Northern Hemisphere Of Mars Research Articles

Evidence for landslides in Sisyphi Cavi (Noachis Terra, Mars): Slope evolution and role of endogenous preparatory factors

The surface of Mars is characterized by the presence of numerous gravity-induced processes and mass movements with greatly variable sizes and peculiarities. Detailed geomorphological studies have recently made it possible to identify many landslide-like landforms along the slopes bordering pits of Sisyphi Cavi in Noachis Terra, the southern hemisphere of Mars. These pieces of evidence are generally characterized by extended trenches, sometimes associated with uphill- or downhill-facing scarps. In this study, the gravity-induced processes observed in this region of Mars, and especially those present in a closed pit of the eastern sector, are described for the first time. A quantitative stress-strain analysis was performed, and it excludes a type of deformation process that could invoke creep processes (“viscosity-driven”) but rather favors instability induced by stress-perturbations in the slope more concentrated over time (“force-driven”). In particular, we performed a parametric analysis on both viscosity and stiffness parameters of the materials involved. It demonstrates that the time necessary for the rheological evolution of deformational processes associated with the observed landforms are compatible with genesis of short-term instabilities. This finding has significant implications for the origin of the depressed forms within and close to the study area, which are characterized by unstable slopes present at their edges. It is therefore not necessary to invoke the role of “viscosity-driven” creep processes to explain the origin of the shapes associated with the observed gravity-induced slope instabilities. The reported results drive towards a new interpretative scenario of morphological evolution of the widespread pits in the study area in terms of efficiency of endogenous processes (such as hypabyssal magmatism) which characterize the studied area of Mars, even if it is not possible to exclude the role of exogenous processes.

Reconciling Mars InSight Results, Geoid, and Melt Evolution With 3D Spherical Models of Convection

AbstractWe investigate the geodynamic and melting history of Mars using 3D spherical shell models of mantle convection, constrained by the recent InSight mission results. The Martian mantle must have produced sufficient melt to emplace the Tharsis rise by the end of the Noachian–requiring on the order of 1–3 × 109 km3 of melt after accounting for limited (∼10%) melt extraction. Thereafter, melting declined; however, abundant evidence for limited geologically recent volcanism necessitates some present‐day melt even in the cool mantle inferred from InSight data. We test models with two mantle activation energies and a range of crustal Heat Producing Element (HPE) enrichment factors and initial core‐mantle boundary temperatures. We also test the effect of including a hemispheric (spherical harmonic degree‐1) step in lithospheric thickness to model the Martian dichotomy. We find that a higher activation energy (350 kJ mol−1) rheology produces present‐day geotherms consistent with InSight results, and crustal HPE enrichment factors of 5–10‐times produce localized melting near or up to present‐day. The 10‐times crustal HPE enrichment is consistent with both InSight and geochemical results and also produces present‐day geoid power spectra consistent with Mars. However, calculations that match the present‐day geoid power spectra require more than 60% melt extraction to produce the Tharsis swell. The addition of a degree‐1 hemispheric dichotomy, as an equatorial step in lithospheric thickness, does not significantly improve upon melt production or the geoid.

Seasonal Thaws under Mid- to Low-pressure Atmospheres on Early Mars

Abstract Despite decades of scientific research on the subject, the climate of the first 1.5 Gyr of Mars' history has not been fully understood yet. Especially challenging is the need to reconcile the presence of liquid water for extended periods of time on the Martian surface with the comparatively low insolation received by the planet, a problem which is known as the Faint Young Sun paradox. In this paper, we use the Earth-like planet surface-temperature model (or ESTM), a latitudinal energy-balance model with enhanced prescriptions for meridional heat diffusion, and the radiative-transfer code EOS to investigate how seasonal variations of temperature can give rise to local conditions which are conducive to liquid-water runoffs. We include the effects of the Martian dichotomy, a northern ocean with either 150 or 550 m of global equivalent layer, and simplified CO2 or H2O clouds. We find that 1.3–2.0 bar CO2-dominated atmospheres can produce seasonal thaws due to inefficient heat redistribution, provided that the eccentricity and the obliquity of the planet are sufficiently different from zero. We also studied the impact of different values for the argument of perihelion. When local favorable conditions exist, they nearly always persist for >15% of the Martian year. These results are obtained without the need for additional greenhouse gases (e.g., H2, CH4) or transient heat-injecting phenomena (e.g., asteroid impacts, volcanic eruptions). A moderate amount (0.1%–1%) of CH4 significantly widens the parameter space region in which seasonal thaws are possible.

