Martian atmospheric Lee waves

The Mariner 9 television pictures of Mars showed areas of extensive mountain lee ware phenomenon in the northern mid-latitudes during winter. In most cases the characteristic wavelength of the lee waves is readily observable and in a few cases the boundaries of the wave patterns, as well as the wavelength, are observed. The cloud patterns resulting from the waves generated by the flow across a mountain or crater are dependent upon the velocity profile of the air stream and the vertical stability of the atmosphere. Using the stability as inferred by the temperature structure obtained from the infrared spectrometer data, a two layer velocity model of the air stream is used in calculations based on the theory of mountain lee waves. The parameters that yield a pattern similar to that in a picture with a well-defined wave configuration are a lower 11 km deep air stream of 40 m/sec and an upper air stream of 85 m/sec. This calculation appears to be an upper limit of the wind speeds, with most of the pictures implying wind speeds of the lower layer to be less than 40 m/sec. These results yield magnitudes generally in agreement with circulation models, in particular, the Leovy and Mintz (1969, J. Atmos. Sci.26, 1167) two layer numerical model. Under not too different conditions they calculate winds of approximately 30 and 70 m/sec in the lower and upper layers, respectively.     

Martian atmospheric particulate spectral end-members recovery from PFS and IRIS data

We present an application of a multivariate analyses technique on data returned by the Planetary Fourier Spectrometer (PFS) instrument on board the ESA’s Mars Express (MEX) spacecraft in order to separate the atmospheric contribution from the observed radiation. We observe that Thermal/Far Infrared spectra returned from Mars, covering almost a whole martian year, can be represented by a linear model using a limited set of end-member spectra. We identify the end-members as the suspended mineral dust and water ice clouds, but no surface signature was found. We improve previous studies performed with data from the Thermal Emission Spectrometer (TES) thanks to the higher spectral resolution of PFS. This allows for distinguishing narrow gaseous bands present in the martian atmosphere. Furthermore, the comparison of results from PFS and TES with data collected in 1971 by the Mariner 9 Infrared Interferometer Spectrometer (IRIS) shows an atmospheric dust component with similar spectral behavior. This might indicate homogeneity of the dust source regions over a time period of more than 30 years.     

Martian atmospheric water vapor observations: 1972–1974 apparition

The patrol of Martian water vapor carried out with the echelle-coudé scanner at McDonald Observatory during the 1972–1974 apparition has produced 469 individual photoelectric scans of Doppler-shifted Martian H₂O lines. Almost an entire Martian year was covered during the 1972–1974 period (L_s = 118?269° and 301?80°). Three types of coverage have been obtained: (1) regular—the slit placed pole to pole on the central meridian; (2) latitudinal—the slit placed parallel to the Martian equator at various latitudes; (3) diurnal—the slit placed parallel to the terminator at several times during a Martian day measured from local noon.Both the seasonal and diurnal effects seem to be controlled by the insolation and not the local topography with respect to the 6.1 mb surface. A slight negative correlation with elevation was noted which improved during the seasons of greater H₂O content. The previous seasonal behavior has been confirmed and amplified. The following are the primary conclusions: (1) The planetwide abundance is low (5?15 μm of ppt H₂O) during both equinoctical periods. (2) The maximum abundance of about 40 μm occurs in each hemisphere after solstice at about 40° latitude in that hemisphere. (3) The latitude of the maximum amount in the N-S distribution precedes the latitude of maximum insolation by 10–20° of latitude. (4) During the “drier” seasons (5–20 μm) near the equinoxes on Mars, the atmospheric water vapor changes by a factor of 2–3x over a diurnal cycle with the maximum near local noon. (5) The effects of the 1973 dust storm during the southern summer reduced the amount of water vapor over the southern hemisphere regions to 3–8 μm.     

Regolith-atmosphere exchange of water and carbon dioxide on Mars: Effects on atmospheric history and climate change

Exchange of CO₂ and H₂O between the Mars regolith and the atmosphere-cap system plays an important role in governing the evolution of the martian atmosphere and the martian climate. Most of the exchangeable CO₂ (perhaps one or two orders of magnitude more than the atmospheric inventory) is currently adsorbed on the deep regolith, and can be “cryopumped” to a large quasipermanent CO₂ cap (not now present) during lowest Mars obliquity (θ). During the obliquity driven regolith-cap CO₂ exchange cycle, the atmospheric pressure varies harmonically between ~0.1 mb (lowest Θ) and ? 20 mb (highest Θ). The regolith buffer plays only a small or negligible role in the seasonal CO₂ pressure variations caused by atmosphere-cap exchange because adsorption greatly inhibits diffusion of the seasonal “pressure wave” into the regolith. In contrast, thermally driven H₂O seasonal exchange between the atmosphere and regolith appears to be in large part responsible for observed seasonal variations in the small atmospheric H₂O inventory. Long term exchange of H₂O may be dominated by transfer between the polar caps and ice in the regolith. Available and potential tests of regolith-atmospheric-cap volatile exchange models using ground-based and spacecraft-based techniques are discussed.     

