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1.
Spectra of Mars from 100 to 360 cm?1 were obtained during three different observation periods from NASA's Kuiper Airborne Observatory. Also, a new thermal model was constructed for the surface of Mars, and synthetic spectra were computed from the models to compare with the observations. The models include the effects of a dusty atmosphere which absorbs, scatters, and reradiates energy. The synthetic spectra show significant effects on disk-averaged brigthness temperatures, as well as absorption features, due to silicate dust. The spectra of Mars, which are ratios of Mars to the Moon, do not fit the synthetic spectra unless the surface emissivities of Mars and the Moon have different dependencies on wavelenght. A possible explanation for this behavior is a difference in soil particle-size distributions between Mars and the Moon, with Mars being depleted in large particles compared to the Moon. Small particles are consistent with clay minerals which have been suggested elsewhere as constituents of the Martian surface.  相似文献   

2.
David Horne  Michael D. Smith 《Icarus》2009,200(1):118-128
The Mars Global Surveyor Thermal Emission Spectrometer (TES) instrument has returned over 200 million thermal infrared spectra of Mars taken between March 1999 and August 2004. This represents one of the most complete records of spatial and temporal changes of the martian atmosphere ever recorded by an orbiting spacecraft. Previous reports of the standard TES retrieval of aerosol optical depth have been limited to those observations taken over surfaces with temperatures above 210 K, limiting the spatiotemporal coverage of Polar Regions with TES. Here, we present an extension to the standard TES retrieval that better models the effects of cold surfaces below 200 K. This modification allows aerosol optical depth to be retrieved from TES spectra over a greater spatiotemporal range than was previously possible, specifically in Polar Regions. This new algorithm is applied to the Polar Regions to show the seasonal variability in dust and ice optical depth for the complete temporal range of the TES database (Mars Year 24, Ls=104°, 1 March 1999 to Mars Year 24, Ls=82°, 31 August 2004).  相似文献   

3.
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.  相似文献   

4.
Dust is a major environmental factor on the surface and in the atmosphere of Mars. Knowing the electrical charge state of this dust would be of both scientific interest and important for the safety of instruments on the Martian surface. In this study the first measurements have been performed of dust electrification using suspended Mars analogue material. This has been achieved by attracting suspended dust onto electrodes placed inside a Mars simulation wind tunnel. The Mars analogue used was from Salten Skov in Denmark, this contained a high concentration of ferric oxide precipitate. Once suspended, this dust was found to consist of almost equal quantities of negatively (46±6%) and positively (44±15%) charged grains.These grains were estimated to typically carry a net charge of around 105e, this is sufficient to dominate the processes of adhesion and cohesion of this suspended dust. Evidence is presented for electrostatic aggregation of the dust while in suspension. Development of a simple instrument for measuring electrical charging of the suspended dust on Mars will be discussed.  相似文献   

5.
In January of 1982 we measured a microwave spectrum of CO in the Martian atmosphere utilizing the rotational J = 1 → 2 transition of CO. We have analyzed data and reanalyzed the microwave spectra of R. K. Kakar, J. W. Waters, and W. J. Wilson, (Science196, 1090–1091, 1977, measured in 1975) and J. C. Good and F. P. Schloerb, (Icarus47, 166–172, 1981 measured in 1980) in order to constrain estimates of the temporal variability of CO abundance in the Martian atmosphere. Our values of CO column density from the data of Karar et al., Good and Schloerb, and our own are 1.7 ± 0.9 × 1020, 3.0 ± 1.0 × 1020, and 4.6 ± 2.0 × 1020cm?2, respectively. The most recent estimate of CO column density from the 1967 infrared spectra of J. Connes, P. Connes, and J.P. Maillard, (Atlas de Spectres Infarouges de Venus, Mars, Jupiter, et Saturne, Editions due Centre National de la Recherche Scientifique, Paris, 1969), is 2.0 ± 0.8 × 1020 cm?2 (L.D.G. Young and A.T. Young, Icarus30, 75–79, 1977). The large uncertainties given for the microwave measurements are due primarily to uncertainty in the difference between the continuum brightness temperature and atmospheric temperatures of Mars. We have accurately calculated the variation among the observations of the continuum (surface) brightness temperature of Mars, which is primaroly a function of the observed aspect of Mars. A more difficult problem to consider is variability of global atmospheric temperatures among the observations, particularly the effects of global dust storms and the ellipticity of the orbit of Mars. The large bars accompanying our estimates of CO column density from the three sets of microwave measurements are primarily caused by an assumed uncertainty of ±10°K in our atmospheric temperature model due to possible dust in the atmosphere. A qualitative consideration of seasonal variability of global atmospheric temperatures among the measurements suggests that there is not strong evidence for variability of the column abundance of CO on Mars, although variability of 0–100% over a time scale of several years is allowed by the data set. The implication for the variability of Mars O2 is, crudely, a factor of two less. We found that the altitude distribution of CO in the atmosphere of Mars was not well constrained by any of the spectra, although our spectrum was marginally better fitted by an altitude increasing profile of CO mixing ratios.  相似文献   