Comparative planetology – Comparing cirques on Mars and Earth using a CNN

New approaches for comparative planetology are vital to recognize and assess possible shared formative processes that shape landforms on different planetary bodies, and in the case of this study to identify possible cirques preserved from past martian climates that may have been more favorable to equatorial ice. We used “RetinaNet”, an augmented Convolutional Neural Network (CNN) initially trained with digital elevation data from over 1950 terrestrial cirques, to identify similar forms along a 50x50km area of the equatorial martian Dichotomy Boundary east of Gale Crater. A significant number of false positive detections associated with CTX stereo pair derived DEM artifacts and tile edges as well as craters were automatically removed. High confidence levels assigned by the machine learning algorithm suggest that the 16-remaining cirque-like forms may have formed and evolved under similar conditions to their terrestrial analogs. Morphometric data extracted for each of these cirque-like forms was statistically compared to terrestrial analog morphometric measures. While cirque length and width were significantly larger than their terrestrial counterparts and the area of these forms was ~150 % larger, on average headwall heights were ~25 % shorter. Allometric relationships suggest that the shape of these martian features changes proportionally as they grow in contrast to terrestrial forms where length increases faster than width and height. This could be due to the weaker gravitational force on Mars (3.721 m/s2) and other effects related to martian climate and environmental conditions, such as cold based glaciation. The identification of cirques in an equatorial region has implications for cryosphere distribution/redistribution and martian geologic and climatic history.

Mapping the Seismicity of Mars With InSight

AbstractThe InSight seismometers have recorded more than 1,300 events. Ninety‐eight of these, named the low‐frequency (LF) family, show energy predominantly below 1 Hz down to ∼0.1 Hz. The Marsquake Service identified seismic phases and computed distances for 42 of these marsquakes, 24 of which have backazimuths. Hence, the locations of the majority of LF family events remain undetermined. Here, we use an envelope shape similarity approach to determine event classes and distances, and introduce an alternative method to estimate the backazimuth. In our analysis, we use the highest quality marsquakes with known distances as templates, including the largest event S1222a, and assign new distances to similar group of events for which distance estimates were not previously available. We find the Tharsis region to be more active than initially perceived on the basis of 5 newly located events near Valles Marineris and Olympus Mons. We relocate two marsquakes with little or no S‐wave energy in the NE of the Elysium Bulge. The event epicenters in Cerberus Fossae follow a north‐south trend due to uncertainties in location, while the fault system is in the NW‐SE direction; therefore, these events are re‐projected along the observed fault system based on our interpretations. The marsquakes in our interpreted catalog are predominantly observed in the northern hemisphere of Mars above the equatorial dichotomy boundary.

Structure Along the Martian Dichotomy Constrained by Rayleigh and Love Waves and Their Overtones

AbstractUsing seismic recordings of event S1222a, we measure dispersion curves of Rayleigh and Love waves, including their first overtones, and invert these for shear velocity (VS) and radial anisotropic structure of the Martian crust. The crustal structure along the topographic dichotomy is characterized by a fairly uniform vertically polarized shear velocity (VSV) of 3.17 km/s between ∼5 and 30 km depth, compatible with the previous study by Kim et al. (2022), https://doi.org/10.1126/science.abq7157. Radial anisotropy as large as 12% (VSH > VSV) is required in the crust between 5 and 40 km depth. At greater depths, we observe a large discontinuity near 63 ± 10 km, below which VSV reaches 4.1 km/s. We interpret this velocity increase as the crust‐mantle boundary along the path. Combined gravimetric modeling suggests that the observed average crustal thickness favors the absence of large‐scale density differences across the topographic dichotomy.