Carbon dioxide: Adsorption on palagonite and partitioning in the Martian regolith

We report new CO₂ adsorption measurements on palagonites. These results are used together with earlier results on basalt and nontronite adsorption to derive a “generic” relationship which is valid to within a factor of 3 for likely mixtures of basalt and weathering products of basalt. The relationship involves only t, P_CO2, and the specific surface area, and is relatively insensitive to mineralogy. It is used to predict the distribution and exchange of CO₂ on Mars. We conclude: (1) One to two orders of magnitude more CO₂ is adsorbed on the regolith than is present in the atmosphere and cap. (2) Nonetheless, most of the initially degassed CO₂ must have been lost to space or must be present as carbonates, especially if there was enough degassed CO₂ to provide a significant early greenhouse effect. (3) Given the derived relationship, the CO₂ vapor pressure curve, and the constraint that the system exhibits the current P_CO2 at the current obliquity, it is possible to predict approximately the atmospheric pressure at any obliquity (with or without a cap) without knowing the total available CO₂ inventory, the regolith mass, the regolith distribution, or its mineralogy, any better than those parameters are currently known.     

The provenance,formation, and implications of reduced carbon phases in Martian meteorites

This review is intended to summarize the current observations of reduced carbon in Martian meteorites, differentiating between terrestrial contamination and carbon that is indigenous to Mars. Indeed, the identification of Martian organic matter is among the highest priority targets for robotic spacecraft missions in the next decade, including the Mars Science Laboratory and Mars 2020. Organic carbon compounds are essential building blocks of terrestrial life, so the occurrence and origin (biotic or abiotic) of organic compounds on Mars is of great significance; however, not all forms of reduced carbon are conducive to biological systems. This paper discusses the significance of reduced organic carbon (including methane) in Martian geological and astrobiological systems. Specifically, it summarizes current thinking on the nature, sources, and sinks of Martian organic carbon, a key component to Martian habitability. Based on this compilation, reduced organic carbon on Mars, including detections of methane in the Martian atmosphere, is best described through a combination of abiotic organic synthesis on Mars and infall of extraterrestrial carbonaceous material. Although conclusive signs of Martian life have yet to be revealed, we have developed a strategy for life detection on Mars that can be utilized in future life‐detection studies.     

The stability and transport of carbon dioxide on Iapetus

Carbon dioxide has been detected associated with Iapetus' dark material by the Cassini spacecraft. This CO₂ may be primordial and/or resulting from ongoing production by photolysis of water-ice in the presence of carbonaceous material [Allamandola, L.J., Sandford, S.A., Valero, G.J., 1988. Icarus 76, 225-252]. Although any primordial CO₂ would likely be complexed with the dark material and thus stable against thermal transport to Iapetus' poles [Buratti, B.J., and 28 colleagues, 2005. Astrophys. J. 622, L149-L152], active production of CO₂ would result in some fraction of the CO₂ being mobile enough to allow the accumulation of CO₂ at Iapetus' poles. We develop a computer model to simulate ballistic transport of CO₂ ice on Iapetus, accounting for Iapetus' gravitational binding energy and polar cold traps. We find that the residence time of CO₂ ice outside the polar regions is very short; a sheet of CO₂ ice near the equator of Iapetus decreases in thickness at a rate of 50 mm year⁻¹. The sublimated CO₂ will ballistically move around Iapetus until it reaches the polar cold traps where it can be sequestered for up to 15 years. If the total surface inventory of CO₂ exceeds 3×¹⁰⁷ kg, the polar ice cap will be permanent. While CO₂ is moving around the surface, a small percentage will eventually reach escape velocity and be lost from the system. As such, a seasonal polar cap is lost at rate of 12% every solar orbit as the CO₂ moves between the two polar cold traps.     

