Valles Marineris Research Articles

Landform evolution of Oudemans crater and its bounding plateau plains on Mars: Geomorphological constraints on the Tharsis ice-cap hypothesis

In this study we address the question of whether the Tharsis rise that occupies ~25 % of the surface area of Mars was once covered by an ice cap, and the sudden ice-cap melting was responsible for the catastrophic development of the Late Hesperian (3.5-3.6 Ga) circum-Tharsis giant (>1000s km in length) outflow channels. To achieve this goal, we conducted geomorphologic mapping across the Oudemans crater basin (~125 km in diameter) at elevations of ~2.7 km to ~5.0 km and its bounding plateau plains at elevations of ~5.3 km to ~6.7 km in the central Tharsis rise. Our work shows that the Oudemans-impact-induced landforms were superposed by a suite of younger landform assemblages, which consist of horn-like peaks, arête-like ridges, cirque-like depressions, hanging-valley-like features, trim-line-like escarpments, lobate ridges, striated, pitted and hummocky terrains, and features resembling drumlins, crag-and-tails and roches moutonnées. A plateau-plain striated terrain on a hummocky surface exhibits streamlined linear ridges that are 400-2000 m wide and up to ~17 km long. The average length-width ratio (~9), shape, surface texture, and associated washboard landform pattern of the linear morphological features in the striated terrain on Mars are comparable to mega-scale glacial lineations (MSGLs) on Earth. Using well-understood Earth analogues as a guide, we interpret the post-Oudemans-impact landform assemblages to have formed during regional ice-sheet-style glaciation. We further suggest the striated terrain on the plateau plains to have been generated by a fast-moving ice stream in a regional ice sheet that filled 4-km deep Oudemans crater and covered the crater-bounding plateau plains in the central Tharsis rise. The volume of the glacier ice stored in the Oudemans crater basin alone is estimated on the order of ~200,000 km3. The shape of the inferred glacier-induced landforms and their cross-cutting relationships require early northward-flowing northward-advancing glaciation, followed by southward-flowing northward-retreating glaciation. The size-frequency distribution of the craters superposed on top of the interpreted glaciated landforms in the mapped area yields a glaciation age of ca. 3.5 Ga, coeval with the estimated age of the interpreted glacial landforms along the 2000-km long Valles Marineris trough zone east of the study area. The inferred glaciation age is also coeval with the development of the circum-Tharsis outflow channels. Although our work supports the Tharsis ice-cap hypothesis, the full extent of the ice cap within and possibly beyond the Tharsis rise remains unconstrained.

Insights into Mars mud volcanism using visible and near-infrared spectroscopy

Mud volcanism (MV) has been a proposed formation mechanism for positive-relief landforms in the lowland, equatorial, and highland regions of Mars. While visible and near-infrared (VNIR) spectroscopy has been used in a few cases to argue for the presence of MV on the surface of Mars, data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) remain underutilized. We conducted a global examination of proposed Mars MV features using CRISM VNIR data. We observe variable hydration states and place constraints on the composition of these features from orbit. We do not confidently identify phyllosilicates, carbonates, or sulfates associated with suggested Martian mud volcanoes. However, specific structures in Valles Marineris exhibit VNIR signatures consistent with unaltered hydrated glass of a volcanic origin and high-Ca pyroxene. CRISM visible data from MV features reveal consistent nanophase ferric oxide signatures on a global scale, although these signatures are not unique to Mars MV materials. Limitations in specific mineral detection are likely due to the fine grain size and/or textural characteristics of putative MV features. While we do not argue in favor of a specific proposed MV site in the context of future robotic or human missions, the insights of this study could be used as a guide for Mars surface exploration.

Tectono‐Magmatic, Sedimentary, and Hydrothermal History of Arsinoes and Pyrrhae Chaos, Mars

AbstractArsinoes and Pyrrhae Chaos are two adjacent chaotic terrains located east of Valles Marineris and west of Arabia Terra, on Mars. In this work, we produced a morpho‐stratigraphic map of the area, characterized by a volcanic bedrock disrupted into polygonal mesas and knobs (Chaotic Terrain Unit) and two nondisrupted units. The latter present a spectral variation, likely associated with hydrated minerals, and they are here interpreted as sedimentary units. The reconstructed geological history of the area starts with the emplacement of the basaltic bedrock, followed by the collapse that caused the formation of the chaotic terrains. Since evidences of volcano‐tectonic activity are widespread across the area (e.g., fissure vents/graben, radial and concentric systems of faults, y‐shaped conjunctions, lava flows, and pit chains), and an intricate system of lava conduits is hypothesized for the occurrence of such features, we propose the possibility that the whole collapse was caused primarily by volcano‐tectonic processes. In a late stage, after the end of the volcano‐tectonic activity, a lacustrine/evaporitic depositional environment could have set, with the deposition of the nondisrupted units. The hydrated minerals found in the periphery of the Chaos could be the result of hydrothermal alteration of the basaltic bedrock.

Ancient Martian Aeolian Sand Dune Deposits Recorded in the Stratigraphy of Valles Marineris and Implications for Past Climates

AbstractAeolian sediment transport, deposition, and erosion have been ongoing throughout Mars's history. This record of widespread aeolian processes is preserved in landforms and geologic units that retain important clues about past environmental conditions including wind patterns. In this study we describe landforms within Melas Chasma, Valles Marineris, that occur in distinct groups with linear to crescentic shapes, arranged with a characteristic wavelength; some possess slope profiles analogous to modern sand dunes yet show evidence for lithification. Based on the features' dimensions, asymmetry, and spatial patterns relative to modern equivalents, we interpret these landforms to be two classes of aeolian bedforms: decameter‐scale megaripples and sand dunes. The presence of superposed erosional features and depositional units indicates that these landforms were cemented and likely ancient. Melas paleodunes are found atop Hesperian‐aged layered deposits, but we estimate them to be younger, likely lithified in the Amazonian period. Although a range of degradation was observed, some paleodunes are >10 m tall and maintain steep lee sides (>25°), an uncommon scenario for terrestrial examples as other geologic processes lead to dune obliteration. The preserved paleobedform geometries are largely consistent with those of modern aeolian indicators, suggesting no major shifts in wind regime or contributing boundary conditions. Finally, we propose that their appearance and context require sequential periods of dune migration, stabilization following catastrophic burial, cementation, differential erosion, exposure, and burial. The presence of wholly preserved duneforms appears to be more common on Mars compared to the Earth and may signal something important about Martian landscape evolution.

The Mars Dust Activity Database (MDAD): A comprehensive statistical study of dust storm sequences

A comprehensive Mars Dust Activity Database (MDAD) over 8 Mars years (MY 24, Ls = 150°to MY 32, Ls = 171°) is compiled from Mars Daily Global Maps. A total of 14,974 dust storm instances are cataloged with area >105 km2 that are visually distinguishable from the surface. A dust storm instance is identified as a dust storm member over multiple sols if storm movement can be tracked. Dust storm sequences are collections of members that have a coherent trajectory from their origination areas over three or more sols. There are 228 sequences, with 125 originating in the northern hemisphere. Sequences primarily originate in Acidalia, Utopia, and Arcadia Planitiae in the northern hemisphere and Aonia–Solis–Valles Marineris and Hellas Basin in the southern hemisphere. Many northern hemisphere originating sequences flush into the southern hemisphere. The primary season for non-global dust events occurs during Ls = 140°– 250°, with secondary seasons in Ls = 300°– 360°in the northern hemisphere and Ls = 10°– 70°in the southern hemisphere. Sequences are classified into three types. Main Member sequences have one dominant member; Continuous Development sequences have many smaller members; and Sequential Redevelopment sequences have repeating, medium-sized members. “Major” sequences have a maximum area >107 km2, influence the zonal-mean global opacity, and exhibit flushing behavior. Major sequences occur over a narrower temporal range and are distinguished from other sequences by the larger size and duration distributions of their constituent members. Major sequences have unique antecedent conditions, with steadily increasing dust storm area in the 6 preceding sols that is significantly distinct from conditions preceding minor sequences.

