The ability to efficiently and effectively explore planetary surfaces is currently limited by the capability of wheeled rovers to traverse challenging terrains, and by pre-programmed data acquisition plans with limited in-situ flexibility. In this paper, we present two novel approaches to address these limitations: (i) high-mobility legged robots that use direct surface interactions to collect rich information about the terrain's mechanics to guide exploration; (ii) human-inspired data acquisition algorithms that enable robots to reason about scientific hypotheses and adapt exploration priorities based on incoming ground-sensing measurements. We successfully verify our approach through lab work and field deployments in two planetary analog environments. The new capability for legged robots to measure soil mechanical properties is shown to enable effective traversal of challenging terrains. When coupled with other geologic properties (e.g., composition, thermal properties, and grain size data etc), soil mechanical measurements reveal key factors governing the formation and development of geologic environments. We then demonstrate how human-inspired algorithms turn terrain-sensing robots into teammates, by supporting more flexible and adaptive data collection decisions with human scientists. Our approach therefore enables exploration of a wider range of planetary environments and new substrate investigation opportunities through integrated human-robot systems that support maximum scientific return.

In this study, we present enigmatic exposures of suspected Cambrian age deposits of the Haushi-Huqf High, Central Oman. The present study area is an uplifted horst-block bounded by north-south oriented normal faults, with onlapping Mesozoic carbonate deposits on its western and eastern flanks, covering an outcrop area of ~1 km2. This exposure reveals decameter to kilometer-scale concentric, nested and coalescing ring-like structures superimposed within a clastic host rock, forming regularly spaced structural highs with lateral thicknesses and heights of one to several meters bounded by several meter wide troughs infilled with recent sediments. The host rock comprises fine to coarse grained, cross stratified quartz arenites, with basal pebbly lags, and with paleocurrents indicating a W-SW paleo-transport direction. The significant textural/mineralogical maturity of these sandstones suggests extensive recycling of older sediments, with the presence of frosted, well rounded grains signifying aeolian input. Establishing the stratigraphic position of the deposit within the regional context is challenging, owing a lack of body fossils, datable strata or correlatable stratigraphy proximal to the study site. However, Uranium-Lead Zircon dating of the host rock does reveal two geochronological populations: Neoarchaean to Paleoproterozoic (2.8-2.5 Ga), likely sourced from Precambrian basement rocks of Northern and Eastern Yemen, and Early Cambrian (~530 Ma), likely sourced from Cambrian-aged alkaline magmatism located within close proximity to the study site. Based upon the above, coupled with the observed textural, mineralogical and depositional characteristics of the deposit, we postulate that a Lower Paleozoic origin (esp. Amin Fm. Of the Haima Supergroup) is likely. Interpreted as fluivial-plain / fluvio-deltaic in origin, these rocks exhibit bioturbation within a select interval in the form of large horizontal/vertical calcite cemented burrows, indicating marine influence and colonization by benthic macrofauna. Furthermore, a thin, laterally continuous deposit of botryoidal calcite is observed, which commonly pinches out between reactivation surfaces. We interpret this deposit as recrystallized bacterially induced precipitates of calcium carbonate, signifying the presence of microbial mats developed during a short-lived period of marine incursion. Petrographic analysis reveals that there is a strong association between the pronounced diagenetic overprint of the study area and the occurrence of this deposit. Ridges structural highs exhibit major chemical compaction and porosity collapse via the development of quartz overgrowths. Conversely, topographic lows between these structures are generally porous and poorly consolidated, being characterized by the presence of calcite cementation and hematite grain coatings. The contrasting mechanical competence of the sandstones forming the topographic highs and lows offer spatial controls over differential weathering and erosion of the study area, resulting in the remarkable diagenetic architecture observed therein. It is proposed that spatially disparate early calcite cementation associated with microbial mat colonization protected the pore system from pervasive chemical compaction, which was extensively removed by meteoric dissolution post-exhumation. The pronounced spatial organization of calcite precipitation and cementation controlling these structures poses fascinating questions regarding the self-organization of microbial mat communities during the Cambrian substrate revolution, hinting at the influence of internal feedback and environmental controls in their nucleation and propagation.

