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Martian deltaic deposits are good indicators of water distribution and provide insight into the climate evolution of Mars [1]. A notable case is the fan deposit located in Jezero crater, currently being studied by the Perseverance rover. Hydrated silica-bearing deposits were identified in this area [2, 3, 4], and the overall stratigraphy and morphology point to an evolution passing through a progradation and a transgression phase, to an erosion episode [5]. All these evidences suggest that this deposit was formed by fluvio-deltaic activity in an ancient lake basin [6] during the late Noachian or early Hesperian epochs [7]. After its formation, the deposit likely suffered a complex and profound exhumation [8] which we will try to constrain through a mass balance analysis.Here, we present the first results of a project seeking to understand the depositional and post-depositional evolution of the Jezero delta, including the study of its hydrographic basin [9]. We will focus on a mass-balance survey, analyzing and comparing the volume of sediments that were eroded from the basin and deposited into the crater. We integrate HRSC, CTX and HiRISE data to create a regional DTM and orthophoto map covering the Jezero crater and its drainage basin. These datasets enable us to estimate the volume of sediments eroded from the drainage basin, as well as the present-day volume of the fan deposit. Finally, we will apply the mass balance model introduced by [10], aiming at evaluating putative sediment offshore loss and post-depositional fan erosion. This will allow to infer the initial volume of the deltaic deposit and test different lake water levels. [1] Di Achille, G. and Hynek, B. M. (2010). Nature Geoscience, Vol. 3 (7),459-463. [2] Pan, L., et al, (2021). Planet. Sci. J., 2(2), 65., [3] Horgan, B., et al, (2020). Icarus, 339. [4] Mangold, N., (2007). J. Geophys. Res. 112(8). [5] Goudge, T. A., et al. (2018). Icarus, 301 58–75. [6] Fassett, C. I., & Head, J. W. (2005). Geophys. Res. Let., 32(14), 1–5., [7] Mangold, N., et al, (2021). Science 10.1126, [8] Quantin-Nataf, C., et al (2021). 52nd LPSC, [9] Goudge, T. A., et al, (2015). J. Geophys. Res. Planets 120., [10] Vaz, D. A., et al, (2020). Earth Planet. Sci. Lett., Vol. 533.

Orbital data from the Messenger spacecraft (1) reveal that part of the Mercury surface is covered by smooth plains, which are interpreted to be flood volcanic material across the planetary surface (2). In this work, we present a detailed geo-structural map of the northern smooth plains between latitudes 29°N and 65°N. Our 1:100.000-scale map is obtained semi-automatically, using an algorithm to map all scarps from a DEM (3,4) followed by visual inspection and classification in ArcGIS. We created a DEM using the raw MLA (Mercury Laser Altimeter) data (1) ,with 500 m/pix, and we used the Mercury Messenger MDIS (Mercury Dual Imaging System) (1,2) base map with 166m per pixel for the classification stage. With this approach, we mapped and characterized 51664 features on Mercury, creating a database with several morphometric attributes (e.g. length, azimuth, scarp height) which we will use to study the tectonic evolution of the smooth plains. In this way, we classified wrinkle ridges’s scarps, ghost craters, rim craters and central peaks. The morphometric parameters of the wrinkle ridges will be quantitatively analyzed, in order to characterizer the possible tectonic process that could have formed them. This map can be considered an enhancement for the north pole of the global geological map of Mercury (1, 5). References Hawkins, S. E., III, et al. (2007), The Mercury Dual Imaging System on the MESSENGER spacecraft, Space Sci. Rev., 131, 247–338.. Denevi, B. W., et al. (2013), The distribution and origin of smooth plains on Mercury, J. Geophys. Res. Planets, 118, 891–907, doi:10.1002/jgre.20075. Alegre Vaz, D. (2011). Analysis of a Thaumasia Planum rift through automatic mapping and strain characterization of normal faults. Planetary and Space Science, 59(11-12), 1210–1221. doi:10.1016/j.pss.2010.07.008 . Vaz, D. A., Spagnuolo, M. G., & Silvestro, S. (2014). Morphometric and geometric characterization of normal faults on Mars. Earth and Planetary Science Letters, 401, 83–94. doi:10.1016/j.epsl.2014.05.022. Kinczyk, M. J., Prockter, L., Byrne, P., Denevi, B., Buczkowski, D., Ostrach, L., & Miller, E. (2019, September). The First Global Geological Map of Mercury. In EPSC-DPS Joint Meeting 2019 (Vol. 2019, pp. EPSC-DPS2019).

The presence of ancient fluvial systems on Mars, known as valley networks, is considered one of the most compelling evidence that liquid water was once stable on the planet's surface. To understand the formation mechanisms of these valleys and to acquire information on the ancient climatic conditions of the planet, we determined the formation time of a sample group of 63 Martian valley networks. Our sample group was divided into two subgroups: valleys with an interior channel (13 valleys); and valleys without visible interior channels (50 valleys). For the first subgroup we estimated the formation time using a method based on the calculation of water and sediment discharges. We assumed four different possibilities: continuous flow; 5% of intermittence, typical of terrestrial humid or sub-humid conditions; 1% as for semiarid or arid environments; and finally, 0.1% for hyper-arid conditions. Once obtained the formation times for each valley we evaluated the erosion rates. Subsequently, the mean erosion rates obtained for the first subgroup of valleys were used to calculate the formation times for the remaining 50 valleys using the ratio between the eroded volume and the erosion rate. For the whole sample group of the fluvial systems, we found formation timescales ranging from 5 × 102 yr to 8 × 106 yr (with a median of 3 × 104 yr) for a continuous sediment flow, while the range is from 1 × 104 yr to 2 × 108 yr (median 5 × 105 yr) with an intermittence of 5%, from 5 × 104 yr to 8 × 108 yr (median 3 × 106 yr) with an intermittence of 1%, and from 5 × 105 yr and to 8 × 109yr (median 3 × 107yr) with a 0.1% intermittence. However, based on our results, a continuous sediment flow as well as an intermittence of 0.1% seem unlikely. Plausible values of formation timescales are instead obtained with intermittencies of 5% and 1% corresponding to humid and semiarid/arid environment, respectively. Our results do not allow to discriminate between the two scenarios; on the contrary the scenario of a permanently cold and icy Noachian Mars can be ruled out by our findings.

Fan deposits located at the mouths of Martian valleys have been interpreted as indicators of wet conditions during Mars history. However, the processes, time and amount of water needed to carve the valleys and form the fans are still debated. Here we present a detailed morphometric and mass balance analysis of valleys and fan-shaped deposits using high resolution topography, which provides new insights into past depositional environments. Based on morphometric and volumetric measurements, we found that several Martian fans previously interpreted as deltas can be categorized into two main types. Type I fans are more numerous, relatively well preserved, are associated with smaller and less mature drainage networks and were deposited on steeper gradients. The balance between eroded and deposited materials indicates that this set of fans might have been formed mainly in subaerial settings by depositional processes other than typical deltaic sedimentation (e.g. alluvial, glacial, mass-wasting in general), since a significant loss of sediment during deposition did not occur (we obtained a volume ratio of eroded vs. deposited materials of approximately 1). Therefore, we propose that the identified Type I fans were not deposited in prevailing subaqueous deltaic settings, but mainly in subaerial conditions with perhaps sporadic presence of ephemeral bodies of standing water within the basins. In contrast, Type II fans are less abundant, highly eroded, were deposited on flatter areas and formed downstream of more mature drainage networks with longer, deeper and wider valleys. The mass balance for this set of fans clearly shows that considerable amounts of sediment were not retained in the fans, implying large offshore transport of sediment during their formation (eroded vs. deposited volume ratios between 3 and 10 are probable). This evidence supports a fluvio-deltaic origin for this class of fans, indicating the existence of paleolakes over substantial periods of time. Based on the collected morphometric measurements and mass balance modeling we conclude that only a small percentage of the fans (Type II fans correspond to ∼ 1 / 3 of the sampled areas) are consistent with the occurrence of favorable and durable conditions for life, i.e. long-lived integrated fluvial, deltaic and lacustrine environments. Whereas, the majority of fans might have been formed in subaerial settings with significant contributions of alternative processes besides fluvial transport and deposition thus not necessarily requiring the occurrence of extended epochs of clement climatic conditions.

