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.     

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.     

The record of impact cratering on the great volcanic shields of the Tharsis region of Mars

Mariner 9 images of the four great volcanic shields of the Tharsis region of Mars show many circular craters ranging in diameter from 100mm to 20 km. Previous attempts to date the volcanoes from their apparent impact crater densities yielded a range of results. The principal difficulty is sorting volcanic from impact craters for diameters $\text{?1}\text{km}$. Many of the observed craters are aligned in prominent linear and concentric patterns suggestive of volcanic origin. In this paper an attempt is made to date areas of shield surface, covered with high resolution images using only scattered small (?1 km) craters of probable impact origin. Craters of apparent volcanic origin are systematically excluded from the dating counts.The common measure of age, deduced for all surfaces studied, is a calculated “crater age” F′ defined as the number of craters equal to or larger than 1 km in diameter per 10⁶km². The conclusions reached from comparing surface ages and their geological settings are: (1) Lava flow terrain surfaces with ages, F′, from 180 to 490 are seen on the four great volcanoes. Summit surfaces of similar ages, F′ = 360 to 420, occur on the rims of calderas of Arsia Mons, Pavonis Mons, and Olympus Mons. The summit of Ascraeus Mons is possibly younger; F′ is calculated to be 180 for the single area which could be dated. (2) One considerably younger surface, F′ < 110, is seen on the floor of Arsia Mon's summit caldera. (3) Nearly crater free lava flow terrain surfaces seen on Olympus Mons are estimated to be less than half the age of a summit surface. The summit caldera floor is similarly young. (4) The pattern of surface ages on the volcanoes suggests that their eruption patterns are similar to those of Hawaiian basaltic shields. The youngest surfaces seem concentrated on the mid-to-lower flanks and within the summit calderas. (5) The presently imaged sample of shield surface, though incomplete, clearly shows a broad range of ages on three volcanoes—Olympus, Arsia, and Pavonis Mons.Estimated absolute ages of impact dated surfaces are obtained from two previously published estimates of the history of flux of impacting bodies on Mars. The estimated ranges of age for the observed crater populations are 0.5 to 1.2b.y. and 0.07 to 0.2b.y. Areas which are almost certainly younger, less than 0.5 or 0.07b.y., are also seen. The spans of surface age derived for the great shields are minimum estimates of their active lifetimes, apparently very long compared to those of terrestrial volcanoes.     

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.     

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.     

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.     

Spectral evidence of volcanic cryptodomes on the northern plains of Mars

The composition and detailed morphology of dome-shaped features located in western Arcadia Planitia and just west of Utopia Planitia were examined in this study utilizing data from Mars Reconnaissance Orbiter and Mars Odyssey sensors. The domes have diameters averaging 1.5 km and heights averaging 160 m, and are generally dark-toned, although some are lighter toned or have split dark and light-toned surfaces. The domes are surrounded by annular deposits comprising, with increasing distance from the domes, dark-toned aprons, light-toned aureoles, and dark-toned aureoles. Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) data over several areas in the western Arcadia region show that spectra from the flanks of several domes have 1 and 2 μm absorption features consistent with the presence of olivine and a high-Ca pyroxene, nominally augite. Modified Gaussian Model (MGM) analysis of these spectra indicates Fe-rich olivine compositions. The tops of domes and the aprons surrounding many domes have negative sloping flat spectra in the near infrared, which is consistent with tachylite-rich, glassy compositions. High Resolution Imaging Science Experiment (HiRISE) images over several domes indicate that relatively high thermal inertia values associated with the tops of domes can be attributed to boulder strewn surfaces. HiRISE images also reveal that light-toned aureoles around domes consist of crenulated ground resembling “brain terrain” textures previously described for ice-rich concentric crater fill elsewhere on the northern plains. The plains surrounding the domes also display lineations that are interpreted to be lava channels or tubes. The combination of volcanic and ice-related features are consistent with the domes having formed as cryptodomes in the near sub-surface. We suggest that the domes could be basaltic in composition if the magmas were degassed and/or highly crystallized, and thus more viscous than typical basaltic magmas. The intrusion of these magmas into an ice-rich horizon would have produced a pervasively jointed chilled margin on the domes, which, once the domes were exposed, would have mechanically weathered to form the dark aprons. The domes could have served as local centers for ice accumulation during periods of high orbital obliquity, which ultimately would have led to the formation of the “brain terrain” surrounding the features. The domes represent late stage volcanic products on the northern plains of Mars and associated features provide more evidence for the role that ice accumulation and modification has played in recent martian history.     

