We apply machine learning techniques to identify and map resurfacing units in the central South Pole−Aitken (SPA) basin using three Lunar Reconnaissance Orbiter (LRO) mission data sets: 321/415 nm and 566/689 nm band reflectance ratios from Hapke photometrically standardized albedo maps and a Terrain Ruggedness Index map using the Wilson et al. method. Other data were considered, but albedo and topography data were key in distinguishing between maria, cryptomaria, and light plains. A two-step image classification approach was applied to the data sets, an unsupervised K-Means algorithm followed by a supervised Maximum Likelihood Classification (MLC) algorithm. K-Means identified four units, one associated with dark smooth maria, two not associated with any particular features, and a fourth associated with edge effects. To further discriminate between the two nonassociated units, the K-Means unit map and an LRO morphologic basemap were used to select multiple training areas for three defined units in the MLC algorithm: mare, cryptomare, and cryptomare/light plains. From the training area values, the MLC unit map showed a distinction between the two prior indistinguishable K-Means units. Our results show (1) that the cryptomare from the MLC algorithm is in good agreement with cryptomaria mapped by J. L. Whitten & J. W. Head, (2) that the presence of scattered maria within large patches of cryptomaria indicates possible incomplete and/or uneven ejecta deposits or sheet flows covering cryptomare surfaces, and (3) a 79% increase in the total extent of cryptomaria compared to that by J. L. Whitten & J. W. Head for the same given study area in central SPA.

Mercury’s surface presents significant challenges for understanding planetary volatile distribution. Previous studies have identified features including hollows, flows, and chaotic terrains as associated with the presence of volatiles. Their formation and connection to Mercury’s volatile inventory remain incompletely characterized. Using Hapke’s radiative transfer model, we conducted detailed photometric analyses of three distinct regions within Mercury’s Raditladi basin that display hollows and flow-like morphologies to quantify regolith properties and their relationship to volatile-driven processes, revealing three key findings. (1) The basin floor regolith exhibits distinct structural characteristics indicating a separate evolutionary pathway. (2) Hollows and surrounding halos demonstrate regolith properties (higher porosity, finer-grained) consistent with slow, low-energy sublimation processes that minimally disrupt intergrain relationships. (3) Areas within the peak ring display photometric signatures indicative of volatile-rich mass wasting flows. The hollows and halos exhibit significantly higher single-scattering albedos compared to other units, suggesting the presence of a unique residual material that remains after volatile sublimation that appears intimately mixed with common regolith components. Previously mapped flow-like features share regolith structural similarities with hollows supporting their derivation from a common volatile-rich layer (VRL). Regions along peak walls display distinctive photometric properties that likely represent remnants of VRL flow sources within the peak ring structure, suggesting that peak rings maintained their volatile composition throughout the flow process. The excavation of hollow-like regolith from impacts on the basin floor suggests either differentiation of the impact melt or burial of volatiles outgassed from the peak ring, deposited on the basin floor, and later buried.

We present a three-dimensional radargram of a 13° x 11° region of Deuteronilus Mensae, produced from 457 Mars Reconnaissance Orbiter Shallow Radar (SHARAD) observations. We assess the viability of the 3D imaging algorithms developed to work with SHARAD observations in mid-latitude regions of interest. The quality of subsurface imaging in topographically complex regions is highly improved due to the proper positioning and mitigation of off-nadir reflections in the resulting image. The initial analysis of debris-covered glaciers using 3D radargrams has yielded results that are consistent with previous 2D-based mapping efforts. However, the use of 3D radargrams has enabled the analysis of 3× more area resulting in more accurate estimates of total ice volume, indicating over 9% more ice than previously estimated. Such discrepancies have important implications for Mars climate history studies and in situ resource utilization. The success of this imaging study paves the way for future 3D radargrams in the martian mid-latitudes and stands to increase our confidence in the distribution of many subsurface features of interest.

The area in the Reiner Gamma swirl studied by Weirich et al. for topographic correlations also displays correlations with the Hapke-model-derived single-scattering albedo, surface roughness, and particle scattering properties with swirl unit. The correlations with single-scattering albedo associate compositional variations in plagioclase and FeO content with swirl unit. The correlations with photometric surface roughness show a rougher surface on-swirl, implying a potentially more porous surface on-swirl compared to off-swirl. This suggests the variations in single-scattering albedo are dominated by the compositional differences and not structural differences, such as compaction. Grain-size differences could still contribute to the albedo variations. Differences in particle scattering properties between on-swirl and off-swirl are counter-indicative of the trend expected from variations in space weathering, unless there is a process to initiate either size sorting or compositional differences. The photometric properties point to a complex interaction of multiple processes to form the swirl units, not a singular dominant process. Variations in weathering, dust mobilization and entrapment, and impact modification may all play a key role.

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 km ^2 study region with a 2.6 m ground sample distance (GSD), and within this region there is a 1 km ^2 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.

The discovery of global elemental volatile compositions, sublimation hollows, and chaotic terrains has significantly reshaped our understanding of Mercury’s geology. These findings suggest the existence of volatile-rich layers (VRLs) extending several kilometers in depth, challenging the traditionally held view of a predominantly volatile-devoid Mercury crust. However, the precise nature and origin of these VRLs remain to be elucidated. The Raditladi basin exhibits morphologies analogous to terrestrial and Martian glaciers. These geomorphological features are potentially derived from impact-exposed VRLs, likely constituted of halite, other semivolatile salts, or organic volatiles. The distinctive rheological traits of substances such as halite substantiate this hypothesis. The inference posits a potential ubiquity of VRLs on a planetary scale, albeit potentially ensconced at considerable depth in specific regions. North polar chaotic terrains elucidate the VRLs’ genesis and temporal evolution. The intense fragmentation of heavily cratered landscapes during their formation indicates a composition dominated by volatiles. This finding postulates a phase of volatile-enriched crustal accretion predating the Late Heavy Bombardment (∼3.9 Ga). Regardless of lost mass, the unaltered basal elevation post-collapse signals a transition to a volatile-free stratum. The exposure of an exhumed lithological substrate within Mercury’s stratigraphy, identifiable in gravimetry as an impacted paleosurface, contests the magma ocean differentiation concept for VRL formation. It infers a grand-scale construct originating from depositional processes, possibly due to the collapse of a transient, hot primordial atmosphere.

The spectrophotometric properties of two study areas in the Ingenii swirl region show that the combined effects of multiple processes are required to explain the regolith’s mineralogical and physical properties. Production of the swirl regions requires mobilization of the regolith in addition to preferential radiation shielding of subareas. The discovery of topographic correlations between on- and off-swirl (dark lanes) clearly shows that the on-swirl regions are statistically lower than the off-swirl dark lanes by 2–3 m. Photometric analyses show no microscale roughness differences between on- and off-swirl, suggesting no differences in the regolith’s fairy-castle structure between the two swirl regions. The photometric properties of one of the study areas suggest that off-swirl dark lanes may have a more complicated grain structure than on-swirl areas. Enhanced abundances of plagioclase are observed on-swirl in both study areas. Enhanced abundances of FeO and orthopyroxene are observed off-swirl in both areas. No variations in olivine or clinopyroxene abundance were observed for either study area. The discovery of topographic correlations coupled with the similarities in structural properties provides new constraints on the types of processes acting on lunar swirl surfaces.

