Lunar swirls: Examining crustal magnetic anomalies and space weathering trends

Abstract

[1] 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.

Evidence for small‐scale collisionless shocks at the Moon from ARTEMIS

“…We cannot conclusively differentiate between these possibilities, but note that the velocity vectors of the reflected population appear to emanate directly from a region of strong crustal magnetic field, as shown in Figure 4 (lower right) (crustal field model from Purucker and Nicholas [2010]). This region, near the crater Firsov, contains albedo anomalies [Blewett et al, 2011]. These albedo features, typically associated with crustal magnetic fields, may indicate local shielding of the surface from space weathering, suggesting very strong localized reflection of the solar wind.…”

Formation of lunar swirls by magnetic field standoff of the solar wind

“…Previous near-infrared observations of lunar swirls show them to be optically immature compared with the surrounding terrains 10 . Space weathering leads to optical maturation of the surfaces of airless bodies and is thought to be caused by two main processes: (1) solar wind sputtering and/or implantation of hydrogen atoms, leading to the formation of nanophase metallic iron blebs and (2) micrometeoroid bombardment that leads to the formation of agglutinitic glass and a reduced vapourdeposited coating 11 .…”

“…Several swirl formation mechanisms have been proposed, including (1) solar wind standoff due to the presence of local magnetic fields, preventing solar wind sputtering and implantation, nanophase iron formation, and the resulting surface darkening associated with space weathering 3 , (2) recent comet impacts or micrometeoroid swarms that scoured the lunar surface, leaving a fine-gained, unweathered material and possibly imparting a remnant magnetization [4][5][6] , and (3) electrostatic levitation and deposition of high-albedo, fine-grained, feldsparenriched dust 7 . The association of all swirls with magnetic field anomalies of varying strength [8][9][10] has driven the development of each of these hypotheses. In this work, we use the unique midinfrared data set from the Diviner Lunar Radiometer to distinguish between these hypotheses.…”

Mission Orbit Design of CubeSat Impactor Measuring Lunar Local Magnetic Field

“…Later, as Apollo missions discovered rocks magnetized from the lunar surface, they found that the lunar magnetic field was distributed locally on the surface (Pearce et al 1972;Collinson et al 1973). Lunar swirl areas with high albedo on the lunar surface, in particular, exhibit high magnetic field strength (Blewett et al 2011). Therefore, the precedent lunar magnetic investigation, the Lunar Prospector mission, gathered magnetic data above the Reiner Gamma swirl, shown in Fig.…”