Other
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p23c1269t&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P23C-1269
Other
[1517] Geomagnetism And Paleomagnetism / Magnetic Anomalies: Modeling And Interpretation, [1595] Geomagnetism And Paleomagnetism / Planetary Magnetism: All Frequencies And Wavelengths, [5440] Planetary Sciences: Solid Surface Planets / Magnetic Fields And Magnetism, [6250] Planetary Sciences: Solar System Objects / Moon
Scientific paper
The magnetic field around the Moon has been successfully observed at nominal and lower altitudes by the lunar magnetometer (LMAG) on the SELENE (KAGUYA) spacecraft in a polar orbit from October 29, 2007 to June 10, 2009. Since the solar activity has been very low during the observation, relatively weak anomalies can be observed even at a nominal altitude of about 100 km. In this paper we report preliminary results of the global mapping in the constancy and optional phases and compare the results with previous global maps (e.g. Richmond and Hood, 2008; Mitchell et al., 2008). The nominal altitude was 70-120 km (mostly 100 +/- 10 km) in the constancy phase (November, 2007 to December, 2008). Based on dataset in the tail lobe and in the lunar wake, magnetic anomaly fields without altitude correction were mapped on 1 x 1 degree bins with 95 % coverage of the lunar surface. We also obtained full-coverage maps of the vector magnetic field at a constant altitude of 100 km after altitude normalization and interpolation of the magnetic anomaly field by the inverse boundary value problem, the EPR method by Toyoshima et al. (2008). After the constancy phase, we subsequently conducted the optional phase in 2009 to observe the magnetic field and plasma at lower altitudes. The altitude was mostly 50-70 km during January to March, and then further lowered by 20-50 km with a pericenter above the South-Pole Aitken basin. We obtained global maps of 1 x 1 degree bins at the low altitudes with 84 % coverage. We also applied our detrending method to the low-altitude dataset of the lunar magnetic field by the Lunar Prospector (LP). and compared them with our maps. As a result, characteristic features in the lunar magnetic anomaly distribution are consistent with each other. The results in the present study indicate that statistically significant magnetic anomalies are distributed over almost the whole lunar surface. Relatively strong anomalies are identified in several basin, basin-antipode and near-crater regions, while the youngest basin on the Moon, the Orientale basin, has no magnetic anomaly. The basin-forming impact model can explain formation of the basin-antipode anomaly in the amplified interplanetary magnetic field (e.g. Mitchell et al., 2008). However, some basins and their antipode regions show magnetic anomalies, and thus it seems difficult to induce significant magnetization due to the interplanetary magnetic field in both regions. These suggest that the early lunar dynamo or the early geodynamo before the Orientale basin formation is preferable as a magnetic field source of the lunar crustal magnetism to the interplanetary magnetic field.
Iijima Yu-ichi
Matsuoka Ayako
Matsushima Masaki
Nakazawa Satoru
Otake Hisashi
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