Ancient Mars Research Articles

Microbialites at Gusev Crater, Mars.

The Mars Exploration Rover Spirit investigated plains at Gusev crater, where sedimentary rocks are present. The Spirit rover’s Athena morphological investigation shows microstructures organized in intertwined filaments of microspherules: a texture we have also found on samples of terrestrial stromatolites and other microbialites. We performed a quantitative image analysis to compare 45 microbialites samplings with 50 rover’s ones (approximately 25,000/20,000 microstructures). Contours were extracted and morphometric indexes obtained: geometric and algorithmic complexities, entropy, tortuosity, minimum and maximum diameters. Terrestrial and Martian textures resulted multifractals, while terrestrial abiogenic minerals showed a simple fractal structure. Mean values and confidence intervals from the Martian images overlapped perfectly with those from terrestrial samples. The probability of this occurring by chance was less than 1/28, p<0.004. Our work show the presumptive evidence of microbialites in the Martian outcroppings explored by “Spirit”, confirming our previous results concerning the Martian outcroppings explored by Opportunity at Meridiani Planum: unicellular life was widespread on the ancient Mars.

Opportunity Rover's image analysis: Microbialites on Mars?

The Mars Exploration Rover Opportunity investigated plains at Meridiani Planum, where laminated sedimentary rocks are present. The Opportunity rover’s Athena morphological investigation showed microstructures organized in intertwined filaments of microspherules: a texture we have also found on samples of terrestrial (biogenic) stromatolites and other microbialites. We performed a quantitative image analysis to compare images (n=45) of microbialites with the images (n=30) photographed by the rover (corresponding, approximately, to 25,000/15,000 microstructures). Contours were extracted and morphometric indexes were obtained: geometric and algorithmic complexities, entropy, tortuosity, minimum and maximum diameters. Terrestrial and Martian textures present a multifractal aspect. Mean values and confidence intervals from the Martian images overlapped perfectly with those from the terrestrial samples. The probability of this occurring by chance is 1/2 8 , less than p<0.004. Terrestrial abiogenic pseudostromatolites showed a simple fractal structure and different morphometric values from those of the terrestrial biogenic stromatolite images or Martian images with a less ordered texture (p<0.001). Our work shows the presumptive evidence of microbialites in the Martian outcroppings: i.e., the presence of unicellular life on the ancient Mars.

Estimating precipitation on early Mars using a radiative-convective model of the atmosphere and comparison with inferred runoff from geomorphology

We compare estimates of atmospheric precipitation during the Martian Noachian–Hesperian boundary 3.8Gyr ago as calculated in a radiative-convective column model of the atmosphere with runoff values estimated from a geomorphological analysis of dendritic valley network discharge rates. In the atmospheric model, we assume CO2–H2O–N2 atmospheres with surface pressures varying from 20mb to 3bar with input solar luminosity reduced to 75% the modern value.Results from the valley network analysis are of the order of a few mmd−1 liquid water precipitation (1.5–10.6mmd−1, with a median of 3.1mmd−1). Atmospheric model results are much lower, from about 0.001–1mmd−1 of snowfall (depending on CO2 partial pressure). Hence, the atmospheric model predicts a significantly lower amount of precipitated water than estimated from the geomorphological analysis. Furthermore, global mean surface temperatures are below freezing, i.e. runoff is most likely not directly linked to precipitation. Therefore, our results strongly favor a cold early Mars with episodic snowmelt as a source for runoff.Our approach is challenged by mostly unconstrained parameters, e.g. greenhouse gas abundance, global meteorology (for example, clouds) and planetary parameters such as obliquity – which affect the atmospheric result – as well as by inherent problems in estimating discharge and runoff on ancient Mars, such as a lack of knowledge on infiltration and evaporation rates and on flooding timescales, which affect the geomorphological data. Nevertheless, our work represents a first step in combining and interpreting quantitative tools applied in early Mars atmospheric and geomorphological studies.

Record of the ancient martian hydrosphere and atmosphere preserved in zircon from a martian meteorite

Mars exhibits ample evidence for an ancient surface hydrosphere. The oxygen isotope compositions of carbonate minerals and alteration products in martian meteorites suggest that this ancient hydrosphere was not in isotopic equilibrium with the martian lithosphere1,2,3,4. Martian meteorite NWA 7533 is composed of regolith breccia from the heavily cratered terrains of ancient Mars and contains zircon grains for which U–Pb ages have been reported5. Here we report variations between the oxygen isotopic compositions of four zircon grains from NWA 7533. We propose that these variations can be explained if the mantle melts from which the zircon crystallized approximately 4.43 Gyr ago had assimiliated 17O-enriched regolith materials, and that some of the zircon grains, while in a metamict state, were later altered by low-temperature fluids near the surface less than 1.7 Gyr ago. Enrichment of the martian regolith in 17O before the zircon crystallized, presumably through exchange with the 17O-enriched atmosphere or hydrosphere during surface alteration, suggests that the thick primary atmosphere of Mars was lost within the first 120 Myr after accretion. We conclude that the observed variation of 17O anomalies in zircon from NWA 7533 points to prolonged interaction between the martian regolith, atmosphere and hydrosphere.

Mineralogy of the Martian Surface

The past fifteen years of orbital infrared spectroscopy and in situ exploration have led to a new understanding of the composition and history of Mars. Globally, Mars has a basaltic upper crust with regionally variable quantities of plagioclase, pyroxene, and olivine associated with distinctive terrains. Enrichments in olivine (&gt;20%) are found around the largest basins and within late Noachian–early Hesperian lavas. Alkali volcanics are also locally present, pointing to regional differences in igneous processes. Many materials from ancient Mars bear the mineralogic fingerprints of interaction with water. Clay minerals, found in exposures of Noachian crust across the globe, preserve widespread evidence for early weathering, hydrothermal, and diagenetic aqueous environments. Noachian and Hesperian sediments include paleolake deposits with clays, carbonates, sulfates, and chlorides that are more localized in extent. The late Hesperian to Amazonian mineralogic record of water is sparser, though sulfates and silica in some locations indicate local availability of ground and surface waters even in the most recent geologic epoch.

Ancient Mars probably too cold for liquid water

Ancient Mars probably too cold for liquid water

The Potential for Biologically Catalyzed Anaerobic Methane Oxidation on Ancient Mars

This study examines the potential for the biologically mediated anaerobic oxidation of methane (AOM) coupled to sulfate reduction on ancient Mars. Seven distinct fluids representative of putative martian groundwater were used to calculate Gibbs energy values in the presence of dissolved methane under a range of atmospheric CO2 partial pressures. In all scenarios, AOM is exergonic, ranging from -31 to -135 kJ/mol CH4. A reaction transport model was constructed to examine how environmentally relevant parameters such as advection velocity, reactant concentrations, and biomass production rate affect the spatial and temporal dependences of AOM reaction rates. Two geologically supported models for ancient martian AOM are presented: a sulfate-rich groundwater with methane produced from serpentinization by-products, and acid-sulfate fluids with methane from basalt alteration. The simulations presented in this study indicate that AOM could have been a feasible metabolism on ancient Mars, and fossil or isotopic evidence of this metabolic pathway may persist beneath the surface and in surface exposures of eroded ancient terrains.

Prolonged magmatic activity on Mars inferred from the detection of felsic rocks

Felsic rocks have not been identified on Mars, a planet that lacks plate tectonics to drive the magmatic processes that lead to evolved silica-rich melts. Spectral observations by the Mars Reconnaissance Orbiter indicate that felsic lithologies occur at multiple localities on Mars and suggest prolonged magmatic activity on ancient Mars.

Visible‐near‐infrared reflectance spectroscopy of volcanic acid‐sulfate alteration in Nicaragua: Analogs for early Mars

Acid‐sulfate weathering at Nicaraguan hydrothermal sites Cerro Negro, Momotombo, and Telica volcanoes and Hervidores de San Jacinto mudpots was characterized as an analog for similar processes that likely operated on early Mars. In situ mineralogical analyses were conducted with a field portable visible near‐infrared spectrometer for comparison to similar Martian data sets. Three classes of alteration minerals were identified: sulfates (gypsum and natroalunite), oxides/hydroxides (hematite and goethite), and phyllosilicates (kaolinite/halloysite, montmorillonite, and saponite), as well as elemental sulfur and hydrated silica phases. Our sites had similar suites of minerals, but frequencies varied with location. The results of this field campaign allow inferences regarding the paleo‐environmental conditions that were likely present at similar relic hydrothermal sites identified on Mars. In particular, sulfates and phyllosilicates could have coevolved under hydrothermal conditions at Noctis Labyrinthus as is seen in Nicaragua. Fe/Mg smectites were detected in areas with pH of 3–4. Alunite spectra at Terra Sirenum demonstrated mineral mixing effects on spectroscopy. Mineral mixing can cause uncertainties in spectral identification due to a dominant spectrum, such as iron minerals, masking another or the suppression of weaker bands. When viewed from orbit, our field sites would likely be dominated by hydrated silica and Mars sites, such as one in Syrtis Major, could have a more diverse mineralogy than the data reveal. Concentrated amorphous silica, such as at Gusev crater, can result from acidic fumarolic activity, while Mg sulfates may indicate a lack of reworking by water. This field spectroscopy study helps confirm and provide insight into hydrothermal processes on ancient Mars.

Hydrodynamics of impact-induced tsunami over the Martian ocean

Large bodies of liquid water ranging from lakes to oceans have been hypothesized to have occupied the surface of ancient Mars episodically. Such inferences have been founded largely on geomorphological observations of putative shoreline features during the period ranging from the 1980s to the early 2000s. High-resolution satellite images obtained during various Mars missions conducted since the early 2000s have enabled detailed sedimentological studies. One phenomenon that might leave sedimentological traces of the purported Martian paleo-oceans is a bolide impact and consequent generation of large tsunami waves. Numerical modeling of impact-induced tsunami waves on a hypothesized northern plains paleo-ocean was performed to elucidate their potential propagation characteristics on Mars, including the ranges of wave height and velocity. When considering a tsunami triggered by a 50km-diameter impact cratering event, the offshore and shore-zone wave heights respectively reached 40–50m and 120m. In the same test scenario, the tsunami wave velocity reached 20m/s near the crater and 16m/s at the shore zone. The wave height and velocity in highly cratered regions, such as Arabia Terra, tend to be relatively low because tsunami inundation is diffused by impact crater rims existing along the tsunami passage.

Is Earth-based scaling a valid procedure for calculating heat flows for Mars?

Heat flow is a very important parameter for constraining the thermal evolution of a planetary body. Several procedures for calculating heat flows for Mars from geophysical or geological proxies have been used, which are valid for the time when the structures used as indicators were formed. The more common procedures are based on estimates of lithospheric strength (the effective elastic thickness of the lithosphere or the depth to the brittle–ductile transition). On the other hand, several works by Kargel and co-workers have estimated martian heat flows from scaling the present-day terrestrial heat flow to Mars, but the so-obtained values are much higher than those deduced from lithospheric strength. In order to explain the discrepancy, a recent paper by Rodriguez et al. (Rodriguez, J.A.P., Kargel, J.S., Tanaka, K.L., Crown, D.A., Berman, D.C., Fairén, A.G., Baker, V.R., Furfaro, R., Candelaria, P., Sasaki, S. [2011]. Icarus 213, 150–194) criticized the heat flow calculations for ancient Mars presented by Ruiz et al. (Ruiz, J., Williams, J.-P., Dohm, J.M., Fernández, C., López, V. [2009]. Icarus 207, 631–637) and other studies calculating ancient martian heat flows from lithospheric strength estimates, and casted doubts on the validity of the results obtained by these works. Here however we demonstrate that the discrepancy is due to computational and conceptual errors made by Kargel and co-workers, and we conclude that the scaling from terrestrial heat flow values is not a valid procedure for estimating reliable heat flows for Mars.

Drainage systems of Lonar Crater, India: Contributions to Lonar Lake hydrology and crater degradation

Lonar, a 1.8-km-diameter impact crater in India, is a rare example of terrestrial impact craters formed in basaltic bedrock. The estimated age of the crater ranges widely from less than 12ka to over 600ka, but the crater preserves a relatively pristine morphology. We conducted a study of various drainage systems of Lonar Crater. The crater floor hosts a shallow 5-m-deep lake, which fluctuates seasonally. Our investigation reveals that the lake level is influenced by surface runoff that is active during the monsoon and groundwater input effective during both the rainy and the dry seasons. The groundwater discharge is observed as springs on the inner rim walls corresponding to weathered vesicular basalt and/or proximal ejecta, which are underlain by thick massive basalt layers. This observation indicates that groundwater movement is lithologically controlled: it passes preferentially through permeable vesicular basalt or proximal ejecta but is hindered in less permeable massive basalt. It is hypothesized that groundwater is also structurally controlled by dipping of basalt layers, interconnectivity of the permeable lithologic units through fractures, and preferential pathways such as fractures within the permeable lithologic units. Investigation on hydrological processes at Lonar Crater and its lake could provide useful insights into purported paleo-crater lakes presumably formed in the basaltic crust of Mars. The Lonar Crater interior shows signs of degradation in the forms of gullies and debris flows, and the Dhar valley incising in the rim leading to form a fan delta. The ejecta surface is characterized by the presence of channels, originating from the rim area and extending radially away from the crater center. The channels probably resulted from surface runoff, and its erosion contributes to the removal of the ejecta. Lonar Crater is a valuable analog site for studying degradation processes with potential application to impact craters occurring on hydrologically active ancient Mars, or to other impact craters on Earth.

