Other
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmgp34a..02g&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #GP34A-02
Other
[1595] Geomagnetism And Paleomagnetism / Planetary Magnetism: All Frequencies And Wavelengths, [5440] Planetary Sciences: Solid Surface Planets / Magnetic Fields And Magnetism
Scientific paper
Although surface and orbital magnetic field measurements demonstrate a pervasive magnetization of lunar crustal materials, the origin of the observed magnetization—especially that of the magnetizing field(s)—remains unresolved. An alternative to the core dynamo hypothesis is that lunar materials acquired their magnetization in transient magnetic fields generated as a consequence of hypervelocity impacts onto the Moon (e.g., Hood and Artemieva, Icarus 193:485-502, 2008). In order to constrain this latter hypothesis, we conducted experiments to quantify the shock remanent magnetization (SRM) of lunar rocks as a function of shock pressure (up to 1 GPa) and ambient magnetic field. Experiments were performed on four Mare basalt cubic samples (14053, 15555, 15556, and 70215) using the laser shock technique described in Gattacceca et al. (PEPI 166:1-10, 2008). After initial measurement of its natural remanent magnetization (NRM) each sample was shocked and its SRM studied through stepwise alternating field (AF) demagnetization. The laser shock technique being non destructive, the same samples were shocked several times at different pressure and ambient field. The preliminary results show that the AF demagnetization spectra of NRM and SRM are sometimes undistinguishable, so that the NRM of some lunar Mare basalts could well have a shock origin. However, the estimated ambient field necessary to account for the intensity of the NRM is on the order of 100 µT (for a shock pressure of 1 GPa), which appears unrealistically high for transient fields generated in hypervelocity impacts, except possibly in the antipodal zone of a basin-forming impact. Future experiments at higher pressures and using other lunar lithologies (in particular breccias) are necessary to better constrain the hypothesis that some lunar magnetic anomalies have a shock origin.
Artemieva Natalia A.
Berthe L.
Boustie Michel
de Resseguier Th.
Fuller Michael M.
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