Secondary impact craters (“secondaries”) are produced during the excavation stage of the cratering process, from material ejected from the primary crater. Assuming that secondaries can be associated with their primary crater, and that the age of the primary crater is known, secondary crater populations could be used as absolute stratigraphic markers. Using secondary craters to indirectly date distant features is not a new method – it was used during the Apollo missions, to determine the ages of both the Copernicus and Tycho impact events. In this work, we exploited the martian secondary crater population as absolute stratigraphic markers, to make new insights into the evolution of lobate debris aprons (LDAs).LDAs are landforms found in the martian mid-latitudes and associated with the presence of past and present near-subsurface ice. It is suggested that these morphologies are the results of the flow of a mixture of ice and debris, which derived from the sensitivity of near-surface ice to fluctuations in climate conditions. LDAs are inferred to have formed in the Late Amazonian. However, age constraints of LDA formation are characterized by large uncertainties due to their complex history of modification by viscous deformation, and degradation by erosion, and ice sublimation. Currently, the LDA rate of deformation is considered extremely slow, if not zero, as there is no evidence for crater deformation.In this work, we exploit the crater population at two LDAs in Tempe Terra and adjacent plain terrains, in the northern hemisphere of Mars. This region is affected by secondary impact craters derived from the primary Maricourt crater, which itself likely formed ~11 Ma. Therefore, LDAs and adjacent terrains in Tempe Terra constitute an ideal site where to extract a range of morphometric parameters through which we aim to assess the downslope deformation of the craters, distinguishing between primary and secondary craters, and discuss the results in terms of their meaning regarding sublimation-related changes and LDAs flow.We show that 1) for most of the craters, the orientation of crater elongation is concordant with the LDA slope direction; 2) crater elongation is independent of the slope; however, 3) primary and secondary craters have distinctive depth-to-diameter ratios.

Gale crater, the landing site of NASA's Curiosity rover, and the mountain at its center, Aeolis Mons, hosts an extensive record of sedimentary rocks, which provide a window into the climate history of Mars. Curiosity has demonstrated that Gale hosted long-lived lakes early in its history, indicating warm, quiescent surface conditions, before transitioning into a period of heightened aridity. Recent investigations using orbital data have suggested that the surface of Mars was intermittently wet late in its history. However, an ongoing challenge is linking these orbital observations to on-ground investigations by rovers. Here we use combined orbital image and topographic data sets to investigate a series of sediment fans and related catchment regions within the wider Gale crater, and regional to Curiosity's exploration zone. These systems can be stratigraphically linked to the sedimentary rocks that Curiosity has investigated. We find that most of the sediment fans are likely alluvial fans, recording intermittent flow conditions, with deposition concentrated near the base of Aeolis Mons. The sediment fans are intermixed with landslide deposits and source canyons have been significantly backfilled. We find that these systems formed after regional geological units which Curiosity has shown to record periods of prolonged aridity. Our study demonstrates that intermittent surface water was likely to be present regionally with Gale crater during or after the exhumation of Aeolis Mons. Curiosity may be able to constrain the source and duration of these late-stage flow events as it ascends Aeolis Mons.

Abstract Knowledge of the constituents of the Martian surface and their distributions over the planet informs us about Mars’ geomorphological formation and evolutionary history. In this research, an unsupervised end-to-end unmixing model using autoencoders is proposed, that can produce physically plausible abundance maps of the surface mineralology from hyperspectral imaging data. 1 Introduction Mars’ formationary and evolutionary history can be inferred by studying the mineralogical constituents of the Martian surface and their distributions. Knowledge of the specific minerals present and their abundances constrain the possible histories of the planet’s surface (Liu et al., 2016). Hyperspectral imaging of Mars from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM; Murchie et al., 2007) provides unprecedented insight into the distribution of surface mineralogy. Usually, minerals are identified from spectral absorption features and comparison to spectral libraries (see Viviano-Beck et al., 2014). This can be incredibly time consuming, and relies upon detailed a priori knowledge of the surface chemistry and geology. In order to obtain constituent mineralogical spectra (endmembers) and their fractional abundances one must perform spectral unmixing. Machine learning methods have been used extensively for Earth based hyperspectral imaging analysis, but only a few works to our knowledge have attempted to produce end-to-end unmixing models: Guo et al. (2015); Palsson et al. (2018, 2017); Zhang et al. (2018). Data obtained from hyperspectral imaging of Mars is essentially of the same format as that obtained from Earth, so similar kinds of analysis can be performed. 2 Method Signal decomposition techniques, namely principal component analysis (PCA) and independent component analysis (ICA) are used in order to investigate the presence - and the approximate number - of distinct, clearly detectable signals (component spectra) within CRISM imaging data. Clustering algorithms are then used to obtain an alternative estimate of the number of distinct identifiable mineralogical components present within the spectra. The intuition is that the optimal number of clusters identified should match the number of components determined through the use of signal decomposition techniques. Autoencoders (a type of neural network consisting of an encoder and decoder function that are trained to reproduce their input to their output) are then trained on the spectra from the image. They learn an approximation of the LMM whereby the weights of the decoder correspond to the endmember spectra and the activations of the encoder are the fractional abundances of the endmembers for a given spectrum (Palsson et al., 2018, 2017). The number of endmembers in the learned approximation to the LMM are then set as the estimates of the number of component signals from PCA and clustering. Figure 1 shows a schematic of this. Learned endmembers are extracted from the networks and abundance maps are produced by projecting the activation of each neuron in the decoder to the pixel location of the input spectrum for all of the spectra in the image. These techniques all get around the requirement of detailed a priori knowledge by making no assumptions about the state of the surface. To our knowledge, this is the first work to address the use of unsupervised neural networks for an end-to-end spectral unmixing of Martian hyperspectral images. Figure 1: Schematic view of an autoencoder used for spectral unmixing. 3 Results and Conclusion The signal decomposition techniques provide strong evidence for the presence of detectable mineralogical signals within the data, and the number of signal components estimated from PCA are consistent with the estimates from clustering. PCA, ICA, and the abundance maps produced by the trained autoencoders all appear to convincingly replicate features of the surface topography. Figure 2 shows an example of this, comparing the quicklook image for phyllosilicates (a false colour RGB image constructed from wavelengths using spectral parameters; Viviano-Beck et al., 2014) to one of the produced abundance maps. This provides strong evidence that these methods have learnt mineralogically significant spectra, and that the autoencoders have learnt a physically plausible approximation to the LMM. This is despite the fact that at no spatial information is provided at any point to any of these methods – their results are purely based on spectral information. Hence, when combined with methods to estimate the number of endmembers present, one can construct an unsupervised end-to-end linear unmixing model using autoencoders, that learns to identify physically plausible mineralogical endmembers. Once trained, this pipeline will allow the large number of CRISM data sets to be characterised and abundances mapped over the surface of the planet. This method is also extendable to any kind of planetary hyperspectral imaging, allowing simple mineralogical mapping on an unprecedented scale. Figure 2: Quicklook image for phyllosilicates (a false colour RGB image made using spectral parameters; Viviano-Beck et al., 2014) alongside one of the produced abundance maps. References Guo, R., et al. (2015). Hyperspectral image unmixing using autoencoder cascade. In 2015 7th Workshop on Hyperspectral Image and Signal Processing: Evolution in Remote Sensing (WHISPERS), volume 2015-June, pages 1–4. IEEE. Liu, Y., et al. (2016). End-member identi- fication and spectral mixture analysis of CRISM hy- perspectral data: A case study on southwest Melas Chasma, Mars. Journal of Geophysical Research: Planets, 121(10):2004–2036. Murchie, S., et al. (2007). Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on Mars Reconnaissance Orbiter (MRO). Journal of Geophysical Re- search, 112(E5):E05S03. Palsson, B., et al. (2018). Hyperspectral Unmixing Using a Neural Network Autoencoder. IEEE Access, 6:25646–25656. Palsson, F., et al. (2017). Neural network hyperspec- tral unmixing with spectral information divergence objective. In 2017 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), pages 755–758. IEEE. Viviano-Beck, et al. (2014). Revised CRISM spectral parameters and summary products based on the currently detected mineral diversity on Mars. Journal of Geophysical Research E: Planets, 119(6):1403–1431. Zhang, X., et al. (2018). Hyperspectral Unmixing via Deep Convolutional Neural Networks. IEEE Geoscience and Remote Sensing Letters, 15(11):1755–1759.