Demagnetization by basin‐forming impacts on early Mars: Contributions from shock, heat, and excavation

AbstractLarge hypervelocity impacts occurred frequently on ancient Mars, leaving many large impact basins visible today. After the planetary dynamo ceased operating, such impacts demagnetized the crust by way of (1) excavation of magnetized material, (2) heating, and (3) shock pressure. We investigate these three demagnetizing processes, both separately and in combination, using hydrocode simulations of large impacts on early Mars at a range of impact energies and using a new parameterization of the shock pressure‐demagnetization behavior of candidate Martian minerals. We find that in general, shock pressure demagnetization is more important than thermal demagnetization, except in the combined case of very large impacts (more than ~1026 J) and low Curie temperature minerals such as pyrrhotite. We find that total demagnetized area has a power law dependence on impact energy (with an exponent of 0.6–0.72) and that depending on the magnetic mineral, the demagnetized area resulting for a given impact energy can vary over approximately an order of magnitude. We develop an empirical model that can be used to calculate total demagnetized area for a given impact energy and magnetic mineral (whose pressure‐demagnetization properties are known). Once a reliable basin scaling law for ancient Mars (i.e., relating impact energy to final basin topography) is derived, this mineral parameterization and empirical model will allow robust constraints to be placed upon the primary Martian magnetic carrier(s).

Science Podcast

The show includes remotely controlled gene expression, evidence for water on ancient Mars, nanopore sequencing advances, and more.

Reproducing hydrogeochemical conditions triggering the formation of carbonate and phyllosilicate alteration mineral assemblages on Mars (Nili Fossae region)

[1] The cooccurrence of Mg-Fe-Ca carbonate and stratigraphically lower, phyllosilicate-bearing rock units, identified in the Nili Fossae region on Mars, may reveal a CO2-driven aqueous alteration process on ancient Mars. We reproduce hydrogeochemical conditions for concurrent carbonate and phyllosilicate formation in rock columns by using hydrogeochemical one-dimensional transport modeling, which is based on chemical equilibrium thermodynamics. Our models assume the isochemical, low-temperature equilibration of ultramafic rocks with pure water at varying atmospheric CO2 partial pressure, water-to-rock ratio, temperature, and rock composition. Equilibration among (1) mineral assemblages of olivine-rich rocks (18–28 wt% MgO), (2) pure water (water-to-rock ratio: 500–50 mol mol−1), (3) CO2 transferred from the atmosphere (CO2 partial pressure lower than ∼2 bars and higher than ∼0.01 bar) at ∼278 K, and (4) 100,000 years of diffusive mass transport create hydrogeochemical conditions enabling the concurrent formation of Mg-rich Mg-Fe-Ca solid-solution carbonate and stratigraphically lower phyllosilicate-rich alteration assemblages in rock columns. The modeled composition of alteration mineral assemblages, their depth distribution, and carbonate composition are similar to the observations from the Nili Fossae region. Higher equilibration temperature (373 K) results in the formation of Ca-dominated Ca-Mg carbonate instead of Mg-rich Mg-Fe-Ca carbonate and in an inverse stratification with phyllosilicate-rich units overlying carbonate-rich units. Modeling results suggest that rocks in the Nili Fossae region, hosting the carbonate and phyllosilicate mineral assemblage, have been exposed to a groundwater alteration process driven by atmospheric CO2 partial pressures ranging between ∼2 bars and ∼0.01 bar at low temperature (∼278 K).

Preservation of Martian Organic and Environmental Records: Final Report of the Mars Biosignature Working Group

The Mars Science Laboratory (MSL) has an instrument package capable of making measurements of past and present environmental conditions. The data generated may tell us if Mars is, or ever was, able to support life. However, the knowledge of Mars' past history and the geological processes most likely to preserve a record of that history remain sparse and, in some instances, ambiguous. Physical, chemical, and geological processes relevant to biosignature preservation on Earth, especially under conditions early in its history when microbial life predominated, are also imperfectly known. Here, we present the report of a working group chartered by the Co-Chairs of NASA's MSL Project Science Group, John P. Grotzinger and Michael A. Meyer, to review and evaluate potential for biosignature formation and preservation on Mars. Orbital images confirm that layered rocks achieved kilometer-scale thicknesses in some regions of ancient Mars. Clearly, interplays of sedimentation and erosional processes govern present-day exposures, and our understanding of these processes is incomplete. MSL can document and evaluate patterns of stratigraphic development as well as the sources of layered materials and their subsequent diagenesis. It can also document other potential biosignature repositories such as hydrothermal environments. These capabilities offer an unprecedented opportunity to decipher key aspects of the environmental evolution of Mars' early surface and aspects of the diagenetic processes that have operated since that time. Considering the MSL instrument payload package, we identified the following classes of biosignatures as within the MSL detection window: organism morphologies (cells, body fossils, casts), biofabrics (including microbial mats), diagnostic organic molecules, isotopic signatures, evidence of biomineralization and bioalteration, spatial patterns in chemistry, and biogenic gases. Of these, biogenic organic molecules and biogenic atmospheric gases are considered the most definitive and most readily detectable by MSL.

