Ancient wet aeolian environments on Earth: clues to presence of fossil/live microorganisms on Mars

Ancient wet aeolian (wet-sabkha) environments on Earth, represented in the Entrada and Navajo sandstones of Utah, contain pipe structures considered to be the product of gas/water release under pressure. The sediments originally had considerable porosity allowing the ingress of living plant structures, microorganisms, clay minerals, and fine-grained primary minerals of silt and sand size from the surface downward in the sedimentary column. Host rock material is of a similar size and porosity and presumably the downward migration of fine-grained material would have been possible prior to lithogenesis and final cementation. Recent field emission scanning electron microscopy (FESEM) and EDS (energy-dispersive spectrometry) examination of sands from fluidized pipes in the Early Jurassic Navajo Sandstone reveal the presence of fossil forms resembling fungal filaments, some bearing hyphopodium-like structures similar to those produced by modern tropical leaf parasites. The tropical origin of the fungi is consistent with the paleogeography of the sandstone, which was deposited in a tropical arid environment. These fossil fungi are silicized, with minor amounts of CaCO₃ and Fe, and in some cases a Si/Al ratio similar to smectite. They exist as pseudomorphs, totally depleted in nitrogen, adhering to the surfaces of fine-grained sands, principally quartz and orthoclase. Similar wet aeolian paleoenvironments are suspected for Mars, especially following catastrophic sediment-charged floods of enormous magnitudes that are believed to have contributed to rapid formation of large water bodies in the northern plains, ranging from lakes to oceans. These events are suspected to have contributed to a high frequency of constructional landforms (also known as pseudocraters) related to trapped volatiles and water-enriched sediment underneath a thick blanket of materials that were subsequently released to the martian surface, forming piping structures at the near surface and constructional landforms at the surface. This constructional process on Mars may help unravel the complex history of some of the piping structures observed on Earth; on Earth, evidence for the constructional landforms has been all but erased and the near-surface piping structures exposed through millions of years of differential erosion and topographic inversion now occur as high-standing promontories. If the features on both Earth and Mars formed by similar processes, especially involving water and other volatiles, and since the piping structures of Earth provided suitable environments for life to thrive in, the martian features in the northern plains should be considered as prime targets for physico/mineral/chemical/microbiological analyses once the astrobiological exploration of the red planet begins in earnest.     

Pingos on Earth and Mars

Pingos are massive ice-cored mounds that develop through pressurized groundwater flow mechanisms. Pingos and their collapsed forms are found in periglacial and paleoperiglacial terrains on Earth, and have been hypothesized for a wide variety of locations on Mars. This literature review of pingos on Earth and Mars first summarizes the morphology of terrestrial pingos and their geologic contexts. That information is then used to asses hypothesized pingos on Mars. Pingo-like forms (PLFs) in Utopia Planitia are the most viable candidates for pingos or collapsed pingos. Other PLFs hypothesized in the literature to be pingos may be better explained with other mechanisms than those associated with terrestrial-style pingos.     

Hydrous olivine alteration on Mars and Earth

Hydrous alteration of olivine macrocrysts in a Martian olivine phyric basalt, NWA 10416, and a terrestrial basalt from southern Colorado are examined using SEM, EPMA, TEM, and µXRD techniques. The olivines in the meteorite contain linear nanotubes of hydrous material, amorphous areas, and fluid dissolution textures quite distinct from alteration identified in other Martian meteorites. Instead, they bear resemblance to terrestrial deuteric alteration features. The presence of the hydrous alteration phase Mg‐laihunite within the olivines has been confirmed by µXRD analysis. The cores of the olivines in both Martian and terrestrial samples are overgrown by unaltered rims whose compositions match those of a separate population of groundmass olivines, suggesting that the core olivines are xenocrysts whose alteration preceded crystallization of the groundmass. The terrestrial sample is linked to deep crustal metasomatism and the “ignimbrite flare‐up” of the Oligocene epoch. The comparison of the two samples suggests the existence of an analogous relatively water‐rich magmatic reservoir on Mars.     