A beneficial outcome of ExoMars Rosalind Franklin Rover (ERFR) 1,2 landing site selection process has been the spinout science from detailed studies of parts of Mars that had not previously been examined in detail. Here, we present the geological description of Aram Dorsum3 (Fig. 1), a well-preserved, flat‐topped, branching, ~85 km long and ~ 1 km wide ridge system in western Arabia Terra that was a ‘top 3’ candidate site during ERFR site selection.Fig 1. CTX Mosaic Showing Aram Dorsum (sinuous ridge running top right to lower left).We use morphostratigraphic mapping of the Aram Dorsum ridge and surrounding area, and detailed morphological observations, to propose a consistent working hypothesis for the geological history of the region. Our observations and mapping reveal Aram Dorsum to be the sedimentary deposits of an extensive aggradational fluvial channel belt system, now preserved in positive relief by differential erosion. The existing ridge was once a large river channel belt set in extensive flood plains, many of which are still preserved.Aram Dorsum is part of a wider set of similar inverted channels found across Arabia Terra4,5, and thus was probably part of a regional fluvial system, demonstrating movement of water and sediment across large distances. Furthermore, several smaller palaeochannel belts feed into the Aram Dorsum ridge from within the local regions, and their setting and network pattern suggest a distributed and local source of water. Aram Dorsum therefore appears to record both regionally and locally distributed sources of water.Combining mapping with HiRISE6 and CTX7 Digital Elevation Model data reveals that the Aram Dorsum alluvial succession is up to 60 m thick, suggesting a formation time of 105 to 107 years by analogy to Earth8. Correlating our observations with previous regional‐scale mapping9 shows that Aram Dorsum formed in the mid‐Noachian, a result supported by impact crater size frequency distribution measurements.The Aram Dorsum formation comprises a succession of what are, by analogy with terrestrial fluvial systems, probably coarse‐grained fluvial channel belt sandstones and finer‐grained overbank deposits. The vertical thickness of alluvial succession equates to several cubic kilometres of fluvial sediments in this study region alone. That other inverted channels elsewhere in Arabia Terra4,5,10 are similar in morphology and scale suggest that similar thicknesses and volumes of mid‐Noachian to late‐Noachian fluvial sediments may be extensive and common in the wider region.Aram Dorsum was an extensive long-lived fluvial system with distributed sources. This suggests that local and regional precipitation (either as rain or as seasonal or repeated snow melt) was the source of water. That Aram Dorsum is one of several similar systems suggests that precipitation was widespread across western Arabia Terra during this period. In contrast, Aram Dorsum's low elevation and distance from the majority of the Valley Networks, argues against the source of water being melting of a distant, high‐altitude, ice sheet, or ice cap11,12. Similarly, the aggradational fluvial depositional setting and the scale of the system do not suggest deposition from multiple short‐lived fluvial flows, as might have occurred due to impact cratering or catastrophic volcanic outgassing temporarily altering the climate12–15. We conclude that Aram Dorsum is one of the oldest fluvial systems described on Mars and indicates climatic conditions that sustained surface river flows on early Mars.References cited

Introduction: Oxia Planum (OP) is the selected landing site for the ESA-Roscosmos ExoMars Programme’s 2022 mission (Figure 1). The descent module and landing platform, Kazachock, will transport the Rosalind Franklin Rover to OP. With the primary goal of searching for signs of past and present life on Mars, Rosalind Franklin will investigate the geochemical environment in the shallow subsurface [1].Figure 1: A) Locations of OP on (A) Mars and (B) in Arabia Terra. Phyllosilicate detections are in red [2]. Estimated/study landing ellipses are in yellow. -3000 m contour is shown in blue. Fluvial channels and sediment fan remnants are evident. C) Designation of mapping ‘Areas’. Oxia Planum: OP lies at the transition between the ancient terrain of Arabia Terra and Chryse Planitia (Figure 1). OP forms a shallow basin, open to the north, characterized by clay-bearing bedrock, and contains units from ~mid-Noachian to ~early-Amazonian in age [3, 4]. There have been at least two distinct phases of aqueous activity within the landing site area. A first phase during the mid-Noachian (estimated age is 4.0 Ga) resulted in ~100 m of layered clay-rich deposits. These comprise Mg/Fe smectites overlain by more Al-rich materials. After a substantial hiatus the second phase of aqueous activity included a fluviodeltaic system. This fluvial activity post-dates the clay-rich layered unit, and is associated with the younger set of channels in Coogoon Vallis, which feeds into the Oxia basin. There is abundant evidence for intense erosion across OP. There are isolated buttes, perhaps remnants of a once-extensive layer that superposed the clay-bearing unit, and a dark, mafic-rich, resistant unit of Amazonian age (