6.
The Thermal Emission Spectrometer aboard the Mars Global Surveyor spacecraft has produced an extensive atmospheric data set, beginning during aerobraking and continuing throughout the extended scientific mapping phase. Temperature profiles for the atmosphere below about 40 km, surface temperatures and total dust and water ice opacities, can be retrieved from infrared spectra in nadir viewing mode. This paper describes assimilation of nadir retrievals from the spacecraft aerobraking period, LS=190°–260°, northern hemisphere autumn to winter, into a Mars general circulation model. The assimilation scheme is able to combine information from temperature and dust optical depth retrievals, making use of a model forecast containing information from the assimilation of earlier observations, to obtain a global, time-dependent analysis. Given sufficient temperature retrievals, the assimilation procedure indicates errors in the a priori dust distribution assumptions even when lacking dust observations; in this case there are relatively cold regions above the poles compared to a model which assumes a horizontally-uniform dust distribution. One major reason for using assimilation techniques is in order to investigate the transient wave behavior on Mars. Whilst the data from the 2-h spacecraft mapping orbit phase is much more suitable for assimilation, even the longer (45–24 h) period aerobraking orbit data contain useful information about the three-dimensional synoptic-scale martian circulation which the assimilation procedure can reconstruct in a consistent way. Assimilations from the period of the Noachis regional dust storm demonstrate that the combined assimilation of temperature and dust retrievals has a beneficial impact on the atmospheric analysis.  相似文献   

7.
This work presents an algorithm for the scientific analysis of individual calibrated measurements from the Planetary Fourier spectrometer (PFS).The instrument, included in the scientific payload of the ESA Mars Express mission to Mars, acquires spectra in the range between 250 and 8200 cm−1, with a sampling step of ∼1 cm−1 and an effective resolution of ∼2 cm−1. The observed radiance depends on several parameters of the atmosphere and surface of Mars as described by the radiative transfer equation. Adopting the very general formalism of Bayesian analysis, we determined which quantities are actually retrievable from individual measurements. Namely, they are: the surface temperature, the column density of dust and water ice aerosols in the atmosphere, the air temperature as a function of altitude (in the indicative range 5-45 km above the surface), the surface pressure, and the column density of water vapor and carbon monoxide. These evaluations are carried out taking into account the noise equivalent radiance (NER) of the instrument and the natural variabilities of the investigated parameters in the Martian environment, as estimated from the expectations of the European Martian Climate Dataset v3.1 (EMCD). Other parameters included in the radiative transfer equation shall be assumed as known, because they are not retrievable from individual measurements due to the instrumental NER or an underconstrained inverse problem: the surface emissivity in the thermal infrared, the optical properties of suspended dust and the analytical shape of dust concentration vs. altitude.During the development of the algorithm devoted to these studies, different approaches were evaluated on the basis of formal, computational and scientific considerations, with the aim to develop the general design of an integrated software package.The resulting code was extensively tested on a wide set of simulated PFS spectra. These spectra were computed from the atmospheric and surface conditions extracted from the EMCD, assumed to be representative of the Martian environment for different values of latitude, local time and season. Their comparison with the retrievals from simulated observations allowed us to evaluate the systematic and random errors affecting the procedures with respect to the different quantities involved. The code evaluates the surface temperature with an error in the order of 1 K, while the vertical air temperature profile is computed with an uncertainty less than 2 K from in the region between 5 and 20 km above the surface, increasing up to 7 K at 50 km. The column opacity of dust, measured in terms of integrated optical thickness at 1100 cm−1, is computed with an error of around 0.13. The surface pressure determination is carried out with a typical uncertainty of 0.2-0.3 millibar. Several auxiliary tests allowed us to study the correlations between the different retrieval errors and the possible causes of incorrect PFS data interpretation. The choice of a suitable model for the dust optical properties is demonstrated to be particularly critical.This paper also presents the first discussion about application of the procedure to actual PFS Martian data. Despite the calibration issues still affecting the determination of absolute radiance in the near-infrared, the algorithm is able to achieve a satisfactory modeling of observations in a wide range of situations.  相似文献   