Lunar swirls are recognized as broad, bright albedo features in various regions of the Moon. These features are often separated by dark off-swirl lanes or terminate against the dark background, such as lunar maria. Prior mapping of swirls has been done primarily by albedo contrast, which is prone to subjectivity. Closer examination of on-swirl areas shows that they are not uniform, making the boundary between on- and off-swirl difficult to map with certainty. We have applied machine learning techniques to address these issues by identifying the number of swirl units and then mapping them based on actual reflectance, or I/F data. Using LROC NAC paired stereo images that are converted to I/F reflectance at a range of incidence angles, we applied both unsupervised K-means clustering and supervised Maximum Likelihood Classification algorithms to classify and map portions of lunar swirls in Reiner Gamma and Mare Ingenii. Results show that the classification maps are a reasonable match to the representative albedos for the two study regions. A third transitionary swirl unit, termed diffuse-swirl, is present in both the maps and the cumulative distribution plots of the reflectance values. Overall, we find that the use of both algorithms provides independent confirmation of both the number and location of these units and their interrelation. More importantly, the algorithms remove mapping subjectivity by using quantitative information. The data and the statistics generated from the maps also have value in future studies by placing limits for categorizing swirl units in different regions on the Moon.

The Moon's bright albedo markings, known as swirls, are defined by broad, bright, on‐swirl areas separated by darker off‐swirl lanes. Their formation mechanism has long been debated and is key for understanding the processing of the lunar surface, the mobility of the lunar soil particles, and the effects of the space environment on planetary surfaces. Here we present, for the first time, evidence that these features do not necessarily cross the surface without regard to topography or local terrain. Within portions of Mare Ingenii on the lunar far‐side, brighter on‐swirl areas have statistically lower mean elevations than adjacent, darker, off‐swirl lanes. These topographic characteristics provide constraints on the plausible formation mechanisms for the swirls in Mare Ingenii, which in turn provide insight into lunar soil migration and evolution. We believe this correlation with topography argues for highly mobile dust transport across the lunar surface.

Small-scale domes with circumferential aprons and concentric aureoles in western Arcadia Planitia (34-41 degrees N, 167-179 degrees E) near Tyndall crater were examined using a suite of datasets including CRISM, THEMIS IR, HiRISE, and CTX. Previous studies based primarily on photogeologic evidence suggested that these domes were analogous to terrestrial felsic cryptodomes to extrusive lava domes. The domes have also been examined using CRISM visible/near infrared to short-wave infrared (VNIR-SWIR) reflectance spectra which indicated the presence of ferrous silicate minerals in association with the domes. This study presents further CRISM spectral evidence for 1) high-Ca pymxene and glass mixtures with, or possibly without, the presence of olivine on the flanks of some domes, 2) 1.3 mu m band absorption features consistent with an Fe-bearing plagioclase or possibly a Fe-rich alkali feldspar in more limited occurrences at the base of some domes, 3) spectral convexity between 3.4 and 3.9 um associated with rocky, light-toned portions on top of some domes which is attributed to the presence of alkali-rich plagioclase or alkali feldspars. New morphologic observations include a pitted cone and arcs of light-toned, "brain terrain" material on the pole-facing upper margins of some aprons which, in combination with ice-associated "brain terrain" on light-toned outer aureoles suggests an association with ice. The morphology of an assortment of domes and association with alkali feldspars suggests they represent a continuum from intrusive cryptodomes to flat extrusive domes, potentially of felsic composition although formation from viscous alkali-rich mafic magmas is not precluded.

Mars Polar Science is an integrated, compelling system that serves as a nearby analogue to numerous other planets, supports human exploration, and habitability. Mars possesses the closest and most easily accessible layered ice deposits outside of Earth, and accessing those layers to read the climate record would be a triumph for planetary science.

Mapping of Viscous Flow Features (VFFs), a general grouping of ice-rich flow features that includes Lobate Debris Aprons (LDA), Concentric Crater Fill (CCF), Lineated Valley Flow (LW), small lobate flows (i.e., glacier-like flows, or GLFs), and arcuate ridges, in the southern hemisphere of Mars shows a dense concentration in Nereidum Montes, along the northern rim of Argyre basin. Further mapping within a subregion in northwest Nereidum Montes (45.3 degrees-48.5 degrees S, 307 degrees-312 degrees E) shows a large number of well-preserved VFFs and ice-rich mantling deposits. Processed SHARAD data across a VFF within the region indicates that it is composed of nearly pure water ice. Model ages obtained from crater counts and their associated size-frequency distributions (SFDs) on both icerich mantling deposits and small lobate VFFs suggest that the deposits stabilized several to tens of Ma ago in the Late Amazonian Epoch, and that small lobate VFFs likely formed due to the mobilization of mantling deposits. SFD for a larger VFF shows a model age of 100 s of Ma, consistent with ages for LDAs in eastern Hellas. Deposition of ice in Nereidum Montes that led to the formation of VFFs likely occurred during periods of high obliquity in the Late Amazonian. Our results show that VFFs have more complete and diverse preservation states in Nereidum Montes than similar features in other regions on Mars. This region contains uniquely well-preserved mantling deposits above arcuate ridges and beyond the margins of lobate VFFs and gully aprons. This key observation ties arcuate ridges to the flow of mantling deposits, part of a continuum model for mid-latitude ice-rich landforms.

