Inorganic chemical investigation by x-ray fluorescence analysis: The Viking Mars Lander

The inorganic chemical investigation added in August 1972 to the Viking Lander scientific package will utilize an energy-dispersive X-ray fluorescence spectrometer in which four sealed, gas-filled proportional counters will detect X-rays emitted from samples of the Martian surface materials irradiated by X-rays from radioisotope sources (⁵⁵Fe and ¹⁰⁹Cd). The output of the proportional counters will be subjected to pulse-height analysis by an on-board step-scanning single-channel analyzer with adjustable counting periods. The data will be returned to Earth, via the Viking Orbiter relay system, and the spectra constructed, calibrated, and interpreted here. The instrument is inside the Lander body, and samples are to be delivered to it by the Viking Lander Surface Sampler. Calibration standards are an integral part of the instrument.The results of the investigation will characterize the surface materials of Mars as to elemental composition with accuracies ranging from a few tens of parts per million (at the trace-element level) to a few percent (for major elements) depending on the element in question. Elements of atomic number 11 or less are determined only as a group, though useful estimates of their individual abundances maybe achieved by indirect means. The expected radiation environment will not seriously hamper the measurements. Based on the results, inferences can be drawn regarding (1) the surface mineralogy and lithology; (2) the nature of weathering processes, past and present, and the question of equilibrium between the atmosphere and the surface; and (3) the extent and type of differentiation that the planet has undergone.The Inorganic Chemical Investigation supports and is supported by most other Viking Science investigations.     

Inference of dust opacities for the 1977 Martian great dust storms from Viking Lander 1 pressure data

A δ-Eddington radiative transfer algorithm is used to compute the thermal tidal heating of a dusty Martian atmosphere for a given set of dust optical depth, effective single scattering albedo, and phase function asymmetry parameter. The resulting thermal tidal forcing is used in a classical atmospheric tidal model to compute the amplitudes of the surface pressure oscillations at the Viking Lander 1 site for the two 1977 Martian great dust storms. Parametric studies show that the dust opacities and optical parameters derived from the Viking Lander imaging data are roughly representative of the global dust haze needed to reproduce the tidal surface pressure amplitudes also observed at Lander 1, except that the model-inferred asymmetry parameter is smaller during the onset of a great storm. The observed preferential enhancement during dust-storm onset of the semidiurnal tide at Viking Lander 1 relative to its diurnal counterpart is shown to be due primarily to the elevation of the tidal heating source in a very dusty atmosphere, although resonant enhancement of the main semidiurnal tidal mode makes an important secondary contribution.     

A sophisticated lander for scientific exploration of Mars: scientific objectives and implementation of the Mars-96 Small Station

A mission to Mars including two Small Stations, two Penetrators and an Orbiter was launched at Baikonur, Kazakhstan, on 16 November 1996. This was called the Mars-96 mission. The Small Stations were expected to land in September 1997 (Ls approximately 178 degrees), nominally to Amazonis-Arcadia region on locations (33 N, 169.4 W) and (37.6 N, 161.9 W). The fourth stage of the Mars-96 launcher malfunctioned and hence the mission was lost. However, the state of the art concept of the Small Station can be applied to future Martian lander missions. Also, from the manufacturing and performance point of view, the Mars-96 Small Station could be built as such at low cost, and be fairly easily accommodated on almost any forthcoming Martian mission. This is primarily due to the very simple interface between the Small Station and the spacecraft. The Small Station is a sophisticated piece of equipment. With the total available power of approximately 400 mW the Station successfully supports an ambitious scientific program. The Station accommodates a panoramic camera, an alpha-proton-x-ray spectrometer, a seismometer, a magnetometer, an oxidant instrument, equipment for meteorological observations, and sensors for atmospheric measurement during the descent phase, including images taken by a descent phase camera. The total mass of the Small Station with payload on the Martian surface, including the airbags, is only 32 kg. Lander observations on the surface of Mars combined with data from Orbiter instruments will shed light on the contemporary Mars and its evolution. As in the Mars-96 mission, specific science goals could be exploration of the interior and surface of Mars, investigation of the structure and dynamics of the atmosphere, the role of water and other materials containing volatiles and in situ studies of the atmospheric boundary layer processes. To achieve the scientific goals of the mission the lander should carry a versatile set of instruments. The Small Station accommodates devices for atmospheric measurements, geophysical and geochemical studies of the Martian surface and interior, and cameras for descent phase and panoramic views. These instruments would be able to contribute remarkably to the process of solving some of the scientific puzzles of Mars.     

