The Search for Topographic Correlations within the Reiner Gamma Swirl

Abstract

Lunar swirls have been traditionally considered to be unaffected by topographic changes. Yet, correlations between areas of high albedo and lower elevations are observed in regions of the Mare Ingenii swirl. Here, we apply similar techniques used at Mare Ingenii to determine if correlations between swirl units and topography also exist within Reiner Gamma. We generate topography using the techniques of stereophotoclinometry to Lunar Reconnaissance Orbiter Camera Narrow Angle Camera images to derive meter- to submeter-scale topography. We choose a 50 km2 study region with a 2.6 m ground sample distance (GSD), and within this region there is a 1 km2 subregion with a 0.8 m GSD. We use surface reflectance data at multiple viewing geometries to classify these regions into different swirl units using machine learning techniques. Statistical analyses of the data show mean height variations between on- and off-swirl of ∼4 m, with on-swirl at a lower elevation. It is not clear how this scale of elevation difference influences the formation of swirl units, but it supports postulations of dust migration and magnetic sorting contributing to their formation.

Photometric Properties within the Reiner Gamma Swirl: Constraining Formation Mechanisms

“…For the Reiner Gamma study area, previously shown to display correlations of swirl unit with topography (Weirich et al 2023), we find that there are also correlations between swirl unit and the Hapke modeling solutions. Differences in single-scattering albedo, photometric surface roughness, and particle scattering behavior is observed that correlate with the units identified by Chuang et al (2021).…”

“…Bright albedo areas (on-swirl) are, on average, lower in elevation by a few meters than the darker albedo areas between them. This correlation has been found for regions in both Mare Ingenii (Domingue et al 2022) and Reiner Gamma (Weirich et al 2023). Maps of OH and/or H 2 O also show a correlation with lower abundances onswirl compared to local background regions just outside the magnetic anomaly (Kramer et al 2011;Hess et al 2020;Clark et al 2024), with evidence that the correlation is dependent on the magnetic field strength (Hess et al 2020;Clark et al 2024).…”

“…Figure 6. Spatially coregistered LROC NAC images (image numbers in red) covering the study region (shown in Figure1) and used in the photometric analyses (this study) and topographic study ofWeirich et al (2023). The spatial coregistration results in the same location in each image corresponding to the same physical location on the lunar surface.…”

Spectrophotometric and Topographic Correlations within the Mare Ingenii Swirl Region: Evidence for a Highly Mobile Lunar Regolith

“…The observations that provide clues to deciphering what other processes are occurring include (1) brightening of the on-swirl spectra without altering the spectral slope or band depths (Pieters et al 2014;Pieters & Noble 2016;Hess et al 2020;Pieters et al 2021), (2) mineral abundance variations between on-and off-swirl (Sato et al 2017;Lemelin et al 2018), (3) potential segregation of the different size fractions of submicroscopic iron (Trang & Lucey 2019;Blewett et al 2021;Pieters et al 2021), (4) no variations in surface roughness (Neish et al 2011;Glotch et al 2015; this study), (5) potential correlations with topography (Domingue et al 2022;Weirich et al 2023), and (6) potential variations in the grain structures and sizes between on-and offswirl (this study).…”

“…Distinctive bright albedo markings, known as lunar swirls, cross the lunar landscape with seemingly little regard for topographic or geologic boundaries (Blewett et al 2011;Syal & Schultz 2015;Denevi et al 2016), though this has recently been disputed (Domingue et al 2022;Weirich et al 2023). They are associated with lunar crustal magnetic anomalies (Hood et al 1979b;Hood & Schubert 1980), though maps comparing crustal magnetic anomalies and swirl locations show that not all lunar magnetic anomalies have an associated swirl (Blewett et al 2011;Denevi et al 2016), and in some cases, the swirl markings extend to nonmagnetic regions outside of the anomaly (Syal & Schultz 2015).…”