Martian Temperature Research Articles

A single-scattering approximation for infrared radiative transfer in limb geometry in the Martian atmosphere

We present a single-scattering approximation for infrared radiative transfer in limb geometry in the Martian atmosphere. It is based on the assumption that the upwelling internal radiation field is dominated by a surface with a uniform brightness temperature. It allows the calculation of the scattering source function for individual aerosol types, mixtures of aerosol types, and mixtures of gas and aerosol. The approximation can be applied in a Curtis–Godson radiative transfer code and is used for operational retrievals from Mars Climate Sounder measurements. Radiance comparisons with a multiple scattering model show good agreement in the mid- and far-infrared although the approximate model tends to underestimate the radiances in realistic conditions of the Martian atmosphere. Relative radiance differences are found to be about 2% in the lowermost atmosphere, increasing to ∼ 10 % in the middle atmosphere of Mars. The increasing differences with altitude are mostly due to the increasing contribution to limb radiance of scattering relative to emission at the colder, higher atmospheric levels. This effect becomes smaller toward longer wavelengths at typical Martian temperatures. The relative radiance differences are expected to produce systematic errors of similar magnitude in retrieved opacity profiles.

Enhanced runout and erosion by overland flow at low pressure and sub-freezing conditions: Experiments and application to Mars

We present the results of laboratory experiments to study the sediment transport and erosional capacity of water at current martian temperature and pressure. We have performed laboratory simulation experiments in which a stream of water flowed over test beds at low temperature (∼−20 °C) and low pressure (∼7 mbar). The slope angle was 14° and three sediment types were tested. We compared the erosive ability, runout and resulting morphologies to experiments performed at ambient terrestrial temperature (∼20 °C) and pressure (∼1000 mbar), and also to experiments performed under low pressure only. We observed that, as expected, water is unstable in the liquid phase at low temperature and low pressure, with boiling and freezing in competition. Despite this, our results show that water at low temperature and low pressure has an equivalent and sometimes greater erosion rate than at terrestrial temperature and pressure. Water flows faster over the sediment body under low temperature and low pressure conditions because the formation of ice below the liquid-sediment contact inhibits infiltration. Flow speed and therefore runout distance are increased. Experiments at low pressure but Earth-ambient temperature suggest that flow speeds are faster under these conditions than under Earth-ambient pressure and temperature. We hypothesise that this is due to gas bubbles, created by the boiling of the water under low atmospheric pressure, impeding liquid infiltration. We have found that both basal freezing and low pressure increase the flow propagation speed – effects not included in current models of fluvial activity on Mars. Any future modelling of water flows on Mars should consider this extra mobility and incorporate the large reduction in fluid loss through infiltration into the substrate.

Water ice cloud formation on Mars is more difficult than presumed: Laboratory studies of ice nucleation on surrogate materials

The role of water ice clouds in the martian water cycle and climate depends on cloud properties such as particle size and number distribution. These properties, in turn, depend on heterogeneous nucleation parameters which are poorly understood. Here we report laboratory experiments performed under martian temperature and water partial pressure conditions (158–185 K, 9 × 10 −7–1 × 10 −4 Torr H 2O) to determine the critical saturation ratio for ice onset, S crit, as a function of temperature and dust composition. Using infrared spectroscopy to monitor ice nucleation and growth, we find a significant barrier to ice formation, with a pronounced temperature dependence. Even on clay minerals which show uptake of non-crystalline water before ice nucleation, we find a saturation ratio of 2.5 or more (RH ice > 250%) is needed to begin ice growth at temperatures near 160 K. These results could lead to changes of four orders of magnitude in the nucleation rate relative to the presumptions used currently in Mars microphysical models, which commonly set the contact parameter, m, to a single value of 0.95. Our results range from m = 0.84 to m = 0.98. For ice nucleation on Arizona Test Dust, the temperature dependence is described by m = 0.0046 * T nucl + 0.1085, while m = 0.0055 * T nucl + 0.0003 on a smectite-rich clay sample. Our findings suggest that cloud formation will be more difficult than previously thought, potentially leading to areas of increased near-surface humidity but generally drier conditions in the atmosphere of Mars, overall.

Distinct hematite populations from simultaneous fitting of Mössbauer spectra from Meridiani Planum, Mars

At Meridiani Planum, Mars, hematite occurs as a lag of ∼5 mm diameter spherules and their fragments and within the matrix of the sulfate‐rich outcrop as <30 μm particles. Well crystalline and chemically pure bulk hematite undergoes a magnetic transition at ∼264 K (Morin transition) that can be detected by Mössbauer spectroscopy and is within the Martian diurnal temperature range. We analyzed outcrop and lag hematite Mössbauer spectra obtained by the Mars Exploration Rover (MER) Opportunity as a function of temperature using a simultaneous fitting procedure to determine the Morin temperature and the temperature interval over which it occurs. Mössbauer spectra for terrestrial hematite‐bearing samples were acquired for comparison at Martian temperatures using a MER‐like spectrometer. Both outcrop and spherule hematites are characterized by two populations of hematite whose Mössbauer sextets have different Morin transition behavior. Compared to pure bulk hematite, the Morin temperature for Martian hematite is lower or not present within the temperature measurement range (190–290 K) and occurs over a wider temperature interval, consistent with reduced crystallinity, reduced particle or crystallite size, and/or chemical impurities (e.g., Al3+, Ti4+, H2O, and OH−). If the Morin transition behavior for outcrop hematite results solely from particle size effects and the nonjarosite ferric doublet is interpreted as superparamagnetic hematite as a working hypothesis, outcrop hematite is characterized by a size distribution of hematite particles ranging from superparamagnetic to possibly ∼30 μm.

Methane adsorption on a martian soil analog: An abiogenic explanation for methane variability in the martian atmosphere

Recent observations suggest methane in the martian atmosphere is variable on short spatial and temporal scales. However, to explain the variability by loss reactions requires production rates much larger than expected. Here, we report results of laboratory studies of methane adsorption onto JSC-Mars-1, a martian soil simulant, and suggest that this process could explain the observations. Uptake coefficient ( γ) values were measured as a function of temperature using a high-vacuum Knudsen cell able to simulate martian temperature and pressure conditions. Values of γ were measured from 115 to 135 K, and the data were extrapolated to higher temperatures with more relevance to Mars. Adsorptive uptake was found to increase at lower temperatures and larger methane partial pressures. Although only sub-monolayer methane surface coverage is likely to exist under martian conditions, a very large mineral surface area is available for adsorption as atmospheric methane can diffuse meters into the regolith. As a result, significant methane may be temporarily lost to the regolith on a seasonal time scale. As this weak adsorption is fully reversible, methane will be re-released into the atmosphere when surface and subsurface temperatures rise and so no net loss of methane occurs. Heterogeneous interaction of methane with martian soil grains is the only process proposed thus far which contains both rapid methane loss and rapid methane production mechanisms and is thus fully consistent with the reported variability of methane on Mars.

Modeling diffusion advection in the mass transfer of water vapor through martian regolith

Diffusion advection is an effect in diffusive multicomponent mass transfer that occurs when the flux vectors of the individual components do not add up to zero. This can be a significant effect for the mass transfer of water vapor from subsurface ice or liquid reservoirs through porous regolith at martian temperatures and pressures. Ignoring diffusion advection and using Fick's law alone to calculate the flux under these conditions will result in an erroneously small value while using a measured flux to calculate a diffusivity will result in an erroneously high value. The inaccuracy in both cases increases with temperature. The literature contains several examples of erroneous treatment of this effect. The correct approach is well-known from other applications of mass transfer and takes diffusion advection into account in the appropriate amount regardless of the temperature and pressure and reduces to the simple Fick's law when conditions warrant. In this way, there is no need to decide under what conditions diffusion advection is or is not important. It can be used in the transition region to pure Knudsen diffusion in a fashion similar to that used with the more limited Fickian approach.

Frequency and temperature dependence in electromagnetic properties of Martian analog minerals

Ground‐penetrating radar (GPR) has the potential to image the Martian subsurface to give geological context to drilling targets, investigate stratigraphy, and locate subsurface water. GPR depth of penetration depends strongly on the electromagnetic (EM) properties (complex dielectric permittivity, complex magnetic permeability, and DC resistivity) of the subsurface. These EM properties in turn depend on the mineralogical composition of the subsurface and are sensitive to temperature. In this study, the EM properties of Martian analog samples were measured versus frequency (1 MHz‐1 GHz) and at Martian temperatures (180–300 K). Results from the study found the following: gray hematite has a large temperature‐dependent dielectric relaxation, magnetite has a temperature‐independent magnetic relaxation, and JSC Mars‐1 has a broad temperature‐dependent dielectric relaxation most likely caused by absorbed water. Two orbital radars, MARSIS and SHARAD, are currently investigating the subsurface of Mars. On the basis of the results of our measurements, the attenuation rate of gray hematite is 0.03 and 0.9 dB/m, magnetite is 0.04 and 1.1 dB/m, and JSC Mars‐1 is 0.015 and 0.09 dB/m at MARSIS and SHARAD frequencies, respectively, and at the average Martian temperature of 213 K. With respect to using GPR for subsurface investigation on Mars, absorbed water will be a larger attenuator of radar energy as high concentrations of magnetite and gray hematite are not found globally on Mars.

