An Ultraviolet Analysis of Lunar Swirls by Night and Day

We report a survey of the lunar surface emphasizing the wispy, sinuous, sometimes looping features called lunar swirls using data from the Lyman Alpha Mapping Project (LAMP) and the Lunar Reconnaissance Orbiter Camera (LROC). We detail several detection classes in which the swirls are identified and confirmed with these two ultraviolet instruments through both independent and combined surveys; many of the swirls were not previously detected in other regions of the electromagnetic spectrum. We hypothesize that this is due at least in part to the unique nighttime normal directional-hemispherical photometric geometry of LAMP at 121.6 nm, which enables rare illumination conditions in which to view these highly surficial deposits. We further examine the population of swirls for their variability in far- and near-ultraviolet (FUV and NUV) reflectance, relative to their local surrounding regolith and global regolith. An examination of swirl relative size compared to albedo, spectral slopes, and coincident crustal magnetic field strengths collected by Lunar Prospector’s Fluxgate Magnetometer show no spatially correlated systematics. However, we also show that at weak magnetic anomalies Ly-α albedo varies substantially and as magnetism increases, Ly-α albedo decreases and reduces in variability. By combining FUV and NUV observations we can more effectively distinguish lunar swirls as a population relative to impact crater deposits and in turn enable an initial assessment of lunar swirl optical and physical properties (roughness, porosity, shock) relative to impact deposits and their surrounding regolith.