Lidar atmospheric measurements on Mars and Earth

The LIDAR instrument operating from the surface of Mars on the Phoenix Mission measured vertical profiles of atmospheric dust and water ice clouds at temperatures around −65 °C. An equivalent lidar system was utilized for measurements in the atmosphere of Earth where dust and cloud conditions are similar to Mars. Coordinated aircraft in situ sampling provided a verification of lidar measurement and analysis methods and also insight for interpretation of lidar derived optical parameters in terms of the dust and cloud microphysical properties. It was found that the vertical distribution of airborne dust above the Australian desert is quite similar to what is observed in the planetary boundary layer above Mars. Comparison with the in situ sampling is used to demonstrate how the lidar derived optical extinction coefficient is related to the dust particle size distribution. The lidar measurement placed a constraint on the model size distribution that has been used for Mars. Airborne lidar measurements were also conducted to study cirrus clouds that form in the Earth’s atmosphere at a similar temperature and humidity as the clouds observed with the lidar on Mars. Comparison with the in situ sampling provides a method to derive the cloud ice water content (IWC) from the Mars lidar measurements.     

Volatiles on Earth and Mars: A comparison

Based on our new and previous determinations of halogens in SNC meteorites, the bulk concentrations of halogens in the SPB, which is thought to be Mars, are estimated. The two-component model for the formation of terrestrial planets as proposed byA. E. Ringwood (Geochem. J. 11, 111–135 (1977) andOn the Origin of the Earth and Moon, Springer-Verlag, New York, 1979) andH. Wa¨nke (Philos. Trans. Roy. Soc. London, Ser. A 303, 287–302 (1981) is further substantiated. It is argued that almost all of the H₂O added to Mars during its homogeneous accretion was converted on reaction with metallic Fe to H₂, which escaped. By comparing the solubilities of H₂O and HCl in molten silicates, the amount of H₂O left in the mantle of Mars at the end of accretion can be related to the abundance of Cl. In this way an H₂O content in the Martian mantle of 36 ppm is obtained, corresponding to an ocean covering the whole planet to a depth of about 130 m.The huge quantities of H₂ produced by the reaction of H₂O with metallic iron should also have removed other volatile species by hydrodynamic escape. Thus it is postulated that the present atmospheres of Venus, Earth, and Mars were formed by degassing the interiors of the planets, after the production of H₂ had ceased, i.e., after metallic iron was no longer available. It is also postulated that the large differences in the amounts of primordial rare gases in the atmospheres of Venus, Earth, and Mars are due mainly to different loss factors.Except for gaseous species, Mars is found to be richer in volatile (halogens) and moderately volatile elements than the Earth. The resulting low release factor of⁴⁰Ar for Mars is attributed to a low degree of fractionation, leading to a relatively small crustal enrichment of even the most incompatible elements like K.     

Erosion by catastrophic floods on Mars and Earth

The large Martian channels, especially Kasei, Ares, Tiu, Simud, and Mangala Valles, show morphologic features strikingly similar to those of the Channeled Scabland of eastern Washington, produced by the catastrophic breakout floods of Pleistocene Lake Missoula. Features in the overall pattern include the great size, regional anastomosis, and low sinuosity of the channels. Erosional features are streamlined hills, longitudinal grooves, inner channel cataracts, scour upstream of flow obstacles, and perhaps marginal cataracts and butte and basin topography. Depositional features are bar complexes in expanding reaches and perhaps pendant bars and alcove bars. Scabland erosion takes place in exceedingly deep, swift floodwater acting on closely jointed bedrock as a hydrodynamic consequence of secondary flow phenomena, including various forms of macroturbulent votices and flow separations. If the analogy to the Channeled Scabland is correct, floods involving water discharges of millions of cubic meters per second and peak flow velocities of tens of meters per second, but perhaps lasting no more than a few days, have occurred on Mars.     

Ionospheric layers of Mars and Earth

We compare the electron densities of two martian ionospheric layers, which we call M1 and M2, measured by Mars Global Surveyor during 9-27 March 1999, with the electron densities of the terrestrial E and F1 layers derived from ionosonde data at six sites. The day-to-day variations are all linked to changes in solar activity, and provide the opportunity of making the first simultaneous study of four photochemical layers in the solar system. The ‘ionospheric layer index’, which we introduce to characterize ionospheric layers in general, varies between layers because different atmospheric chemistry and solar radiations are involved. The M2 and F1 layer peaks occur at similar atmospheric pressure levels, and the same applies to the M1 and E layers.     