The final phases of the Viking mission to Mars

Of the four spacecraft that the Viking Project put into operation at Mars in the summer of 1976, one continues to acquire data periodically. The missions of the two orbiters were terminated by the depletion of their attitude-control gas: Orbiter 2 in July 1978 and Orbiter 1 in August 1980. Lander 2 was shut down in April 1980 because of degradation of its batteries. Lander 1 is programmed to continue acquiring a modest number of imaging, meteorology, and ranging data periodically until December 1994. During its final year Orbiter 1 continued to produce excellent data from its full complement of instruments—two cameras, two infrared instruments (thermal mapper and water vapor detector), and the radio subsystem. The major emphasis was on photography, with 10,000 images being acquired. These included two very large swaths of high-resolution contiguous coverage of the Martian surface and the completion of the moderate-resolution mapping of nearly the entire surface, as well as miscellaneous other observations. The majority of these images has not been processed and examined, but the others have revealed many previously unobserved features and have greatly enhanced the base for a geological understanding of the planet. The history of Viking mission operations is brought up to date.     

Topography and Geologic Characteristics of Aeolian Grooves in the South Polar Layered Deposits of Mars

The topographic and geologic characteristics of grooves and groove-like features in the south polar layered deposits near the Mars Polar Lander/Deep Space 2 landing sites are evaluated using Mariner 9 images and their derived photoclinometry, normalized using Mars Orbiter Laser Altimeter data. Although both Mariner 9 and Viking images of the south polar layered deposits were available at the time of this study, Mariner 9 images of the grooves were selected because they were generally of higher resolution than Viking images. The dimensions and slopes of the grooves, together with orientations that nearly match the strongest winds predicted in the Martian Global Circulation Model and directions inferred from other wind indicators, suggest that they formed by aeolian scour of an easily erodible surface. Most grooves are symmetric and V-shaped in transverse profile, inconsistent with an origin involving extensional brittle deformation. Although the grooves strike along slopes and terraces of the south polar layered deposits, the variable depths and lack of terracing within the grooves themselves indicate that any stratigraphy in the uppermost 100 m of the polar layered deposits is composed of layers of similar, and relatively low, resistance. The grooves do not represent landing hazards at the scale of the Mariner 9 images (72-86 m/pixel) and therefore probably would not have affected Mars Polar Lander and Deep Space 2, had they successfully reached the surface.     

Characterization of rock populations on planetary surfaces: Techniques and a preliminary analysis of Mars and Venus

Characteristics of rock populations on the surfaces of Mars and Venus can be derived from analyses of rock morphology and morphometry data. We present measurements of rock sizes and sphericities made from Viking lander images using an interactive digital image display system. The rocks considered are in the gravel size range (16–256 mm in diameter). Mean sphericities, form ratios, and roundness factors are found to be very similar for both Viking lander sites. Size distributions, however, demonstrate differences between the sites; there are significantly more cobble size fragments at VL-2 than at VL-1. A model calling for aphanitic basalts emplaced as ejecta or lava flows at the Viking sites is supported by the rock shape, size, and roundness data.Morphologic features pertaining to the modification history of a rock are considered for Mars and Venus. A multi-parameter clustering algorithm is utilized to objectively categorize martian and venusian rocks in terms of various criteria. Erosional markings such as flutes are demonstrated to be most important in separating VL-1 rock morphologic groups, while rock form (i.e., shape) represents the primary separator of subpopulations at VL-2 and the Venera landing sites. Fillets are common around VL-1 and Venera 10 fragments. Obstacle scours occur frequently only at VL-1. Cavities in rocks are ubiquitous at all lander sites except Venera 9. Eolian processes, possibly assisted by local solution weathering, are a strong candidate for the origin of cavities and flutes in martian rocks.     

Convective vortices on Mars: a reanalysis of Viking Lander 2 meteorological data, sols 1-60

Dust devil data from Mars is limited by a lack of data relating to diurnal dust devil behaviour. Previous work looking at the Viking Lander meteorological data highlighted seasonal changes in temporal occurrence of dust devils and gave an indication of typical dust devil diameter, size, and internal dynamics. The meteorological data from Viking Lander 2 for sols 1 to 60 have been revisited to provide detailed diurnal dust devil statistics. Results of our analysis show that the Viking Lander 2 experienced a possible 38 convective vortices in the first 60 sols of its mission with a higher occurrence in the morning compared to Earth, possibly as a result of turbulence generated by the Lander body. Dust devil events have been categorised by statistical confidence and intensity. Some initial analysis and discussion of the results is also presented. Assuming a similar dust loading to the vortices seen by Mars Pathfinder, it is estimated that the amount of dust lofted in the locality of the Lander is approximately 800 ± 10 kgsol⁻¹km⁻².     

Location of Viking 1 Lander on the surface of Mars

A location of the Viking 1 Lander on the surface of Mars has been determined by correlating topographic features in the lander pictures with similar features in the Viking orbiter pictures. Radio tracking data narrowed the area of search for correlating orbiter and lander features and an area was found on the orbiter pictures in which there is good agreement with topographic features on the lander pictures. This location, when plotted on the 1:250,000 scale photomosaic of the Yorktown Region of Mars (U.S. Geological Survey, 1977) is at 22.487°N latitude and 48.041°W longitude.     

Possible fossil H2O liquid-ice interfaces in the Martian crust

Throughout the northern equatorial region of Mars, extensive areas have been uniformly stripped, roughly to a constant depth. These terrains vary widely in their relative ages. A model is described here to explain this phenomenon as reflecting the vertical distribution of H₂O liquid and ice in the crust. Under present conditions the Martian equatorial regions are stratified in terms of the stability of water ice and liquid water. This arises because the temperature of the upper 1 or 2 km is below the melting point of ice and liquid is stable only at greater depth. It is suggested here that during planetary outgassing earlier in Martian history H₂O was injected into the upper few kilometers of the crust by subsurface and surface volcanic eruption and lateral migration of the liquid and vapor. As a result, a discontinuity in the physical state of materials developed in the Martian crust coincident with the depth of H₂O liquid-ice phase boundary. Material above the boundary remained pristine; material below underwent diagenetic alteration and cementation. Subsequently, sections of the ice-laden zone were erosionally stripped by processes including eolian deflation, gravitational slump and collapse, and fluvial transport due to geothermal heating and melting of the ice. The youngest plains which display this uniform stripping may provide a minimum stratigraphic age for the major period of outgassing of the planet. Viking results suggest that the total amount of H₂O outgassed is less than half that required to fill the ice layer, hence any residual liquid eventually found itself in the upper permafrost zone or stored in the polar regions. Erosion stopped at the old liquid-ice interface due to increased resistance of subjacent material and/or because melting of ice was required to mobilize the debris. Water ice may remain in uneroded regions, the overburden of debris preventing its escape to the atmosphere. Numerous morphological examples shown in Viking and Mariner 9 images suggest interaction of impact, volcanic, and gravitational processes with the ice-laden layer. Finally, volcanic eruptions into ice produces a highly oxidized friable amorphous rock, palagonite. Based on spectral reflectance properties, these materials may provide the best analog to Martian surface materials. They are easily eroded, providing vast amounts of eolian debris, and have been suggested (Toulmin et al., 1977) as possible source rocks for the materials observed at the Viking landing sites.     

Comparison of knobs on mars to isolated hills in eolian,fluvial and glacial environments

Positive isolated features or knobs have been observed on Mars since Mariner 9 first photographed the planet in 1972. More recently, the Viking Orbiters photographed the surface at increased resolution. With the use of Viking photomosaics, a systematic search for knobs was completed. The knobs were characterized by length, width, geographic location, proximity to streaks and geologic surroundings. Similar isolated features on Earth eroded by fluvial, glacial, and eolian processes were studied and measured. Comparison of length-to-width ratios of Martian knobs to isolated hills on Earth indicate that the Martian knobs are most similar to the isolated hills formed in a hyper-arid environment. The terrestrial features were probably formed initially when solid rock was fractured, then wind erosion, starting at the fractures, continued to sweep away sediments leaving isolated hills. Such hills in fluvial and glacial environments have length-to-width ratios significantly higher than those of the Martian knobs. Other diagnostic features associated with such environments are absent in the case of the Martian knobs. Moreover, streaks, splotches, dunes and pitted and fluted rocks, all indicative of a eolian regime, are associated with the Martian knobs.     

Viking 1 Lander on the surface of mars: Revised location

Late in 1977, the periapsis altitude of the Viking Orbiters was lowered from 1500 to 300 km. The higher resolution of pictures taken at the lower altitude (8 m/pixel) permitted a more accurate determination of the location of the Viking 1 Lander by correlating topographic features seen in the new pictures with the same features in lander pictures. The position of the lander on Viking Orbiter picture 452B11 (NGF Rectilinear) is line 293, sample 1099. This location of the Viking 1 Lander has been used in a revision of the control net of Mars (M.E. Davies, F.Y. Katayama, and J.A. Roth, R2309 NASA, The Rand Corp., Feb. 1978). The new areographic coordinates of the lander are lat 22.483° N and long 47.968° W. The new location is estimated to be accurate to within 50 m.     

The geology of the Viking Lander 2 site revisited

Reevaluating the geologic history of the prior Mars landing sites provides important ground truth for recent and ongoing orbital missions. At the Viking 2 Lander (VL2) site, topographic measurements of relict landforms indicate that at least 100 m of sedimentary mantle material has been stripped away. The observed paucity of impact craters <100 m in diameter suggests that resurfacing processes (likely in the form of the recent deposition and removal of thin 1-10 m mantle layers) continue up to the present. A dearth of craters in the 100-500 m diameter range, however, also necessitates erosion of a thicker mantle layer. Partially inverted chains of secondary craters from nearby Mie Crater indicate that the mantle was already in place when the impact occurred. The density of craters superposed on Mie ejecta is consistent with a Late Hesperian age and provides a minimum age constraint for the mantle's emplacement. The thermophysical properties of the surface around VL2 as observed with Thermal Emission Imaging System (THEMIS) data indicate that the landing site occurs in an intracrater region that may typify mid to high northern latitude sites. Elevated thermal inertias of a pedestal crater superposed atop a larger pedestal crater suggest that rocky or indurated material can be created by impacts into sedimentary targets. Rock abundances at VL2 are consistent with the addition of impact-emplaced material from the missing small impact crater population documented in this study. Thus, the VL2 site may be a reasonable proxy for the landscape expected at the upcoming Phoenix Lander site.     

Orbital history of the Martian satellites with inferences on their origin

Recent Viking results indicate the Martian satellites are composed of carbonaceous chondritic material, suggesting that Phobos and Deimos were once asteroids captured by Mars. On the other hand, the low eccentricities and inclinations of their orbits on the equator of Mars argue against that hypothesis. This paper presents detailed calculations of the tidal evolution of Phobos and Deimos, considering dissipation in both Mars and its satellites simultaneously and using a new method applicable for any value of the eccentricity. In particular, including precession of the satellites' orbits indicates that they have always remained close to their Laplacian plane, so that the orbital planes of Phobos and Deimos switched from near the Martian orbital plane to the Martian equator once the perturbations due to the planetary oblateness dominated the solar perturbations, as they do presently. The results show that Deimos has been little affected by tides, but several billion (10⁹) years ago, Phobos was in a highly eccentric orbit lying near the common plane of the solar system. This outcome is obtained for very reasonable values of dissipation inside Mars and inside Phobos. Implications for the origin of the Martian satellites are discussed.     

