Rock abundance, defined as the surface's fractional area covered by rocks, is used to characterize the Moon's regolith, decipher its impact history, and assess potential landing sites. By definition, it should be agnostic to rock-size distributions. However, it has been suggested that rock abundances, derived from surface temperatures measured by the Lunar Reconnaissance Orbiter (LRO) Diviner radiometer, are not. Systematic analyses of the effect of rock-size distributions on Diviner-derived rock abundances have been hindered by the laborious nature of manually mapping individual boulders from optical images. Here, we conduct such an analysis from automated boulder detections in high-resolution LRO Narrow Angle Camera images using BoulderNet, a boulder segmentation machine-learning model. We present a comparison of BoulderNet- and Diviner-derived rock abundances and find that, although both data sets are strongly correlated, rock abundances derived from thermophysical modeling are underestimated in areas with a greater proportion of smaller rocks relative to larger ones.

A primary axiom in geoscience is that the evolution of plants drove global changes in river dynamics. Notably, the apparent sinuosity of rivers, derived from the variance of sediment accretion direction measured in rocks, substantially increased when land plants evolved, around 425 million years ago. This led to the hypothesis that the rise of vegetation triggered river meandering. Recent studies of barren, meandering rivers challenge this notion, but the Paleozoic shift in the geometry of river deposits remains unexplained. Here, we suggest that it occurred because vegetation changes how river bends move through space. Using satellite images to monitor river migration, we found that bank vegetation alters the orientation of point bar accretion, resulting in a 62% increase in the inferred variance of flow direction. These results explain why meandering rivers have been underrecognized in prevegetation stratigraphy.

Extensive dune fields nearly encircle the equatorial regions of Titan, Saturn's largest moon. Dunes evolve in response to environmental change, offering a record of recent geologic and climate history. A global analysis reveals that Titan's dunes become more narrowly spaced and increasingly more regular along a continuous eastward transport path, starting east of the Xanadu region, around the equator, and terminating abruptly at Xanadu's western margin. Xanadu is a rugged, tectonically active, water‐ice‐rich region with low topography and a thin layer of atmospherically deposited organic‐rich material. Our results demonstrate that windblown grains must withstand long transport distances. Furthermore, environmental conditions along the eastern margin of Xanadu set a template over which dunes evolve, only gradually modified as sediment supply or availability increases downwind. Together, these results highlight the oversized impact that Xanadu has on Titan's dune fields, which in turn play a critical role in regulating Titan's sedimentary and carbon cycles.

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.

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.

The surface of Titan is composed of varied geomorphic units indicative of a vivid depositional, erosional and tectonic history. Dominant at Titan's equatorial regions are vast eolian landscapes of dunes, sand sheets, yardangs and wind streaks. These features reveal the action of wind in time and space, which has moved and shaped unconsolidated materials across the surface. Cassini Visual and Infrared Mapping Spectrometer (VIMS) spectra of these materials are most consistent with organics, and particle sizes from Cassini Synthetic Aperture Radar (SAR) vary from dust to cobbles [1]. Most grains appear to be sand-sized, based on the predominance of SAR-dark (smooth at 2 cm) material organized into dune forms at the equator, and models for wind requirements to build dunes on Titan [2]. Dunes cover ~15% of Titan’s surface, or 13 million km2 [3, 4] in the form of linear dunes 1-2 km wide and spaced by 1-4 km [5]. This type and size of dune is dominant in the Arabian and African deserts and is also known as longitudinal [6], referring to the net direction of the transport of sand, which aligns with dune crests [7, 8]. All dunes visible in the Cassini SAR imagery have now been traced down their long axes, revealing regional and global orientations (proxy for wind) and distributions, controlled by obstacles and regional elevations. Over 30,000 dunes have been traced (Fig. 1), and given SAR image coverage, this represents ~40% of all dunes thought to be present based on sand sea locations from the Cassini Imaging Science Subsystem (ISS), meaning we may expect as many as 75,000 dunes to exist on Titan. A total dune length of 1.309 million km has now been calculated from the measured dunes; extrapolated to all of Titan, this length would be 3.273 million km. Using an average dune width of 1 km and corresponding height of 100 m from a 0.1-0.2 dune height:width relationship [9] and isolated measurements [10] we find a total measured dune sand volume of 130,900 km3. If scaled up to all dunes thought to be present, the total volume of sand from dunes alone of 327,250 km3 falls within previous estimates for sand volumes [11, 4, 12]; however, those studies also included sand sheets without detectable dunes. Thus, this new measurement may reveal greater sand volumes from dunes alone than previously thought. This represents a significant material volume that has been moved through wind action, even if from locations close to the (unknown) source. At higher latitudes, several distinct regions of SAR-bright dunes or wind-carved ridges or yardangs are also present (Fig. 2). These can be found in flat plains [13], where they may be inactive dunes, or on the elevated, fluvially carved domes of the midlatitudes, postulated to be volcanic laccoliths [14]. Ash or otherwise derived fine organic grains would be ideally soft yardang materials, comparable to those on Earth, and reveal that winds can also remove substrate on Titan, similar to the action of wind in locations on Mars [15]. Statistical comparisons between possible yardangs support their existence on the domes but are consistent with them being dunes in other locations [16]. The dome yardangs would have resulted from removal of fine-grained materials and loss to the atmosphere as airborne particles and eventually other surfaces – new estimates of the volume of yardang erosion on one small dome, based on yardang heights of ~100 m from shadows, is ~125 km3, and there are a handful of identified other similar yardang regions. Creation of dust from dune sand movement has not yet been estimated (and there are significant uncertainties about material properties) but with yardang processes could yield large volumes that now reside in unknown locations, including interdunes, high latitude plains, lakes and seas. SAR and ISS bright streaks are visible at low to midlatitudes on Titan, similar in orientation to the dunes where they overlap, and found behind obstacles [17, 18]. Their SAR brightness is consistent with a larger particle size, which may be supported by lower density materials, but wind streaks are also often identified with fine particle sizes. This reveals yet another sand and dust location on Titan. Yardangs and wind streaks, along with the ubiquitous equatorial dunes, confirm a general W-E flow of wind, with some N or S deviations that may be reflections of a global undulatory wind pattern at high latitudes. The Dragonfly mission will study dune regions in depth and will reveal particle sizes and compositions, nature of the interdune, level of dune activity and sand (and perhaps dust) movement at the present day, and magnitude and direction of modern winds [19]. These observations will anchor our understanding of eolian processes in the Solar System. [1] Le Gall, A. et al. 2010, Icarus 207, 948-958. [2] Lorenz, R.D. et al. 2006, Science 312, 724-727. [3] Le Gall, A. et al. 2011, Icarus 213, 608-624. [4] Rodriguez, S. et al. 2014, Icarus 230, 168-179. [5] Radebaugh, J. et al. 2008, Icarus 194, 690-703. [6] Courrech du Pont et al. 2024; Earth-Science Reviews, 104772. [7] Lorenz and Radebaugh 2009; Geophysical Research Letters 36. [8] Lucas et al. 2014; Geophysical Research Letters 41, 6093-6100. [9] Lancaster, N. 1995, Geomorphology of Desert Dunes. [10] Neish, C.D. et al. 2010. Icarus 208, 385-394. [11] Arnold, K. 2013, BYU MS Thesis. [12] Lorenz, R.D. et al. 2008, Geophysical Research Letters 35. [13] Lopes, R. et al. 2020. Nature Astronomy 4, 228-233. [14] Schurmeier, L. et al. 2023, Icarus 404, 115664. [15] Kerber, L. et al. 2011. Icarus 216, 212-220. [16] Northrup, D. et al. in progress. [17] Malaska, M.J. et al. 2016. Icarus 270, 183-196. [18] Cohen-Zada, A. et al. 2016. Aeolian Research 20, 108-125. [19] Barnes, J.W. et al. 2021. The Planetary Science Journal 2, 130.Fig. 1. Dunes traced in Shangri-La region of Titan. ISS basemap. Dunes may still be present in large, dark areas, though there is not SAR coverage.Fig. 2. SAR-bright yardangs on an eroded dome. From T64, northern midlatitudes. Arrow shows SAR illumination direction.

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

Stabilization of riverbanks by vegetation has long been considered necessary to sustain single-thread meandering rivers. However, observation of active meandering in modern barren landscapes challenges this assumption. Here, we investigate a globally distributed set of modern meandering rivers with varying riparian vegetation densities, using satellite imagery and statistical analyses of meander-form descriptors and migration rates. We show that vegetation enhances the coefficient of proportionality between channel curvature and migration rates at low curvatures, and that this effect wanes in curvier channels irrespective of vegetation density. By stabilizing low-curvature reaches and allowing meanders to gain sinuosity as channels migrate laterally, vegetation quantifiably affects river morphodynamics. Any causality between denser vegetation and higher meander sinuosity, however, cannot be inferred owing to more frequent avulsions in modern non-vegetated environments. By illustrating how vegetation affects channel mobility and floodplain reworking, our findings have implications for assessing carbon stocks and fluxes in river floodplains.