The High Resolution Imaging Channel (HRIC) of the Spectrometer and Imagers for Mpo Bepicolombo Integrated Observatory – System (SIMBIO-SYS) onboard the BepiColombo mission to Mercury, is the visible imaging camera devoted to the detailed characterization of the Hermean surface. The potential huge amount of data that HRIC can produce must cope with the allocated mission resources in terms of power, data volume, and pointing maneuvers while accomplishing the scientific objectives of the mission. The purpose of this work is to present a preliminary approach for planning the HRIC observations during the nominal scientific phase and to discuss the outcomes of a test simulation which highlights the complexity of the planning process and the possible conflicts with respect to available resources.

Craters cross-cut by faults are used as markers to obtain fault geometric and kinematic properties.Assumingthattheshapeofthesecraterswasoriginallycircular,itispossibletomeasure the horizontal and vertical components of fault displacement as well as the slip trend. By applying trigonometric relations, slip plunge, displacement magnitude, fault true dip and fault rake can be derived from the observed values. An example application of this method on craters faulted by lobate scarps on Mercury shows that most of these inferred reverse faults have moderate oblique-slip trends. Moreover, the derived dips of thrusts vary over a wide range of angles. Some preliminary results in terms of fault rake compared with fault dip, strike and latitude are pre- sented together with a pilot study to test and discriminate global tectonic models suggested for the evolution of Mercury. The possibility of estimating quantitative fault parameters through remotely sensed data provides significant assistance in the structural characterization of faults on planetary surfaces.

We used a comprehensive 2-D and 3-D basin-filling morphodynamical model to explore the effects of changing hydrologic and sedimentary conditions on delta formation under martian conditions. Spatial and temporal deposition of sediment into a body of standing water was simulated using event-based time stepping (e.g. seasons). River and sediment discharge were calculated using the Darcy–Weisbach equation for width- and depth-averaged flow velocity and well-known and tested terrestrial sediment transport predictors modified for application to martian flows. A range in sediment grain sizes was determined from both landers and orbiting spacecraft data in order to include grain sizes typical of Mars and yet representative of the martian deltas. Several different scenarios of seasonal river discharge and sediment supply were explored to encompass a range of possible formation conditions. With the ability to track sediment as it is transported throughout the basin, it is apparent that non-negligible amounts of material are moved beyond the delta-forming region. This loss of sediment increased with river discharge, increasing the gap between the calculated and modeled formation timescales. These results have important implications for the formation timescales of the deltas and the small number of identifiable deltas on Mars today. Formation timescales that consider only the supply of sediment to the system and do not take into account factors affecting deposition and delta formation are underestimates of the actual amount of time needed to form the deposits. The lack of identifiable deltas in many paleolakes is likely a result of significant sediment transport beyond the channel mouth, causing the expected delta deposit to be draped throughout the basin.

Photointerpretation is the technique generally used to map and analyze the tectonic features existent on Mars surface. In this study we compare qualitatively and quantitatively two tectonic maps based on the interpretation of satellite imagery and a map derived semi-automatically. The comparison of the two photointerpreted datasets allowed us to infer some of the factors that can influence the process of lineament mapping on Mars. Comparing the manually mapped datasets with the semi-automatically mapped features allowed us to evaluate the accuracy of the semi-automatic mapping procedure, as well as to identify the main limitations of the semi-automatic approach to mapping tectonic structures from MOLA altimetry. Significant differences were found between the two photointerpretations. The qualitative and quantitative comparisons showed how mapping criteria, illumination conditions and scale of analysis can locally influence the interpretations. The semi-automatic mapping procedure proved to be mainly dependent on data quality; nevertheless the methodology, when applied to MOLA data, is able to produce meaningful results at a regional scale.

Determining absolute surface ages for bodies in the Solar System is, at present, only possible for Earth and Moon with radiometric dating for both bodies and biologic proxies such as fossils for Earth. Relative ages through cratering statistics are recognized as one of the most reliable proxies for relative ages, calibrated by lunar geologic mapping and Apollo program sample returns. In this work, we have utilized the Mars Reconnaissance Orbiter’s ConTeXt Camera’s images which provide the highest resolution wide-scale coverage of Mars to systematically crater-age-date the calderas of 20 of Mars’ largest volcanoes in order to constrain the length of time over which these volcanoes – and major volcanic activity on the planet, by extension – were active. This constitutes the largest uniform and comprehensive research on these features to date, eliminating unknown uncertainties by multiple researchers analyzing different volcanoes with varied data and methods. We confirm previous results that Mars has had active volcanism throughout most of its history although it varied spatially and temporally, with the latest large-scale caldera activity ending approximately 150 ma in the Tharsis region. We find a transition from explosive to effusive eruption style occurring in the Hesperian, at approximately 3.5 Ga ago, though different regions of the planet transitioned at different times. Since we were statistically complete in our crater counts to sizes as small as ∼60 m in most cases, we also used our results to study the importance of secondary cratering and its effects on crater size–frequency distributions within the small regions of volcanic calderas. We found that there is no “golden rule” for the diameters secondaries become important in crater counts of martian surfaces, with one volcano showing a classic field of secondaries ∼2 crater diameters from the center of its primary but not affecting the size–frequency distribution, and another clearly showing an influence but from no obvious primary.