Spatiotemporal evolution, mineralogical composition, and transport mechanisms of long-runout landslides in Valles Marineris, Mars

Long-runout landslides with transport distances of >50 km are ubiquitous in Valles Marineris (VM), yet the transport mechanisms remain poorly understood. Four decades of studies reveal significant variation in landslide morphology and emplacement age, but how these variations are related to landslide transport mechanisms is not clear. In this study, we address this question by conducting systematic geological mapping and compositional analysis of VM long-runout landslides using high-resolution Mars Reconnaissance Orbiter imagery and spectral data. Our work shows that: (1) a two-zone morphological division (i.e., an inner zone characterized by rotated blocks and an outer zone expressed by a thin sheet with a nearly flat surface) characterizes all major VM landslides; (2) landslide mobility is broadly dependent on landslide mass; and (3) the maximum width of the outer zone and its transport distance are inversely related to the basal friction that was estimated from the surface slope angle of the outer zone. Our comprehensive Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) compositional analysis indicates that hydrated silicates are common in landslide outer zones and nearby trough-floor deposits. Furthermore, outer zones containing hydrated minerals are sometimes associated with longer runout and increased lateral spreading compared to those without detectable hydrated minerals. Finally, with one exception we find that hydrated minerals are absent in the inner zones of the investigated VM landslides. These results as whole suggest that hydrated minerals may have contributed to the magnitude of lateral spreading and long-distance forward transport of major VM landslides.

Craters in the vicinity of Valles Marineris region, Mars: Chronological implications to the graben and pits activities

Graben and pits are features closely associated with the Valles Marineris (VM) region on Mars. Earlier studies indicated that they are likely precursors for the VM trough formation, and thus they may assist in our understanding of how long the trough formation prevailed in the vicinity of VM. This study aims to understand how the graben and pit formation varied chronologically and spatially within a ~100 km vicinity of the VM region. We examined 1516 craters and found 48 craters that are superposed/cross-cut by graben, pits, and troughs or vice-versa with adequate ejecta or floor area for dating. Tithonium region graben and troughs cross-cut the craters around ~3.7 Ga. In the Ophir region, pits are formed on or post ~3.92 Ga at different elevations and have variable depths. Pital crater in the Ophir region interestingly hosts: 1) a broad catena ~14 km wide crosscutting its NE rim likely formed on or post to ~2.61 Ga, which inferred to be one-tenth to the adjoining Candor Chasma width of VM, 2) lobe like deposits associated with the catena emplaced over the Pital ejecta formed around ~1.14 Ga and 3) ~2 km wide pit superposed the lobe that reveals pit activity plausibly prolonged during Mid-Amazonian. Overall, our results likely point towards the contribution of graben and pits in the modification/development of peripheral areas of VM up to at least Mid-Amazonian. Thus, this study substantiated that the period and extent of graben and pit activities varied around the VM region.

