HR: 14:25h
AN: GP22A-04    [PDF]
TI: Magnetic Effects of Impacts on the Moon
AU: * Halekas, J S
EM: jazzman@ssl.berkeley.edu
AF: Space Sciences Laboratory, University of California, 7 Gauss Way, Berkeley, CA 94720-7450 United States
AU: Lin, R P
EM: rlin@ssl.berkeley.edu
AF: Space Sciences Laboratory, University of California, 7 Gauss Way, Berkeley, CA 94720-7450 United States
AU: Mitchell, D L
EM: mitchell@ssl.berkeley.edu
AF: Space Sciences Laboratory, University of California, 7 Gauss Way, Berkeley, CA 94720-7450 United States
AB: Lunar Prospector (LP) electron reflectometer data indicate a variety of magnetic signatures associated with lunar impact sites, ranging from nearly complete demagnetization signatures to central magnetic anomalies. Smaller impact craters (D $< \sim$150 km) of all ages show evidence of demagnetization, with a higher percentage of younger craters displaying clear symmetric demagnetization signatures. Among larger impact structures, those of Imbrian and younger age still tend to show demagnetization, while older impact sites of Nectarian and Pre-Nectarian age often have central magnetic anomalies (sometimes superimposed upon a larger demagnetized region) with peak fields ranging from a few nanotesla to $\sim$100 nT. Most demagnetization signatures extend beyond the main rim of the visible impact structure, sometimes to a distance of several main rim radii. Consideration of the peak shock pressures produced by impacts indicates that most of the demagnetized region should not be heated above the Curie point, therefore indicating the importance of shock demagnetization in producing the observed demagnetization signatures. Central magnetic anomalies, on the other hand, tend to lie inside the transient cavity region of larger impact structures, suggesting that these features could be produced by thermal remanence in impact melt rocks, shock remanence in the highly shocked central uplift regions, or a combination thereof. Careful analyses of magnetic features associated with lunar impact sites, and comparison with terrestrial data from both laboratory experiments and field work, can be used to constrain the age history and physical characteristics of lunar remanent magnetism.
DE: 1521 Paleointensity
DE: 1540 Rock and mineral magnetism
DE: 6022 Impact phenomena
DE: 6055 Surfaces and interiors
DE: 6250 Moon (1221)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting