Martian Valley Networks Research Articles

The Formation of Martian River Valleys by Impacts

We explore the role of large impacts in creating the Martian valley networks. Recent dating shows that some large impact basins are contemporaneous with the valley networks. The mass deposited (and volatiles released) by impacts is large, and comparable with the mass from the Tharsis volcanic construct. Steam atmospheres formed after large impacts can produce more than 600 m of rainfall, followed by rainfall from water-vapor greenhouse atmospheres, and snowmelt. The erosion rates from impacts that created the currently visible craters are somewhat less than the erosion rates suggested for the Noachian (4.2 to 3.82 Gya). There are several possible explanations for this difference, and it is possible that erosion rates are overestimated because the burial of small craters by global debris layers from impacts has not been considered. Rainfall after the Noachian was low because the impact rate and CO2 pressure declined. We suggest tests of the hypothesis that impacts caused the river valleys.

Characterization of fluvial activity in Parana Valles using different age-dating techniques

Martian valley networks provide the best evidence that the climate on Mars was different in the past. Although these features are located primarily in heavily cratered terrain of Noachian age (>3.7 Ga), the ages of the features and the time when they were active is not well understood. From superposed craters several recent global studies determined that most valley networks formed during the Late Noachian to Early Hesperian; however, there were some disparities between the techniques. In this study, our principal objective was to test the reliability of the different age-dating techniques to better understand their accuracy and limitations. We applied these techniques to Parana Valles using a variety of high-resolution images taken from different instruments that allow us to identify smaller craters ( D > 125 m) while providing sufficient coverage to support a statistically reliable sampling of crater populations, which is necessary to reduce the uncertainties in age determination. Our results indicate that Parana Valles formed during the Early Hesperian Period but that the crater density ( D > 353 m) is heterogeneous inside the Parana Valles basin. The crater population decreases from the headwaters downstream recording a resurfacing event that is most likely related to the erosion of downstream sub-basins. The terrain near the source area is Late Noachian to Early Hesperian in age while terrains closer to the outlet are Early to Late Hesperian in age. Crater densities ( D > 125 m) inside the valley are also heterogeneous and record several resurfacing events on the valley floor. Where the width of the valley network narrows to <2 km we found evidence of an Amazonian age eolian deposit that is a relatively thin layer of only few meters that was probably deposited as a result of topographic influences. Our results validate the reliability of several proposed age-dating techniques, but we also determined the accuracy and applicability of these techniques. Our results also demonstrate that crater populations can be used to not only determine the relative ages of valley networks, but also to map the distribution of sedimentary materials and the extent of resurfacing events that occurred after valley network formation.

Roaming zones of precipitation on ancient Mars as recorded in valley networks

The 10 largest valley networks in the Terra Sabaea, Arabia Terra, and Meridiani Planum regions of Mars were mapped, crater age dated, and analyzed by geomorphology, stream order, and drainage density to understand changes in fluvial erosion during early Martian history. All of these networks demonstrate characteristics consistent with formation by precipitation. Many appear to be in different stages of preservation, with both highly eroded and pristine valleys sometimes appearing in the same network. In some cases, the valley network morphologies and crater age dating indicate multiple periods of formation. The results from this research place precipitation‐driven formation of the Martian valley networks in Terra Sabaea, Arabia Terra, and Meridiani Planum in the late Noachian and early Hesperian epochs (∼3.6–3.8 billion years ago). Our age estimates do not extend into earlier or later Martian history, and the spread in these ages indicates they did not all form or cease formation at the same time. The difference in age between the oldest and youngest valley networks in Terra Sabaea, Arabia Terra, and Meridiani Planum analyzed in this work is ∼210 ± 50 Ma. Within this range are valley networks that have distinctly separate ages and those that appear to be coeval. This research suggests the late Noachian and early Hesperian were characterized by roaming zones of precipitation that occurred during either continuously warmer and thicker atmospheric conditions or intermittently clement conditions, with precipitation occasionally returning to previously rainy regions and overall continuing near Meridiani Planum longer than in Terra Sabaea.