Variations in Martian Lithospheric Strength Based on Gravity/Topography Analysis

AbstractWe applied localized gravity/topography admittance and correlation analysis, as well as the Markov chain Monte Carlo method, to invert for loading and flexural parameters of 21 subregions on Mars with five distinct tectonic types. The loading styles of the five tectonic types are distinct: The surface and subsurface loading in the polar and plain regions can be assumed to be largely uncorrelated, in contrast to the correlated loading associated with the volcanic montes and Valles Marineris. For the impact basins, we consider the initial topographic depression and mantle plug before postimpact surface loading. Our analyses yield four main results: (1) The inverted effective lithospheric thickness (Te) is highly dependent on assumptions of loading type. (2) There is a trend of increasing Te from the Noachian southern highlands (20–60 km) to the Hesperian northern lowlands (>90 km) and from the Hesperian Elysium Mons (<55 km) to the Hesperian/Amazonian Olympus Mons (>105 km). These Te estimates are consistent with the thermal states at the time of loading, corresponding to a global secular cooling history with decreasing heat flux. (3) Our analyses suggest high‐density basaltic surface loading at the volcanic montes and Isidis basin, in contrast to the low‐density sedimentary surface loading at the Utopia and Argyre basins. (4) We find some degree of correlation between the surface and subsurface loading for the northern polar cap and the northern plains, likely due to earlier, larger polar deposits and ancient buried features, respectively.

The Tsiolkovskiy crater landslide, the moon: An LROC view

Evidence suggests that the lobate flow feature that extends ~72 km outward from the western rim of Tsiolkovskiy crater is a long runout landslide. This landslide exhibits three (possibly four) morphologically different parts, likely caused by local conditions. All of these, plus the ejecta of Tsiolkovskiy crater, and its mare fill are approximately of the same crater model age, i.e., ~3.55 ± 0.1 Ga. The enormous size of this landslide is unique on the Moon and is a result of a combination of several geometric factors (e.g., its location relative to Fermi crater), and that Tsiolkovskiy crater was an oblique impact that produced an ejecta forbidden zone on its western side (Schultz, 1976). The landslide formed in this ejecta free zone as the rim of Tsiolkovskiy collapsed and its debris flowed across the relatively smooth, flat floor of Fermi crater. In this location, it could be easily identified as a landslide and not ejecta. Its mobility and coefficient of friction are similar to landslides in Valles Marineris on Mars, but less than wet or even dry terrestrial natural flows. This suggests that the Mars landslides may have been emplaced dry. The high density of small craters on the landslide is likely an illusion caused by the effects of age related differences in regolith thickness on crater morphology, and the presence of the abundant young, circular secondary craters produce by debris ejected from distant fresh craters.

Evaluation of wet and dry recurring slope lineae (RSL) formation mechanisms based on quantitative mapping of RSL in Garni Crater, Valles Marineris, Mars

Recurring slope lineae (RSL) are narrow (0.5–5 m) low-albedo features that incrementally lengthen down steep slopes during warm seasons, fade in colder seasons, and recur each Mars year. To reduce the effort involved in manually mapping and analyzing each RSL in Garni crater, we developed Mapping and Automated Analysis of RSL (MAARSL) to analyze a set of orthorectified High Resolution Imaging Science Experiment (HiRISE) images and a digital elevation map. MAARSL along with manual mapping allowed us to detect RSL, compute descriptive statistics, and characterize changes over time. We mapped 2910 RSL in 22 orthoimages, from Mars Year (MY) 31 solar longitude (Ls) 133.0° to MY32 Ls 323.7°. The MAARSL results confirmed that RSL lengthening and fading occur concurrently on slopes with the same orientation and many times within some individual RSL. Slope angles of RSL and a slope slump show that some RSL start, stop, and have mean slope angles that are below the angle of repose. Our analysis shows that RSL are actively lengthening on at least one slope-facing direction in all HiRISE observations of the crater. We also found that NE-, N-, and NW-facing RSL in Garni crater lengthened during times of increasing shortwave insolation, while S- and SW-facing RSL lengthened during increasing and decreasing shortwave insolation. A (non-orthorectified) HiRISE image acquired shortly after the MY34 dust storm and shows RSL on every slope-facing direction, which is anomalous with respect to observations prior to the dust storm.We find that dust removal and deposition could explain the darkening and fading (respectively) of RSL, and could also explain the apparent lack of material being transported. Observations of RSL lengthening and fading occur concurrently on slopes could suggest overprinting of dry granular flows. Dry flows could also explain the significant lengthening activity of every slope-facing direction after a fresh layer of dust was deposited via the MY34 dust storm. Alternatively, briny shallow subsurface flows are consistent with observations of RSL on slopes below the angle of repose and those that exhibit concurrent lengthening and fading. However, the most significant problem with briny RSL flows is accessing a source of briny water and removing excess salt from the regolith.