Introduction: The ExoMars 2022 Rosalind Franklin rover is scheduled to be launched in summer 2022 with a suite of instruments to investigate the Martian surface and near sub-surface [1]. The context instruments: the Panoramic Camera (PanCam), composed of the two Wide Angle Cameras (WACs), and High Resolution Camera (HRC), and the Infrared Spectrometer for ExoMars (ISEM) will be imperative in the selection of drill and analysis sites. The PanCam stereo imaging system will be the primary mode of scientific observation during the mission with two multispectral WACs in the Visible to Near Infrared (VNIR, 440-1000 nm) range mounted at the top of the 2 meter mast [2]. Within the 36° field of view of the PanCam WACs, HRC will provide 5° field of view colour images at up to submillimetre resolutions [2]. Lastly, ISEM can them be utilised within the WAC/HRC field of views to provide 1° spot size, hyper-spectral coverage in the Near to Mid (1150-3300 nm) Infrared range [3]. In preparation for the mission, spectral analysis tools are being developed to automate as much of the analysis process as is feasible to reduce time and effort costs during mission tactical planning and analysis, as well as improving ability to discriminate between different minerals of interest. Here we report on our effort to constrain the spectral and spatial response of the context instruments for ExoMars using Martian meteorite targetsMartian Meteorite Imaging: This study used instruments emulators for PanCam WAC, ISEM (extended to 300-2500 nm range to provide coverage of PanCam filter wavelengths for comparison) and HRC to investigate the spectral response of a variety of SNC meteorites, to determine the instrument spectral and spatial capabilities and build reliable mission analysis tools. Preliminary analysis has been undertaken on the largest of the Martian meteorite samples. Meteorites were imaged at minimum mission configuration, in semi-directional lighting and operated under mission-similar protocols [2]. The Shergottite Tissint, BM2012, M1, was imaged to assess the instrument ability to distinguish visual and spectral features in the fresh face of the specimen. The PanCam emulator data was first flat-fielded, and environmentally colour corrected and radiometrically corrected using the ExoSpec Software developed by the PanCam science team [4]. Preliminary Results. The fresh face of Tissint is comprised of olivine macrocrysts with black glass veins [5]. These features can be distinguished visually in both the WAC and HRC images (Figure 1). These features, however, are too small to target alone with the hyperspectral instrumentation. To probe the spectral response of these regions a 530-570-670 decorrelation stretch was applied to highlight variation associated with a characteristic olivine spectral feature in this region, shown in Figure 2. This decorrelation stretch does show significant spectral variation between the dominant face material and the black glass veins.Figure 1. Tissint BM.2012,M1, (Left) RGB imaged with RWAC PanCam emulator at 2m. (Right) Colour imaged with HRC emulator at 2 m.The spatial resolution difference in the instrument, an order of five times higher for HRC at this distance, is clear. The multispectral data show a similar shape profile to the hyper-spectral data set over approximately the same region of interest (ROI) figure 3 with an offset in reflectance due in part to the instrument’s throughput of the different narrow band filters [6], shown in Figure 3. A contribution could also be present from the viewing angle of the sample versus the target, hence surface corrections will also be investigated in this instance. To further aid in the detection of minerals of interest, the hyperspectral data will be utilised to develop a spectral parameter map to target olivine. This map will then be tested on the Tissint WAC images to evaluate the information yield.Figure 2. Tissint BM.2012,M1, LWAC with decorrelation stretch applied at 530-570-670 (represented as red, green and blue respectively).Figure 3. Tissint BM 2012,M1, VNIR reflectance spectra from PanCam and ISEM emulator, reflectance offset cause by the filter throughput and anomaly at 740nm where WAC transition occurs [4], (inset) Tissint BM2012, M1 with PanCam and Hyperspectral ROI.Following the completion of the Tissint, the type specimens of the SNC group: Nahkla BM1913,26, Shergotty BM 41021 and Chassigny BM 1985M173, (Figure 4) will then be investigated to compare the spectral properties of the samples and the instrument ability to discriminate between them. This will inform mission processing while analysing a target against the Martian surface.Figure 4. HRC colour images of other target Martian SNC’s (a) Nahkla BM 1913,26, (b) Chassigny BM1985M173 (c) Shergotty BM 41021 at 2m distance.Further Meteorite Imaging: Iron, pallasite and chondritic meteorites have also been imaged to add variety to the spectral sampling pool. As well as in the interest of the instrument spectral and spatial response, meteorite finds on Mars have been a rising topic of interest [7], they represent an interesting avenue to study questions of habitability beyond earth [8, 9]. We also aim to develop methods of identifying meteorite targets on Mars from spectral and visual feature detection for the ExoMars instrument pipelines.References: [1] Vago J. L. et al. (2017) Astrobiology, 17, 471-510 [2] Coates A. J. et al. (2017) Astrobiology, 17, 511-541. [3] Korablev O. I. et al. (2017) Astrobiology, 17, 542-564. [4] Allender E. J. et al. (2018) Image and Signal Processing for remote sensing XXIV, 10789, 1078901. [5] Chennaoui Aoudjehane H. et al. (2012) Science, 338, 6108, 785-788. [6] Cosuins. C. R. et al. (2012) Planetary and Space Science, 71, 80-100. [7] Ashley J. W. (2015) CosmoELEMENTS, 10-11 . [8] Schröder C. et al. (2016) Nature communications, 7, 13459. [9] Tait. A. W. (2019) LPSC L, #1387.

