Demagnetization of Martian Crust by Large Impacts

Details Demagnetization of Martian Crust by Large Impacts Demagnetization of Martian Crust by Large Impacts

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.p42a0549m&link_type=abstract

American Geophysical Union, Fall Meeting 2001, abstract #P42A-0549

Physics

1219 Local Gravity Anomalies And Crustal Structure, 5420 Impact Phenomena (Includes Cratering), 6225 Mars

Scientific paper

The magnetic anomaly map of Mars derived from Mars Global Surveyor magnetic data shows no magnetic signature inside large basins such as Hellas, Argyre and Isidis, but it does show some appreciable anomalies over the immediate surroundings of these basins. This implies that the large impacts that produced these giant basins demagnetized the entire crust beneath the basins. To investigate the extent of the impact effects, we first assess the excavation by determining the crustal thickness beneath the basins under the assumption that the observed gravity anomaly arises from the surface topography and the undulation of the crust-mantle interface. Using the resulting crustal structure, we then model the neighboring small magnetic anomalies to determine the degradation of crustal magnetization as a function of distance from the impact site. This provides a means to constrain the extent of the shock effects and the initial temperature distribution immediately after the impact. The impacts have generated shock pressures of about 3 GPa at the edge of the basins, implying that shock was a major factor in the demagnetization of the crust beneath the basins. The magnetic effects of the initial shock wave and the heat resulting from isentropic decompression following the impact are then investigated. We also modeled the thermal evolution of the crust beneath the basins and possible remagnetization of small source bodies in the surroundings to establish that the impacts occurred in the absence of the core field.

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