Mapping Mars’s Eastern Valles Marineris

Abstract. The purpose of this mapping project was to create a cartographically accurate representation of an Exploration Zone at the Eastern Valles Marineris outflow region within equatorial Mars. There are numerous problems associated with mapping planetary surfaces. Data and imagery for Exploration Zones at a spatial and spectral resolution sufficient for human landing site evaluation and traverse planning have not been acquired yet. Additionally, as technology evolves, it is very difficult to extrapolate which mapping technologies will be used in the near and far future. In order to create this map, assumptions about the future of mapping had to be made, publicly released data for the area of interest had to be sourced, and data analysis had to be performed. One of the key elements of a successful mission is how to communicate the geospatial aspects of the mission planning process to the general public. The results show that using existing data and traditional static cartographic methods, even extra-terrestrial geographic discoveries can be made and disseminated to the public in an attractive and easily understood format.

Nonhydrostatic Stress State in the Martian Interior for Different Rheological Models

We perform the analysis of nonhydrostatic stress field in the Martian interior for two types of heterogeneous elastic models: the ones with a lithosphere and the ones with a lithosphere and probable melting zones within it. Numerical modeling of the system of elastic equilibrium equations for a gravitating planet is carried out on a 1x1 arc degree spherical grid down to a depth of 1000 km. The boundary conditions are specified by the topography and gravity field data determined relative to a hydrostatic equilibrium spheroid taken as a reference surface. High maximum shear stresses in the zones of high tensile stresses are assumed as the criterion for selecting the probable marsquake sources. Irrespective of the type of a rheological model, the zones of the high shear and tensile stresses in the crust and mantle of Mars arc revealed beneath Hellas Planitia, Argyre Planitia, Mare Acidalia, Arcadia Planitia plain, and Valles Marineris.

Tectonic evolution of Juventae Chasma, Mars, and the deformational and depositional structural attributes of the four major light-toned rock exposures therein

Juventae Chasma, a canyon peripheral to the Valles Marineris trough system, is the product of a unique merger of a Martian chaotic terrain depression and an extensional (tectonic) chasm. The chaotic terrain portion is set along a NNE-SSW axis, while a linear trough (the chasm component) is present along a WNW-ESE axis. Within the chasm are four discrete bodies of layered, light-toned rocks of sedimentary origin, Features A–D. The chaotic terrain component formed during the Early Hesperian as a result of expulsion of liquid water along pre-existing planes of weaknesses resulting from a WNW-ENE compression. The chasm component formed in response to NE-SW extension during the Middle to Late Amazonian. The light-toned Features A–D are layered at <2 m scale. A dark-toned material, previously interpreted as interstratified with the light-toned layers, is a secondary accumulation deposited after the light-toned rocks were lithified and exposed at the Martian surface. The bedding configurations within Features A, C, and D indicate eolian sand deposition; whereas a lacustrine or low-energy eolian origin is more fitting for Feature B. Features A–D also record Early Hesperian compressional events in the form of joints. Bedding joints, formed in response to release of an overburden, are also found. In addition, closed, elliptical outcrop patterns of inward dipping layers are also identified; these are either folds (structural basins) or erosional surfaces cutting three-dimensional eolian cross-beds.