8.
Clay mineral-bearing deposits previously discovered on Mars with near infrared (λ=0.3-5 μm) remote sensing data are of major significance for understanding the aqueous history, geological evolution, and past habitability of Mars. In this study, we analyzed the thermal infrared (λ=6-35 μm) surface properties of the most extensive phyllosilicate deposit on Mars: the Mawrth Vallis area. Clay mineral-bearing units, which in visible images appear to be relatively light-toned, layered bedrock, have thermal inertia values ranging from 150 to 460 J m−2 K−1 s−1/2. This suggests the deposits are composed of a mixture of rock with sand and dust at 100-meter scales. Dark-toned materials that mantle the clay-bearing surfaces have thermal inertia values ranging from 150 to 800, indicating variable degrees of rockiness or induration of this younger sedimentary or pyroclastic unit. Thermal Emission Spectrometer (TES) spectra of the light-toned rocks were analyzed with a number of techniques, but none of the results shows a large phyllosilicate component as has been detected in the same surfaces with near-infrared data. Instead, TES spectra of light-toned surfaces are best modeled by a combination of plagioclase feldspar, high-silica materials (similar to impure opaline silica or felsic glass), and zeolites. We propose three hypotheses for why the clay minerals are not apparent in thermal infrared data, including effects due to surface roughness, sub-pixel mixing of multiple surface temperatures, and low absolute mineral abundances combined with differences in spatial sampling between instruments. Zeolites modeled in TES spectra could be a previously unrecognized component of the alteration assemblage in the phyllosilicate-bearing rocks of the Mawrth Vallis area. TES spectral index mapping suggests that (Fe/Mg)-clays detected with near infrared data correspond to trioctahedral (Fe2+) clay minerals rather than nontronite-like clays. The average mineralogy and geologic context of these complex, interbedded deposits suggests they are either aqueous sedimentary rocks, altered pyroclastic deposits, or a combination of both.  相似文献   

9.
Spectroscopic remote sensing in the infrared and (sub)millimeter range is a powerful technique that is well suited for detecting minor species in planetary atmospheres (Planet Space Sci. 43(1995) 1485). Yet, only a handful of molecules in the Mars atmosphere (CO2, CO and H2O along with their isotopic species, O3, and more recently H2O2 and CH4) have been detected so far by this method. New high performance spectroscopic instruments will become available in the future in the infrared and (sub)millimeter range, for observations from the ground (infrared spectrometers on 8 m class telescopes, large millimeter and submillimeter interferometers) and from space, in particular the Planetary Fourier Spectrometer (PFS) aboard Mars Express (MEx), and the Heterodyne Instrument for the Far-Infrared (HIFI) aboard the Herschel Space Observatory (HSO). In this paper we will present results of a study that determines detectability of minor species in the atmosphere of Mars, taking into account the expected performance of the above spectroscopic instruments. In the near future, a new determination of the D/H value is expected with the PFS, especially during times of maximum H2O abundance in the martian atmosphere. PFS is also expected to place constraints on the abundance of several minor species (H2O2,CH4,CH2O, SO2, H2S, OCS, HCl) above any local outgassing sources, the hot spots. It will be possible to obtain complementary information on some minor species (O3,H2O2, CH4) from ground-based infrared spectrometers on large telescopes. In the more distant future, HIFI will be ideally suited for measuring the isotopic ratios with unprecedented accuracy. Moreover, it should be able to observe O2, which has not yet been detected spectroscopically in the IR/submm range, as well as H2O2. HIFI should also provide upper limits for several species that have not yet been detected (HCl, NH3, PH3) in the atmosphere of Mars. Some species (SO, SO2,H2S, OCS, CH2O) that may be observable from the ground could be searched for with present single-dish antennae and arrays, and in the future with the Atacama Large Millimeter Array (ALMA) submillimeter interferometer.  相似文献   