Sinton crater, Mars: Evidence for impact into a plateau icefield and melting to produce valley networks at the Hesperian–Amazonian boundary

The majority of martian valley networks are found on Noachian-aged terrain and are attributed to be the result of a ‘warm and wet’ climate that prevailed early in Mars' history. Younger valleys have been identified, though these are largely interpreted to be the result of localized conditions associated with the melting of ice from endogenic heat sources. Sinton crater, a 60 km diameter impact basin in the Deuteronilus Mensae region of the dichotomy boundary, is characterized by small anastomosing valley networks that are located radial to the crater rim. Large scale deposits, interpreted to be the remains of debris covered glaciers, have been identified in the area surrounding Sinton, and our observations have revealed the occurrence of an ice rich fill deposit within the crater itself. We have conducted a detailed investigated into the Sinton valley networks with all the available remote data sets and have dated their formation to the Amazonian/Hesperian boundary. The spatial and temporal association between Sinton crater and the valley networks suggest that the impact was responsible for their formation. We find that the energy provided by an asteroid impact into surficial deposits of snow/ice is sufficient to generate the required volumes of melt water needed for the valley formation. We therefore interpret these valleys to represent a distinct class of martian valley networks. This example demonstrates the potential for impacts to cause the onset of fluvial erosion on Mars. Our results also suggest that periods of glacial activity occurred throughout the Amazonian and into the Hesperian in association with variations in spin orbital parameters.

Scaling relations for large Martian valleys

The dendritic morphology of Martian valley networks, particularly in the Noachian highlands, has long been argued to imply a warmer, wetter early Martian climate, but the character and extent of this period remains controversial. We analyzed scaling relations for the 10 large valley systems incised in terrain of various ages, resolvable using the Mars Orbiter Laser Altimeter (MOLA) and the Thermal Emission Imaging System (THEMIS). Four of the valleys originate in point sources with negligible contributions from tributaries, three are very poorly dissected with a few large tributaries separated by long uninterrupted trunks, and three exhibit the dendritic, branching morphology typical of terrestrial channel networks. We generated width‐area and slope‐area relationships for each because these relations are identified as either theoretically predicted or robust terrestrial empiricisms for graded precipitation‐fed, perennial channels. We also generated distance‐area relationships (Hack's law) because they similarly represent robust characteristics of terrestrial channels (whether perennial or ephemeral). We find that the studied Martian valleys, even the dendritic ones, do not satisfy those empiricisms. On Mars, the width‐area scaling exponent b of −0.7–4.7 contrasts with values of 0.3–0.6 typical of terrestrial channels; the slope‐area scaling exponent θ ranges from −25.6–5.5, whereas values of 0.3–0.5 are typical on Earth; the length‐area, or Hack's exponent n ranges from 0.47 to 19.2, while values of 0.5–0.6 are found on Earth. None of the valleys analyzed satisfy all three relations typical of terrestrial perennial channels. As such, our analysis supports the hypotheses that ephemeral and/or immature channel morphologies provide the closest terrestrial analogs to the dendritic networks on Mars, and point source discharges provide terrestrial analogs best suited to describe the other large Martian valleys.

Topography of valley networks on Mars from Mars Express High Resolution Stereo Camera digital elevation models

Martian valley networks have been identified mainly in the Noachian heavily cratered uplands. The geometry of valley networks can be studied using Mars Orbiter Laser Altimeter (MOLA) altimetry, which is sufficient to map large valleys without a detailed 3‐D shape of valley networks. Imaging from the Mars Express High Resolution Stereo Camera (HRSC) is used to generate digital elevation models (DEMs) with resolution ≤50 m and vertical accuracy &lt;60 m. We studied valleys near Huygens crater and in the Aeolis region both in the Noachian bedrock and on the West Echus plateau in Hesperian bedrock. HRSC DEMs in these areas show that (1) drainage density is 3 times higher than is observed in MOLA data, (2) degree of ramification is 1 order more than with MOLA, (3) transverse valley profiles show a V shape more accurately and a minimum depth of ∼20 m, and (4) higher drainage density shows greater headward extension that is not correlated to greater valley depth. The deepest valleys (400 m) are found in the Huygens region, where the density in the DEM is 0.1 km−1, compared to shallow valleys (&lt;100 m) of the Echus region, where the density is higher (∼0.3 km−1). These regional differences are due to spatially variable preservation and bedrock lithology. Longitudinal profiles suggest variations in duration of activity: profile concavity is only developed in some Noachian terrains. Valleys visible in HRSC images correspond to topographic features in DEMs showing the same geometry as terrestrial valleys thought to be formed by overland flows and seepage.