Eolian sedimentation on Earth and Mars: Some comparisons

Eolian sediments on Earth are mostly formed from quartz; they consist, in large part, of eolian sand deposits in deserts, silt and loess deposits in and adjoining present and former glaciated areas, and finally clay-sized particles carried in suspension for relatively long distances and deposited in oceanic areas by winds. The quartz particles in these regimes originally came from a granitic source; stresses in granitic rock formation, glacial action, and wind abrasion are largely responsible for making the particles available for the three kinds of eolian deposits. With respect to eolian sediments on Mars, it appears that an entirely different set of criteria must apply, but some critical parameters can usefully be compared. Evidence for free quartz on Mars is lacking and sand-sized particles are probably basaltic, although there does appear to be a deficit in the sand size range. Glacial action does not appear to be available as a large-scale particle producer but high-velocity winds could be efficient producers of very fine particles. Fine particles may aggregate in a similar way to that observed in the Australian regions where “parna” is seen; this could supply a silt mode on Mars. Impact experiments with basalt in eolian abrasion devices suggest that basalt sand-sized particles fragment rapidly to produce silt and clay-sized detritus. Cohesive forces must be more effective on Mars since the gravitational contribution to the bond/weight ratio (R) is lowe; if R = 1 at about 100 μm on Earth, then R = 1 at about 140 μm on Mars and a much greater range of deposits will be stable. Compared to the terrestrial situation, both larger and smaller particles can be expected to make significant contributions to eolian sediments on Mars. The low gravity and the high speed of moving particles and the relatively weak rock material of which they are composed will allow large-scale fine particle production.     

The oxygen-isotopic composition of Earth and Mars

Abstract— The small difference between the O-isotopic mass fractionation lines of the Earth and Mars has been measured precisely using a laser fluorination system. The precision achieved from the two sample sets is better than ±0.014‰, with the offset (Δ¹⁷O) between Mars and Earth measured as +0.321‰. This result shows that all the Shergotty—Nakhla—Chassigny (SNC) meteorites define a high level of isotopic homogeneity, comparable to that of crustal material on the Earth, indicating that these meteorites originate, unequivocally, from a single, common parent body (Mars). Allan Hills 84001, with its ancient age (4.56 Ga), shows that any initial heterogeneity imparted into Mars from the nebula was homogenised very early in the formation history of the planet.     

Power law of dust devil diameters on Mars and Earth

Estimates from visual surveys of the frequency of dust devils, even at terrestrial localities known for their abundance, vary by some four orders of magnitude, making a quantitative hazard assessment difficult. Here I show (1) that new high-quality observations from Mars fit a power law size distribution, (2) that such a power law population can unify the discrepant terrestrial surveys, and (3) that the populations on the two planets appear similar.     

The rate of granule ripple movement on Earth and Mars

The rate of movement for 3- and 10-cm-high granule ripples was documented in September of 2006 at Great Sand Dunes National Park and Preserve during a particularly strong wind event. Impact creep induced by saltating sand caused ∼24 granules min⁻¹ to cross each cm of crest length during wind that averaged ∼9 m s⁻¹ (at a height well above 1 m), which is substantially larger than the threshold for saltation of sand. Extension of this documented granule movement rate to Mars suggests that a 25-cm-high granule ripple should require from hundreds to thousands of Earth-years to move 1 cm under present atmospheric conditions.     

Zones of photosynthetic potential on Mars and the early Earth

Ultraviolet radiation is more damaging on the surface of Mars than on Earth because of the lack of an ozone shield. We investigated micro-habitats in which UV radiation could be reduced to levels similar to those found on the surface of present-day Earth, but where light in the photosynthetically active region (400-700 nm) would be above the minimum required for photosynthesis. We used a simple radiative transfer model to study four micro-habitats in which such a theoretical Martian Earth-like Photosynthetic Zone (MEPZ) might exist. A favorable radiation environment was found in martian soils containing iron, encrustations of halite, polar snows and crystalline rocks shocked by asteroid or comet impacts, all of which are known habitats for phototrophs on Earth. Although liquid water and nutrients are also required for life, micro-environments with favorable radiation environments for phototrophic life exist in a diversity of materials on Mars. This finding suggests that the lack of an ozone shield is not in itself a limit to the biogeographically widespread colonization of land by photosynthetic organisms, even if there are no other UV-absorbers in the atmosphere apart from carbon dioxide. When applied to the Archean Earth, these data suggest that even with the worst-case assumptions about the UV radiation environment, early land masses could have been colonized by primitive photosynthetic organisms. Such zones could similarly exist on anoxic extra-solar planets lacking ozone shields.     

Mars and Earth: Comparison of cold-climate features

On Earth, glacial and periglacial features are common in areas of cold climate. On Mars, the temperature of the present-day surface is appropriate for permafrost, and the presence of water is suspected from data relating to the outgassing of the planet, from remote-sensing measurements over the polar caps and elsewhere on the Martian surface, and from recognition of fluvial morphological features such as channels. These observations and the possibility that ice could be in equilibrium with the atmosphere in the high latitudes north and south of ±40° latitude suggest that glacial and periglacial features should exist on the planet. Morphological studies based mainly on Viking pictures indicate many features that can be attributed to the action of ice. Among these features are extensive talus aprons; debris avalanches; flows that resemble glaciers or rock glaciers; ridges that look like moraines; various types of patterned ground, scalloped scarps, and chaotically collapsed terrain that could be attributed to thermokarst processes; and landforms that may reflect the interaction of volcanism and ice.     

Comparison of Earth and Mars as differentiated planets

Histories of the terrestrial planets are traceable to combinations of to five large-scale postaccretion processes: planetary differentiation, crustal differentiation, outgassing, plate tectonics, and recycling. All have operated on Earth to make a planet that was early differentiated into core, mantle, and crust and at very nearly the same time outgassed to form a differentiated crust, atmosphere and oceans. This gave rise to plate tectonics, recycling and thus two-way communication of the surface crust-atmosphere-ocean system with lower crust and upper mantle. Recycling of the Martian surface is probably restricted to limited chemical weathering of thin alteration surfaces of primary minerals because of the extreme slowness of diffusion controlled alteration where surfaces are not stripped by solution. There is evidence for neither subsidence of sedimentary basins nor subduction zones; thus internal recycling and two-way surface-interior communication is improbable. All sedimentary particles produced by mechanical erosion on Mars through its history are still at the surface or shallowly buried by later sediment. Any atmospheric components reacted with weathering crust are removed from the atmosphere. These and exospheric escape processes must have early reduced an original denser atmosphere to its present pressure after an early episode of planetary differentiation coupled to crustal differentiation and out-gassing. The early history of Mars may have been something like that of Earth until weathering and gas escape drew down its atmosphere.     

Dust devil sediment flux on Earth and Mars: Laboratory simulations

Laboratory simulations using the Arizona State University Vortex Generator (ASUVG) were run to simulate sediment flux in dust devils in terrestrial ambient and Mars-analog conditions. The objective of this study was to measure vortex sediment flux in the laboratory to yield estimations of natural dust devils on Earth and Mars, where all parameters may not be measured. These tests used particles ranging from 2 to 2000 μm in diameter and 1300 to 4800 kg m⁻³ in density, and the results were compared with data from natural dust devils on Earth and Mars. Typically, the cores of dust devils (regardless of planetary environment) have a pressure decrease of ∼0.1-1.5% of ambient atmospheric pressure, which enhances the lifting of particles from the surface. Core pressure decreases in our experiments ranged from ∼0.01% to 5.00% of ambient pressure (10 mbar Mars cases and 1000 mbar for Earth cases) corresponding to a few tenths of a millibar for Mars cases and a few millibars for Earth cases. Sediment flux experiments were run at vortex tangential wind velocities of 1-45 m s⁻¹, which typically correspond to ∼30-70% above vortex threshold values for the test particle sizes and densities. Sediment flux was determined by time-averaged measurements of mass loss for a given vortex size. Sediment fluxes of ∼10⁻⁶-10⁰ kg m⁻² s⁻¹ were obtained, similar to estimates and measurements for fluxes in dust devils on Earth and Mars. Sediment flux is closely related to the vortex intensity, which depends on the strength of the pressure decrease in the core (ΔP). This study found vortex size is less important for lifting materials because many different diameters can have the same ΔP. This finding is critical in scaling the laboratory results to natural dust devils that can be several orders of magnitude larger than the laboratory counterparts.     

Terraforming: making an Earth of Mars

As we understand more about life on Earth and about the chemical and biological potential of other planets and objects in our solar system, it's not too much of a leap to consider creating a habitable environment on another planet. Scientists have begun to ponder the possibility of transforming Mars, the most Earthlike of the nearby planets. Various scenarios have been proposed, and in many ways these scenarios duplicate the processes that transformed the early Earth. Here we look at some of the possibilities.     