IntroductionIn 2023 the Rosalind Franklin rover will land on Mars at Oxia Planum, as part of the European Space Agency’s ExoMars programme. Transverse Aeolian Ridges (TARs), periodic bedrock ridges (PBRs), dust devils, dust devil tracks, and/or windstreaks are common within the rover’s landing ellipse. These aeolian features can be used to characterize the paleo and contemporary aeolian environment of the landing region before the start of rover operations. Here we present new measurements of the orientation, morphologies, and directionality of TARs, PBRs, windstreaks, and active dust devils, in order to better understand the wind regime at the landing site, on a continuum of spatial and temporal scales. Methods We used machine learning (Novelty or Anomaly Hunter – HiRISE [NOAH-H])[1] and manual mapping-derived TAR and PBR distributions, as well as feature orientation and crest-line lengths to elucidate regional wind patterns in a 640 km2 area of Oxia Planum (Fig.1). The area was gridded into 160 four km2 quadrants, with every second quadrant analyzed. TAR crestlines were manually digitized as continuous and discontinuous ripples, based on NOAH-H ontological classes (Barrett et al., in prep). Continuous ripples are found at a variety of scales (metres to tens of metres in across-bedform length) and consist of patches of parallel ripples which merge into one another. Discontinuous ripples are features in which the aeolian bedforms are separated by areas of non-aeolian material, including those that are isolated on the surface and those which form part of a sparse patch overlying any non-aeolian material. PBRs were identified based on NOAH-H bedrock classes, as well as their morphology and texture, similar to PBRs found elsewhere on Mars[2] and Earth[3].We used multiple change detection techniques on HiRISE, HRSC, and CaSSIS imagery to determine migration rates of TARs and to track active dust devils and analyze wind streaks [4-8].Results and DiscussionWe digitized the crestlines of 7989 continuous ripples and 2764 discontinuous ripples. TAR along-crestline lengths range from 1.1 m to 556 m. Meter-scale TARs are common across the study area but decameter-scale TARs are uncommon, and are primarily found in topographic lows. Irrespective of the scale of the bedform, we found crestline azimuths to be consistent across the study area. Based upon terrestrial megaripple research using the difference in albedo to determine the stoss and lee slopes of ripples in the Argentinian Puna[9], coupled with the crestline azimuths determined from digitizing the landforms, we posit that the winds responsible for the expression of TARs in Oxia Planum blew from the NW-NNW towards the SE-SSE (Fig.2). Crestlines for 457 PBRs were digitized, and found to be longer than TAR crestline-lengths: PBRs have ridge-crests that range in length from ~4 m to just over 600 m. Azimuths of PBRs were found to be substantially different than TARs, requiring winds to have blown from the N-NNE or the S-SSE, accounting for 180° ambiguity. However, analysis of coregistered and orthorectified repeat HiRISE imagery over 11 Earth years showed no appreciable movement in TAR fields in the study area.Two active dust devils were identified in the study area using HRSC images. One dust devil moved from the NW to the SE, while the second travelled from the SW to the NE. From a pair of CTX images taken 50 Earth days apart, 6 active dust devils and 649 dust devil tracks and/or windstreaks were identified. The features are predominantly oriented in a WNW-ESE direction with a secondary NEN-SWS noted for a few of the tracks (Fig.2).The computed azimuths for TARs, PBRs, dust devils and dust devil tracks and/or windstreaks are markedly different (Fig.2), suggesting that different formative winds would have been necessary to result in the directionality of bedforms, landforms, and dust devils we currently see in Oxia Planum. These results pose important questions about the wind regime in this area. When were the winds responsible for TARs and PBRs active? And if contemporary winds are not responsible for TAR and PBR orientation, when did the wind regime shift? To begin answering these questions, our work will focus on comparing the results from this morphological study with modelled climate data in order to help determine when and why the wind regime changed.Looking forwards to the surface mission, the surface platform for the Rosalind Franklin rover will carry a meteorological package that will provide in situ wind measurements. We can compare those data to our morphologically- and modelled-derived results. The rover itself will be able to analyze the granulometry of TARs and the bedrock strata of PBRs using imaging data, further assisting us to characterize the winds from a geomorphological standpoint. These datasets will provide further understanding of the aeolian regime of the Oxia Planum area and provide valuable insight into the climatic history of Mars. References[1] Barrett et al. (In Prep). NOAH-H, a deep-learning, terrain analysis system: results for the ExoMars Rover candidate landing sites.[2] Montgomery et al. (2012). Journal of Geophysical Research: Planets, 117(E3).[3] Hugenholtz et al. (2015). Aeolian Research, 18, 135-144.[4] Balme et al. (2008). Geomorphology, 101(4), 703-720.[5] Greeley et al. (2004). Geophysical research letters, 31(24).[6] Leprince et al. (2007). IEEE Transactions on Geoscience and Remote Sensing, 45(6), 1529-1558.[7] Reiss et al. (2011). Icarus, 215(1), 358-369.[8] Grindrod et al (2018). Journal of Geophysical Research: Planets, 123(7), 1881-1900.[9] Favaro et al. (2020). Icarus, 113765.

Introduction: Inverted channel belts have been recognized on Mars [1,2]. A channel belt represents an extensive fluvial package of sediments which usually formed from lateral migration and aggradation of a river over time [3]. An inverted channel belt is created because the sediment package developed an inversion of relief as some sections were infilled by, or formed from, a more resistant material than the neighboring terrains. The surrounding terrains, less resistant to the erosion were removed, leaving the more resistant sediments upstanding [3] and often organized into characteristic sinuous ridges. This process implies that the fluvial system that deposited the material associated with the channel belt structure must have been active and stable for a long time (about 105-107 years [1]), and then a major change occurred, moving from a period of deposition to a period of erosion. The discovery of these features on Mars could have a major role for the dry-cold versus warm-wet climate debate [4]. Here, we present results from a mapping study in support of an inverted channel belt system developed within the degraded and partially buried Arago crater,in south-east Arabia Terra.Methodology: HRSC-MOLA DEM [5] and CTX mosaic [6,7] data were ingested into ArcGIS software to study the general context of the study area, and to assist analysis of stratigraphy. A digital morphostratigraphic map (scale 1:10,000) was constructed using the available HiRISE [8] image and represents our interpretation of the area. Units are divided into three main groups:(i) The ‘Ridge formation‘ (units with strong correlation to the main ridges and likely represent fluvially-deposited material), (ii) ‘Basal units, (terrains stratigraphically below the inverted systems, or unrelated to them), (iii) ‘Miscellaneous units’ (heterogeneous materials, erosional remnants). The focus of the mapping was to determine the relationships between the sinuous ridge segments and the proximal surrounding terrains.Observations: Arago crater is in Middle Noachian [9] terrains, and is bordered by valley networks [10] at north and south, suggesting that the area was influenced by fluvial processes. Water probably filled Arago crater and the surrounding topographic lows, evolving into temporary paleo-lakes or basins. The studied system is found at the south-west of Arago crater and here we refer to it informally as Arago Dorsum. Arago Dorsum is a continuous, branched, inverted network. Each branch of the system presents a variation in cross section style, expressing a different erosional stage[11]. The branches present smooth or cratered upper surfaces, and the longest segments are connected to smaller, secondary ridges. The Arago Dorsum ridges are upstanding and set within a low-reliefelevated material, demonstrating that they are resistant to erosion. The ridges are both laterally and vertically separated, organised in a multilevel structure.Results: In the Ridge Formation sequence (Fig. 1), the main mapped ridges units (Urf 1-2, Srf 1-2, Lrf 1-2-3) are set at different stratigraphical levels and distributed within both Marginal units (Mrf 1-2) and the lower Transitional units (Trf 1-2-3), which correspond to ~65 m of vertical deposits (Fig. 2). Mapping allowed the recognition of other fine-scale features including: (i) more resistant thin layers visible at the flanks of the main ridges, or distributed in the Marginal units, (ii) the presence of smaller and secondary sinuous ridges which connect and disconnect at different stratigraphical levels, (iii) the presence of polygonal networks, possibly connected with secondary groundwater infilling, (iv) boulders and mass wasting falling from the ridges.Figure 1: Gemorphic map of the “Arago Dorsum” system. The track A-A1 is presented in Fig. 2.Figure 2: Morphostratigraphic profiles(vertical exaggeration x 20) presenting the main mapped units (indicated with labels on the top) and the interpretation (bottom). The cross-section A-A1 track is indicated in Fig. 1.Interpretation: Based on the recognised fine-scale features, ridge morphologies, distribution and relationship of the mapped units, we interpret Arago Dorsum to represent the expression of an aggrading fluvial system, now preserved as an inverted channel belt. Specifically, the alternation of more resistant (ridges and layers) and the less resistant (Marginal-Transitional) units is in line with a flood plain sequence with preserved overbank deposits and discrete or stacked channel bodies. The three main ridges identified in the mapping area represent three periods of deposition. As other ridges have been recognised at CTX observation scale, the sequences reported here include only part of the Arago Dorsum stratigraphy, which may be even more complex, and probably even more long lived.Conclusions: We interpret the Arago ridge system to be fluvial in origin, preserved in positive relief and now modified by differential erosion. Our observations and mapping reveal the inverted channel candidate to be the sedimentary deposits of an extensive aggradational fluvial channel-belt system, probably active in the Mid-Noachian. Valley networks inflowing Arago crater possibly supplied the channel-belt. There is a succession with at least 65 m vertical thickness of fluvial sediments here. Aram Dorsum, in western Arabia Terra (over 2000 km distance and over 1500 m elevation difference from Arago) presents very similar characteristics, including (i) age, (ii) morphology, (iii) vertical thicknesses of sediments, and (iv) the presence of polygonal networks developed in the units associated with the ridge development. These similarities suggest that similar thicknesses, volumes, and secondary processes (burial, erosion, groundwater alteration) of mid-Noachian fluvial sediments may be extensive and common in Arabia Terra. The presence of two (probably more) inverted channel belts, dated to the Mid-Noachian provide supports a past climate with widespread precipitation across Arabia Terra during this period.References:[1] Balme et al.,(2020), JGR Planets,https://doi.org/10.1029/2019JE006244. [2] Liu et al.,(2020), Earth and Planetary Science Letters, https://doi.org/10.1016/j.epsl.2021.116854. [3] Hayden et al.,(2019), Icarus, https://doi.org/10.1016/j.icarus.2019.04.019.[4] Wordsworth et al.,(2016), Annual Review of Earth and Planetary Sciences, 10.1146/annurev-earth-060115-01235.[5] Fergason et al.,(2018), Astrogeology PDS Annex, U.S. Geological Survey. http://bit.ly/HRSC_MOLA_Blend_v0. [6] Dickson et al.,(2018), LPSC, 2480. [7] Malin et al., (2007), JGR Planets10.1029/2006JE002808. [8] McEwen et al.,(2007), JGR Planets, https://doi.org/10.1029/2005JE002605. [9] Tanaka et al.,(2014), GeologicMap of Mars: USGS Scientific Investigations SeriesMap 3292, scale 1:20,000,000, pamphlet 43 p. [10] Hynek et al.,(2010), Journal of Geophysical Research, https://doi.org/10.1029/2009JE003548. [11] Mirino et al.,(2020), LPSC, 1500. [10] Mirino et al.,(2020), LPSC 1492.