Computer simulation of the role of groundwater seepage in forming Martian valley networks

The role of groundwater in forming Martian valley networks is simulated in a computer model as seepage erosion by contributing to surface runoff and as seepage weathering by causing accelerated weathering of bedrock, which makes its subsequent erosion and removal easier. Simulation results show that seepage erosion cannot mobilize large grain size sediment and is marginally effective at generating integrated valley networks with realistic rates of aquifer recharge. On the other hand, seepage weathering may play a major role in forming Martian valley networks. Seepage weathering combined with fluvial runoff creates stubby deep canyons with abrupt headwalls that are similar in morphology to terrestrial and Martian valley systems attributed to erosion by groundwater. Depending on the relative contribution of groundwater weathering to surface runoff erosion, a continuum of valley network morphology can be generated. Eolian modification masks the original differences in fluvial landforms, making different scenarios visually more similar. Martian valley networks may have developed through a range of combinations of runoff erosion and seepage weathering, which can complicate the interpretation of the processes based on final landform morphology. Unequivocal identification of seepage involvement of valley incision on Mars may not be possible without knowledge of subsurface properties (hydraulic conductivity, layering, degree of cementation, etc.) and the grain sizes of sediment transported through the valley systems.

Automatic mapping of valley networks on Mars

Martian valley networks bear some resemblance to terrestrial drainage systems, but their precise origin remains an active research topic. A limited number of valley networks have been manually mapped from images, but the vast majority remains unmapped because standard drainage mapping algorithms are inapplicable to valleys that are poorly organized and lack spatial integration. In this paper, we present a novel drainage delineation algorithm specially designed for mapping the valley networks from digital elevation data. It first identifies landforms characterized by convex tangential curvature, and then uses a series of image processing operations to separate valleys from other features having a convex form. The final map is produced by reconnecting all valley segments along drainage directions. Eight test sites on Mars are selected and manually mapped for valley networks. The algorithm is applied to the test sites and delineated networks are compared to mapped networks using a series of quantitative quality factors. We have found a good agreement between delineated and mapped networks. In the process of comparing manual and delineated networks some shortcomings of manual mapping became apparent. We argue that delineated networks are indeed of better quality than the networks manually mapped from images. Although the algorithm has been developed to study Martian surface, it may also be relevant to terrestrial geomorphology.

Topographically derived maps of valley networks and drainage density in the Mare Tyrrhenum quadrangle on Mars

A novel, automated technique for delineating Martian valley networks from digital terrain data is applied to the Mare Tyrrhenum quadrangle on Mars, yielding a detailed map for the entire quadrangle. The resultant average value of drainage density for the Noachian part of the quadrangle is D ≈ 0.05 km−1, an order of magnitude higher than the value inferred from a global map based on Viking images, and comparable to the values inferred from the precision mapping of selected focus sites. Valleys are omnipresent in Noachian terrain even outside the “highly dissected” Npld unit. This suggests fluvial erosion throughout the Noachian, implying widespread precipitation. The map of continuous drainage density is constructed to study spatial variations of D. This map reveals significant variations in degree of dissection in Noachian on scale of &gt;100 km. These variations do not correlate with any terrain parameter and their origin requires further study.

Interior channels in Martian valley networks: Discharge and runoff production

The highland valley networks are perhaps the most compelling evidence for widespread fluvial activity on Mars .3.5 Ga. However, determining the hydrology of these features has been difficult owing to poor image resolution and the lack of available topographic data. New orbital imaging reveals 21 late-stage channels within valley networks, which we use to estimate formative discharges and to evaluate water supply mechanisms. We find that channel width and associated formative discharge are comparable to terrestrial valley networks of similar area and relief. For 15 narrow channels in basin-filling networks, likely episodic runoff production rates up to centimeters per day and first-order formative discharges of ;300‐3000 m 3 /s are similar to terrestrial floods supplied by precipitation. Geothermal melting of ground ice would produce discharges ;100 times smaller per unit area and would require pulsed outbursts to form the channels. In four large valleys with few tributaries, wider channels may represent large subsurface outflows or paleolake overflows, as these four channels originate at breached basin divides and/or near source regions for the catastrophic outflow channels.