Interdune areas and purported playa-type environments in Saturn’s moon Titan’s dune fields show substantial spatial variability in radar backscatter expression. Using examples from Death Valley, the Middle East, and northern China, this work evaluates terrestrial causes of spatial backscatter heterogeneity in similar aeolian environments. It introduces the importance of temporal change detection in interdune area backscatter expression. Using optical images, time-series radar synthetic aperture radar images, and coordinated meteorological and river discharge data (where available), backscatter variations are related to spatially changing sedimentary environments within sediment-limited areas, i.e., interdune and playas, and temporally changing surface or near-surface moisture conditions. In terrestrial environments, backscatter expression varies over seasonal and annual timescales as a function of the cumulative history of surface change, primarily driven by changes in surface and near-surface moisture from either precipitation or groundwater table rise and fall. On Titan, evidence for equatorial methane flow channels suggests that arid-climate surfaces may undergo temporal evolutions like those observed on Earth. Fluid flow and evaporite formation play crucial roles in the existence and alteration of patterns in Earth’s interdunes. By analogy, these mechanisms are also expected to be at work on Titan. Despite differences between terrestrial and Titan radar observations, considering surface dynamics and evolution over time on Titan may be critical for analyzing its arid, equatorial environments.

Sand ripples record interactions between planetary surfaces and environmental flows, providing paleoenvironmental archives when preserved into rocks. Two main ripple types form in sand: drag ripples, common in water, and impact ripples, exclusive to windblown surfaces. Enigmatic meter-scale aeolian ripples on Mars have been assumed to be impact ripples, though ground and orbiter-based observations suggest they may be drag ripples instead. Here, we report on low-pressure wind tunnel experiments in which large ripples formed and evolved from a flat bed. Observations demonstrate that impact and large ripples grow from distinct mechanisms. Large-ripple size aligns with predictions from drag-ripple theory, and associated sand fluxes are greater than predicted for impact ripples. These findings are inconsistent with an impact-ripple origin and instead suggest that large martian ripples are drag ripples. Windblown drag ripples constitute an untapped record of atmospheric evolution on planetary bodies with tenuous or ephemeral atmospheres across the Solar System.

As winds blow over sand, grains are mobilized and reorganized into bedforms such as ripples and dunes. In turn, sand transport and bedforms affect the winds themselves. These complex interactions between winds and sediment render modeling of windswept landscapes challenging. A critical parameter in such models is the aerodynamic roughness length, z0, defined as the height above the bed at which wind velocity predicted from the log law drops to zero. In aeolian environments, z0 can variably be controlled by the laminar viscous sublayer, grain roughness, form drag from bedforms, or the saltation layer. Estimates of z0 are used on Mars, notably, to predict wind speeds, sand fluxes, and global circulation patterns; yet, no robust measurements of z0 have been performed over rippled sand on Mars to date. Here, we measure z0 over equilibrated rippled sand beds with active saltation under atmospheric pressures intermediate between those of Earth and Mars. Extrapolated to Mars, our results suggest that z0 over rippled beds and under active saltation may be dominated by form drag across a plausible range of wind velocities, reaching values up to 1 cm-two orders of magnitude larger than typically assumed for flat beds under similar sediment transport conditions.

Candidate glaciovolcanic landforms have been identified across Mars, suggesting that volcano-ice interactions may have been relatively widespread in areas that once contained extensive surface and near-surface ice deposits. To better constrain the detection of glaciovolcanism in Mars' geological record, this study has investigated and characterized the petrology, geochemistry, and mineralogy of three intraglacial volcanoes and an interglacial volcano in the & THORN;& oacute;risj & ouml;kull area of southwest Iceland. Our results show that glaciovolcanism creates abundant, variably altered hyaloclastite and hyalotuff that is sufficiently geochemically and mineralogically distinctive from subaerially erupted lava for identification using instruments available on Mars rovers and landers. Due to the lower gravity and atmospheric pressure at the surface of Mars, hyaloclastite and hyalotuff are also more likely to form in greater abundance in Martian glaciovolcanoes. Our results support that magmatism following deglaciation likely triggers decompression melting of the shallow mantle beneath Iceland, creating systematic changes in geochemistry and mineralogy. Glaciation can also suppress magmatism at its peak, encouraging the formation of shallow fractionated magma chambers. As such, it is possible for the crustal loading of an ice cap to enhance igneous diversity on a planet without plate tectonism, creating glass-rich, altered, and mineralogically diverse deposits such as those discovered in Gale crater by the Curiosity rover. However, as the eroded products of glaciovolcanism are similar to those formed through hydrovolcanism, the presence of a glaciovolcanic landform at the source is required to confirm whether volcano-ice interactions occurred at the sediment source. The ancient Martian climate has been long debated with scientists hypothesizing that the river channels and lake beds preserved on the surface today formed in either a warm and wet environment or a cold and icy environment, with heating events driving large-scale melting. One such heating event includes volcanism. This study investigated the chemical and mineralogical impact of volcano-ice interactions in Iceland using techniques available to Mars rovers and landers to improve the detection of these deposits on Mars. Our results show that deposits rich in glass and the early products of low temperature alteration (palagonite, clays, zeolites) are likely to be more prevalent on Mars compared to the Earth due to differences in gravity between the two planets. Furthermore, the presence of a thick ice cap on Mars may encourage a diversity of lava compositions to form in shallow magma chambers as the weight of a thick ice cap can suppress volcanism. These types of deposits are identifiable using Mars rover and lander techniques, but due to their similarities to other volcanic units that may have erupted in the presence of water, a candidate glaciovolcanic landform is needed to confirm that these deposits are from volcano-ice interactions. Glaciovolcanism creates large deposits of altered fragmented volcanic glass distinct from subaerial volcanism Glaciation can suppress magmatism, driving geochemical and mineralogical diversity in an area once deglaciation starts Glaciovolcanism may have occurred on Mars with explosive phreatomagmatic units more likely under Mars' planetary conditions

Polygonal terrain on Mars can form via thermal contraction and subsequent fracturing of the permafrost layer and covers much of the surface poleward of similar to 60 degrees. In similar terrains on Earth, seasonal freeze-thaw processes create a range of diverse landforms, including several in which clasts on the surface congregate into sorted circles and polygons. In the Martian northern lowlands, several investigations into boulder patterns have come to differing conclusions on whether analogous organization of clasts is present on Mars, whether there is an association between boulders and polygonal fracture margins, and what periglacial process may cause such organization in the modern environment that does not support seasonal melt. To address this discrepancy, we identify and measure boulders in the Martian northern lowlands with the Martian Boulder Automatic Recognition System (MBARS) and assess boulder spatial patterns to determine if boulders are organized into the margins of underlying fracture polygons. Sixty (60) Images from the High-Resolution Imaging Science Experiment (HiRISE) camera aboard the Mars Reconnaissance Orbiter (MRO) with priorly identified and measured polygons make up our survey, in which MBARS characterized 20 million boulders. We find that boulder patterns are not random across the northern lowlands and tend to be clustered with varying intensity. However, analysis of boulder pairwise distances shows that boulders are not generally organized into the 5-10 m polygonal patterns expected from an alignment of boulders to fracture margins. The lack of widespread polygonal organization of boulders indicates that processes responsible for the modern fracture polygons cannot organize meter-scale boulders towards their margins. This greatly reduces the likelihood of any terrestrial-like freeze-thaw organization occurring since the formation of the modern polygonal terrain in the Martian northern lowlands. Isolated instances of boulder patterns consistent with polygonal organization are found at the northern end of our survey. These instances could indicate a restriction of boulder-organizing processes only to the near-polar terrains but are better explained as selective preservation of paleo-organization. Plain language summary: We have abundant evidence that the near-polar terrains on Mars have water ice buried at or very near the surface, much like on Earth. As this ice-rich surface cools in the winter, regularly spaced, roughly hexagonal cracks appear forming so-called "polygonal terrain". In similar permafrost-dominated terrains on Earth, the presence of liquid water near the surface can cause rocks on the surface to be pushed outward during freezing. This eventually leads to the formation of stone circles or stone piles outlining the polygons, often forming large networks of sorted polygons. Using high-resolution images of Mars, we can see boulders as small as 1 m across, and it has been suggested that these boulders might also be organized into the edges of polygons on Mars. This raised the question: did these patterns form through Earth-like, wet processes? Or is there a way to make these patterns without liquid water? To answer this question, we surveyed sixty (60) images of Mars and used the Martian Boulder Automatic Recognition System (MBARS) to identify and measure the boulders in each image, totaling 20 million boulders. We determined that the boulders are not organized into a polygonal pattern, except in a few rare cases. Because the boulders are not organized, it is unlikely that any Earth-like wet processes or an unknown dry process is pushing boulders towards the edges of the fracture polygons. In the few places we do see this organization, it might be a pattern formed sometime in Mars' past when liquid water could exist at or near the surface.

Sand dune morphology is indicative of complex system interactions at a wide range of spatial and temporal scales that govern dune topographic structure. We created an object-oriented topographic framework based on slope attitude, curvature, and contextual analysis to map and characterize sand dune morphology at White Sands National Park, New Mexico, USA that limits empiricism and reliance on a priori knowledge of dune field structure and dynamics. We used eight LiDAR-derived digital elevation models with our framework to segment sand dunes and characterize dune morphology from 2007 to 2020 and evaluated dune field behavior and resilience. The segmentation is 92% accurate relative to manual mapping. From the segmentation, we calculated dune statistics, including height, width, length, area, volume, area-surface area ratio, circularity, migration rate, and aggradation rate. We found these statistics compared well with prior research. We identified a trend toward fewer dunes with greater area and volume from 2007 to 2020, which may be related to typical dune field maturation or short-term (seasonal to decadal) fluctuations related to weather and dune processes. Changes in dune migration rate and sand flux depended on the strength and directionality of seasonal southwesterly winds and likely periods of intense precipitation or drought. Trends identified in this study can be considered a baseline from which longterm trends identified through on-going monitoring can be evaluated. This research highlights current dependence on incomplete models for mapping and characterizing dunes and landscape resilience, and the need to quantitatively formalize numerous geomorphological concepts.

Assessing the past habitability of Mars and searching for evidence of ancient life at Jezero crater via the Perseverance rover are the key objectives of NASA's Mars 2020 mission. Onboard the rover, PIXL (Planetary Instrument for X-ray Lithochemistry) is one of the best suited instruments to search for microbial biosignatures due to its ability to characterize chemical composition of fine scale textures in geological targets using a nondestructive technique. PIXL is also the first micro-X-ray fluorescence (XRF) spectrometer onboard a Mars rover. Here, we present guidelines for identifying and investigating a microbial biosignature in an aeolian environment using PIXL-analogous micro-XRF (mu XRF) analyses. We collected samples from a modern wet aeolian environment at Padre Island, Texas, that contain buried microbial mats, and we analyzed them using mu XRF techniques analogous to how PIXL is being operated on Mars. We show via mu XRF technique and microscope images the geochemical and textural variations from the surface to similar to 40 cm depth. Microbial mats are associated with heavy-mineral lags and show specific textural and geochemical characteristics that make them a distinct biosignature for this environment. Upon burial, they acquire a diffuse texture due to the expansion and contraction of gas-filled voids, and they present a geochemical signature rich in iron and titanium, which is due to the trapping of heavy minerals. We show that these intrinsic characteristics can be detected via mu XRF analyses, and that they are distinct from buried abiotic facies such as cross-stratification and adhesion ripple laminations. We also designed and conducted an interactive survey using the Padre Island mu XRF data to explore how different users chose to investigate a biosignature-bearing dataset via PIXL-like sampling strategies. We show that investigating biosignatures via PIXL-like analyses is heavily influenced by technical constraints (e.g., the XRF measurement characteristics) and by the variety of approaches chosen by different scientists. Lessons learned for accurately identifying and characterizing this biosignature in the context of rover-mission constraints include defining relative priorities among measurements, favoring a multidisciplinary approach to the decision-making process of XRF measurements selection, and considering abiotic results to support or discard a biosignature interpretation. Our results provide guidelines for PIXL analyses of potential biosignature on Mars.