How Particles in the Martian Atmosphere Influence the Thermal Protection Structure of the Descent Module <Emphasis Type="Italic">EXOMARS-2</Emphasis>

Methods for calculating heat and erosion impact caused by particles in the Martian atmosphere on the heat protection of the descent module EXOMARS-2 during descent in the atmosphere are presented. Atmosphere models corresponding to climatic conditions when landing on the Martian surface are investigated for the landing site Oxita Planum.     

Possibilities for the detection of hydrogen peroxide-water-based life on Mars by the Phoenix Lander

The Phoenix Lander landed on Mars on 25 May 2008. It has instruments on board to explore the geology and climate of subpolar Mars and to explore if life ever arose on Mars. Although the Phoenix mission is not a life detection mission per se, it will look for the presence of organic compounds and other evidence to support or discredit the notion of past or present life.The possibility of extant life on Mars has been raised by a reinterpretation of the Viking biology experiments [Houtkooper, J. M., Schulze-Makuch, D., 2007. A possible biogenic origin for hydrogen peroxide on Mars: the Viking results reinterpreted. International Journal of Astrobiology 6, 147-152]. The results of these experiments are in accordance with life based on a mixture of water and hydrogen peroxide instead of water. The near-surface conditions on Mars would give an evolutionary advantage to organisms employing a mixture of H₂O₂ and H₂O in their intracellular fluid: the mixture has a low freezing point, is hygroscopic and provides a source of oxygen. The H₂O₂-H₂O hypothesis also explains the Viking results in a logically consistent way. With regard to its compatibility with cellular contents, H₂O₂ is used for a variety of purposes in terran biochemistry. The ability of the anticipated organisms to withstand low temperatures and the relatively high water vapor content of the atmosphere in the Martian arctic, means that Phoenix will land in an area not inimical to H₂O₂-H₂O-based life. Phoenix has a suite of instruments which may be able to detect the signatures of such putative organisms.     

A search for a nonbiological explanation of the Viking Labeled Release life detection experiment

The Viking Labeled Release (LR) data obtained on Mars satisfy the criteria established for a biological response. The importance of the issue, especially when viewed against the harsh environment on Mars, requires careful consideration of possible nonbiological reactions that may have produced false positive results. A $\text{3}\text{1}\text{2}\text{-}\text{year}$ laboratory effort to investigate possible chemical, physical, and physicochemical agents or mechanisms has been concluded. Among nonbiological possibilities, hydrogen peroxide, putatively on Mars, emerged as the principal candidate. When placed on analog Mars soils prepared to match the Viking inorganic analysis of the Mars surface material, hydrogen peroxide did not duplicate the LR Mars data. When other materials were used as substrate, hydrogen peroxide could be made to evoke the type of responses obtained by the LR Mars experiment. However, essential criteria concerning the formation, accuumulation, and preservation of hydrogen peroxide to qualify it as the active agent on Mars have not been met and new data show it to be essentially absent from the Mars atmosphere. The presence of a biological agent on Mars must still be considered. This interpretation of the LR results is strengthened by a recent report that the Viking organic analysis instrument (GCMS) failed to detect organics in an Antarctic soil in which the LR instrument had demonstrated the presence of microorganisms.     

The prospects for life on Mars: A pre-Viking assessment

Mariner 9 has provided a refutation or reinterpretation of several historical claims for Martian biology, and has permitted an important further characterization of the environmental constraints on possible Martian organisms. Four classes of conceivable Martian organisms are identified, depending on the environmental temperature, T, and water activity, a_w: Class I, high T, high a_w; Class II, low T, high a_w; Class III, high T, low a_w; and Class IV, low T, low a_w. The Viking lander biology experiments are essentially oriented toward Class I organisms, although arguments are given for the conceivable presence on Mars of organisms in any of the four classes. Organisms which extract their water requirements from hydrated minerals or from ice are considered possible on Mars, and the high ultraviolet flux and low oxygen partial pressure are considered to be negligible impediments to Martian biology. Large organisms, possibly detectable by the Viking lander cameras, are not only possible on Mars; they may be favored. The surface distribution of Martian organisms and future search strategies for life on Mars are discussed.     