Terrestrial models for extraterrestrial life: methanogens and halophiles at Martian temperatures

Cold environments are common throughout the Galaxy. We are conducting a series of experiments designed to probe the low-temperature limits for growth in selected methanogenic and halophilic Archaea. This paper presents initial results for two mesophiles, a methanogen, Methanosarcina acetivorans, and a halophile, Halobacterium sp. NRC-1, and for two Antarctic cold-adapted Archaea, a methanogen, Methanococcoides burtonii, and a halophile, Halorubrum lacusprofundi. Neither mesophile is active at temperatures below 5 °C, but both cold-adapted microorganisms show significant growth at sub-zero temperatures (−2 °C and −1 °C, respectively), extending previous low-temperature limits for both species by 4–5 °C. At low temperatures, both H. lacusprofundi and M. burtonii form multicellular aggregates, which appear to be embedded in extracellular polymeric substances. This is the first detection of this phenomenon in Antarctic species of Archaea at cold temperatures. The low-temperature limits for both psychrophilic species fall within the temperature range experienced on present-day Mars and could permit survival and growth, particularly in sub-surface environments. We also discuss the results of our experiments in the context of known exoplanet systems, several of which include planets that intersect the Habitable Zone. In most cases, those planets follow orbits with significant eccentricity, leading to substantial temperature excursions. However, a handful of the known gas giant exoplanets could potentially harbour habitable terrestrial moons.

Mars laser hygrometer.

We have designed and built a miniature near-IR tunable diode laser (TDL) spectrometer for measuring in situ the water vapor mixing ratio either in the Martian atmosphere or thermally evolved from Martian soil or ice samples. The laser hygrometer uses a thermoelectrically cooled single-mode distributed-feedback TDL at 1.87 microm to scan over a selected vibration-rotation line of both H2O and CO2 near 5327.3 cm(-1). A working prototype that weighs only 230 g has been built and used to generate spectra whose analysis demonstrates precision sensitivities as fine as 1 part in 10(6) by volume in 1 s or 0.1 part in 10(6) in 10 s at Martian pressures and temperatures. Absolute uncertainties of approximately 5% are calculated.

Stability of hydrous minerals on the martian surface

The presence of water-bearing minerals on Mars has long been discussed, but little or no data exist showing that minerals such as smectites and zeolites may be present on the surface in a hydrated state (i.e., that they could contain H 2O molecules in their interlayer or extra-framework sites, respectively). We have analyzed experimental thermodynamic and X-ray powder diffraction data for smectite and the most common terrestrial zeolite, clinoptilolite, to evaluate the state of hydration of these minerals under martian surface conditions. Thermodynamic data for clinoptilolite show that water molecules in its extra-framework sites are held very strongly, with enthalpies of dehydration for Ca-clinoptilolite up to three times greater than that for liquid water. Using these data, we calculated the Gibbs free energy of hydration of clinoptilolite and smectite as a function of temperature and pressure. The calculations demonstrate that these minerals would indeed be hydrated under the very low- P (H 2O) conditions existing on Mars, a reflection of their high affinities for H 2O. These calculations assuming the partial pressure of H 2O and the temperature range expected on Mars suggest that, if present on the surface, zeolites and Ca-smectites could also play a role in affecting the diurnal variations in martian atmospheric H 2O because their calculated water contents vary considerably over daily martian temperature ranges. The open crystal structure of clinoptilolite and existing hydration and kinetic data suggest that hydration/dehydration are not kinetically limited. Based on these calculations, it is possible that hydrated zeolites and clay minerals may explain some of the recent observations of significant amounts of hydrogen not attributable to water ice at martian mid-latitudes.

The Radiative Effects of Martian Water Ice Clouds on the Local Atmospheric Temperature Profile

Mars Pathfinder made numerous discoveries, one of which was a deep temperature inversion that extended from about 15 km down to 8 km above the surface. It has been suggested by Haberle et al. (1999. J. Geophys. Res. 104, 8957–8974.) that radiative cooling by a water ice cloud may generate such an inversion. Clouds can strongly affect the local air temperature due to their ability to radiate efficiently in the infrared and due to the low air mass of the martian atmosphere, which allows the temperature to change during the relatively short lifetime of a cloud. We utilize a time-dependent microphysical aerosol model coupled to a radiative–convective model to explore the effects water ice clouds have on the local martian temperature profile. We constrain the dust and water vapor abundance using data from the Viking Missions and Mars Pathfinder. Water ice clouds with visible optical depths of τ≥0.1 form readily in these simulations. These clouds alter the local air temperature directly, through infrared cooling, and indirectly, by redistributing atmospheric dust. With this model we are able to reproduce the temperature inversions observed by Mars Pathfinder and Mars Global Surveyor.

Neutral upper atmospheres of Venus and Mars

Numerous measurements of the neutral upper atmosphere above 100 km have been made from spacecraft over Venus and over Mars. The Venus exospheric temperatures are unexpectedly low (less than 300°K near noon and less than 130°K near midnight). These very low temperatures may be partially caused by collisional excitation of CO 2 vibrational states by atomic oxygen and partially by eddy cooling. The Venus atmosphere is unexpectedly insensitive to solar EUV variability. On the other hand, the Martian dayside exospheric temperature varies from 150°K to 400°K over the 11-year solar cycle, where CO 2 15-μm cooling may be less effective because of lower atomic oxygen mixing ratios. On Venus, temperature increases with altitude on the dayside (thermosphere), but decreases with altitude from 100 to 150 km on the nightside (cryosphere). However, dayside Martian temperatures near solar minimum for maximum planet-sun distance and low solar activity are essentially isothermal from 40 km to 200 km. During high solar activity, the thermospheric temperatures of Mars sharply increase. The Venus neutral upper atmosphere contains CO 2, O, CO, C, N 2, N, He, H, D and hot nonthermal H, O, C, and N, while the dayside Mars neutral upper atmosphere contains CO 2, O, O 2, CO, C, N 2, He, H, and Ar. There is evidence on Venus for inhibited day-to-night transport as well as superrotation of the upper atmosphere. Both atmospheres have substantial wave activity. Various theoretical models used to interpret the planetary atmospheric data are discussed.

The spatial and seasonal distribution of Martian clouds and some meteorological implications

The spatial and seasonal distributions of Martian atmospheric clouds, organized according to simple morphologic criteria, exhibit distinct patterns. When interpreted self‐consistently using analogies to terrestrial cloud forms and Martian temperature, wind direction, and water vapor measurements, patterns of cloud occurrence provide some loose constraints on global‐scale near‐surface wind speed, static stability, and humidity. We have examined all Mariner 9 and Viking Orbiter images for this study; we concentrate primarily on the larger Viking data set. Whenever observations are possible, relatively high near‐surface winds appear to follow the seasonal cap edges during early fall, late winter, and spring. Moderate to high winds are also inferred in mid‐latitudes for mid southern winter and in low latitudes, mainly in the steeply sloping areas of Tharsis, near the solstices. At other times, lower winds are suspected. Hemispheric asymmetries are traced to differences in atmospheric hydration state and to global dust storm related effects on the atmospheric temperature structure and the north polar cap recession schedule. Cloud occurrence data suggest that the near‐surface daytime static stability is low in the northern hemisphere during summer and at low latitudes during mid northern spring. Relatively high static stability is deduced near the winter poles and globally during the dust storm season. In spite of low atmospheric temperatures, the correspondingly low absolute humidity apparently precludes the formation of thick water ice clouds at high latitudes in mid to late autumn and winter in both hemispheres and in southern mid‐latitudes during early winter. During northern spring and summer, saturation conditions seem to be easily achieved at mid‐latitudes, and condensate clouds are abundant; the situation is complicated by atmospheric dust in southern spring and summer. Low latitudes generally appear to be farther from saturation than mid‐latitudes, and clouds generally form more easily in the northern hemisphere than in the south during corresponding seasons.