Stratification of Heterogeneity in the Lithosphere of Mars From Envelope Modeling of Event S1222a and Near Impacts: Interpretation and Implications for Very‐High‐Frequency Events

AbstractWe have modeled the high‐frequency seismogram envelopes of the large event S1222a and four recently identified near impacts recorded by the InSight mission by introducing a stratification of velocity and attenuation into a multiple‐scattering approach. We show that a simple conceptual model composed of a strongly diffusive, weakly attenuating layer overlying a transparent medium captures the essential features of the observed envelopes. The attenuation profiles reveal that the minimal extension of heterogeneities at depth is of the order of 20 km in the vicinity of InSight and 60 km on the path to S1222a. We interpret this result as an indication that the Martian crust as a whole is at the origin of the strong scattering. Our heterogeneity model suggests that the sources of a number of distant Very‐high‐Frequency seismic events are shallow and located to the south or in close vicinity of the Martian dichotomy.

A new approach to retrieve total electron content based on dual-band echoes of MARSIS radar sounder

This paper proposes a new dual-band difference (DBD) method to retrieve total electron content (TEC) in Martian ionosphere with the dual-band echoes of the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS). It establishes the relationship between the group delay difference of two-band echoes and the plasmas frequency. Then the Martian ionospheric parameters are solved with this equation. Then the TEC is calculated by integrating the vertical distribution model of Mars electron density. This method is used to calculate the TEC of the typical ionosphere in the southern hemisphere of Mars, and the comparison with previous results validates this method. The experiments prove that this method can not only calculate the TEC of dayside and nightside in different periods, but also effectively eliminate the influence of ionospheric dispersion on radar echoes. Moreover, the time variation characteristics of the ionosphere are analyzed. According to the characteristics of this algorithm, the error sources are analyzed. By calculating the influence of different parameters on the results, it is proved that the maximum error of the algorithm is less than 0.1 TECU.

Investigating the feasibility of an impact-induced Martian Dichotomy

A giant impact is commonly thought to explain the dramatic contrast in elevation and crustal thickness between the two hemispheres of Mars known as the “Martian Dichotomy”. Initially, this scenario referred to an impact in the northern hemisphere that would lead to a huge impact basin (dubbed the “Borealis Basin”), while more recent work has instead suggested a hybrid origin that produces the Dichotomy through impact-induced crust-production. The majority of these studies have relied upon impact scaling-laws inaccurate at such large-scales, however, and those that have included realistic impact models have utilised over-simplified geophysical models and neglected any material strength. Here we use a large suite of strength-including smoothed-particle hydrodynamics (SPH) impact simulations coupled with a more sophisticated geophysical scheme of crust production and primordial crust to simultaneously investigate the feasibility of a giant impact on either hemisphere of Mars to have produced its dichotomous crust distribution, and utilise spherical harmonic analysis to identify the best-fitting cases. We find that the canonical Borealis-forming impact is not possible without both excessive crust production and strong antipodal effects not seen on Mars’ southern hemisphere today. Our results instead favour an impact and subsequent localised magma ocean in the southern hemisphere that results in a thicker crust than the north upon crystallisation. Specifically, our best-fitting cases suggest that the projectile responsible for the Dichotomy-forming event was of radius 500–750 km, and collided with Mars at an impact angle of 15–30° with a velocity of 1.2–1.4 times mutual escape speed (∼6–7 km/s).

A Positive Feedback Between Crustal Thickness and Melt Extraction for the Origin of the Martian Dichotomy.

