Magnetic signature of the South Pole-Aitken (SPA) basin: Character, origin, age, thickness and depth

Details Magnetic signature of the South Pole-Aitken (SPA) basin: Character, origin, age, thickness and depth Magnetic signature of the South Pole-Aitken (SPA) basin: Character, origin, age, thickness and depth

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p43a..06p&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #P43A-06

Physics

[5440] Planetary Sciences: Solid Surface Planets / Magnetic Fields And Magnetism, [5455] Planetary Sciences: Solid Surface Planets / Origin And Evolution, [5475] Planetary Sciences: Solid Surface Planets / Tectonics, [5480] Planetary Sciences: Solid Surface Planets / Volcanism

Scientific paper

Two new magnetic maps of the Moon, from Lunar Prospector and SELENE, shed new light on the origin of SPA, the largest and oldest of the recognized lunar basins. The more detailed of the two maps, derived from Lunar Prospector (LP) magnetometer observations (Purucker and Nicholas, JGR, in press), has a wavelength resolution of 64 km, and is developed from 30 km mean altitude LP observations. A set of WNW-trending linear to arcuate magnetic features, evident in both the radial and scalar observations, cover much of a 1000 km wide region centered on the NW corner of SPA. These features are also recognized, albeit with lower resolution, from the 100 km mean altitude SELENE maps (Tsunakawa et al, Space Science Reviews, in press). The magnetizations inferred from the magnetic field observations, in excess of 0.2 A/m for a crustal thickness of 50 km, mean that the source body is almost certainly in excess of 1 km thick, and more likely, 10 km thick, for reasonable magnetization values. The source body is not at the surface because the magnetic features show no first-order correspondence to any surface topographic or structural feature, with the possible exception of a short section of the inner ring of SPA. Proximity of the magnetic features to SPA suggests that they may be related to the formation of the basin, or its subsequent history. Patchy mare basalts of inferred Imbrian-age are emplaced within SPA, in local 'ponds', and are inferred to have been emplaced through dikes, directly from mantle sources. The location of the magnetic features show some general correlation with the mare ponds. The resolution of the magnetic field observations is inadequate to determine the width of the magnetic sources, and it is plausible that they may represent dike swarms, analagous to terrestrial dike swarms, emplaced when a primordial lunar dynamo was active. Alternative explanations, such as the remnants of an Fe-rich SPA-forming projectile, or the amplification of ambient magnetic fields by an impact-generated plasma cloud, do not explain the lineated character of the features. Scalar magnitude of magnetic field over SPA basin based on model of Purucker and Nicholas (JGR, in press).

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