15:15h
AN: P23A-06
TI: Lunar Magnetism: IRMs Normalization and Impact Related Magnetization.
AU: * Fuller, M
EM: mfuller@soest.hawaii.edu
AF: HIGP-SOEST, University of Hawaii, Honolulu, HI 96822, United States
AU: Halekas, J
EM: jazzman@ssl.berkeley.edu
AF: Space Science Laboratory, University of California Berkeley, Berkeley, CA 94720, United States
AU: Adachi, T
EM: tomoko.adachi@ssedmail.gsfc.nasa.gov
AF: Solar System Exploration, NASA Goddard Space Flight Center, Greenbelt, MD 20771, United States
AU: Kletetschka, G
EM: gkletets@pop600.gsfc.nasa.gov
AF: Solar System Exploration, NASA Goddard Space Flight Center, Greenbelt, MD 20771, United States
AU: Kletetschka, G
EM: gkletets@pop600.gsfc.nasa.gov
AF: Institute of Geology, Charles University, Prague, 16502, Czech Republic
AU: Kletetschka, G
EM: gkletets@pop600.gsfc.nasa.gov
AF: Department of Physics, Catholic University of America, Washington, 20064, United States
AU: Kohout, T
EM: tomkohout@volny.cz
AF: Division of Geophysics, Charles University, Prague, 16502, Czech Republic
AB: Models of lunar magnetism need to explain: (1) strong Natural Remanent Magnetization (NRM), indicated by IRMs normalization, in some of the returned Apollo Mare Basalts and Melt Rocks with ages from about 3.85Ae to 3.65 Ae, (2) magnetic anomalies antipodal to the young basins of a similar age, (3) the absence of major magnetic anomalies over these same basins and the presence of minor anomalies over uplifted basement. (4) strong fields with scale lengths of homogeneity of the order of kms, or less, are found over the Cayley Formations and similar material. Observation (1) has frequently been taken to require the presence of a lunar dynamo. However, this presents a dilemma. If there were a lunar dynamo at that time, why were the basin melt sheets not magnetized in the field of the dynamo. It is also an uncomfortable coincidence that the dynamo is only extant close to the time of heavy bombardment. Given these difficulties and questions of the efficiency of dynamo action in a lunar core, it is worth reexamining other possible explanations of lunar magnetism. Hood's model accounts for the antipodal anomalies, while the observations at Vredefort (Carpozen, et al., 2003) may account for the anomalies over central peaks and uplifted ring structures in major basins. Experimental work by Crawford and Schultz (1999) has demonstrated that impacts of projectiles traveling at kms/sec generate magnetic fields. Srnka et al, (1979) showed that magnetic fields can be recorded by shock with demagnetization characteristics similar to thermal remanent magnetization. The question that remains is whether all of the observed lunar magnetization can be explained directly by impact related magnetization, or indirectly through magnetization acquired in the remanent fields of material magnetized by impacts.
DE: 5734 Magnetic fields and magnetism
DE: 6022 Impact phenomena (5420, 8136)
DE: 6030 Magnetic fields and magnetism
DE: 6250 Moon (1221)
SC: Planetary Sciences [P]
MN: 2007 Joint Assembly