This 1:30,000 scale geological map describes Oxia Planum, Mars, the landing site for the ExoMars Rosalind Franklin rover mission. The map represents our current understanding of bedrock units and their relationships prior to Rosalind Franklin's exploration of this location. The map details 15 bedrock units organised into 6 groups and 7 textural and surficial units. The bedrock units were identified using visible and near-infrared remote sensing datasets. The objectives of this map are (i) to identify where the most astrobiologically relevant rocks are likely to be found, (ii) to show where hypotheses about their geological context (within Oxia Planum and in the wider geological history of Mars) can be tested, (iii) to inform both the long-term (hundreds of metres to similar to 1 km) and the short-term (tens of metres) activity planning for rover exploration, and (iv) to allow the samples analysed by the rover to be interpreted within their regional geological context.

Periodic Bedrock Ridges (PBRs) are repeating, symmetrical, wind-transverse, bedrock-abraded linear ridges that occur on Mars as parallel sets. Here, we extend our previous survey of PBRs at Oxia Planum - the landing site of ESA's ExoMars Rosalind Franklin rover - to include three additional sites along the margins of the circum-Chryse basin to understand patterns in PBR orientation and occurrence. We analyzed PBR crestline orientation at each study site and found them to be consistent across this large region, but their orientations do not align with global circulation model winds, suggesting contemporary winds are not responsible for PBR development. Furthermore, we used observations of landscape-level stratigraphic relationships at Oxia Planum to constrain the formation age of PBRs to be late Noachian to early Amazonian. Their consistent orientations and age suggest that the Chryse-margin PBRs formed concurrently and represent modification of an ancient palaeosurface. In addition, we find a tendency for PBRs to preferentially occur in regions where Fe/Mg-rich phyllosilicate minerals were detected in hyperspectral remote sensing data. We conclude that regional scale aeolian processes formed the circum-Chryse PBRs, and that exposed bedrock with Fe/Mg-rich phyllosilicate detections were either more susceptible to PBR formation, or better preserve PBRs than other regional lithologies.

Oxia Planum, Mars, is the future landing site of the ExoMars Rosalind Franklin rover mission, which will search for preserved biosignatures in a phyllosilicate-bearing unit. Overlying the mission-important phyllosilicate-bearing rocks is a dark, capping unit-known here as the Low albedo, Thin, Resistant (LTR) unit-which may have protected the phyllosilicate-bearing unit over geologic time from solar insolation and radiation. However, little is known about the origin of the LTR unit. Here, we map the LTR unit and investigate its distribution and morphology across 50,000 km2 using a variety of orbital remote sensing data sets. The characteristics of the LTR unit include draping palaeo-topographic surfaces, deposition over a wide elevation range, and a consistent vertical thickness that can be best explained by airfall deposition including a primary or reworked volcanic palaeo-ashfall. Previous research suggests that the LTR unit was not significantly buried, and we find it to be preferentially preserved with a high mechanical strength in discrete deposits representing palaeo-topographic lows. We suggest this could be attributed to localized cementation via upwelling groundwater. This scenario suggests that most of the phyllosilicate-bearing exposures may not have been protected over geologic time, as the uncemented LTR sediment would have easily been removed by erosion. However, our observations indicate that the scarped margins of the LTR unit deposits probably exposed regions of the once protected phyllosilicate-bearing unit. These areas could be key science targets for the ExoMars Rosalind Franklin rover mission.

