Timing of the dynamo through impact demagnetization on Mars: what can be done?

Details Timing of the dynamo through impact demagnetization on Mars: what can be done? Timing of the dynamo through impact demagnetization on Mars: what can be done?

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmgp11b0074l&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #GP11B-0074

Physics

1517 Magnetic Anomalies: Modeling And Interpretation, 1541 Satellite Magnetics: Main Field, Crustal Field, External Field, 1595 Planetary Magnetism: All Frequencies And Wavelengths, 5440 Magnetic Fields And Magnetism, 6225 Mars

Scientific paper

Large impactors modify the properties of the lithosphere. On Mars, the lack of magnetic field measurable over the largest impact craters Mars (Hellas, Argyre, Isidis) is usually interpreted as locally non magnetized areas. These very large impacts demagnetized the crust, by thermal, shock or excavation processes. It is usually thought that they took place after magnetic dynamo had shut down, as post-impact material did not acquire a new magnetization. It should thus be possible to give a relative timing of when the Martian dynamo died out. In order to improve this timing, it is important to ascertain if smaller impact craters have significantly demagnetized the lithosphere to produce magnetic signature measurable by the current Mars Global Surveyor magnetic field experiment. We assume the demagnetization to be restricted within the excavation area. Craters are first simulated within a homogeneously magnetized lithosphere. A 100 km diameter crater will be associated with a 1 nT signature at 150 km altitude, while a 250 km diameter crater will produce a 1 nT signal at 400 km altitude. These simulations are valid providing that the lithosphere was homogeneously magnetized, thus producing no remanent magnetic field outside. We extend these tests to more complex magnetization distributions. We present and discuss these forward simulations. We then compare our results to actual measurements and finally to magnetic field predictions using a regional scheme to invert the magnetic data. We finally discuss the pertinence of new, low-altitude, magnetic field measurements.

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