Dunes form where winds blow over a bed of mobile sediment grains – conditions that are common in our solar system. On Earth, dunes abound in arid continental interiors and along sandy coastlines. Dune fields have also been recognized on Venus, Mars, Saturn's moon Titan, and Pluto. In response to the different boundary conditions and other environmental forcings, dunes adopt a rich diversity of shapes, sizes, and behaviors. Thus, people around the globe and over centuries have developed a rich vocabulary to describe dunes and their complexity. As a result, existing dune nomenclature often includes redundant terms with differing definitions across scientific communities. Previous studies have endeavored to link dune shape to environmental forcing, usually by means of correlation. Although instructive, correlation-based classifications can be misleading if not based on an underlying mechanics and if dune morphogenetic classes are not uniquely defined. Here, we synthesize existing dune terminology and use the last two decades of research on dune morphodynamics to propose three complementary dune classification schemes based on: (1) descriptive dune gemorphology, (2) morphodynamic processes, and (3) fluid mechanics and physics of sediment transport. The first classification relates dune types to geomorphic setting, presence or absence of vegetation or obstacles, and dune shape (including planform shape, and cross-sectional symmetry or asymmetry). Dune classes can be further subdivided where the direction of sand transport is known independently. The second classification relates dune types and shapes to bed properties (sand-covered vs partially starved bed) and wind forcing (directional variability or the relative strengths and directions of wind modes) that together influence dune dynamics (growth, migration, elongation) and select the dominant processes by which dunes are shaped and oriented relative to the resultant transport direction. The third classification relates, for different planetary environments, the range of possible dune sizes, from minimum to maximum wavelength, to flow regime (rough or smooth) and response of sediment transport, which influence the coupling between sand bed topography, fluid flow, and sediment transport. These characteristic lengths are useful scales for comparative geomorphology. The three classification schemes provide complementary information. Together, they form a unified framework for geomorphologists, sedimentologists, geographers, physicists, and others to describe windblown sand dunes on Earth and beyond through their shape, dynamics, and size as a response to winds and boundary conditions.

The joint NASA-ESA Mars sample return campaign aims to return up to 31 sample tubes containing drilled sedimentary and igneous cores and regolith. The titanium alloy tubes will initially still be sealed when they are retrieved. Several types of measurement will be carried out on sealed samples in the pre-basic characterization phase of scientific investigation. We show that powder x-ray diffraction (XRD) analysis can be successfully carried out on sealed samples using an x-ray source at the I12 beamline of Diamond Light Source synchrotron. Our experiment used an analog sample tube and a Martian regolith analog (Icelandic basaltic sand). The titanium walls of the tube analog give strong but few diffraction peaks, making identification of the major constituent mineral phases feasible. A more significant constraint on quantification of mineral phase abundances by this XRD technique is likely to be the grain size of the sample. This technique opens up the possibility of initial mineralogical analysis of samples returned from Jezero crater without opening the sample tubes and the potential changes to the sample that entails.