The climate of early Mars could have supported a complex hydrological system. Analysis of ancient deltaic deposits and valley networks reveals the presence of a planet-wide equipotential surface in the northern lowlands, indicative of the existence of a vast ocean on Mars 3.5 billion years ago.

The Tsenkher structure, in the Gobi-Altai region of Mongolia, was studied using a wide array of remote sensing data and field observations. The structure has a shallow, 3.6 km wide, central depression bordered by a near-circular ridge (putative crater rim) with breaches to the northwest. The central depression is obliterated partially by fluvial infill through these breaches. Outside the ridge, the western side is a rugged terrain, but the eastern half is characterized by a concentric outer ridge that occurs at about one radius distance from the inner ridge. Although intrusion, salt tectonics and maar crater hypotheses cannot be completely ruled out, its morphology strongly implies an impact origin for the Tsenkher structure. If of impact origin, it has a well-preserved morphology and its position in the basin fills indicates that the formation may have occurred relatively recently, sometime during the late Tertiary or Quaternary. The outer ridge morphology is similar to rampart craters on Mars, whose formation has been attributed to fluidization of a water-rich target layer and ejecta materials, or to atmospheric entrainment and deposition of ejected materials. However, other hypotheses including erosional remnant of ejecta blanket, erosional scarp of structural rim uplift, multi-ring or deeply eroded crater rim of a peak-ring crater are also possible at this stage. A complex fluvial and probable lacustrine history is envisaged within the Tsenkher structure. The structure is also associated with archaeology, including Paleolithic and Bronze Age remains.

Deltaic depositional systems are the most prominent evidence suggesting the existence of long-lasting standing bodies of water on Mars. Due to this genetic link, Martian deltas are fundamental for the reconstruction of the paleohydrological cycles and paleoclimates of Mars, testifying to the occurrence of past climatic conditions that created hydrological settings quite different from those of modern Mars. Ancient terrains of Mars are covered with additional signatures of past water. Branching channel systems on Mars, known as “valley networks,” have long been viewed as some of the best evidence that water flowed across the surface. Recent data, including topography and high-resolution imagery, have shed new light on valley network formation. It is now believed that most valley networks were formed by precipitation and surface runoff instead of groundwater processes. Two main planet-wide equipotential surfaces that encompass complete topographic enclosures within and along the margins of the northern lowlands. The inferred levels could represent two paleoshorelines of a past ocean covering the northern hemisphere of Mars during its early history. These boundaries are generally consistent with the “Arabia shoreline” previously suggested from geomorphologic and topographic observations and also with the global distribution and age of valley networks. Reconstructed scenario implies that climatic conditions allowed the occurrence of a hydrosphere presenting similarities with that of Earth, and integrating valleys, deltas, lakes, an ocean encircling the planet, and possibly a number of suitable niches for life to exist.

[1] Remote sensing studies of possible Martian paleolakes have hinted at the presence of paleoshorelines on Mars, although have never been unequivocally identified. Recently-acquired sub-meter scale High Resolution Imaging Science Experiment (HiRISE) images of Shalbatana Vallis reveal the first direct evidence of strandlines along a delta formed within an intravalley lake during the Hesperian epoch (3.4 Ga). HiRISE images show where water from a 57-km-long valley built a delta, flowed over its subaerial plain, and finally debouched into a more than 450-m-deep lake, forming chutes in the subaqueous part of the deposit. At present, the studied system contains some of the most pristine, distinctive, and recent lacustrine evidence among all the candidate Martian paleolakes. The associated sedimentary deposits provide a valuable target for future in-situ analyses aimed at the characterization of the hydrology, climate, and biological potential of ancient Mars.