10.
Michael D Smith 《Icarus》2004,167(1):148-165
We use infrared spectra returned by the Mars Global Surveyor Thermal Emission Spectrometer (TES) to retrieve atmospheric and surface temperature, dust and water ice aerosol optical depth, and water vapor column abundance. The data presented here span more than two martian years (Mars Year 24, Ls=104°, 1 March 1999 to Mars Year 26, Ls=180°, 4 May 2003). We present an overview of the seasonal (Ls), latitudinal, and longitudinal dependence of atmospheric quantities during this period, as well as an initial assessment of the interannual variability in the current martian climate. We find that the perihelion season (Ls=180°-360°) is relatively warm, dusty, free of water ice clouds, and shows a relatively high degree of interannual variability in dust optical depth and atmospheric temperature. On the other hand, the aphelion season (Ls=0°-180°) is relatively cool, cloudy, free of dust, and shows a low degree of interannual variability. Water vapor abundance shows a moderate amount of interannual variability at all seasons, but the most in the perihelion season. Much of the small amount of interannual variability that is observed in the aphelion season appears to be caused by perihelion-season planet-encircling dust storms. These dust storms increase albedo through deposition of bright dust on the surface causing cooler daytime surface and atmospheric temperatures well after dust optical depth returns to prestorm values.  相似文献   

11.
This work is devoted to the analysis of the variation of albedo measured by orbiting instruments with atmospheric opacity on Mars. The study has been conduced by analysing Mars Global Surveyor Thermal Emission Spectrometer (MGS-TES) data from martian regions with different surface albedo.In support of these data, synthetic spectra with different surface albedo and atmospheric opacities have been computed, so that a comparison has been performed. The synthetic spectra have been retrieved by using two different grain sizes for suspended dust (0.5 and 1.2 μm), allowing a comparison between the two models and the observations.Using the DCI, a parameter describing the quantity of dust deposited on the surface, the effectiveness of the single scattering approximation has been tested for low atmospheric opacity by analysing the quality of the linear fit up to different atmospheric opacity.For more opaque conditions two kinds of fits have been applied to the data, linear and second-order degree polynomial. In this case, we found that the polynomial fit better describes the observations.The analysis of these data made it possible to notice a peculiar trend, already reported by Christensen (1988), of the albedo over Syrtis Major after the occurrence of dust storms, but, differently from that work, now the study of DCI together with atmospheric opacity and albedo allowed us to robustly confirm the hypothesis made by Christensen.Finally, the comparison between observations and synthetic spectra computed with models with different particles grain sizes indicates that dust particles of 0.5 μm diameter are the most effective to change the aerosol atmospheric opacity on Mars.  相似文献   

12.
The time evolution of atmospheric dust at high southern latitudes on Mars has been determined using observations of the south seasonal cap acquired in the near infrared (1-2.65 μm) by OMEGA/Mars Express in 2005. Observations at different solar zenith angles and one EPF sequence demonstrate that the reflectance in the 2.64 μm saturated absorption band of the surface CO2 ice is mainly due to the light scattered by aerosols above most places of the seasonal cap. We have mapped the total optical depth of dust aerosols in the near-IR above the south seasonal cap of Mars from mid-spring to early summer with a time resolution ranging from one day to one week and a spatial resolution of a few kilometers. The optical depth above the south perennial cap is determined on a longer time range covering southern spring and summer. A constant set of optical properties of dust aerosols is consistent with OMEGA observations during the analyzed period. Strong variations of the optical depth are observed over small horizontal and temporal scales, corresponding in part to moving dust clouds. The late summer peak in dust opacity observed by Opportunity in 2005 propagated to the south pole contrarily to that observed in mid spring. This may be linked to evidence for dust scavenging by water ice-rich clouds circulating at high southern latitudes at this season.  相似文献   