A North/South difference in crustal thickness is likely at the origin of the Martian dichotomy in topography. Recent crustal thickness maps were obtained by inversion of topography and gravity data seismically anchored at the InSight station. On average, the Martian crust is 51-71km thick with a southern crust thicker by 18-28km than the northern one. The origin of this crustal dichotomy is still debated although the hypothesis of a large impact is at present very popular. Here, we propose a new mechanism for the formation of this dichotomy that involves a positive feedback between crustal growth and mantle melting. As the crust is enriched in heat-producing elements, the lid of a one-plate planet is hotter and thinner where the crust is thicker, inducing a larger amount of partial melt below the lid and hence a larger rate of melt extraction and crustal growth. We first demonstrate analytically that larger wavelength perturbations, that is, hemispherical perturbations, grow faster because smaller wavelengths are more attenuated by thermal diffusion. We then use a parameterized thermal evolution model with a well-mixed mantle topped by two different lids characterized by their thermal structures and thicknesses to study the growth of the crust in the two hemispheres. Our results demonstrate that this positive feedback can generate a significant crustal dichotomy.

Impact craters and the observability of ancient martian shorelines

The existence of possible early oceans in the northern hemisphere of Mars has been researched and debated for decades. The nature of the early martian climate is still somewhat mysterious, but evidence for one or more early oceans implies long-lasting periods of habitability. The primary evidence supporting early oceans is a set of proposed remnant shorelines circling large fractions of the planet. The primary features are thought to be older than 3.6 Ga and possibly as old as 4 Ga, which would make them some of the oldest large-scale features still identifiable on the surface of Mars. One question that has not been thoroughly addressed, however, is whether shorelines this old could survive modification and destruction processes like impact craters, tectonics, volcanism, and hydrology in recognizable form. Here we address one of these processes—impact cratering—in detail. We use standard crater counting age models to generate synthetic, global populations of craters and intersect them with hypothetical shorelines, tracking portions of the hypothetical shoreline that are directly impacted. The oldest shorelines (≥4 Ga) are at least 70 % destroyed by direct impacts. Shorelines of any age >3.6 Ga are dissected into relatively short, discontinuous segments no larger than about 40 km when including the effects of craters larger than 100 m in radius. When craters smaller than 500 m in radius are excluded, surviving segment lengths can be as large as ∼1000 km. The oldest shorelines exhibit fractal structure after impacts, presenting as a discontinuous collection of features over a range of scales. If the features are truly shorelines, high-resolution studies should find similar levels of destruction and discontinuity. However, our results indicate that observing shorelines as old as 4 Ga, should they exist, is a significant challenge and raises questions about prior mapping efforts.

Early crustal processes revealed by the ejection site of the oldest martian meteorite

The formation and differentiation of the crust of Mars in the first tens of millions of years after its accretion can only be deciphered from incredibly limited records. The martian breccia NWA 7034 and its paired stones is one of them. This meteorite contains the oldest martian igneous material ever dated: ~4.5 Ga old. However, its source and geological context have so far remained unknown. Here, we show that the meteorite was ejected 5–10 Ma ago from the north-east of the Terra Cimmeria—Sirenum province, in the southern hemisphere of Mars. More specifically, the breccia belongs to the ejecta deposits of the Khujirt crater formed 1.5 Ga ago, and it was ejected as a result of the formation of the Karratha crater 5–10 Ma ago. Our findings demonstrate that the Terra Cimmeria—Sirenum province is a relic of the differentiated primordial martian crust, formed shortly after the accretion of the planet, and that it constitutes a unique record of early crustal processes. This province is an ideal landing site for future missions aiming to unravel the first tens of millions of years of the history of Mars and, by extension, of all terrestrial planets, including the Earth.

