Other
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p23c1272h&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P23C-1272
Other
[5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering, [5421] Planetary Sciences: Solid Surface Planets / Interactions With Particles And Fields, [5440] Planetary Sciences: Solid Surface Planets / Magnetic Fields And Magnetism, [6250] Planetary Sciences: Solar System Objects / Moon
Scientific paper
The origin of the lunar swirls is an outstanding puzzle in lunar geoscience. In addition, the swirls lie at the intersection of broader issues in planetary science, including planetary magnetism (e.g., the origin of the magnetized crust via core dynamo versus impact processes) and the relative importance of solar wind exposure versus micrometeoroid bombardment in producing the optical effects of space weathering. Many of the unusual high-albedo features known as lunar swirls are associated with crustal magnetic anomalies, and many of the magnetic anomalies are found near the antipodes of major impact basins. The leading hypotheses that have been advanced for the formation of the swirls are: (a) regolith disturbance caused by the relatively recent impact of a comet coma, cometary fragments or cometary meteor swarms; and (b) atypical space weathering as a result of the magnetic anomaly shielding the surface from solar wind ion bombardment. Apollo subsatellite instruments, whose coverage was limited to equatorial and mid-latitudes, first revealed the existence of lunar crustal magnetic anomalies. The Lunar Prospector (LP) mission provided global data and has led to the discovery of additional regions of magnetized crust. We have conducted a series of studies on lunar magnetic and albedo anomalies using LP magnetometer data and Clementine multispectral images. Three of these magnetic anomalies have only been recently identified. Newly discovered magnetic anomalies near the craters Abel, Stofler, and Hartwig do not appear to harbor unusual albedo markings. The magnetic anomaly near Rima Sirsalis has long been known from Apollo data. A small sinuous swirl to the northwest may be related to the Sirsalis magnetic anomaly or could be a southern extension of Reiner Gamma. Our examination of images for Rima Sirsalis has led to the identification of an additional loop-shaped marking on Oceanus Procellarum and some possible anomalous bright patches in the nearby highlands. Our new LP maps of scalar field strength show that previously identified swirls near Hopmann, Firsov, and in western Mare Moscoviense do coincide with magnetic anomalies. On the basis of this work, our preliminary finding is that most, perhaps all, swirl-like albedo patterns are co-located with crustal magnetic anomalies, but not all magnetic anomalies exhibit unusual albedo patterns. Plots of Clementine color ratio versus reflectance for small areas show spectral trends that are consistent with a lesser degree of maturation for surfaces within the high-reflectance portions of swirls compared with the normal background, which is consistent with either mode of formation discussed above. Additional analysis of Clementine spectral data, combined with new observations from LRO and other spacecraft can help to further characterize these enigmatic features.
Blewett Dave T.
Coman Ecaterina I.
Gillis-Davis Jeffery J.
Hawke Bernard Ray
Purucker Michael E.
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