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