Crater streaks in the Chryse Planitia region of Mars: Early Viking results

High-resolution images of Chryse Planitia and eastern Lunae Planum from the early revolutions of Viking Orbiter I permit detailed analyses of crater-associated streaks and interpretation of related eolian processes. A total of 614 light and dark streaks were studied and treated statistically in relation to: (1) morphology, morphometry, and orientation, (2) “parent” crater size and morphology, (3) terrain type in which they occured, (4) topographic elevation, and (5) meteorological data currently being acquired by Viking Lander I. Three factors are apparent: (1) light streaks predominate, (2) most streaks form in association with fresh bowl-shaped craters, and (3) most light streaks are of the “parallel” type, whereas dark streaks are approximately evenly divided between convergent and parallel forms; moreover, very few light or dark streaks are divergent or fan-shaped. Light streaks have an average azimuth of 218° (corresponding to winds from the northeast), which approximates the orientation of 197 ± 14° for eolian “drifts” observed by the Viking Lander imaging team (Binder et al., 1977). This lends support to the hypothesis that light streaks are deposits of windblown sediments. Dark streaks are oriented at an azimuth of 42° (approximately opposite that of light streaks) and are nearly in line with the dominant wind direction currently recorded by the Viking meteorology instruments (Hess et al., 1977). Although the size of the sample area is not uniform among the various terrain types, the highest frequency of streaks per unit area occurs in the knobby terrain. This is partly explained by the probable production of fine-grained material (weathered from the knobs) to form streaks and other eolian features, and the higher wind turbulence generated around the knobs. The lowest frequency of streaks occurs on the elevated plateaus. The light streaks in Chryse Planitia appear to be relatively stable and to result from deposition of windblown material during times of relatively high velocity northeasterly winds. Dark streaks are more variable and probably result from erosion by southwesterly winds. Both types will be monitored during the extended Viking mission and the results compared with lander data.     

Issues and options for a Martian calendar

In the past 125 years, more than 70 authors have published ideas for keeping time on Mars, describing how to divide the Martian day and Martian year into smaller units. The Martian prime meridian was established in the mid-19th century, and the design of the Martian clock has been standardised at least since the Viking missions of the 1970s. Scientists can tell time on Mars; however, despite the constant stream of data that is downlinked from Mars these days, there is still no standardised system for expressing the date on Mars. Establishing a standard epoch—at a specific time of year on Mars, and a specific Martian year—should be the next priority in Martian timekeeping as a minimal system required for the physical sciences. More elaborate ideas, including the number and length of weeks and months, and names thereto, can be deferred for the present, but may become important considerations in coming years.     

Altered basaltic glass: A terrestrial analog to the soil of Mars

Analyses of Martian surface soil by Viking and Earth-based telescopes have been interpreted as indicating a regolith dominated by the weathering products of mafic or ultramafic rocks. Basaltic glass has previously been proposed as a more likely precursor than crystalline rock, given the low efficiency of surface weathering under present Martian conditions. On Earth large volumes of basaltic glass formed by quenching of magma by water. A similar interaction, between magma and ground ice, may have been a common occurrence on Mars. On the basis of this scenario palagonite, the alteration product of basaltic sideromelane glass, was studied as a possible analog to Martian soil. Samples from Iceland, Alaska, Antarctica, Hawaii, and the desert of New Mexico and Mexico were examined by optical and scanning electron microscopy, electron microprobe analysis, X-ray diffraction, spectrophotometry, and magnetic and thermogravimetric analysis. We suggest that palagonite is a good analog to the surface soil of Mars in chemical composition, particle size, spectral signature, and magnetic properties. Our model for the formation of fine-grained Martian surface soil begins with eruptions of basaltic magma through ground ice, forming deposits of glassy tuff. Individual glass shards are then altered by low-temperature hydrothermal systems to palagonitic material. Dehydration and aeolian abrasion strip the alteration rinds from the glass, and wind storms distribute the silt-sized palagonitic fragments in a planet-wide deposit.