The Winchcombe meteorite fell on February 28, 2021 and was the first recovered meteorite fall in the UK for 30 years, and the first UK carbonaceous chondrite. The meteorite was widely observed by meteor camera networks, doorbell cameras, and eyewitnesses, and 213.5 g (around 35% of the final recovered mass) was collected quickly-within 12 h-of its fall. It, therefore, represents an opportunity to study very pristine extra-terrestrial material and requires appropriate careful curation. The meteorite fell in a narrow (600 m across) strewn field similar to 8.5 km long and oriented approximately east-west, with the largest single fragment at the farthest (east) end in the town of Winchcombe, Gloucestershire. Of the total known mass of 602 g, around 525 g is curated at the Natural History Museum, London. A sample analysis plan was devised within a month of the fall to enable scientists in the UK and beyond to quickly access and analyze fresh material. The sample is stored long term in a nitrogen atmosphere glove box. Preliminary macroscopic and electron microscopic examinations show it to be a CM2 chondrite, and despite an early search, no fragile minerals, such as halite, sulfur, etc., were observed.

Impact cratering is one of the fundamental processes throughout the history of the Solar System. The formation of new impact craters on planetary bodies has been observed with repeat images from orbiting satellites. However, the time gap between images is often large enough to preclude detailed analysis of smaller-scale features such as secondary impact craters, which are often removed or buried over a short time period. Here we use a seismic event detected on Mars by the NASA InSight mission to investigate secondary cratering at a new impact crater. We strengthen the case that the seismic event that occurred on Sol 1034 (S1034a) is the result of a new impact cratering event. Using the exact timing of this event from InSight, we investigated the resulting new impact crater in orbital image data. The S1034a impact crater is approximately 9 m in diameter but is responsible for over 900 secondary impact events in the form of low albedo spots that are located at distances of up to almost 7 km from the primary crater. We suggest that the low albedo spots formed from relatively low energy ejecta, with individual ejecta block velocities less than 200 m s-1. We estimate that the low albedo spots, the main evidence of secondary impact processes at this new impact event, fade within 200-300 days after formation.

Introduction: Numerous inverted fluvial channels occur on the surface of Mars [e.g. 1, 2, 3], and are found mainly in Late Noachian-Early Hesperian terrains [e.g. 6], and often within Arabia Terra [e.g. 1, 3]. A well-studied example is Aram Dorsum, a sinuous branched ridge interpreted as an inverted channel belt [7]. Sub-units within Aram Dorsum present a strong association with different types of decameter-scale, polygonally-patterned terrains:(i) Narrow-Fracture polygons, (ii) Wide-Fracture polygons, (iii) Narrow-Ridge polygons, (iv) Vein-like ridges, and (v) “meter-scale” polygons [7]. The mapping of the Aram Dorsum system shows that these types of polygons present both a distinct spatial distribution and a consistent stratigraphic pattern[7]. Developing a better understanding of the possible causes (local or regional) and formation processes of these polygonal terrains may offer an opportunity for a deeper understanding of the processes involved in inverted channel formation and development. We performed a regional survey within Arabia Terra to identify similar polygonal terrains and morphologies associated with other inverted systems. The main focus was on determining whether these polygon types are present within other terrains associated with inverted channels on Mars, and determine if the spatial/stratigraphic distribution observed in Aram Dorsum is consistent across the region.Method: A database of inverted channels systems in Arabia Terra [8]was compared with HiRISE (25 cm/pixel, [9]) and CTX (6 m/pixel, [10]) image coverage using ArcGIS software. 205 HiRISE images were used for the identification of the polygonised terrains (observation-scale 1:2000). The observations have been made for all the inverted channels which were covered by at least one HiRISE image (Fig.1a). The result of the survey was a new database of polygonal terrain types associated with inverted channels, to which a simplified Aram-like morphological classification division was also applied (Fig.1b).Figure 1: a-Studied HiRISE images which cover part of inverted channels(blue lines [8]). White colours indicate presence of polygonal-grounds. Black colours indicate absence of polygonal-grounds. b-Distribution of Aram Dorsum-like polygonal terrains.Results: From the regional survey, Aram Dorsum-like polygons have been observed in association with many of inverted channels covered by HiRISE images found in Arabia Terra (Fig.2). 100 HiRISE images (out of 205 observed) have shown at least one polygonal type. The polygons have been found mainly associated with the main ridge itself or with the surrounding material adjacent to the inverted feature. Some materials close to the inverted channels may be characterised by only one type of polygonal morphology, and in this case fracture polygons or narrow ridge polygons are the most common types. Some examples of inverted channel deposits contain several types of polygonal features and it is difficult to define when a given type of polygon ends and another type begins. From the regional survey it was difficult to define a unique stratigraphic relationship between the polygonal terrains, and several inverted channels in Arabia Terra present unique morphologies and stratigraphy. However, a trend has been observed: fracture polygon types with clear morphology are usually found on top of the inverted channel, within erosional windows where the ‘capping unit’ has been removed, or on the closest associated materials. Narrow ridges or Vein-like polygons are usually developed within surrounding materials or sometimes in the lower parts of the main ridge (where exposed).Meter-scale polygons, or densely polygonal terrains, were found in proximity of craters linked to the inverted channels, or they have been observed between other polygonal fractures and between the narrow ridges polygons.Interpretation: The Polygonal terrains have been observed in proximity to inverted channel features, on top of the ridge, along the flanks and within ridge-related materials (sometimes interpreted to be overbank deposits [7]) which could be distributed within the inverted channels in erosional windows. The identification of the same types of Aram Dorsum-like polygonal features in so many areas in Arabia Terra suggest that a common phenomenon could be found to explain their formation and development within these fluvial deposits. The persistence of the spatial distribution and a regional stratigraphical trend suggest a connection with the physical proprieties (e.g. grain size, induration, thickness) of the inverted channel deposited materials (fluvial origin) and their response to either (i) a regional stress, if the polygons formed underground as joints, or (ii) a surface process such as desiccation, thermal contraction or possibly a combination of the two. HiRISE images, selected in other areas with no inverted channels have been also checked to evaluate if such a fine-scale polygonal features could be distributed also somewhere else not in association with the inverted channel bodies. Based on preliminary observations on 10 HiRISE samples (randomly chosen) we have not been able to identify these small-scale polygonal terrains. However, since dust and impact materials were present, the survey will be expanded in future studies.Figure 2: Example of Aram Dorsum-like polygonal terrains found in Arabia Terra region. a- Narrow ridge polygons, b- Wide fracture polygons, c- Meter-scale polygons (small domes) and Narrow fractures polygons.Conclusions: Many other Aram Dorsum-like polygonal terrains have been observed and mapped in and around inverted channels in Arabia Terra, suggesting that inverted channels are likely to be observed associated with this type of polygonised terrains. A general spatial-stratigraphical trend has been observed, but deeper studies on selected candidates are necessary to confirm this. We will therefore perform more detailed morphological mapping choosing the a variety of inverted channel candidates in the area to further explore this possibility. More HiRISE images not associated to inverted channel bodies are also going to be controlled.References: [1]Davis et al.,(2016), Geology, G38247.1. [2]Williams et al.,(2013), Icarus 225:308- 324. [3]Chuang & Williams,(2018), Journal of Maps, 14:2, 652-660. [4]Williams et al.,(2013), Icarus 225:308-324. [5]Williams et al.,(2007), Utah Geological Association, pp. 221-235. Salt Lake City, Publication, 36. [6]Tanaka et al.,(2014), Geologic Map of Mars: USGS Scientific Investigations Series Map 3292, scale 1:20,000,000, pamphlet 43 p. [7]Balme et al.,(2020), JGR Planets, https://doi.org/10.1029/2019JE006244. [8]Mirino et al.,(2020), LPSC 1492. [9]McEwen et al.,(2007), JGR Planets,https://doi.org/10.1029/2005JE002605. [10]Malin et al.,(2007), JGR Planets, 10.1029/2006JE002808.