Midnight on the Red Planet

Recording the deep chill of the witching hour on Mars is an evocative enough idea-surely there's a short story there somewhere-but it is also important for an understanding of the planet. It is not so much a matter of simply knowing the Martian temperature in the dead of night as of finding out how the different parts of that diverse world cool down from the lesser chill that passes for the warmth of day. By taking temperature readings at selected times around the clock, it is possible to find out how rapidly the surface materials absorb and give off heat-a property called thermal inertia. This can help determine whether given parts of the surface are dominated by sand, rocks or boulders, while relating also to such factors as the role of the winds in distributing heat around the planet. The Viking orbiters each carry a heat sensor-an Infrared Thermal Mapper (IRTM)-for this purpose, and have been scanning the planet since the day they arrived, weeks before the landers descended to the surface. In August of 1976, for example, it was the IRTM temperature measurements that led to the conclusion that the Martian residual north-polar cap consists almost entirely of water, since the readings were too high for frozen carbon dioxide but low enough for water ice. The polar caps, however, respond more to seasonal than to diurnal effects. It is the rest of the surface that requires careful day-and-night study. Readings just before dawn show how cold the ground has gotten during the night; sunrise measurements reveal the beginnings of the day's warming, while readings during the afternoon show just how much heat the surface material has actually taken in. Sundown and the coming of night show the curve reversing, as the stored heat is given off. To complete the cycle, a midnight reading should show the surface approaching its coldest point, which will be monitored in the pre-dawn hours.

Differential transmission of sunlight on Mars: Biological implications

A euphotic zone seems to exist at about 1 cm subsurface in the Martian epilith. At this depth visible light is still intense enough to be utilized by conceivable photosynthetic organisms; but the germicidal ultraviolet intensities at the Martian surface have been reduced to values manageable by terrestrial life. Such euphotic zone organisms would experience moderately high Martian temperatures at equatorial latitudes and can be dispersed readily during global dust stroms. During such storms the Martian euphotic zone may reach the surface. The aerosol content of the Martian atmosphere can be monitored by multiband single line scans of the sun at large zenith angles by the Viking lander camera; and the postulated euphotic zone organisms can be searched for with the Viking lander sample arm and biology experiments.

Infrared thermal mapping experiment: The Viking Mars orbiter

The Mars infrared thermal mapper (IRTM) will be carried on the scan platform of the orbiter of the Viking 1975 mission. The IRTM is a multichannel radiometer with several detectors in each of six spectral regions. This instrument will measure the reflected solar radiation and surface thermal emission from the area viewed by the orbiter imaging system with nominal 5 km resolution. Extensive additional areas will be covered for which simultaneous imaging will not be available. The spectral channels are selected to be sensitive to surface emissivity variations and provide good temperature resolution over the entire range of Martian temperatures. These observations will allow determination of the surface kinetic temperature and thermal balance, and by coverage of the dark hemisphere, a search for regions with anomalous cooling can be made. Observations of ground frosts or clouds will help to determine their composition, and in the case of extensive H 2O frosts, will allow the local water vapor pressure to be estimated.

Thermal conductivity of particulate basalt as a function of density in simulated lunar and Martian environments

As part of an effort to properly define the thermophysical model of the lunar surface, experimental data have been obtained to determine the thermal conductivity of a particulate basalt sample (37 to 62 μ diameter) as a function of density in a simulated lunar temperature and pressure environment. A sample at six different densities ranging from 0.79 g/cm3 to 1.50 g/cm3 was investigated by using Ronald B. Merrill's method of thermal conductivity measurement. Recent measurements of the conductivity of the Apollo 11 lunar sample are included for comparison. Kenneth Watson's equation for the thermal conductivity of powders in a vacuum, K = A + BT3, has been curve-fitted to the vacuum data for each density. The coefficients A and B are useful for application in thermophysical models of the lunar surface. Thermal conductivity data were also obtained under simulated Martian temperature and pressure environment at four of the densities. A separate effort was made to determine the maximum density obtainable with the specific sample to draw qualitative conclusions concerning the ambiguous value of density yielded by the Russian Luna 13 in situ density experiment. Thermal conductivity of particulate basalt was found to be a definite function of density in a simulated lunar environment and that function has been established. However, under simulated Martian environmental conditions, density and temperature had only a slight effect on thermal conductivity.

Response of fungi to diurnal temperature extremes.

REPEATED freezing and thawing of bacteria is generally considered to be lethal1,2, but Aerobacter aerogenes and a Pseudomonas species have survived and grown well in experiments simulating Martian temperature extremes of about +25° C to −75° C (ref. 3). The bacteria spent only about 4.5 h above 0° C with a maximum near 25° C in each 24 h cycle. Growth rates in liquid media were found to be comparable with the non-cycled controls held at 25° C. In similar work with desert algal-lichen soil crusts4, the algae survived repeated freezing and thawing but did not grow during the treatment. The algae were grown later on a modified Pochon solution incubated at 27° C–30° C. The diurnal temperature extremes were −79° C or −195° C for 15 h and 22° C for 9 h for periods of 1–7 days. As far as is known, no comparable work has been done on the response of fungi to diurnal temperature extremes.