13.
A complete Mars year of measurements of atmospheric water vapor in the south arctic have been obtained from the Viking Orbiters. Analysis of the observations indicates that, except for the south remnant cap, the southern hemisphere of Mars is devoid of any substantial reservoirs of water in contact with the atmosphere, and that, in the summer time, the top layer of soil is desiccated. Small amounts of water ice are incorporated into the annual CO2 cap; this water is released at the cap margin when it retreats in the spring. The first global dust storm resulted in heating of the south arctic atmosphere and a transport of water in from the equatorial region. The second global dust storm had a negligible effect on atmospheric water vapor; the dust contained little water.  相似文献   

14.
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15.
J.F. Bell III  T.M. Ansty 《Icarus》2007,191(2):581-602
We acquired high spectral and spatial resolution hyperspectral imaging spectrometer observations of Mars from near-UV to near-IR wavelengths (∼300 to 1020 nm) using the STIS instrument on the Hubble Space Telescope during the 1999, 2001, and 2003 oppositions. The data sets have been calibrated to radiance factor (I/F) and map-projected for comparison to each other and to other Mars remote sensing measurements. We searched for and (where detected) mapped a variety of iron-bearing mineral signatures within the data. The strong and smooth increase in I/F from the near-UV to the visible that gives Mars its distinctive reddish color indicates that poorly crystalline ferric oxides dominate the spectral properties of the high albedo regions (as well as many intermediate and low albedo regions), a result consistent with previous remote sensing studies of Mars at these wavelengths. In the near-IR, low albedo regions with a negative spectral slope and/or a distinctive ∼900 nm absorption feature are consistent with, but not unique indicators of, the presence of high-Ca pyroxene or possibly olivine. Mixed ferric-ferrous minerals could also be responsible for the ∼900 nm feature, especially in higher albedo regions with a stronger visible spectral slope. We searched for the presence of several known diagnostic absorption features from the hydrated ferric sulfate mineral jarosite, but did not find any unique evidence for its occurrence at the spatial scale of our observations. We identified a UV contrast reversal in some dark region spectra: at wavelengths shorter than about 340 nm these regions are actually brighter than classical bright regions. This contrast reversal may be indicative of extremely “clean” low albedo surfaces having very little ferric dust contamination. Ratios between the same regions observed during the planet-encircling dust storm of 2001 and during much clearer atmospheric conditions in 2003 provide a good direct estimate of the UV to visible spectral characteristics of airborne dust aerosols. These HST observations can help support the calibration of current and future Mars orbital UV to near-IR spectrometers, and they also provide a dramatic demonstration that even at the highest spatial resolution possible to achieve from the Earth, spectral variations on Mars at these wavelengths are subtle at best.  相似文献   

16.
Recent geological observations in the northern mid-latitudes of Mars show evidence for past glacial activity during the late Amazonian, similar to the integrated glacial landsystems in the Dry Valleys of Antarctica. The large accumulation of ice (many hundreds of meters) required to create the observed glacial deposits points to significant atmospheric precipitation, snow and ice accumulation, and glacial flow. In order to understand the climate scenario required for these conditions, we used the LMD (Laboratoire de Météorologie Dynamique) Mars GCM (General Circulation Model), which is able to reproduce the present-day water cycle, and to predict past deposition of ice consistent with geological observations in many cases. Prior to this analysis, however, significant mid-latitude glaciation had not been simulated by the model, run under a range of parameters.In this analysis, we studied the response of the GCM to a wider range of orbital configurations and water ice reservoirs, and show that during periods of moderate obliquity (? = 25-35°) and high dust opacity (τdust = 1.5-2.5), broad-scale glaciation in the northern mid-latitudes occurs if water ice deposited on the flanks of the Tharsis volcanoes at higher obliquity is available for sublimation. We find that high dust contents of the atmosphere increase its water vapor holding capacity, thereby moving the saturation region to the northern mid-latitudes. Precipitation events are then controlled by topographic forcing of stationary planetary waves and transient weather systems, producing surface ice distribution and amounts that are consistent with the geological record. Ice accumulation rates of ∼10 mm yr−1 lead to the formation of a 500-1000 m thick regional ice sheet that will produce glacial flow patterns consistent with the geological observations.  相似文献   