Barchan dune asymmetry: Observations from Mars and Earth

Barchan dune asymmetry refers to the extension of one barchan limb downwind. It is a common dune form on Earth and also occurs on Mars and Titan. A new classification of barchan limbs is presented where three types of limb morphology are identified: linear, kinked and beaded. These, along with other dune-scale morphological signatures, are used to identify three of the causes of barchan asymmetry on Mars: bi-directional winds, dune collision and the influence of inclined topography.The potential for specific dune asymmetric morphologies to indicate aspects of the formative wind regime on planetary surfaces is shown. For example, the placement of dune limbs can indicate the general direction and relative strength of formative oblique winds; an extreme barchan limb length may indicate a long duration oblique wind; a kinked limb may be evidence of the passage of a storm; beaded limbs may represent surface-wave instabilities caused by an increase in wind energy parallel to the dune. A preliminary application of these signatures finds evidence for bi-modal winds on Mars. However, these and other morphological signatures of wind direction and relative strength should be applied to planetary landforms with caution as more than one process (e.g., bi-modal winds and collision) may be operating together or sequentially on the dunefield. In addition, analysis should be undertaken at the dunefield scale and not on individual dunes. Finally, morphological data should be acquired from similar-scale dunes within a dunefield.In addition to bi-modal wind regimes on Mars, the frequent parallel alignment of the extended barchan limb to the dune suggests that dune collision is also an important cause of asymmetry on Mars. Some of the more complex dunefield patterns result from a combination of dune collision, limb extension and merging with downwind dunes.Dune asymmetric form does not inhibit dune migration in the Namib Desert or on Mars. Data from the Namib suggest that dune migration rates are similar for symmetric and asymmetric dunes. Further modeling and field studies are needed to refine our understanding of the potential range of limb and dune morphologies that can result from specific asymmetry causes.     

Tsunamis on Mars: Earth analogues of projected Martian sediment

Bolide impacts on Mars, within the proposed ocean boundaries (“contacts 1 and 2”) in the northern lowlands, would certainly have generated ultra high energy waves similar to tsunamis on Earth. Impacts into putative Noachian and Hesperian seas of variable areal extents and depths would have experienced high-energy inundations (transgressions), which would have left an imprint in the stack of deposits adjacent to the proposed shorelines. On Earth, the principal influencing factors for tsunami-wave energy are the character of shoreline topography and coastal water depth, which control wave compression and shoreline friction. Shorelines with narrow embayments and steep offshore gradients produce wave compression and increased collision of grains within the carried load contrasted with linear shorelines and shallow offshore gradients that dissipate energy. Steep offshore gradients produce concentrated major wave friction with the bed engendering high kinetic energy in the wave during emplacement of tsunami-generated sediment, which differs from shallow offshore beds that produce lower frictional effects over a wider area and drawdown of wave energy. Thus, overprinting of transported quartz grains on Earth is greatest where wave energy is highest, attenuated down to minor or nil overprinting where wave energy is less. Such grain overprinting in the form of energy-induced microtextures would also be observed in other grain types such as olivine and plagioclase, as such mineralogies are expected to dominate the Martian landscape based on orbital and local field (lander and rover) perspectives. Kinetic energy variation in tsunamis is controlled more by the square of velocity than mass, the resulting collisional effects of which produce swarms of v-shaped percussion microfeatures on quartz and other silicate mineral surfaces when velocity and compression are highest. This work indicates that a valid test for the ocean hypothesis is targeting “coastal” areas adjacent to narrow embayments where offshore depths are known to be highest, as possible tsunami-emplaced sediments, especially those that have been protected from atmospheric conditions through relatively rapid burial, may reveal a high frequency of percussion cracks, features of which appear to be unique to such terrestrial environments.     

Polygonal cracks in bedrock on Earth and Mars: Implications for weathering

Polygonal crack systems with domal microrelief imaged by the Mars Exploration Rover (MER) Opportunity show remarkable similarity to terrestrial crack systems developed on outcrop surfaces. Study of Jurassic Navajo Sandstone surfaces show development of crack systems in relatively isotropic host rock as a result of tensile weathering stresses. These terrestrial analogs are utilized to understand potential weathering processes on Mars.     

High albedo dune features suggest past dune migration and possible geochemical cementation of aeolian sediments on Mars

High albedo features are identified in association with barchan dunes in an equatorial inter-crater dune field on Mars using images from the MRO mission. This paper describes the morphometric properties of these features and their association with the present barchan dune field. We propose that these features are cemented aeolian deposits that form at the foot of the dune avalanche face. A possible terrestrial analog exists at White Sands National Monument, in south-central New Mexico, USA. The presence of these features suggests past episodes of dune migration in inter-crater dunefields and liquid water in the near sub-surface in sufficient quantity to cause the cementation of aeolian dune sediment.