The Stimson formation is a late-infilling eolian sandstone in Gale crater, Mars that formed from sand accumulation in a dune field analogous to the modern active Bagnold dune field, enabling a unique opportunity to compare the past to the present dune fields on Mars. Previous work suggested that the Stimson has a coarser grain-size distribution than the active Bagnold dunes based on three images of the Stimson. We analyze grain size in the Naukluft and Emerson plateaus of the Stimson by observing 115 images throughout the formation to classify textures and quantitatively measuring grains in eight representative individual images. Results indicate that the Stimson has a primary grain size mode at <200 mu m. In addition, more than 50% of the observed Stimson rock targets display a coarser grain population with a long-tailed distribution including grains similar to 600-1200 mu m. The primary grain size mode is similar to that observed in the Bagnold dunes, but the coarse grain size mode was neither observed in the Bagnold dunes nor in ripples adjacent to the dune field. Models for saltation mechanics indicate that the favored grain size for eolian transport on Mars, similar to 100-200 mu m, is independent of atmospheric density, though atmospheric density affects the wind speeds at which grains can be transported by winds. We conclude that the source of the Stimson dunes was more proximal and coarser than the source of the Bagnold dunes and that the paleoatmosphere was likely not significantly denser than the modern Martian atmosphere.

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.

As sand moves across Earth's landscapes, the shapes of individual grains evolve, and microscopic textures accumulate on their surfaces. Because transport processes vary between environments, the shape and suite of microtextures etched on sand grains provide insights into their transport histories. For example, previous efforts to link microtextures to transport environments have demonstrated that they can provide important information about the depositional environments of rocks with few other indicators. However, such analyses rely on 1) subjective human description of microtextures, which can yield biased, error-prone results; 2) nonstandard lists of microtextures; and 3) relatively large sample sizes (>20 grains) to obtain reliable results, the manual documentation of which is extremely labor intensive. These drawbacks have hindered broad adoption of the technique. We address these limitations by developing a deep neural network model, SandAI, that classifies scanning electron microscope images of modern sand grains by transport environment with high accuracy. The SandAI model was developed using images of sand grains from modern environments around the globe. Training data encompass the four most common terrestrial environments: fluvial, eolian, glacial, and beach. We validate the model on quartz grains from modern sites unknown to it, and Jurassic-Pliocene sandstones of known depositional environments. Next, the model is applied to two samples of the Cryogenian Bråvika Member (of contested origin), yielding insights into periglacial systems associated with Snowball Earth. Our results demonstrate the robustness and versatility of the model in quickly and automatically constraining the transport histories recorded in individual grains of quartz sand.