IntroductionIn almost every planetary surface investigation, the characterization from a camera is a common initial step [1]. Mission Control is developing a science autonomy system called Autonomous Soil Assessment System: Contextualizing Rocks, Anomalies and Terrains in Exploratory Robotic Science (ASAS-CRATERS). It can enable automated surface characterization on planetary missions, which can benefit a wide range of science investigations and rover navigation alike. It can perform terrain classification and novelty detection using convolutional neural networks, and data aggregation to produce relevant data products for supporting science operations. Built on cutting-edge algorithms and off-the-shelf computing components, it offers low-cost ways to speed up tactical decision-making in next-generation commercial lunar missions.Background and MotivationAutonomy in Science OperationsSeveral factors are increasingly driving the need for autonomy in science operations. In traditional Mars rover operations, visual surface characterization and subsequent analysis and decision-making takes place in day-long tactical cycles [2]. Upcoming commercial lunar rover missions will have reduced latency, short lifetimes, and constrained bandwidth shared across several payloads. This will result in a need for rapid tactical decision-making processes with limited data, leaving little time for analysis, target identification, and making decisions. Payload operators may not receive data in a timely fashion, or worse, may not receive some data at all. Autonomous onboard terrain classification offers a way to downlink light-weight data products and reduce the bottleneck in scientific terrain assessment. Autonomous classification and novelty detection increase the chances of detecting novel/sparse features (e.g., lunar outcrop or pyroclasts) that may otherwise be missed or not downlinked when driving and other mission needs are prioritized.Application to Lunar GeologyWhile dedicated science instruments that reveal mineralogical and elemental composition improve our understanding of geological processes, a rover’s navigation sensors can document the morphology, morphometry, and composition of surface materials, regardless of primary investigation goals. High-resolution colour images and 3D data from stereo cameras provide information such as the size-frequency distribution and physical characteristics of craters and rocks, and regolith properties. All this offers valuable insight into the geologic setting. To provide a practical output as a science support tool for several types of missions, a classification scheme is being developed that segments a surface image into geological features that are visually distinct based on morphology, tone, and texture. This will be adapted for specific missions. See Figure 1 for a hand-labelled example.Figure 1: Hand-labelled lunar terrain classification example. Letters indicate crater degradation; P: Pristine; S: Semi-Degraded; G: Ghost. Right: original Yutu-1 image. Credit: CNSA.TechnologyAlgorithms and SoftwareASAS-CRATERS comprises three algorithms. First, the terrain classifier consists of a deep-learning encoder-decoder style network which classifies each image pixel into semantic terrain labels. Second, the novelty detector uses a semi-supervised convolutional neural network architecture with an autoencoder module and a binary classifier that work in series. Third, a data aggregator will combine the outputs on map tiles that are useable by onboard algorithms, lightweight for more efficient downlink, and enables faster backroom analysis and integration into GIS tools. See Figure 2 for a conceptual illustration of how ASAS-CRATERS outputs would be aggregated onto map tiles.Figure 2: Hand-made illustration of aggregating terrain classifier data on orthorectified map tiles.In the near future, additional algorithms will be developed to extend the capabilities of this autonomy system. This primarily includes an autonomous instrument targeting capability so that lunar science instruments, on rovers in particular, can use ASAS-CRATERS to identify and select features for targeting.Sensors and Computing HardwareASAS-CRATERS will be embedded on the Q8S, a high-performance, low-power Xilinx Zynq UltraScale+ System-on-Chip FPGA designed by Xiphos Technologies, which will fly in 2020. The Q8S consumes 3W at minimum and measures 90g and 80x80x22.3mm. Embedded on a flight-ready COTS system, ASAS-CRATERS can be rapidly integrated onto payload suites, rovers, and landers, offering low-cost advanced computing capabilities.Concept of OperationsPrior to deployment on a mission, ASAS-CRATERS’ machine learning algorithms will require training using relevant expert-labelled images from lunar and analogue datasets. Once a mission begins, the algorithms will be updated with images collected in situ. ASAS-CRATERS can then be used to classify terrain and detect features during nominal rover operations. The science team can integrate ASAS-CRATERS data products into their terrain analysis and make decisions on whether specific features merit deeper investigation using onboard instruments.Use Cases and BenefitsASAS-CRATERS can benefit science missions in several ways. First, it can support science operations in tactical cycles. Novelty detection can aid scientists that may miss features or spend valuable time in looking for them. The terrain classifier data products are low-dimensional representations which optimizes downlink. The classification itself can speed up scientific analysis in rapid tactical cycles and this becomes increasingly more useful in complex scenes diverse in mineralogy and lithology. Second, for high-priority features, onboard algorithms can perform instrument targeting and data triage for downlink prioritization. Third, as a semantically useful terrain representation, it can be used by advanced robotics algorithms to enable autonomous and intelligent navigation. Fourth, in human exploration architectures, ASAS-CRATERS can be embedded with crewed systems to provide autonomous capabilities that can support astronauts in geological field excursions.Field Tests and DemonstrationsThe terrain classifier was first developed by Mission Control under the Autonomous Soil Assessment System project [3]. In 2019, it was used to classify eight Mars-relevant terrain types in real-time at ~15 FPS (see Figure 3 for an example). This was a part of tests in Iceland under SAND-E (Semi-Autonomous Navigation for Detrital Environments), a NASA PSTAR funded project led by Dr. Ryan Ewing at Texas A&M University.Figure 3: Classifier output overlaid on one camera image during a SAND-E traverse in Iceland field tests.While ASAS-CRATERS is a multi-mission payload, near-term demonstrations are targeted for upcoming lunar missions in 2022 and 2023.AcknowledgementsThe authors would like to thank the Canadian Space Agency (CSA) for funding the development of ASAS-CRATERS and previous technology developments.References[1] Francis R. et al. (2014) SpaceOps. DOI: 10.2514/6.2014-1798. [2] Gaines D. et al. (2016) PlanRob, 115-125. [3] Faragalli M. et al. (2018) i-SAIRAS.