Extraction of Martian valley networks from digital topography

We have developed a novel method for delineating valley networks on Mars. The valleys are inferred from digital topography by an autonomous computer algorithm as drainage networks, instead of being manually mapped from images. Individual drainage basins are precisely defined and reconstructed to restore flow continuity disrupted by craters. Drainage networks are extracted from their underlying basins using the contributing area threshold method. We demonstrate that such drainage networks coincide with mapped valley networks verifying that valley networks are indeed drainage systems. Our procedure is capable of delineating and analyzing valley networks with unparalleled speed and consistency. We have applied this method to 28 Noachian locations on Mars exhibiting prominent valley networks. All extracted networks have a planar morphology similar to that of terrestrial river networks. They are characterized by a drainage density of ∼0.1 km−1, low in comparison to the drainage density of terrestrial river networks. Slopes of “streams” in Martian valley networks decrease downstream at a slower rate than slopes of streams in terrestrial river networks. This analysis, based on a sizable data set of valley networks, reveals that although valley networks have some features pointing to their origin by precipitation‐fed runoff erosion, their quantitative characteristics suggest that precipitation intensity and/or longevity of past pluvial climate were inadequate to develop mature drainage basins on Mars.

Comparing morphologies of drainage basins on Mars and Earth using integral‐geometry and neural maps

We compare morphologies of drainage basins on Mars and Earth in order to confine the formation process of Martian valley networks. Basins on both planets are computationally extracted from digital topography. Integral‐geometry methods are used to represent each basin by a circularity function that encapsulates its internal structure. The shape of such a function is an indicator of the style of fluvial erosion. We use the self‐organizing map technique to construct a similarity graph for all basins. The graph reveals systematic differences between morphologies of basins on the two planets. This dichotomy indicates that terrestrial and Martian surfaces were eroded differently. We argue that morphologies of Martian basins are incompatible with runoff from sustained, homogeneous rainfall. Fluvial environments compatible with observed morphologies are discussed. We also construct a similarity graph based on the comparison of basins' hypsometric curves to demonstrate that hypsometry is incapable of discriminating between terrestrial and Martian basins.

Environmental effects of large impacts on Mars.

The martian valley networks formed near the end of the period of heavy bombardment of the inner solar system, about 3.5 billion years ago. The largest impacts produced global blankets of very hot ejecta, ranging in thickness from meters to hundreds of meters. Our simulations indicated that the ejecta warmed the surface, keeping it above the freezing point of water for periods ranging from decades to millennia, depending on impactor size, and caused shallow subsurface or polar ice to evaporate or melt. Large impacts also injected steam into the atmosphere from the craters or from water innate to the impactors. From all sources, a typical 100-, 200-, or 250-kilometers asteroid injected about 2, 9, or 16 meters, respectively, of precipitable water into the atmosphere, which eventually rained out at a rate of about 2 meters per year. The rains from a large impact formed rivers and contributed to recharging aquifers.

Hypsometric analysis of Margaritifer Sinus and origin of valley networks

The formation of Martian valley networks has been debated since their discovery. The relative roles of groundwater sapping and fluvial runoff processes have different implications on Martian paleoclimate. This paper uses a hypsometric analysis technique that has been tested on terrestrial landforms to analyze the hypsometric attributes of watershed basins in the Margaritifer Sinus region on Mars using Mars Orbiter Laser Altimeter (MOLA) gridded topographic data. On the basis of quantitative characteristics of their hypsometric attributes, the majority of the basins (covering ∼3/5 of the study area) look more like terrestrial basins of sapping origin, and a significant number of basins (covering ∼1/5 of the study area) are more fluvial like. The classification of the rest of the basin is less certain at the presently available resolution of the digital elevation model (DEM). Overlay with Viking photomosaic indicates that the classification is generally consistent with the morphology shown in Viking images. Although this analysis alone cannot make a sure determination of valley network origin, combined with other morphometric analysis, the results from this study are consistent with a valley network formation by precipitation‐recharged groundwater sapping, suggesting a warm and wet climate for early Mars.