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.     

Fluid transport on Earth and aeolian transport on Mars

Experimental data on cohesion-free particle transport in fluid beds are applied, via a universal scaling relation, to atmospheric transport of fine grains on Mars. It may be that cohesion due to impact vitrification, vacuum sintering, and adsorbed thin films of water are absent on Mars—in which case the curve of threshold velocity versus grain size may show no turnup to small particle size, and one micron diameter grains may be injected directly by saltation into the Martian atmosphere more readily than 100 micron diameter grains. Curves for threshold and terminal velocities are presented for the full range of Martian pressures and temperatures. Suspension of fine grains is significantly easier at low temperatures and high pressures; late afternoon brightenings of many areas of Mars, and the generation of dust storms in such deep basins as Hellas, may be due to this effect.     

An analytic study of impact ejecta trajectories in the atmospheres of Venus,Mars, and Earth

Calculations have been made to determine the effects of atmospheric drag and gravity on impact ejecta trajectories on Venus, Mars, and the Earth. The equations of motion were numerically integrated for a broad range of body sizes, initial velocities, and initial elevation angles. A dimensionless parameter was found from approximate analytic solutions which correlated the ejecta range, final impact angle, and final impact velocity for all three planets.     

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.     

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.     

Determining the possible building blocks of the Earth and Mars

Abstract— To determine the possible building blocks of the Earth and Mars, 225,792,840 possible combinations of the bulk oxygen isotopic and chemical compositions of 13 chondritic groups at 5% mass increments were examined. Only a very small percentage of the combinations match the oxygen isotopic composition, the assumed bulk FeO concentration, and the assumed Fe/Al weight ratio for the Earth. Since chondrites are enriched in silicon relative to estimates of the bulk Earth, none of the combinations fall near the terrestrial magmatic fractionation trend line in Mg/Si‐Al/Si space. More combinations match the oxygen isotopic composition and the assumed bulk FeO concentration for Mars. These combinations fall near the trend for shergottite meteorites in Mg/Si‐Al/Si space. One explanation for the difficulty in forming Earth out of known chondrites is that the Earth may be composed predominately of material that did not survive to the present day as meteorites. Another explanation could be that significant amounts of silicon are sequestered in the core and/or lower mantle of the Earth.     

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.     

Earth and Venus: A comparative study

The observed density of Venus is about 2% smaller than would be expected if Venus were a twin planet of the Earth, possessing an identical internal composition and structure. In principle, this could be explained by a process of physical segregation of metal particles from silicate particles in the solar nebula prior to accretion, so that Venus accreted from relatively metal-depleted material. However, this model encounters severe difficulties in explaining the nature of the physical segregation process and also the detailed chemical composition of the Earth's mantle. Two alternative hypotheses are examined, both of which attempt to explain the density difference in terms of chemical fractionation processes. Both of these hypotheses assume that the relative abundances of the major elements Fe, Si, Mg, Al, and Ca are similar in both planets. According to the first hypothesis, a larger proportion of the total iron in Venus is present as iron oxide in the mantle, so that the core-to-mantle ratio is smaller than in the Earth. This model implies that Venus is more oxidized than the Earth, with its lower intrinsic density (i.e., corrected to equivalent pressures and temperatures) due to the larger amount of oxygen present. The difference between oxidation states is attributed to differing degrees of accretional heating arising from the relatively smaller mass of Venus. On the other hand, the second hypothesis maintains that Venus is more reduced than the Earth, with its mantle essentially devoid of oxidized iron. The difference intrinsic densities is attributed to the Earth accreting at a lower temperature than Venus as a result of the Earth's greater distance from the center of the nebula. As a result, large amounts of sulfur accreted on the Earth but not on Venus. The sulfur, which entered the core, is believed to have increased the mean density of the Earth because of its relatively high atomic weight. The hypothesis also implies that most of the Earth's potassium, because of its chalcophile properties, entered the core.These hypotheses are evaluated in the light of existing data. The second hypothesis leads to an intrinsic density for Venus which is only 0.4% smaller than that of the Earth. This difference is much smaller than is believed to exist. A wide range of chemical evidence is found to be unfavorable to this second hypothesis, but to be consistent with the interpretation that Venus is more oxidized than the Earth, as required by the first hypothesis.     

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.