A test for secular variation of the Martian magnetic field

Details A test for secular variation of the Martian magnetic field A test for secular variation of the Martian magnetic field

Apr 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja.....7394p&link_type=abstract

EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #7394

Computer Science

Scientific paper

The strength of the Martian magnetic field in the old southern highlands is difficult to explain in terms of what we think we know about Mars. Perhaps what we have interpreted as a thermal remanent magnetization held in the lithosphere of Mars is really a dynamo field that is not working in a regime comparable to the earth's field. If the source of the Martian magnetic field is a dynamo, the longest wavelength fields should undergo secular variation. To test this idea we selected two, two-month periods during the Mars Global Surveyor mapping mission, separated by one Martian year, for comparison. These periods, centered in June, 2000 and May, 2002, are from the start of the southern hemisphere fall. We selected night-time observations, binned them into 1 degree bins, calculated median values, and fit a minimum curvature surface to these data. Maps of the radial, theta, and phi component differences between the two times are mostly less than 5 nT, and the maps have an along-track structure. We see little evidence for large scale structures in the difference maps down to the accuracy of the magnetometer (0.5 nT for night time conditions). Simple scaling arguments from the quadrupole part of the terrestrial dynamo field suggests reorganization times of 150 years at present rates of secular variation. The fields in the Cimmeria region are approximately 250 nT at the altitude of the mapping mission and so, if they were part of a dynamo dominated by quadrupolar fields, might experience temporal variations of 1.5 nT/year. There is as yet no evidence for secular variation in the magnetic field data spanning one Martian year. However, a longer time span of data, and a new mission later in the decade, would allow a more rigorous test of this result.

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