Controls on Martian hydrothermal systems: Application to valley network and magnetic anomaly formation

Models of hydrothermal groundwater circulation can quantify limits to the role of hydrothermal activity in Martian crustal processes. We present here the results of numerical simulations of convection in a porous medium due to the presence of a hot intruded magma chamber. The parameter space includes magma chamber depth, volume, aspect ratio, and host rock permeability and porosity. A primary goal of the models is the computation of surface discharge. Discharge increases approximately linearly with chamber volume, decreases weakly with depth (at low geothermal gradients), and is maximized for equant‐shaped chambers. Discharge increases linearly with permeability until limited by the energy available from the intrusion. Changes in the average porosity are balanced by changes in flow velocity and therefore have little effect. Water/rock ratios of ∼0.1, obtained by other workers from models based on the mineralogy of the Shergotty meteorite, imply minimum permeabilities of 10−16m2during hydrothermal alteration. If substantial vapor volumes are required for soil alteration, the permeability must exceed 10−15m2. The principal application of our model is to test the viability of hydrothermal circulation as the primary process responsible for the broad spatial correlation of Martian valley networks with magnetic anomalies. For host rock permeabilities as low as 10−17m2and intrusion volumes as low as 50 km3, the total discharge due to intrusions building that part of the southern highlands crust associated with magnetic anomalies spans a comparable range as the inferred discharge from the overlying valley networks.

Morphometric measurements of martian valley networks from Mars Orbiter Laser Altimeter (MOLA) data

Morphometric measurements of martian valley networks using Mars Orbiter Laser Altimeter (MOLA) topographic data yield mean valley width values of1548 m and depth values of. Our analysis of changes in valley shape with latitude and wall slope with depth indicate infilling and mass wasting processes have not greatly altered the original valley shape; thus valley network morphometry is dominantly due to channel formation mechanisms. Both U‐ and V‐shaped profiles are observed, commonly within the same valley network system. The average U‐shaped valley is slightly deeper (18 m) and significantly wider (1313 m) than its V‐shaped counterpart. Valley networks have decreasing width‐to‐depth ratios and increasing wall slopes as valley depth increases. Our observations are consistent with a two‐phase valley network formation model. (1) Valleys initially form via surface runoff, a process that creates V‐shaped profiles and quasi‐dendritic form. The observed linear correlation of top width and depth (below 125 m depth) suggests the depth of vertical incisement governs top width. (2) Reactivation of the same valleys by headward extending sapping processes widens the channel to form U‐shaped cross sections in downstream reaches. The availability of liquid water within a few hundred meters of the surface appears to be a necessary requirement for valley network formation. Mean valley depth decreases by ∼50 m from equatorial to higher latitudes (∼50°), contrary to the relationship predicted if the sapping depth was governed by the ice‐water boundary. Deeper equatorial valley networks may result from latitudinal variations in the availability of water or formation efficiency.

Origin of the valley networks on Mars: a hydrological perspective

The geomorphology of the martian valley networks is examined from a hydrological perspective for the compatibility with an origin by rainfall, globally higher heat flow, and localized hydrothermal systems. Comparison of morphology and spatial distribution of valleys on geologic surfaces with terrestrial fluvial valleys suggests that most martian valleys are probably not indicative of a rainfall origin, nor are they indicative of formation by an early global uniformly higher heat flow. In general, valleys are not uniformly distributed within geologic surface materials as are terrestrial fluvial valleys. Valleys tend to form either as isolated systems or in clusters on a geologic surface unit leaving large expanses of the unit virtually untouched by erosion. With the exception of fluvial valleys on some volcanoes, most martian valleys exhibit a sapping morphology and do not appear to have formed along with those that exhibit runoff morphology. In contrast, terrestrial sapping valleys form from and along with runoff valleys. The isolated or clustered distribution of valleys suggests localized water sources were important in drainage development. Persistent groundwater outflow driven by localized, but vigorous hydrothermal circulation associated with magmatism, volcanism, impacts, or tectonism is, however, consistent with valley morphology and distribution. Snowfall from sublimating ice-covered lakes or seas may have provided an atmospheric source of water for the formation of some valleys in regions where the surface is easily eroded and where localized geothermal/hydrothermal activity is sufficient to melt accumulated snowpacks.