Impact craters that form on every planetary body provide a record of planetary surface evolution. On heavily cratered surfaces, new craters that form often overlap antecedent craters, but it is unknown how the presence of antecedent craters alters impact crater formation. We use overlapping complex crater pairs on the lunar surface to constrain this process and find that crater rims are systematically lower where they intersect antecedent crater basins. The rim morphology of the new crater depends on the depth of the antecedent crater and the degree of overlap between the craters. Our observations suggest that new craters do not always obliterate underlying topography and that transient rim collapse is altered by antecedent topography. This study represents the first formalization of the influence of antecedent topography on rim morphology and provides process insight into a common impact scenario relevant to the geology of potential Artemis landing sites.

Boulders are ubiquitous on rocky planets and provide valuable information about planetary processes. The abundance, size, and distribution of boulders offer insights into the primary processes that form them and the secondary processes that modify their position and size. However, the roles of varying environmental processes, including cryospheric processes, are poorly known. In this study, we analyze over 20 million boulders in the northern lowlands of Mars (50-70 degrees N) to evaluate their distribution and identify environmental factors that might influence their clustering. We used spatial statistics to quantify the degree of boulder clustering across the northern plains. We found two latitudinal trends: overall decreasing clustering with increasing latitude (50-70 degrees N) and a sub-trend of increased clustering at higher latitudes (65-70 degrees N). Our findings suggest that boulder distribution patterns are linked to the latitude-dependent mantle (LDM) and subsurface ice. Boulders exhibit higher spatial clustering at higher latitudes, where the ice is thick and continuously present, and the LDM is more pristine. Lower clustering occurs at lower latitudes or regions where the ice loss is likely during interglacial periods, and the LDM degrades, exposing more boulders of varying sizes. We also discovered an anomalous region where boulder clustering is nearly random, located on the edge of the Alba Mons Patera. This area displays distinct geophysical characteristics compared to the rest of the lowlands. Although these characteristics do not indicate a specific process for the variation of boulder distribution in this study, the data suggest a coupling between cryospheric processes and boulder evolution, warranting further research. Boulders are common on rocky planets and can provide important information about boulder-forming processes and displacement. We studied over 20 million boulders on the northern plains of Mars to learn more about how they are distributed across the planet and what factors might influence their placement. We found that boulders are more likely clustered in areas with more ice below the surface. We also discovered an area north of Alba Mons where boulders seem to be scattered randomly, and the surface properties are different than elsewhere in the northern plains. This may be due to the repeated deposition and removal of ice in this area, but more research is needed to fully understand these patterns. The level of boulder clustering follows latitudinally varying mantle distribution and degradation states The topographic, geophysical, and surface characteristics of northern Alba Patera indicate a higher presence of subsurface ice Landscape ages across the Martian northern lowlands may affect variations in boulder distributions

Abstract Dust dynamics influence planetary atmospheres. However, the settling velocity of dust—and thus its residence time in the atmosphere—is often mispredicted. Challenging, indirect experiments involving few ideal particles revealed that dust settling velocity deviates from Stokes' law under rarefied atmospheres. While useful, such experiments are inadequate to simulate more complex scenarios, including variable particles sizes and shapes. Here, we present direct measurements of settling velocity for spherical particles under Earth‐to‐Mars atmospheric pressures using time‐resolved particle image velocimetry (TR‐PIV), and validate their robustness with existing models. Our results demonstrate that TR‐PIV provides a relatively simple approach to quantifying dust settling velocity from direct observations of over 10,000 particles, enabling systematic investigations of dust settling under realistic scenarios. Such experiments will have significant implications for our understanding of Mars' past, present, and future ‐ from providing a tool to decipher its sedimentary record to enhancing predictive capabilities of atmospheric models.