17.
One of the most puzzling aspects of Mars is that organics have not yet been found on the surface. The simplest of organic molecules, methane, was detected in the Martian atmosphere for the first time in 2003. The existence and behavior of methane on Mars is of great significance, as methane is a potential biomarker. In this paper we review our current understanding of possible sources and sinks of methane on Mars. We also investigate the role of other trace species in the maintenance and removal of methane from the atmosphere, as well as of other organic material from the surface. In particular, we examine the exogenous, hydrogeochemical—especially serpentinization—and biological sources, for supplying methane to Mars. We suggest that comets and meteorites are the least likely, whereas low-temperature serpentinization is the most plausible of all candidates to explain the methane observations. Nevertheless, it is premature to rule out the role of biology in producing methane on Mars, in view of available data. It is important to note that the loss of methane to surface must also be factored into any “source” scenarios for methane. Ordinary heterogeneous loss process to surface tends to be very slow. On the other hand, a reactive surface could potentially accelerate the destruction of methane. If correct, it would imply that a larger source of methane is present than currently estimated on the basis of photochemical loss alone. A reactive surface can also explain why no organic material has ever been detected on the Martian surface. The surface could become reactive if some oxidizer were present. We suggest that vast quantities of a powerful oxidant, hydrogen peroxide, can be produced in electrochemistry triggered by electrostatic fields generated in the Martian dust devils and dust storms, and in normal saltation process close to the surface. Finally, current observations are inadequate to prove or disprove the existence of life on Mars, now or in the past. The question of extraterrestrial life is a fundamental one, and it should be addressed meticulously on future missions to Mars. Measurements planned on the Mars Science Laboratory (MSL), especially carbon isotopes and chirality, will go a long way in meeting this goal. A brief overview of the MSL Mission and measurements relevant to the question of life and habitability of Mars is also presented in this paper.  相似文献   

18.
James B. Pollack 《Icarus》1979,37(3):479-553
In this paper, we review the observational data on climatic change for the terrestrial planets, discuss the basic factors that influence climate, and examine the manner in which these factors may have been responsible for some of the known changes. Emphasis is placed on trying to understand the similarities and differences in both the basic factors and their climatic impacts on Venus, the Earth, and Mars. Climatic changes have occurred on the Earth over a broad spectrum of time scales that range from the elevated temperatures of Pre-Cambrian times (～109 years ago), through the alternating glacial and interglacial epochs of the last few million years, to the small but significant decadal and centurial variations of the recent past. Evidence for climatic change on Mars is given by certain channel features, which suggest an early to intermediate aged epoch of warmer and wetter climate, and by layered polar deposits, which imply more recent periodic climate variations. No evidence for climatic change on Venus exists as yet, but comparison of its present climate state with that of outer terrestrial planets offers important clues on some of the mechanisms affecting climate. The important determinants of climate for a terrestrial planet include the Sun's output, astronomical perturbations of its orbital and axial characteristics, the gaseous and particulate content of its atmosphere, its land surface, volatile reservoirs, and its interior. All these factors appear to have played major roles in causing climatic changes on the terrestrial planets. Despite a lower solar luminosity in the past, the Earth and Mars have had warmer periods in their early history. In both cases, a more reducing atmosphere may have been the responsible agent through an enhanced greenhouse effect. In this paper, we present detailed calculations of the effect of atmospheric pressure and composition on the temperature state of Mars. We find that the higher temperature period is easier to explain with a reducing atmosphere than with the current fully oxidizing one. Both the very high surface temperature and massive atmosphere of Venus may be the result of the solar flux being a factor of two higher at its orbit than at the Earth's orbit. This difference may have led to a runaway greenhouse effect on Venus, i.e., the emplacement of volatiles entirely in the atmosphere rather than mostly in surface reservoirs. But if Venus formed with relatively little or no water, it may have always had an oxidizing atmosphere. In this case, a lower solar luminosity would have led to a moderate surface temperature in Venus' early history. Quasi-periodic variations in orbital eccentricity and axial obliquity may have contributed to the alternation between Pleistocene glacial and interglacial periods in the case of the Earth and to the formation of the layered polar deposits in the case of Mars. In this paper, we postulate that two mechanisms, acting jointly, account for the creation of the laminated terrain of Mars: dust particles serve as nucleation centers for the condensation of water vapor and carbon dioxide. The combined dust-H2O-CO2 particle is much larger and so has a much higher terminal velocity than either a dust-H2O or a plain dust particle. As a result, dust and water ice are preferentially deposited in the polar regions. In addition, we postulate that the obliquity variations are key drivers of the periodic layering because of their impact on both atmospheric pressure and polar surface temperature, which, in turn, influence the amounts of dust and water ice in the atmosphere. But eccentricity and precessional changes probably also play important roles in creating the polar layers. The drifting of continents on the Earth has caused substantial climatic changes on individual continents and may have helped to set the stage for the Pleistocene ice ages through a positioning of the continents near the poles. While continental drift apparently has not occurred on Mars, tectonic distortions of its lithosphere may, in some circumstances, cause an alteration in the mean value of that planet's obliquity, which would significantly impact its climate. Atmospheric aerosols can influemce climate through their radiative effects. In the case of the Earth, volcanic aerosols appear to have contributed to past climatic changes, while consideration needs to be given to the future impact of man-generated aerosols. In the case of Mars, the atmospheric temperature structure and thereby atmospheric dynamics are greatly altered by suspended dust particles. The sulfuric acid clouds of Venus play a major role in its heat balance. Cometary impacts may have added substantial quantities of water vapor and sulfur gases to Venus' atmosphere and thus have indirectly affected its cloud properties. Calculations presented in this paper indicate substantial changes in surface temperature accompany these compositional changes.  相似文献   