Navigation and communication network for the Valles Marineris Explorer (VaMEx)

With recent advances in robotics and space technology for the exploration of our Solar System, innovative mission concepts are being proposed to further extend our knowledge of our neighbouring planets and their satellites. VaMEx, abbreviation for Valles Marineris Explorer, is an example of such an initiative. VaMEx aims to survey the canyons of the Valles Marineris, for the duration of one year. A cluster of robotic elements is tasked with the planetary exploration activities. Due to the hazardous environment, it is required that these elements navigate autonomously, broadcast position information and exchange science data during the operational phase of the mission. To support these functions, a VaMEx space segment composed of one (or more) orbiter satellite(s) is proposed. Three possible swarm localization schemes were investigated: 1) radio positioning, 2) cartographic triangulation of ground features from optical images and 3) cartographic triangulation of radar persistent scatters. For each of the proposed navigation concepts, a suitable orbit constellation solution was assessed. Each solution was evaluated in terms of orbit stability, control effort and communications performance using metrics specific to each of the three concepts (length of pass, visibility gaps, geometry constraints, etc.). With the described navigation concept and mission analysis results, a preliminary operational architecture for the VaMEx space segment is conceived, taking into account existing technologies, communications performance, overall mission complexity and feasibility.

Deep-seated gravitational slope deformation scaling on Mars and Earth: same fate for different initial conditions and structural evolutions

Abstract. Some of the most spectacular instances of deep-seated gravitational slope deformation (DSGSD) are found on Mars in the Valles Marineris region. They provide an excellent opportunity to study DSGSD phenomenology using a scaling approach. The topography of selected DSGSD scarps in Valles Marineris and in the Tatra Mountains is investigated after their likely similar postglacial origin is established. The deformed Martian ridges are larger than the deformed terrestrial ridges by 1 to 2 orders of magnitude with, however, a similar height-to-width ratio of ∼0.24. The measured horizontal spreading perpendicular to the ridges is proportionally 1.8 to 2.6 times larger for the Valles Marineris ridges than the Tatra Mountains and vertically 2.9 to 5.1 times larger, suggesting that starting from two different initial conditions, with steeper slopes in Valles Marineris, the final ridge geometry is now similar. Because DSGSD is expected to now be inactive in both regions, their comparison suggests that whatever the initial ridge morphology, DSGSD proceeds until a mature profile is attained. Fault displacements are therefore much larger on Mars. The large offsets imply reactivation of the DSGSD fault scarps in Valles Marineris, whereas single seismic events would be enough to generate DSGSD fault scarps in the Tatra Mountains. The required longer activity of the Martian faults may be correlated with a long succession of climate cycles generated by the unstable Martian obliquity.

A deep groundwater origin for recurring slope lineae on Mars.

The recurring slope lineae on Mars have been hypothesized to originate from snow melting, deliquescence, dry flow or shallow groundwater. Except for the dry flow origin, these hypotheses imply the presence of surficial or near-surface volatiles, placing the exploration and characterization of potential habitable environments within the reach of existing technology. Here we present observations from the High Resolution Imaging Science Experiment, heat-flow modelling and terrestrial analogues, which indicate that the source of recurring slope lineae could be natural discharge along geological structures from briny aquifers within the cryosphere, at depths of approximately 750 m. Spatial correlation between recurring slope lineae source regions and multi-scale fractures (such as joints and faults) in the southern mid-latitudes and in Valles Marineris suggests that recurring slope lineae preferably emanate from tectonic and impact-related fractures. We suggest that deep groundwater occasionally surfaces on Mars in present-day conditions. Observations and heat-flow modelling suggest that briny groundwater surfacing from fractures forms recurring slope lineae on Mars.