Several lunar samples collected during the Apollo missions were kept sealed and stored in controlled conditions in order to be studied decades later exploiting future, more advanced capabilities. Two of the preserved samples are Apollo 17 double drive tube 73002/73001. The double drive tube extracted a core sample of the Light Mantle deposit at Station 3 in the Taurus-Littrow Valley (Figure 1). As part of the NASA Apollo Next Generation Sample Analysis (ANGSA) program, samples 73002 and 73001 became available to study in 2019 and 2022, respectively [1][2]. The Apollo 17 double drive tube sampled the Light Mantle deposit material down to a depth of 70.6 cm; the effective material length of each tube is 21.3 cm for 73002 and 34.9 cm for 73001 (some material was lost during sampling). This represents an unprecedented opportunity to study the Light Mantle deposit to previously unsampled depths.The Light Mantle deposit represents the only extraterrestrial landslide to have ever been studied in-situ. The Light Mantle is a 5-km-long deposit that formed from debris mobilised from the South Massif, a 2.2-km-high mountain in Taurus-Littrow Valley [3][4]][5]. The origin and hypermobility of the Light Mantle remain debated. The recently opened Apollo 17 double drive tube 73002/73001 provides a new set of samples to investigate the origin and the emplacement mechanisms of the Light Mantle.Prior to dissection and opening of the sample containers, the double drive tube was scanned using X-ray computed tomography (XCT) [6] so that a digital, high-resolution 3D dataset of the whole core sample is available and represents one of the ‘next generation’ capabilities now available to researchers to interrogate the data using novel approaches and obtain new insights into lunar material and processes. Additionally, the 3D dataset preserves the 3D context of all the subsamples extracted from the original core sample.In this work, we used high-resolution X-ray computed tomography (XCT) scans and high-resolution scans of thin sections of the upper 20 cm of the core, sample 73002, and conduct 3D clast-size analysis and investigation of clast morphological fabric. The aims of this work are to:Present a 3D data processing workflow that can be used as a basis for future investigations of lunar core samples. Demonstrate potential scientific information that can be extracted from 3D analysis of lunar core samples. Within this framework, we conduct: (1) 3D grain size analysis and compare the results with grain size analyses conducted on the grains extracted during the dissection of the core sample; (2) 3D analysis of clast size distribution. Additionally, as part of our investigation of the emplacement mechanism of the Light Mantle, we use 2D continuous thin sections (backscattered electron maps) of sample 73002 to search for diagnostic clast fabric similar to those generated during the friction experiments conducted in simulated lunar landslides [7]. The clast fabric is called Clast Cortex Aggregate (CCA) and it’s constituted by a central clast surrounded by nano-scale fine material (Figure 2).The data analysis and visualization of the XCT dataset of core sample 73002 were performed using 3D visualization software Avizo 2022.2 by ThermoFisher. We customized our workflow and established a best-practice protocol so that they can be used as reference for future analysis of 73001. We used backscattered electron (BSE) maps of the sample’s thin sections (73002,6011; 73002,6012; 73002,6013; 73002,6014) [8] to search for (CCAs).The results of clast-size distribution show that the sample is characterised by lack of the largest clast-size fraction in the top 4-5 cm, which we attribute to the fragmentation of larger regolith-hosted clasts and bedrock by space weathering and meteoroid bombardment. The observation of an uppermost layer presenting characteristics of reworked regolith is consistent with results from previous studies of lunar regolith and from other works conducted on 73002 as part of the ANGSA program [8][9]. Moreover, we found extensive presence of CCAs. The formation of CCAs in natural and lab-simulated landslides is attributed to granular flow dynamics, presence of nanoparticles, and adhering forces between such particles. Therefore, we concluded that the presence of CCAs in sample 73002 represents the first evidence that the Light Mantle was emplaced as a granular flow. This work shows that valuable information can be extracted from the 3D analysis of lunar core samples and, more generally, it shows the potential of morphometric and morphological clast analysis using high resolution XCT dataset and thin sections combined.Our work represents the first study to conduct a 3D clast analysis of a lunar regolith core sample. As such, it constitutes an important step in showing the novel information that can be extracted, and presenting a potential workflow for studying lunar regolith core samples that will be collected during future missions to the Moon. REFERENCES. [1] Shearer et al. (2020). AGU Fall Meeting. Abstract V013-0001. [2] Shearer et al. (2022). 53rd LPSC. Abstract 2546. [3] Schmitt (1973). Science, 182(4113), 681–690. [4] Lucchitta (1977). Icarus, 30(1), 80–96. [5] Kokelaar et al. (2017). JGR:Planets, 122(9), 1893-925. [6] Gross et al. (2023). https://curator.jsc.nasa.gov/lunar/angsa_attachments/aapreliminary_20catalog/preliminary_73001-73002_catalog.pdf. [7] Magnarini et al. (2023). JGR:Planets, 128(6), e2022JE007520. [8] Bell et al. (2024). Submitted to JGR:Planets – In review. [9] Neuman et al. (2024). Submitted to Science – In review.Figure 1 – a) Oblique view of Taurus-Littrow Valley; the yellow dot shows the location of the Apollo 17 landing site (LROC/NAC image M1266925685L. Image credit: NASA/GSFC/ASU); b) A frame from the original footage recorded from the Lunar Rover Vehicle onboard camera the showing astronaut Gene Cernan extracting the double drive tube containing material from the Light Mantle deposit. c) Double drive tube in the ground prior extraction (AS17-137-20981. Image credit: NASA). The yellow star in the three panel shows the location where the double drive tube core sample 73002/73001 was collected. Figure 2 – Comparison of Clast Cortex Aggregates (CCAs). (a-b) CCAs generated during the friction experiments conducted on anorthosite-bearing gouges by [7]; (c-f) CCAs found in the Apollo 17 core sample 73002. The red dotted lines and the white dotted line in (d) show the corona of finer fragments found around clasts.