Simulation of the Martian spectral radiance in the presence of atmospheric dust

The interest towards Mars is nowadays renewed as various satellites, already launched or foreseen for the future, will visit this planet, providing a new wealth of data. In particular, infrared spectroscopic observations need a parallel modelling effort for a proper interpretation of observations. The goal of our modelling is to evaluate the influence of a non negligible fraction of dust particles on intensity and profile of atmospheric Martian spectra. The joint effects of the atmosphere and the surface materials have been also accounted for. For the modelling, a version of the MODTRAN code, expressly modified for application to the Mars environment, has been used. As an example of the materials forming dust dispersed in the atmosphere and on the surface, we have considered andesite. Indices of refraction (n and k) of this material have been derived from laboratory measurements. The obtained results can have an important impact on the interpretation of infrared spectra that instruments such as TES (Thermal Emission Spectrometer), on board the Mars Global Surveyor, and PFS, in the Mars Express mission, will provide.     

The regulation of carbon dioxide and climate: Gaia or geochemistry

This is a review of the Gaia hypothesis which postulates a condition of planetary homeostasis affecting chemical composition and climate. Some criticisms are answered and a new model is introduced for the long term regulation of the mean surface temperature through the biological control of CO₂ partial pressure.     

Thermal modeling of shock melts in Martian meteorites: Implications for preserving Martian atmospheric signatures and crystallization of high‐pressure minerals from shock melts

The distribution of shock melts in four shergottites, having both vein and pocket geometry, has been defined and the conductive cooling time over the range 2500 °C to 900 °C calculated. Isolated 1 mm² pockets cool in 1.17 s and cooling times increase with pocket area. An isolated vein 1 × 7 mm in Northwest Africa (NWA) 4797 cools to 900 °C in 4.5 s. Interference between thermal haloes of closely spaced shock melts decreases the thermal gradient, extending cooling times by a factor of 1.4 to 100. This is long enough to allow differential diffusion of Ar and Xe from the melt. Small pockets (1 mm²) lose 2.2% Ar and 5.2% Xe during cooling, resulting in a small change in the Ar/Xe ratio of the dissolved gas over that originally trapped. With longer cooling times there is significant fractionation of Xe from Ar and the Ar/Xe ratio increases rapidly. The largest pockets show less variation of Ar/Xe and likely preserve the original trapped gas composition. Considering all of the model calculations, even the smallest isolated pockets have cooling times greater than the duration of the pressure pulse, i.e., >0.01 s. The crystallization products of these shock melts will be unrelated to the peak shock pressure experienced by the meteorite.     

The Argentinean Patagonia and the Martian landscape

Throughout the Cenozoic Era, the geological history of the Argentinean Patagonia was dominated by basaltic volcanism and glacial and periglacial environments. Several geological and geomorphological processes that concurred to the sculpting of the landscape of this area could have been similar to those responsible of the shaping of the Martian surface. In this work a survey of some high-resolution satellite images of the Argentinean Patagonia is performed in order to identify possible geomorphological analogs of the Martian surface. Several morphologies that resemble Martian features are presented and discussed. They consist of proglacial and periglacial features, relatively small circular depressions, gullies, fan-deltas, eolian streaks, and diluvial dunes. Results suggest that the Argentinean Patagonia appears to consist of an interesting terrestrial analog for the Martian landscape. Furthermore, the study area shows to be interesting in order to test robotic instruments and human missions equipment, to train astronauts of future human expeditions to Mars, and to perform astrobiological experiments.     

Electron energy deposition in carbon dioxide

The processes by which energetic electrons lose energy in a weakly ionized gas of carbon dioxide are discussed and a consistent set of electron impact cross-sections is compiled. Calculations of the excitations, ionizations and neutral particle heating produced by the absorption of electrons in carbon dioxide gas are carried out for fractional ionizations ranging from 10^?2 to 10^?6.     