The plains of Aurorae and Ophir in the equatorial region of Mars display geomorphic evidence indicative of extensive but generally short-lived paleohydrological processes. Elaver Vallis in Aurorae Planum south of Ganges Chasma is an outflow channel system >180 km long, and here inferred to have formed by cataclysmic spillover flooding from a paleolake(s) contained in the Morella crater basin. Ganges Cavus is an enormous 5-km-deep depression of probable collapse origin located in the Morella basin. The fluid responsible for the infilling of the Morella basin likely emerged at least partially through Ganges Cavus or its incipient depression, and it may have been supplied also from small-scale springs in the basin. Similar paleohydrological processes are inferred also in Ophir Planum. It is reasonable to assume that water, sometimes sediment-laden and/or mixed with gases, was the responsible fluid for these phenomena although some of the observed features could be explained by non-aqueous processes such as volcanism. Water emergence may have occurred as consequences of ground ice melting or breaching of cryosphere to release water from the underlying hydrosphere. Dike intrusion is considered to be an important cause of formation for the cavi and smaller depressions in Aurorae and Ophir Plana, explaining also melting of ground ice or breaching of cryosphere. Alternatively, the depressions and crater basins may have been filled by regional groundwater table rising during the period(s) when cryosphere was absent or considerably thin. The large quantities of water necessary for explaining the paleohydrological processes in Aurorae and Ophir Plana could have been derived through crustal migration from the crust of higher plains in western Ophir Planum where water existed in confined aquifers or was produced by melting of ground ice due to magmatic heating or climatic shift, or from a paleolake in Candor Chasma further west.

[1] An intravalley paleolake (more than 400 m deep) was detected along the course of Shalbatana Vallis from the evidence of shorelines and the occurrence of a few fan-delta deposits (including a Gilbert-type delta). The fronts of all the sedimentary deposits strikingly match the same topographic contours (2800 and 3000 m below the Martian datum), indicating the paleolake water levels under which they formed. Also, the corresponding shorelines are visible along the Shalbatana Vallis walls. The peculiar settings of the lake suggest that Shalbatana Vallis was impounded during its final hydrological activity and that ponding of water lasted enough time to allow the formation and evolution of the lacustrine system. Water source is uncertain, but a composite sapping mechanism is hypothesized in order to take into account the amount of water required to excavate, transport, and deposit the materials found in the deposits. Previous works and new crater counting computations indicate that the paleolake was active during the Hesperian epoch; therefore, at that time, surface conditions were different from those of modern Mars and supportive of flow and ponding of water. It is unclear whether the hydrological activity was sustained entirely by a favorable climatic regime and secondary regional factors like volcanism, impact cratering, and tectonism could have also triggered/accelerated the local groundwater activity, implying that the system could have evolved relatively independent from climatic conditions. The latter eventuality and the regional importance of this research advised against an extrapolation of its results to the overall debate about Martian climatic-geomorphological evolution.

[1] Using the new High Resolution Stereo Camera (HRSC) data and other Martian data sets, we reconstructed the hydrological history of an unnamed complex crater in the Xanthe Terra region. The crater hosted a lacustrine basin fed by a dense and centripetal drainage system, developed along its inner rim, and by the Tyras Vallis channel. Where the Tyras Vallis opens into the crater, a prominent delta-like feature is visible, characterized by a central terrace and two small longitudinal scarps. This deposit has been used as sedimentary recorder of the crater lake history and allowed assessment of the overall hydrological evolution. Two major stands of the water level have been inferred at 700 and 550 m above the crater floor, based on the correlation between the morphology and topography of the fan and the crater floor deposits. Our reconstruction reveals a complex sedimentary evolution of the fan, which underwent deltaic and alluvial sedimentation, as a result of the different lake water levels and Tyras Vallis supplies. A dominant erosional evolution of the fan-delta was determined by the interaction between the fluvial characteristics and basin wave regime. Wave height analysis and morphological comparison with terrestrial analogues support this hypothesis. The lacustrine activity could be chronologically placed between the Late Noachian and the Hesperian. The climatic conditions could have allowed the recharge of the regional groundwater system by precipitation and episodic fluvial activity. However, also heating effects of cratering could have affected the system, rejuvenating or accelerating the recharge of the local aquifer.