Seismic sources of InSight marsquakes and seismotectonic context of Elysium Planitia, Mars

Since early 2019, the InSight mission has proven that Mars is seismically active, with more than 900 seismic events recorded. Among them, several events have characteristics close to terrestrial tectonic earthquakes. Most of these events are located on the major graben system of Cerberus fossae and, a little further north, on the secondary system of Grjotá Valles. In this study, we invert the seismic moment tensors for nine of these tectonic marsquakes characterized by high quality data. Seven of them are located on Cerberus fossae/Grjotá Valles and two of them are located near the Martian dichotomy. The moment tensors allow us to interpret the nature and depth of the seismic sources at the origin of these events. In our approach, we invert the P and S body waveforms, the PP, SS, PPP and SSS secondary phase maximum amplitudes and we look for solutions with surface waves weaker than the Martian noise. From our results on moment tensors, we determine that all our events have been triggered at moderate depths of 15–36km. We deduce that the seven events located on Cerberus fossae have geometries similar to the fractures and are generated by tectonics. This activity is supposed to result from the reactivation of previous faults and fractures, which would have been initially induced by the propagation of volcanic dikes at depth. The two dichotomy events are due to deep compressive fracturing of the Martian lowlands. They are therefore triggered by the planetary thermal contraction. Our results are in strong agreement with recent studies on the event depths and on the previous moment tensors calculated for two events.

Alkali magmatism on Mars: an unexpected diversity

Despite an apparent north/south topographic dichotomy that formed >4.0 Ga, the young Martian meteorites (<2.4 Ga) and first-order remote sensing observations revealed a surface of Mars that is uniformly basaltic. This simplistic vision has been challenged by the discovery of a brecciated meteorite and additional spacecraft data that all point to the presence of alkaline igneous rocks, thereby demonstrating an unexpected igneous diversity on Mars. In the present paper, we review a variety of effusive alkaline rocks (basalts to trachytes) recognized so far in the southern hemisphere of Mars as observed from a unique 4.47 Ga Martian meteorite, as well as ground, and orbital data. The complementary of effusive alkaline rocks and plutonic orthopyroxene-rich rocks in early Mars is discussed. We propose that mantle-derived magmas at high extent of melting at rather low pressure either erupted forming orthopyroxene-rich lavas, or crystallized at shallow crustal depths, fractionating orthopyroxene which sank to the bottom of the chamber and residual alkaline magmas which erupted at the surface of Mars. Widespread low pressure fractionation processes could also be related to heavy bombardment on the early Martian crust generating melt sheets that ultimately differentiated. The Noachian crust is more diverse than being merely basaltic.

Rheological and Mechanical Layering of the Crust Underneath Thumbprint Terrains in Arcadia Planitia, Mars

AbstractIn the area of Arcadia Planitia in the Northern hemisphere of Mars, mounds indicating fluid and sediment emissions have been already recognized. Here, we show that through fractal and fracture‐spacing analyses of a large vent population it is possible to infer the mechanical layering of the underlying subsurface. Our work includes the mapping of an entire population of 9,028 vents over an area of 122,000 km2. The analysis of mound distribution at the surface led to the formulation of inferences about the subsurface feeding conduits, and to the identification of three mechanical discontinuities at c. 4–5, c. 14–23, and c. 50–55 km. This evidence matches the mechanical stratigraphy recorded by the InSight NASA mission, and is in agreement with independent previous subsurface global modeling, supporting our conclusions.

