of the surface stations. If in addition a total duration of one year or more for the mission can be expected, and a drift on the order of 1 nT per year for the ground-based magnetometer, it might even be possible to detect some dynamo-related secular variation. In addition to the map of the Martian magnetic field which will be produced by the Mars Surveyor 1 orbiter, these groundbased local main field measurements will provide original information on the present and past magnetic field of Mars, and then on its present and past core dynamics. As is the case for the Earth, different possible controlling plasma processes will lead to different convection patterns inside the magnetosphere and therefore different magnetic signatures at the planetary surface. Continuous recordings of the transient variations of the magnetic field on board landers will then provide constraints on the convection within the Martian magnetosphere, that is a small magnetosphere where the ionosphere lies at great heights relative to the dimensions of the magnetospheric cavity.

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