Lithospheric drift on early Mars: Evidence in the magnetic field

The crustal magnetic anomalies on Mars may represent hot spot tracks resulting from lithospheric drift on ancient Mars. As evidence, an analysis of lineation patterns derived from the ΔBr magnetic map is presented. The ΔBr map, largely free of external magnetic field effects, allows excellent detail of the magnetic anomaly pattern, particularly in areas of Mars where the field is relatively weak. Using cluster analysis, we show that the elongated anomalies in the martian magnetic field form concentric small circles (parallels of latitude) about two distinct north pole locations. If these pole locations represent ancient spin axes, then tidal force on the early lithosphere by former satellites in retrograde orbits may have pulled the lithosphere in an east–west direction over hot mantle plumes. With an active martian core dynamo, this may have resulted in the observed magnetic anomaly pattern of concentric small circles. As further evidence, we observe that, of the 15 martian giant impact basins that were possibly formed while the core dynamo was active, seven lie along the equators of our two proposed paleopoles. We also find that four other re-magnetized giant impact basins lie along a great circle about the mean magnetic paleopole of Mars. These 11 impact basins, likely the result of fallen retrograde satellite fragments, indicate that Mars once had moons large enough to cause tidal drag on the early martian lithosphere. The results of this study suggest that the magnetic signatures of this tidal interaction have been preserved to the present day.

Photochemical and climate consequences of sulfur outgassing on early Mars

Ancient Mars might have been warm and wet compared to today, but climate models have trouble reproducing this warmth, partly because of the faintness of the young Sun and partly because of inherent limitations to CO 2–H 2O greenhouse warming. In particular, Rayleigh scattering of incoming sunlight by a dense, CO 2-rich atmosphere leads to a high planetary albedo, thereby reducing the amount of sunlight absorbed by the planet. It has been recently suggested that the presence of 1–100 ppmv SO 2 in Mars' early atmosphere might have provided enough additional greenhouse warming to maintain a warm, wet early Mars. We show, however, that this warming should have been more than offset by cooling from sulfate and sulfur aerosols in early martian atmosphere. Hence, the paradox of Mars' early climate remains unresolved.

Sources and sinks of clay minerals on Mars

The recent identification of clay minerals on the Martian surface using visible–near infrared reflectance spectroscopy has had a profound effect on our view of aqueous alteration on Mars. Smectite, chlorite, kaolin group, and serpentine group minerals have been detected using the CRISM and OMEGA spectrometers, with Fe/Mg-smectite and chlorite varieties being the dominant types discovered throughout the ancient crust. Aqueous, eolian, and impact processes have transported and recycled some of these clays such that their current locations may not accurately reflect their formation environments. However, detrital clays could prove useful for constraining transport pathways and sediment provenance. Here we discuss the impact craters and channels that comprise the Uzboi–Ladon–Morava system, including Holden, Eberswalde, and Ladon craters, which represents a large-scale sediment sink for clay minerals derived from the surrounding Noachian crust. This system contains thick deposits of clay mineral-bearing strata that likely record a wide range of alluvial, fluvial, lacustrine, and eolian processes that provide direct insight into the Martian clay cycle. Broad concepts of sediment sources, sinks, and sediment transport paths can be outlined using orbital data, but future in situ exploration of the Martian sedimentary rock record will be necessary to distinguish fully between detrital and authigenic clay minerals, and thus to determine environmental conditions and transitions on ancient Mars.

Diverse aqueous environments on ancient Mars revealed in the southern highlands

High-resolution spectral images reveal many new exposures of hydrated minerals across the Noachian southern highlands of Mars. Several different phyllosilicates are observed, with inferred accompanying phases ranging from zeolites to sulfates to chlorides, each in distinct geologic settings. Hydrated sulfates are observed in several locations at mid-latitudes, and likely formed independently from the equatorial sulfates. These assemblages suggest a greater diversity of aqueous environments on ancient Mars than has previously been recognized, and their distribution implies that alteration was widespread during the Noachian Period, not restricted to a few locations.