Paleointensity and Rock Magnetism of Martian Nakhlite Meteorite Miller Range 03346: Evidence for Intense Small‐Scale Crustal Magnetization on Mars

AbstractThe martian dynamo’s strength and duration are essential for understanding Mars' habitability and deep interior dynamics. Although most northern volcanic terranes were likely emplaced after the martian dynamo ceased, recent data from the InSight mission show stronger than predicted crustal fields. Studying young volcanic martian meteorites offers a precise, complementary method to characterize the strength of the martian crustal field and examine its implications for past dynamo activity. We present the first rock and paleomagnetic study of nine mutually oriented samples from the martian Nakhlite meteorite Miller Range (MIL) 03346, which is well‐suited for paleomagnetic analysis due to its well‐known age (1,368 ± 83 Ma) and lack of significant aqueous, thermal, and shock overprinting. Rock magnetic analysis, including quantum diamond microscope imaging, showed that the natural remanent magnetization (NRM) is carried by Ti‐magnetite crystals containing µm‐scale ilmenite exsolution lamellae, which can accurately record ancient magnetic fields. Demagnetization of the NRM revealed a high coercivity magnetization interpreted to date from the age of eruption based on its intensity, unidirectionality, and a passing fusion crust baked contact test. Paleointensities of four samples reveal a 5.1 ± 1.5 µT paleofield, representing the most reliable martian paleointensity estimates to‐date and stronger than the 2 µT surface fields measured by InSight. Modeling shows that the observed fields can be explained by an older subsurface magnetized layer without a late, active dynamo and support a deeply buried, highly magnetized crust in the northern hemisphere of Mars. These results provide corroborating evidence for strong, small‐scale crustal fields on Mars.

Oceans, Lakes, and Stromatolites on Mars

Billions of years ago, the Northern Hemisphere of Mars may have been covered by at least one ocean and thousands of lakes and rivers. These findings, based initially on telescopic observations and images by the Mariner and Viking missions, led investigators to hypothesize that stromatolite fashioning cyanobacteria may have proliferated in the surface waters, and life may have been successfully transferred between Earth and Mars via tons of debris ejected into the space following bolide impact. Studies conducted by NASA’s robotic rovers also indicate that Mars was wet and habitable and may have been inhabited in the ancient past. It has been hypothesized that Mars subsequently lost its magnetic field, oceans, and atmosphere when bolides negatively impacted its geodynamo and that the remnants of the Martian seas began to evaporate and became frozen beneath the surface. As reviewed here, twenty-five investigators have published evidence of Martian sedimentary structures that resemble microbial mats and stromatolites, which may have been constructed billions of years ago on ancient lake shores and in receding bodies of water, although if these formations are abiotic or biotic is unknown. These findings parallel the construction of the first stromatolites on Earth. The evidence reviewed here does not prove but supports the hypothesis that ancient Mars had oceans (as well as lakes) and was habitable and inhabited, and life may have been transferred between Earth and Mars billions of years ago due to powerful solar winds and life-bearing ejecta propelled into the space following the bolide impact.

Baroclinic waves in the northern hemisphere of Mars as observed by the MRO Mars Climate Sounder and the MGS Thermal Emission Spectrometer