19.
Images of Mars were obtained at 20 wavelengths between 0.35 and 1.10 μm during the 1973 opposition using the MIT MKIII silicon vidicon imaging system at the 88-in. telescope of the Mauna Kea Observatory, Hawaii. The observations covered a 3-hr interval on Day 2 of the 1973 Solis Lacus dust storm. At blue wavelengths two huge crescent-shaped anomalous brightenings surrounded the central dust storm in the early morning but faded during the morning; they were probably deposits of H2O frost or low level haze that was degassed from the regolith in Solis Lacus. The north polar hood, which was nonsymmetrically oriented about the north pole, faded and receded during the observing period. Regions of known dust storm activity could be clearly distinguished, and the images revealed dust cloud activity in Chryse as well. Relative reflectance spectra generated from the images showed compositional variations within the Erythraeum M. dark area complex: Margaritifer S. and Eastern Erythraeum M. have similar ferrosilicate mineralogy, but have stronger ferrosilicate absorption bands than Pyrrhae R. and Eos. Western Erythraeum M. and northern Eos were contaminated by high albedo dust. Reflectance spectra obtained from orbit around Mars could provide higher spatial resolution and more complete coverage of the dark areas, yielding an opportunity to correlate geologic features with crustal petrology. An orbiting spectrometer could also provide spectra in the compositionally diagnostic wavelength range 1–4 μm, where the Earth's atmosphere contains intense absorption bands.  相似文献   

20.
An AOST Fourier spectrometer of the Phobos-Soil project is intended for studying Mars and Phobos by means of measurements of IR radiation spectra of the Martian surface and atmosphere, the Phobos surface, and the spectrum of solar radiation passing through the Martian atmosphere on its limb. The main scientific problems to be solved with the spectrometer on Mars are measurements of methane content, search for minor constituents, and study of diurnal variations in the temperature and atmospheric aerosol. The spectrometer will also study the Martian and Phobos surface both remotely and after landing. The spectral range of the instrument is 2.5?C25 ??m, the best spectral resolution (without apodization) is 0.6 cm?1, and the instantaneous field of view is 2.5°. The recording time of one spectrum is equal to 5 s in solar observations and 50 s in observations of Mars and Phobos. The instrument has self-thermal stabilization and two-axis pointing systems, as well as a built-in radiation source for flight calibration. The spectrometer mass is 4 kg, and power consumption is up to 13 W. Scientific problems, measurement modes, and, briefly, engineering implementation of the experiment are discussed in this work.  相似文献   

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