Lunar swirls: Examining crustal magnetic anomalies and space weathering trends

Abstract

We have used multispectral images from Clementine and data from Lunar Prospector's magnetometer to conduct a survey of lunar crustal magnetic anomalies, prominent lunar swirls, and lesser known swirl markings to provide new information on the nature of swirls and their association with magnetic anomalies. We find that all swirls and swirl-like albedo patterns are associated with areas of magnetized crust, but not all areas of magnetized crust are colocated with swirl-like albedo anomalies. All observed swirls exhibit spectral characteristics similar to immature material and generally have slightly lower FeO values compared with their surroundings as determined with a multispectral iron-mapping method. We discuss these results in relation to the various hypotheses for swirl formation. The comet impact hypothesis for lunar swirls would not predict a difference in the spectrally determined FeO content between swirls and nearby ordinary surfaces. The compositional difference could be explained as a consequence of (1) magnetic shielding of the surface from the solar wind, which could produce anomalous space weathering (little darkening with limited reddening) and potentially alter the predictions of the multispectral iron-mapping algorithm while the compositional contrast could be enhanced by delivery of lower-FeO ejecta from outside the swirl; and (2) accumulation of fine plagioclase-rich dust moving under the influence of electric fields induced by solar wind interactions with a magnetic anomaly. Therefore, we cannot at present clearly distinguish between the solar wind shielding and electrostatic dust accumulation models for swirl formation. We describe future measurements that could contribute to solution of the puzzle of swirl origin. Copyright 2011 by the American Geophysical Union.