We have utilized THEMIS, MOLA, CTX and HiRISE data sets to investigate the morphologic and topographic characteristics of the northeast flank of Apollinaris Mons, a region with evidence for significant erosion of volcanic deposits. Using ArcGIS software, we mapped the geology of the northeast flank and obtained age estimates using crater size-frequency distributions from crater counts. Of the eight mapped units, three (Apollinaris Mons upper, mid-, and lower flank units) represent volcanic flank materials in various states of preservation. The Late Noachian-Early Hesperian upper flank unit is massive and contains joint-like vertical structures along the scarp faces of two large plateaus whose upper surfaces likely represent the original surface or near-surface deposits of Apollinaris Mons. Downslope-facing plateau scarps have up to 500 m of relief. Positioned below this unit are the mid-flank and lower flank units, each representing eroded surfaces within Apollinaris Mons flank materials that have stabilization ages between the Late Hesperian to Early Amazonian. Mantling material in the region contains cavities and boxwork-like textures that resemble patterns in terrestrial eroded pyroclastic flow deposits. Dome-shaped mounds west of the mapping region have morphologic similarities to terrestrial fumarolic mounds or possibly inverted impact craters. Both the texture and features suggest widespread pyroclastic deposits adjacent to Apollinaris Mons. Using MOLA gridded topography, we estimate that ~308 km3 of materials have been eroded along the flanks of the volcano. Statistical and histogram data from the thickness values of eroded materials shows that up to ~300 m of material has been removed from the majority of flank surfaces. Assuming steady state erosion of flank surfaces, we estimate an area-normalized loss rate of ~0.859 nm/yr for northeast Apollinaris Mons. This erosion rate is within the long-term range for Mars (~0.01–10 nm/yr) as estimated from MER landing site geology by Golombek et al. [2006].

The Greater Meridiani Planum region on Mars is a key locale for a diverse range of fluvial landforms. Valley networks in this region have a range of geomorphologic styles that include negative relief, positive relief, or some combination of both along their lengths. Using high-resolution ∼5–6 m/pixel orbital images in ArcGIS Desktop software, we mapped previously under-recognized fine-scale valley networks within the Greater Meridiani Planum region and recorded their geomorphic characteristics as feature attributes. The objectives in using the mapped features are to 1) document the full range of valley network morphologic types in the region, 2) document changes in morphologic types both on a regional scale and along the valley network segments, and 3) to use the mapped features along with other geologic information from previous studies to better understand landscape evolution in the Greater Meridiani Planum region.

Morphological characterization of valley networks in three exposures of ancient cratered highlands (N-hc1) in the greater Meridiani Planum region yields insight into the Martian aqueous history. From our mapping, key regional differences are apparent in fine-scale valley network attributes including morphologic type, planimetric form, density, and links to candidate paleolakes. This information, combined with crater retention age (inferred exposure age), provides new details on the relative timing and nature of aqueous processes in the region. Newly identified pitted-type valley networks have morphological similarity to terrestrial pitted landforms in an evaporite setting. We interpret the pitted valley networks to reflect late-stage groundwater processes concentrated along the former fluvial conduits. Evidence from this study indicates that localized reactivation of valley networks occurred during or after exhumation of eastern N-hc1 unit.