The climatology of baroclinic waves in the northern hemisphere of Mars is investigated through analysis of observations by the infrared sounders on Mars Reconnaissance Orbiter (MRO) and Mars Global Surveyor (MGS). We focus on the lowest scale height above the surface, where the waves have a large impact on the Martian dust cycle. Profiles retrieved by the MRO Mars Climate Sounder (MCS) rarely reach the lower atmosphere at the season and location of interest. To fill this gap, we turn to observations in the MCS B1 channel (32 μm) when the instrument is viewing the surface. The signature of baroclinic waves appears in these data because of dust-related emission from the lower atmosphere and wave-induced variations of surface temperature. We supplement the MCS data with measurements of temperature at the 610-Pa pressure level from the MGS Thermal Emission Spectrometer (TES). Both data sets provide systematic coverage in latitude and longitude at two local times. Characteristics of baroclinic waves are derived through analysis of observations with a combined duration of about 8 Mars years. Basic results include least-squares solutions for wave amplitude and period at zonal wavenumber 1–3; the resolution is 4∘ in latitude and 14 solar days in time of observation. There is a strong similarity between the baroclinic waves observed by MCS and TES, which confirms the sensitivity of the MCS B1 channel to wave activity at pressures near 610 Pa. In all 8 Mars years, the baroclinic waves exhibit periodic transitions among modes with different zonal wavenumbers and a distinctive solstitial pause. Although the weather in each Mars year is unique in some respects, a composite of results from all years reveals a well-defined wave climatology. At each zonal wavenumber, large amplitudes are restricted to a pair of seasonal windows positioned symmetrically about the winter solstice. The wave-2 mode is strongest in early autumn and near the vernal equinox, whereas wave 3 is the dominant mode in mid-autumn and mid-winter, immediately before and after the solstitial pause. The interaction between baroclinic waves and dust storms is investigated through comparisons with spacecraft measurements of dust opacity. A strong wave-3 mode is often present during the initial growth phase of large, seasonal dust storms, which reflects the importance of wave-generated frontal dust storms in triggering these events. The wave-3 amplitude then decreases rapidly as the dust storm evolves; this occurs routinely in all Mars years considered here in connection with both mid-autumn “A” storms and mid-winter “C” storms. In some years A-storm suppression of the wave-3 mode marks the beginning of the solstitial pause. These results provide a basis for testing and development of Mars General Circulation Models as well as context for interpreting contemporaneous observations, such as spacecraft images of frontal and flushing dust storms.

Did Martian valley networks substantially modify the landscape?

Valley networks are ancient drainage systems incised on the southern hemisphere of Mars, and stand as evidence that liquid water once sculpted its surface. The duration of valley network activity and the sources of water are key questions in deciphering the timing of water stability on early Mars, but remain poorly constrained. In this study we address two questions: Did Martian valley networks evolve for sufficiently long to establish their own erosional basins, or do their profiles primarily reflect landscape pre-incision topography? And were these valleys precipitation-fed or spring-fed? Our analysis uses the theoretical framework built to describe the shape of steady-state river profiles on Earth to compare and analyze the concavity of 62 valley network longitudinal profiles on Mars. Using non-linear fits to valley profiles we evaluate the degree to which valley networks are consistent with fluvial steady-state. The fit enables the identification of valley network concavity index and area-discharge exponent, which we then interpret in terms of the theoretical framework to discuss valley network maturity and water source. Our results show that the majority of valley networks do not have concave or even smooth profiles, and did not substantially modify their surrounding landscape. We observe disparity in concavity indexes of valley networks belonging in the same integrated basins, indicating different stages of landscape evolution and lack of synchronous valley development. However, our results identify six valley networks consistent with fluvial steady-state and areally uniform precipitation.

Reconstructing paleolakes in Nepenthes Mensae, Mars, using the distribution of putative deltas, coastal-like features, and terrestrial analogs

Nepenthes Mensae is an equatorial region situated north of the Martian dichotomy, northwest of Gale crater. It is characterized by a NW-SE-oriented belt of interconnected depressions, Late Noachian to Early Hesperian in age, with knobby terrains with residual relief. The highlands south of Nepenthes Mensae, Middle Noachian in age, correspond to the Licus Vallis region, which is dissected by drainage networks with valley mouths located along the dichotomy boundary scarp. This work presents a detailed geomorphological analysis of ten fan-shaped and fifty-four coastal-like benches identified in Nepenthes Mensae. The combination of detailed mapping, morphological and morphometric analyses, spatial-altitudinal distribution relationships, crater counting, spectral analysis, and comparison with terrestrial analogs suggest that (1) the fan-shaped and coastal-like benches are likely putative Gilbert-type deltas and paleoshore platforms, respectively, and (2) these features may be attributable to paleoshorelines developed along the margins of an ancient inner sea or interconnected paleolakes. These findings reveal the important morphogenetic role that liquid water played in the evolution of Nepenthes Mensae and Licus Vallis regions during the Late Noachian-Early Hesperian transition, and contribute to contextualize the continuous findings on the environmental and climatic conditions of the nearby Gale crater during such time period.