AbstractIn this paper we address two problems associated with data‐limited dynamic spacecraft exploration: data‐prioritization for transmission, and data‐reduction for interpretation, in the context of ESA ExoMars rover multispectral imaging. We present and explore a strategy for selecting and combining subsets of spectral channels captured from the ExoMars Panoramic Camera, and attempt to seek hematite against a background of phyllosilicates and basalts as a test case scenario, anticipated from orbital studies of the rover landing site. We compute all available dimension reductions on the material reflectance spectra afforded by 4 spectral parameter types, and consider all possible paired combinations of these. We then find the optimal linear combination of each pair whilst evaluating the resultant target‐vs.‐background separation in terms of the Fisher Ratio and classification accuracy, using Linear Discriminant Analysis. We find ∼50,000 spectral parameter combinations with a classification accuracy >95% that use 6‐or‐less filters, and that the highest accuracy score is 99.6% using 6 filters, but that an accuracy of >99% can still be achieved with 2 filters. We find that when the more computationally efficient Fisher Ratio is used to rank the combinations, the highest accuracy is 99.1% using 4 filters, and 95.1% when limited to 2 filters. These findings are applicable to the task of time‐constrained planning of multispectral observations, and to the evaluation and cross‐comparison of multispectral imaging systems at specific material discrimination tasks.

The Taurus-Littrow Valley, location of the Apollo 17 landing site, hosts recent, late-Copernican geomorphological landforms and tectonic structures, namely the Light Mantle avalanche deposit and the Lee-Lincoln lobate scarp. The Light Mantle deposit represents a unique case of a hypermobile avalanche on the Moon (El-Baz 1972; Schmitt et al. 2017). The Lee-Lincoln lobate scarp is the surface expression of a recent thrust fault (Watters et al. 2010), which is considered to be the source of strong seismic shaking throughout Taurus-Littrow Valley (van der Bogert et al. 2012, 2019), and potentially still active (Watters et al. 2019).The Light Mantle represents the only extraterrestrial landslide for which an absolute age is provided (70-110 Ma), thanks to the Apollo 17 returned samples (e.g., Schmitt et al. 2017). Therefore, the Light Mantle deposit can be used as a geomorphological marker and time constraint for surface changes that occurred since its emplacement. By applying the principle of superposition, surface changes superposed on the Light Mantle deposit, and on the slope from which it was generated (the NE-facing slope of the South Massif), must post-date the landslide event. For example, small scale grabens (10-20 m wide) associated with the Lee-Lincoln lobate scarp are found superposed on the Light Mantle unit (Watters et al. 2010). These troughs likely formed less than 50 Ma and are thought to be generated by the flexural bending of the hanging wall (Watters et al. 2010, 2012). Similarly, boulder tracks, whose survival time is estimated to range up to 35 Ma (e.g., Arvidson et al. 1976; Kumar et al. 2019), are found on the NE-facing slope of the South Massif, therefore evidence that boulder falls have occurred after the Light Mantle landslide event.Here, we extend the body of evidence of surface changes that have affected the South Massif since the emplacement of the Light Mantle deposit. We map boulder tracks, areas of disturbed regolith, linear slope structures, and other structures associated with the summit of the South Massif. We identified features (i.e., slope structures oblique to contours, the Nansen Moat and the trough at the NE-base of the Sout Massif) directly related to back-thrust faults associated with the Lee-Lincoln thrust fault, which are re-activating the buried fault that bounds Taurus-Littrow Valley; we identified other features (i.e., crestal graben-like structures, slope structures parallel to contours) that derived from gravitational adjustment following basal slope support removal due to back-thrust faulting. Moreover, the overlapping relationships between the boulder tracks and regolith disturbance suggests that continuous slope deformation has been affecting the NE-facing slope. We attribute the efficiency of the process to repeated ground-shaking perturbation, which maintains the slope in a perpetually unstable state.We conclude that the NE-facing slope of the South Massif has been recently and continuously affected by slope deformation processes. We suggest that the efficiency of these processes is the product of lasting, and perhaps ongoing, effects of activity of the Lee-Lincoln thrust fault, coupled with the influence of the subsurface geometry of the valley inherited from the impact basin formation.

Abstract Martian meteorites represent the only samples of Mars available for study in terrestrial laboratories. In addition to their crystallization and surface ejection ages, these samples provide a detailed understanding of the geochemistry of the martian crust. One of the major outstanding problems regarding martian meteorites is locating the exact source regions on Mars, although the composition and texture of these meteorites limits the source craters to mostly igneous provinces. To help find source craters, we present an updated global catalog of impact craters greater than 3 km diameter with thermally distinct radial patterns (“rays”), which could represent recent impact events. We defined search criteria for identifying rayed craters, assigning a confidence level to each crater, and noted the presence or absence of associated secondary craters. Using daytime and nighttime thermal infrared image data we identified 118 craters with thermally distinct radial patterns between ±60° latitude, of which 89 had not appeared in previous catalogs. We discuss some potential uses of this new catalog in terms of understanding the morphology, location, and composition of each crater. Our preliminary analysis demonstrates the potential future use of this catalog in finding the source location of martian meteorites in regions of sufficient thermal contrast.

The first billion years of Martian geologic history consisted of surface environments and landscapes dramatically different from those seen today, with flowing liquid water sculpting river channels and ponding to form bodies of water. However, the hydro‐climatic context, the frequency, and the duration under which these systems existed remain uncertain. Addressing these fundamental questions may improve our understanding of early Mars climate. Here, we reconstruct a long‐lived archive consisting of an array of fluvial systems inside the Antoniadi crater––one of the largest lake basins on Mars (9.58 × 10 4 km 2 ). We found that the fluvial activity occurred throughout four major intermittent active intervals during the Late Noachian to Early Amazonian (∼3.7 to >2.4 Ga). This resulted in at least two major lakes, which formed during periods of markedly increased surface runoff production. The record of these four riverine phases is preserved in fluvial ridges, valley networks, back‐stepping or down‐stepping fan‐shaped landforms, and terrace‐like formations within an outlet canyon. These morphologies point to lake‐controlled base‐level fluctuations suggestive of episodic precipitation‐fed surface runoff punctuated by intermittent catastrophic floods that were capable of breaching crater‐lake rims and incising outlet canyons. Fluvial‐deposit thickness, junction angles of channels, and lake morphometry suggest that riverine systems lasted at least 10 3 –10 6 years and episodically occurred under primarily arid and semi‐arid climates. These findings place new regional constraints on the fluvial frequency, longevity, and climatic regime of one of the largest Martian lakes, thereby bolstering the hypothesis that episodic warming likely punctuated the planet's early history.