The distribution, composition, and particle properties of Mars mesospheric aerosols: An analysis of CRISM visible/near-IR limb spectra with context from near-coincident MCS and MARCI observations

The Compact Reconnaissance Imaging Spectral Mapper (CRISM) onboard the Mars Reconnaissance Orbiter (MRO) obtains pole-to-pole observations (i.e., full MRO orbits) of vertical profiles for visible/near-IR spectra (λ= 0.4–4.0 μm), which are ideally suited to identifying the composition and particle sizes of Mars ice and dust aerosols over 50–100 km altitudes in the Mars mesosphere. Within the coverage limitations of the CRISM limb data set, a distinct compositional dichotomy is found in Mars mesospheric ice aerosols. CO2 ice clouds appear during the aphelion period of Mars orbit (Solar Longitudes, Ls ∼ 0–160°) at low latitudes (∼20S–10N) over specific longitude regions (Meridiani, Valles Marineris) and at typical altitudes of 55–75 km. Apart from faint water ice hazes below 55 km, mesospheric H2O ice clouds are primarily restricted to the perihelion orbital range (Ls∼160 – 350°) at northern and southern mid-to-low latitudes with less apparent longitudinal dependences. Mars mesospheric CO2 clouds are presented in CRISM spectra with a surprisingly large range of particle sizes (cross section weighted radii, Reff = 0.3 to 2.2 μm). The smaller particle sizes (Reff ≤1 μm) appear concentrated near the spatial (latitude and altitude) boundaries of their global occurrences. CRISM spectra of mesospheric CO2 clouds also show evidence of iridescence, indicating very narrow particle size distributions (effective variance, Veff ∼ 0.03) and so very abrupt CO2 cloud nucleation. Furthermore, these clouds are sometimes accompanied by altitude coincident peaks in 1.27 μm O2 dayglow, which indicates very dry, cold regions of formation. Mesospheric water ice clouds generally exhibit small particle sizes (Reff = 0.1–0.3 μm), although larger particle sizes (Reff = 0.4–0.7 μm) appear infrequently. On average, water ice cloud particle sizes decrease with altitude over 50–80 km in the perihelion mesosphere. Water ice mass appears similar in clouds over a large range of observed cloud particle sizes, with particle number densities increasing to ∼10 cm−3 for Reff = 0.2 μm. Near coincident Mars Climate Sounder (MCS) temperature and aerosol profile measurements for a subset of CRISM mesospheric aerosol measurements indicate near saturation (H2O and CO2) conditions for ice clouds and distinct mesospheric temperature increases associated with mesospheric dust loading. Dayside (3 pm) mesospheric CO2 clouds with larger particle sizes (Reff ≥0.5 μm) scatter surface infrared emission in MCS limb infrared radiances, as well as solar irradiance in the MCS solar band channel. Scattering of surface infrared emission is most strikingly presented in nighttime (3 am) MCS observations at 55–60 km altitudes, indicating extensive mesospheric nighttime CO2 clouds with considerably larger particle sizes (Reff∼7 μm). Mesospheric CO2 ice clouds present cirrus-like waveforms over extensive latitude and longitude regions (10°×10°), as revealed in coincident Mars Color Imager (MARCI) nadir imaging. Solar tides, gravity waves, and the large orbital variation of the extended thermal structure of the Mars atmosphere influence all of these behaviors. Mesospheric dust aerosols appear infrequently over the non-global (planet encircling) dust storm era of the CRISM limb data set (2009–2016), and exhibit smaller particle sizes (Reff = 0.2–0.7 μm) relative to dust in the lower atmosphere. One isolated case of an aphelion (Ls = 96°) mesospheric dust layer with large dust particle sizes (Reff ∼2 μm) over Syria Planum may reflect high altitude, non-local transport of dust over elevated regions.

