Lunar swirls are some of the most beautiful yet mysterious features on the Moon. They are characterized by their unusual albedo markings, which are wispy or sinuous in form. Swirls are often associated with the invisible presence of notable magnetic anomalies. They are found without any topographic expression of their own and occur across mare or highland terrain. We have recently re-examined the spectroscopic properties of swirls using data from the Moon Mineralogy Mapper in order to determine whether there are compositional distinctions associated with their bright and dark markings. The data are consistent with the features being locally derived (rather than addition of a significant foreign component), but their albedo variations do not follow any common alteration or mixing pattern for lunar materials. Specifically, the spectral properties of swirls are not consistent with normal ‘space weathering’ of exposed lunar materials that results from the accumulation of nanophase metallic iron on soil grains when exposed to the harsh environment on the lunar surface. Instead, the observed characteristics of swirls argue for a difference in micro-scale texture of swirl regolith structure compared to that of nearby local soils. Some rearrangement of the fine components is also likely at swirls.
Key issues to explore in the lunar environment are the effects that a relatively strong local magnetic field may have on small electrostatic forces that control interaction between soil grains. The mobility of the finest fraction is another key question. In addition, all regolith evolution processes occur in the strong diurnal cycling involving solar radiation ? exposure from visible to near-infrared electromagnetic radiation (heat) and solar wind energetic particles. If we could understand the direct cause and effect between the magnetic anomalies and the character and patterns in these enigmatic swirls, we would go a long way toward constraining the origin of the magnetic signatures themselves ? which in turn would ultimately constrain the early history of the Moon