Investigation of the Slater Plains: A Candidate Region for Landed Exploration

INVESTIGATION OF THE SLATER PLAINS: A CANDIDATE REGION FOR LANDED EXPLORATION T. Samaddar1, T. Frueh1, B.J. Thomson1, C.A. Nypaver2, 1Dept. of Earth, Environmental, and Planetary Sciences, University of Tennessee, Knoxville, TN, USA ([email protected]), 2Smithsonian Institution, National Air and Space Museum, Washington, D.C., USA Introduction: The Artemis III mission represents NASA’s first attempt to land astronauts on the lunar surface in more than 50 years. This renewed interest in the Moon, and the south pole is partially motivated by the presence of potential water/volatiles in the permanently shadowed regions (PSRs) of the poles. The recent Artemis III update by NASA down selected 9 potential landing regions across the lunar south pole [1]. We investigate one of these newly selected regions named the “Slater plains” (Fig. 1). It is located north of Slater crater (88°S, 111°E) and consists of typical polar highlands topography with multiple PSR’s [2] in its vicinity. We conduct an initial investigation of the morphology and surface properties of the region through a multi-wavelength approach utilizing radar and high-resolution optical data. Our goal is to assess the feasibility of landing in this region and generate a detailed geomorphological map of the region as a guide for landing site selection. Data: We used LRO Mini-RF radar data (monostatic S band; bistatic X band) and stokes parameters (S1, S2, S3, S4) derived products [3] to investigate the surface roughness and presence of boulders in the region. We used Chandrayaan 2 DFSAR (Dual Frequency Synthetic Aperture Radar; monostatic L band) calibrated datasets (from ISSDC) for similar stokes parameter retrieval and comparison with the S-band surface roughness results. We utilized LROC Wide Angle Camera (WAC) imagery (~100 m/px) as the basemap and LROC Narrow Angle Camera (NAC) imagery (0.5 m/px) [4] for a finer-scale analysis and comparison with the observed radar signals. We also assessed the general morphology of the region using LOLA (Lunar Orbiter Laser Altimeter) elevation and slope data. Methodology: We used the CPR (Circular Polarization Ratio), m-χ (m-chi) and Yamaguchi 4-component decomposition [5-6] technique for the Mini-RF and DFSAR datasets to study the physical properties of the lunar surface in this region. The m-χ and Yamaguchi decomposition helps to differentiate between the different scattering behaviors observed in the upper lunar regolith, namely double bounce, depolarized (volumetric), and single bounce scattering of radar signals. These scattering components are represented by the red, green, and blue colours in the m-χ and Yamaguchi RGB image, respectively. We used CPR data to study the presence of radar wavelength sized particles in the surface/near subsurface within Slater Plains region. We also used the slope and DEM data to evaluate topographically flat regions suited for spacecraft landing. We utilized the controlled NAC polar [7] imagery to identify small craters and the presence of boulder fields. We also assessed the Earth and Sun visibility data to further characterize the regions’ landing potential. Results: Data from Mini-RF and DFSAR highlight variations in surface roughness across the region. The X band bistatic data, however, has an extensive radar shadow area which makes interpretation difficult. Small fresh craters are marked by their distinctive ejecta material which are visible as bright spots in the S1 (total backscatter power), DFSAR HV cross polarization amplitude, Yamaguchi and m-χ RGB image (Fig. 2). The bright spots in the PSR’s are rough ejecta from small fresh craters. These green-yellow patches (m-χ image) show a dominance of depolarized (volumetric) scattering. These patches, within the PSR’s could be very suitable sites for sampling. Although depolarized scattering is indicative of possible ice/water-ice mixed within the regolith (near surface) [5], Figure 1 – a) LROC WAC (100m) mosaic with the selected landing regions and b) zoomed in controlled LROC NAC (1 m) mosaic of Slater plains with the PSR’s marked with orange polygons in the region b a these bright patches are most likely rough ejecta from fresh craters which happen to lie within these PSRs. Some of the smaller bright spots in the region denote small craters in the hundreds of meters scale. Minimal large boulders or boulder fields were observed in any of the radar datasets used. Similar results are observed with the NAC imagery as well. The region appears largely hazard-free, but boulders remain valuable for sampling due to their role in impact history, space weathering, and astronaut navigation. The m-χ decomposition results show the overall dominance of single bounce scattering (blue in mχ) in the region which is consistent with the presence of fine-grained regolith material (mature highland). The elevation and slope data show that the region has an undulating topography (average slope ~9º, minimum slope of 0.5° to maximum slope of >24°), with PSRs located in topographic depressions or crater floors. Much of the geology of the region is dominated by a typical highland plains unit of Nectarian aged material as well as pre Nectarian basin materials and is heavily cratered/eroded (Fig. 4) [8]. Discussion: Our combined analysis of radar, elevation, and optical data highlights a potential primary Artemis III landing site in the Slater Plains region, marked by the black hashed ellipse (Fig. 4). This site was chosen based on low average slopes (<7°) (Fig. 3) and the general absence of large boulders or boulder fields, aside from small craters (mostly ~50 m, few >100 m). Sun and Earth visibility values range from ~0.40 to 0.60 [9], ensuring adequate lighting for surface operations and uninterrupted Earth communication. Recent studies also show the potential presence of SPA (South Pole Aitken) basin material in this region based on compositional analysis [10]. This combination of safe terrain, fair visibility, and accessible PSR and potential SPA sampling sites make Slater Plains a reasonable candidate landing site for Artemis III based on spacecraft landing requirements [11]. Detailed geomorphological mapping is in progress, while additional parameters like Terrain Ruggedness Index (TRI), rock abundance and ShadowCam images for boulders are being assessed to further refine the characterization of the landing site. Acknowledgement: We thank the LROC team and the Mini-RF teams for providing the data on the PDS and for the extended derived products used in this study. We acknowledge the use of data from Chandrayaan-II of the Indian Space Research Organisation (ISRO), archived at the Indian Space Science Data Centre (ISSDC). References: [1] Gannon J. and Wasser M. (2024) NASA Headquarters. [2] Barker M. K., et al. (2023) Planet. Sci. J, 4, 183. [3] Stokes G.G., (1852) Trans. Cambridge. Phil. Soc, 9, 399. [4] Robinson M. S., et al. (2010) Space Sci. Rev., 150, 81– 124. [5] Raney R. K., et al. (2012) JGR Planets, 117, 0–22. [6] Yamaguchi R., et al. (2005) IEEE Transactions, 43-8. [7] Archinal B., et al. (2023) LPSC, LIV, Abstract #2333. [8] Krasilnikov, S. S., et al. (2023) Icarus, 394, 115422. [9] Mazarico E.M., et al. (2011) Icarus, 211, 1066-81. [10] Moye C. G., et al. (2025) LPSC, LVI, Abstract #2522. [11] NASA 2020: Artemis Plan: NASA Lunar Exploration Program Overview. [12] Fortezzo, C.M., et al. (2020) LPSC, LI, Abstract #2760 Figure 2 – Mini -RF S - band mχ radar signatures showing bright yellow/green spots and patches as small fresh craters with ejecta material. The blue background denotes dominance of smooth lunar regolith Figure 4 – Proposed landing site (striped) within the Slater plains region. Yellow polygons mark the PSR’s of interest in the vicinity . The Geologic units consist of – Ntp (Nectarian Terra Mantling & Plains, pNb (pre - Nectarian Basin) [12] Figure 3 – LOLA Slope map of the region