The case against vast glaciation in Valles Marineris, Mars

The Valles Marineris of Mars form the largest system of interconnected canyons in the Solar System, where morphological, mineralogical, and structural evidence of widespread glaciation has been recently reported. However, neither precipitation models nor global water budgets can account for such a colossal fill, and the hypothesis has thus far remained unchallenged by additional scrutiny. Here, we present the first thorough case against a Valles Marineris glaciation by describing new evidence that precludes the existence of a glacier. Most crucially, we review High Resolution Imaging Science Experiment (HiRISE) images of chaos terrain in Candor Chasma — previously interpreted as remnant glacial ice — and identify layered, boulder-rich scarps bearing no similarity to scarps of massive ice in Promethei Terra or the North Polar Layered Deposits. We also find no significant differences in the structure, morphology, and composition of chaos terrain in Candor and the Chryse Planitia region, which suggests Candor's Chaos, like Chryse's, is fractured highland terrain. We also review several other key supports for the glacial hypothesis, including the coincidence of an apparent glacial trimline with the water-bearing mineral jarosite, and the apparent presence of glacial features including kettle holes and sandur plains. These too are found to have more plausible explanations with non-glacial origins including tectonic reorganisation, groundwater sapping, and chaotic fracturing. We conclude that the Valles Marineris glacial hypothesis is inconsistent with both observed morphology and our understanding of the ancient Martian climate, and we find no evidence to support its existence.

Recent seismicity in Valles Marineris, Mars: Insights from young faults, landslides, boulder falls and possible mud volcanoes

Current seismicity of Mars is poorly known. Geodynamic models and analysis of surface faults indicate that Mars could be seismically active globally, particularly within the Tharsis region. However, published geologic constraints on such activity are sparse. In this study, we use geomorphologic observations and crater size–frequency age determinations gleaned from high-resolution orbiter data to demonstrate that the Valles Marineris region is recently seismo-tectonically active. The chasmata shows evidence of reactivated dip-slip faults that cross-cut the chasmata walls and floors and indicates up to 1–2 km total vertical displacement along the trough bounding faults. More than 16000 boulder fall occurrences with pristine trails are observed throughout the chasmata wall with an average slope of 25 degrees. The boulder falls are interpreted to have been triggered by recent seismic shaking from the shallow marsquakes occurring along the chasmata faults, possibly in the last thousands of years. Synthetic ground motion models indicate several MW 4–6 marsquakes at shallow depths (∼1–6 km) are required to produce these canyon-wide boulder falls. In addition, the presence of many young landslides (22–790 Ma) proximal to the reactivated trough bounding faults and formation of thousands of possible mud volcanic cones throughout the chasmata floor all suggest marsquake-triggered shaking in the past tens to hundreds of million years, corresponding to Late to Middle Amazonian Epochs. We estimate formation of 20 m to 1.3 km diameter fresh impact craters around the chasmata had negligible contribution to the recent seismicity. Therefore, Valles Marineris tectonism is an important source of marsquakes that may be readily detectable by the upcoming InSight seismometers.

Episodic and Declining Fluvial Processes in Southwest Melas Chasma, Valles Marineris, Mars

AbstractThere is abundant evidence for aqueous processes on Noachian terrains across Mars; however, key questions remain about whether these processes continued into the Hesperian as the martian climate became less temperate. One region with an extensive Hesperian sedimentary record is Valles Marineris. We use high‐resolution image and topographic data sets to investigate the fluvial systems in the southwest Melas basin, Valles Marineris, Mars. Fluvial landforms in the basin exist across a wide area, and some are preserved as inverted channels. The stratigraphy of the basin is complex: Fluvial landforms are preserved as planview geomorphic features and are also interbedded with layered deposits in the basin. The fluvial morphologies are consistent with formation by precipitation‐driven runoff. Fluvial processes in the basin were episodic, suggesting multiple wet and dry periods. During dry periods, mantling material accumulated, and significant volumes of sediment were eroded, inverting fluvial channels. During wet periods, inverted channels and mantling material infilling valleys were incised by further fluvial erosion. These trends for episodic fluvial processes are similarly reflected in the central depression of the southwest Melas basin, previously described as a paleolake. Ultimately, fluvial processes in the basin gradually shut down, becoming geographically restricted, and then ceased entirely. We show that branching valley networks are also present on the plateaus above Melas and Ius Chasma, which converge on the heads of tributary canyons. These suggest that precipitation‐driven runoff processes also extended onto the plateaus of Valles Marineris.