Abstract In the absence of consistent meteorological data on Mars, the morphology of dunes can be employed to study its atmosphere. Specifically, barchan dunes, which form under approximately unimodal winds, are reliable proxies for the dominant wind directions. Here, we characterize near‐surface winds on Mars from the morphology of >700,000 barchans mapped globally on the planet by a convolutional neural network. Barchan migration is predominantly aligned with known southern‐summer atmospheric circulation patterns—northerly at mid‐latitudes and cyclonic near the north pole—with the addition of an anti‐cyclonic north‐polar component that likely originates from winds emerging from the ice cap. Locally, migration directions deviate from regional trends in areas with high topographic roughness. Notably, obstacles <100 km such as impact craters are efficient at deflecting surface winds. Our database, which provides insights into planetary‐scale aeolian processes on modern‐day Mars, can be used to constrain global circulation models to assist with predictions for future missions.

Preferential flow between rivers and aquifers in alluvial floodplains may be a core component of shallow groundwater transport and, consequently, its understanding is key to modelling and managing groundwater resources. At a clay wedge separating present-day streamflow and bank storage from an adjacent shallow aquifer, we image a suspected sand-dominated structure. This structure cuts through the clay wedge and possesses temporally dynamic electrical resistivity as seen in time-lapse electrical resistivity tomographic (ERT) images collected over a 61-day study period. During days 11-12, following heavy rainstorms, the cross section of the electrically resistive sand fades into the background resistivity structure, reappearing the following day. This research shows that preferential flow can be imaged in time-lapse ERT in buried sand-dominated structures between a floodplain and the adjacent river. Our analysis demonstrates that sand conduits can transport infiltrated rainwater from the floodplain into the river as a bank spring and, hypothetically, at high-stage streamflow, from the river into the adjacent shallow aquifer. In both directions, these conduits for preferential flow exert an important control on the regulation and distribution of water, sediments and contaminants. This phenomenon will help hydrological models to incorporate more real-world phenomena and ultimately better prepare groundwater managers to sustainably steward shallow groundwater resources.

Long-term and seasonal geomorphological changes at Padre Island, Texas are identified and linked with potential external drivers. Aerial and satellite images from 1950 to 2018, monthly images from 2019 to 2020, and a 2018 LiDAR data set are used to assess long-term and seasonal geomorphological changes within a 50 km(2) area of Padre Island near Port Mansfield, Texas. Trends in landcover are evaluated by mapping and comparing the relative areal coverage of each facies. Vegetated dunes, absent initially, emerged in the fore-island and expanded into the back-barrier to cover 14% of the study area. The active vegetation-free back-barrier dune field steadily decreased in areal extent from 12% to 6% as vegetation spread. Nebkha dune coverage fluctuated between 4% and 7%. Expansive microbial mats colonized the wind tidal and deflation flats surrounding the vegetated dunes and back-barrier dune field giving rise to a remarkably different landscape over the 50-year period studied. An assessment of external forcing factors identifies increased rates of relative sea level rise and decreased sediment influx as the most likely primary factors driving the geomorphological changes. These changes have induced a widespread shift toward stabilization of island sediments by vegetation and microbial mats, which in turn has starved the back-barrier of sediments resulting in low rates of accretion and increased flooding. These findings highlight the sensitivity of the back-barrier and, in particular, the dune facies to changes in sea level and sediment supply, and show that microbial mats are effective at stabilizing island sediments and may be harbingers to barrier island response to rising sea level. As shown in this study, long-term monitoring of geomorphic facies changes and topography can detect important shifts in the island state that can be used to inform decision making for these sensitive coastal landscapes.