Production and detection of carbon dioxide on Iapetus

Cassini VIMS detected carbon dioxide on the surface of Iapetus during its insertion orbit. We evaluated the CO₂ distribution on Iapetus and determined that it is concentrated almost exclusively on Iapetus’ dark material. VIMS spectra show a 4.27-μm feature with an absorption depth of 24%, which, if it were in the form of free ice, requires a layer 31 nm thick. Extrapolating for all dark material on Iapetus, the total observable CO₂ would be 2.3 × 10⁸ kg.Previous studies note that free CO₂ is unstable at 10 AU over geologic timescales. Carbon dioxide could, however, be stable if trapped or complexed, such as in inclusions or clathrates. While complexed CO₂ has a lower thermal volatility, loss due to photodissociation by UV radiation and gravitational escape would occur at a rate of 2.6 × 10⁷ kg year⁻¹. Thus, Iapetus’ entire inventory of surface CO₂ could be lost within a few decades.The high loss/destruction rate of CO₂ requires an active source. We conducted experiments that generated CO₂ by UV radiation of simulated icy regolith under Iapetus-like conditions. The simulated regolith was created by flash-freezing degassed water, crushing it into sub-millimeter sized particles, and then mixing it with isotopically labeled amorphous carbon (¹³C) dust. These samples were placed in a vacuum chamber and cooled to temperatures between 50 K and 160 K. The samples were irradiated with UV light, and the products were measured using a mass spectrometer, from which we measured ¹³CO₂ production at a rate of 2.0 × 10¹² mol s⁻¹. Extrapolating to Iapetus and adjusting for the solar UV intensity and Iapetus’ surface area, we calculated that CO₂ production for the entire surface would be 1.1 × 10⁷ kg year⁻¹, which is only a factor of two less than the loss rate. As such, UV photochemical generation of CO₂ is a plausible source of the detected CO₂.     

Matching Martian crustal magnetization and magnetic properties of Martian meteorites

Abstract— Magnetic properties of 26 (of 32) unpaired Martian meteorites (SNCs) are synthesized to further constrain the lithology carrying Martian magnetic crustal sources. Magnetic properties of ultramafic cumulates (i.e., Chassigny, Allan Hills [ALH] 84001) and lherzolitic shergottites (ALH 77005, Lewis Cliff [LEW] 88516) are one or two orders of magnitude too weak to account for the crustal magnetizations, assuming magnetization in an Earth‐like field. Nakhlites and some basaltic shergottites, which are the most magnetic SNCs, show the right intensity. Titanomagnetite is the magnetic carrier in the nakhlites (7 meteorites), whereas in most basaltic shergottites (11 meteorites) it is pyrrhotite. Dhofar (Dho) 378, Los Angeles, and NWA 480/1460 and 2046 are anomalous basaltic shergottites, as their magnetism is mainly due to titanomagnetite. Pyrrhotite should be among the candidate minerals for the magnetized Noachian crust.     

The quantity and condition of Martian underground water

It is widely accepted that Mars holds a quantity of water in its surface crustal region but the amount is unknown. The present arguments quantify this suspicion, offering an estimate of the quantity on the basis of certain consequences of the comparison between the present observed compositions of the atmospheres of the planets Earth, Venus, and Mars, and the inferred compositions of the mantles of the icy satellites. The results are consistent with alternative estimates such as they are but offer possibilities of regarding the problems of the crustal region of Mars in a different way.     

The Martian Nonhydrostatic Components of Moment-of-Inertia

The author puts forward the proposal in this paper that all the terrestrial planets (Venus, the Earth, and Mars) as well as the Moon deviate from hydrostatic equilibrium to some degree. The Earth's level of deviation of these four celestial bodies is minimum, and that of Mars is maximum. Moreover, the author estimates Martian nonhydrostatic components of the principal moments-of-inertia using five models for the interior of Mars. Comparison with other terrestrial planets shows that setting the range of mean moment-of-inertia ratio, I/MR², in 0.345 ~ 0.355for Mars is reasonable. This revised version was published online in July 2006 with corrections to the Cover Date.     

MAIC-2, a latitudinal model for the Martian surface temperature, atmospheric water transport and surface glaciation

The Mars Atmosphere-Ice Coupler MAIC-2 is a simple, latitudinal model, which consists of a set of parameterisations for the surface temperature, the atmospheric water transport and the surface mass balance (condensation minus evaporation) of water ice. It is driven directly by the orbital parameters obliquity, eccentricity and solar longitude (L_s) of perihelion. Surface temperature is described by the Local Insolation Temperature (LIT) scheme, which uses a daily and latitude-dependent radiation balance. The evaporation rate of water is calculated by an expression for free convection, driven by density differences between water vapor and ambient air, the condensation rate follows from the assumption that any water vapour which exceeds the local saturation pressure condenses instantly, and atmospheric transport of water vapour is approximated by instantaneous mixing. Glacial flow of ice deposits is neglected. Simulations with constant orbital parameters show that low obliquities favour deposition of ice in high latitudes and vice versa. A transient scenario driven by a computed history of orbital parameters over the last 10 million years produces essentially monotonically growing polar ice deposits during the most recent 4 million years, and a very good agreement with the observed present-day polar layered deposits. The thick polar deposits sometimes continue in thin ice deposits which extend far into the mid latitudes, which confirms the idea of “ice ages” at high obliquity.