Introduction: Fragmentation of rocky surfaces upon meteor impacts often generates fields of boulders around impact craters. Ejected boulders sometimes possess sufficient kinetic energy to create secondary craters, increasing overall crater density and introducing biases when estimating crater retention ages. Characterizing the kinetic energy of ejected boulders is required to correct such biases in age determinations [1]. However, the vast number of resolvable boulders around single impact craters has rendered morphometric studies of impact-generated boulders challenging. As a result, few boulder fields have been studied [2–11], impeding systematic analyses of the role of, e.g., impactor energy and target properties on spalled boulder properties. To enable more extensive analyses of boulder morphometrics, we developed BoulderNet [12], a machine learning-based algorithm that automatically detects the boulder outlines and characterizes their morphometrics from high-resolution satellite images. Here, we use BoulderNet around over 40 young and fresh impact structures on the lunar surface (i.e., without visible degradation) to better understand the role of the impactor energy and target properties in the boulder ejection process.Methods: A couple of improvements to the previously published version of BoulderNet [12] were implemented. First, the model architecture was modified from Mask R-CNN [13] to YOLOv8 [14], leading to refined outline detections (thanks to the anchor-free nature of YOLOv8). Second, boulders around lunar cold spots and fresh impact craters (directly relevant to this study) were added to the training dataset. Overall, these changes resulted in the detection of smaller boulder sizes and an increase in recall and precision for most boulder sizes.This updated version of BoulderNet was then used to investigate the youngest and freshest impact craters on the lunar surface - the so-called cold spots [15]. Cold spots smaller than 400 m in diameter were excluded from this study because most of their associated boulders are close to or below the limit of resolution of LRO NAC images [16]. A total of 42 cold spots were studied - 5 located in mare, 36 in highlands, and one on the floor of a larger impact crater - with diameters ranging from 420 to 2300 m. Boulder outlines were automatically detected within 1–4 radii away from the crater center. Boulder morphometrics (size, aspect ratio, orientation, spatial density, and location) were then automatically extracted and analyzed.Fragmentation of rocky materials generates fragment-size populations that roughly follow a power-law distribution, N(>D)=C.D-β, where N is the cumulative number of fragments with diameter > D, and β and C are constants. The slope parameter, β, varies with fragmentation process and history [3]. To further compare boulder populations around cold spots, we fit such a power law for each cold spot (including boulders with diameters greater than 2–4 m depending on image resolution). Results: As expected, more boulders are generated around larger impacts (Fig. 1). Furthermore, preliminary results suggest that the slope parameter, β, spans a wider range of values for smaller crater diameters (< 1000 m; β ~ -2.5 to -7.0), but clusters around -2.5 to -3.5 for larger craters (Fig. 2). Surprisingly, the correlation between the size of the largest boulders generated by a given impact and crater size is relatively weak (Fig. 3), especially in lunar highlands.Fig 1. Number of boulders larger than 4 m as a function of primary crater diameter. Only boulders within 1 radius away from the crater rim are selected. Colors reflect terrain type. Symbol size reflects the resolution of NAC images from which detections were made (larger circle = coarser resolution). Fig 2. Slope parameter, β, of boulder populations around lunar cold spots as a function of primary crater diameter. Results from other studies are also shown for comparison. The range of catastrophic disruption for asteroid collisions is highlighted in gray. Fig 3. 99.9th percentile of equivalent boulder diameter as a function of primary crater diameter.Discussion and Conclusions: The general absence of correlation between the size of the largest boulders generated by a given impact and crater size hints at the importance of fragmentation history and the likely presence of pervasive fractures in the lunar crust, especially in highlands. This interpretation is possibly corroborated by our observation of larger variations in β for lunar craters smaller than a kilometer in diameter, which could be explained by more heterogeneous crustal materials in the first tenths of meters. We emphasize that the role of target lithology (mare vs. highlands) is difficult to assess due to the relatively small number of very fresh impact craters therein. To address this caveat, we will analyze boulders around fresh martian craters in similarly young lava flows.References: [1] Melosh (1984) Icarus 59.[2] Shoemaker (1965) JPL Tech. Rept.[3] Hartmann (1969) Icarus 10.[4] Vickery (1986) Icarus 67.[5] Bart & Melosh (2010) Icarus 209.[6] Krishna et al. (2016) Icarus 264.[7] Pajola et al. (2017) Icarus 296.[8] Pajola et al. (2019) PSS 165.[9] Watkins et al. (2019) JGR Planets 124.[10] Pajola et al. (2021) Universe 7, 82.[11] Mistick et al. (2022) Icarus 376.[12] Prieur et al. 2023, JGR Planets 128.[13] He et al. arXiv:1703.06870.[14] Ultralytics: YOLOv8 (2024), https://github.com/ultralytics/ultralytics.[15] Williams et al. (2018) JGR Planets 123.[16] Robinson et al. (2010) Space Sc. Rev. 150.

ReachBot is a robot concept for the planetary exploration of caves and lava tubes, which are often inaccessible with traditional robot locomotion methods. It uses extendable booms as appendages, with grippers mounted at the end, to grasp irregular rock surfaces and traverse these difficult terrains. We have built a partial ReachBot prototype consisting of a single boom and gripper, mounted on a tripod. We present the details on the design and field test of this partial ReachBot prototype in a lava tube in the Mojave Desert. The technical requirements of the field testing, implementation details, and grasp performance results are discussed. The planning and preparation of the field test and lessons learned are also given.

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.

As natural access points to the subsurface, lava tubes and other caves have become premier targets of planetary missions for astrobiological analyses. Few existing robotic paradigms, however, are able to explore such challenging environments. ReachBot is a robot that enables navigation in planetary caves by using extendable and retractable limbs to locomote. This paper outlines the potential science return and mission operations for a notional mission that deploys ReachBot to a martian lava tube. In this work, the motivating science goals and science traceability matrix are provided to guide payload selection. A Concept of Operations (ConOps) is also developed for ReachBot, providing a framework for deployment and activities on Mars, analyzing mission risks, and developing mitigation strategies

Windblown dunes are common features in our solar system, forming on planetary surfaces that span wide ranges in gravity and both atmospheric and sediment properties. The patterns formed by their crests, which are readily visible from orbital images, can record information about recent changes in boundary conditions, such as shifts in wind regime or varying sediment availability. Here, we demonstrate that the density of dune interactions (where neighboring crestlines are close to each other) within a dune field is an indicator of such changes. Using orbiter-based images of 46 dune fields on Earth and Mars, we compiled a database of pattern parameters including dune spacing, crestline orientation, and interaction density. Combined with sediment fluxes derived from ERA5-Land data and a martian global circulation model, we also compiled dune turnover time scales (the time it takes for a dune to migrate one dune length) for each investigated dune field. First, we show that dune fields undergoing changes in boundary conditions display higher than expected dimensionless interaction indices. Second, dune fields with longer turnover times display a wider range in interaction indices on both Earth and Mars because they are more likely to be observed while still adjusting to recent changes in boundary conditions. Thus, a dune field’s interaction index offers a novel tool to detect and possibly quantify recent environmental change on planetary surfaces.