Small stations: still viable low-cost lander for Mars scouts
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Mars landers↗
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Murray, B. C.
Publications and source records attributed to Murray, B. C..
Spring and Summer Changes at the South Pole as Seen by the Mars Orbiter Camera
The Mars Orbiter Camera (MOC) on the Mars Global Surveyor (MGS) spacecraft has been able to follow individual features as the CO2 frost disappears and exposes the material underneath. Because the orbit of MGS is inclined at an angle of 93 degrees relative to the equator, the spacecraft gets especially good coverage of the ring at 87 degrees latitude. The following is a list of phenomena that have been seen during the spring and summer at the South Pole: (1) Circular depressions that are approximately ten meters deep and hundreds of meters in diameter. They are found only within the residual polar cap, the part that survives the summer. The high areas between the depressions are flat-topped mesas whose sides are concave circular arcs. In some places the depressions form patterns that exhibit north-south symmetry, suggesting some control by sunlight; (2) Dark layers that are exposed on the walls of the mesas. Each layer is at most a few meters thick. The dark layers might accumulate during climatic episodes of high atmospheric dust content, or they might accumulate during the annual cycling of dusty CO2; (3) Albedo differences that develop during the summer within the residual cap. These include subtle darkening of the floors of the depressions relative to the mesas and occasional major darkening of the floors, especially near the edge of the cap. The floors and mesas form a distinct stratum, suggesting they represent a distinct compositional boundary. For instance the floors may be water and the mesas may be CO2; (4) Small dark features that appear in spring on the seasonal frost outside the residual cap. Some of the features have parallel tails that are clearly shaped by the wind. Others are more symmetric, like dark snowflakes, with multiple branching arms. After the CO2 frost has disappeared the arms are seen as troughs and the centers as topographic lows; (5) Polygons whose sides are dark troughs. Those that are outside the residual cap seem to disappear when the frost disappears. The polygons and the dark snowflakelike structures may be related, and suggest that CO2 frost may form cohesive slabs; (6) Irregular depressions outside the residual cap. They look like degraded versions of the circular depressions inside the residual cap, and may be a remnant of the cap's changing location; and (7) Areas of burial and exhumation of circular depressions. Thomas et al. give an example with a sharp boundary: On one side the depressions are buried and on the other side they are exposed. In other cases there are rounded troughs up to one kilometer wide, which are dark in summer and appear to have eroded down below the floor of the circular depressions.
Ingersoll, A. P.↗
Polar Layered Deposits: Preliminary Stratigraphic Assessment from MGS Observations
Global and hemispheric climatic, volcanic and impact events that modulated the formation of the Martian polar layered deposits can be revealed by detailed stratigraphic analyses of well-exposed sequences of those layers. Complete three-dimensional Mars Orbiting Laser Altimeter (MOLA) topography of the north and south polar deposits is now available, and very abundant Mars Orbiter Camera (MOC) imagery that is well calibrated is becoming available. This paper presents an assessment of the polar stratigraphic potential based on observations from Mars Global Surveyor (MGS) mapping cycles through M7. Additional information can be found in the original extended abstract.
Murray, B. C.↗
The Residual Polar Caps of Mars: Geological Differences and Possible Consequences
The Martian polar regions have been known to have thick layered sequences (presumed to consist of silicates and ice), CO2 seasonal frost, and residual frosts that remain through the summer: H2O in the north, largely CO2 in the south. The relationship of the residual frosts to the underlying layered deposits could not be determined from Viking images. The Mars Orbiter Camera on Mars Global Surveyor has provided a 50-fold increase in resolution that shows more differences between the two poles. The north residual cap surface has rough topography of pits, cracks, and knobs, suggestive of ablational forms. This topography is less than a few meters in height, and grades in to surfaces exposing the layers underneath. In contrast, the south residual cap has distinctive collapse and possibly ablational topography emplaced in four or more layers, each approx. two meters thick. The top surface has polygonal depressions suggestive of thermal contraction cracks. The collapse and erosional forms include circular and cycloidal depressions, long sinuous troughs, and nearly parallel sets of troughs. The distinctive topography occurs throughout the residual cap area, but not outside it. Unconformities exposed in polar layers, or other layered materials, do not approximate the topography seen on the south residual cap. The coincidence of a distinct geologic feature, several layers modified by collapse, ablation, and mass movement with the residual cap indicates a distinct composition and/or climate compared to both the remainder of the south polar layered units and those in the north.
Thomas, P. C.↗
The Mars oxidant experiment (MOx) for Mars '96
The MOx instrument was developed to characterize the reactive nature of the martian soil. The objectives of MOx were: (1) to measure the rate of degradation of organics in the martian environment; (2) to determine if the reactions seen by the Viking biology experiments were caused by a soil oxidant and measure the reactivity of the soil and atmosphere: (3) to monitor the degradation, when exposed to the martian environment, of materials of potential use in future missions; and, finally, (4) to develop technologies and approaches that can be part of future soil analysis instrumentation. The basic approach taken in the MOx instrument was to place a variety of materials composed as thin films in contact with the soil and monitor the physical and chemical changes that result. The optical reflectance of the thin films was the primary sensing-mode. Thin films of organic materials, metals, and semiconductors were prepared. Laboratory simulations demonstrated the response of thin films to active oxidants.
Flight Experiment↗
Thermal studies of Martian channels and valleys using Termoskan data
The Termoskan instrument on board the Phobos '88 spacecraft acquired the highest spatial resolution thermal data ever obtained for Mars. Included in the thermal images are 2 km per pixel observations of 4 major channel and valley systems: Shalbatana Vallis; Simud Vallis, Hydraotes Chaos, and the associated outflow channel connecting it with the eastern end of Vallis Marineris; Al-Qahira Vallis; and Ma'adim Vallis. Simultaneous broad band visible channel data were obtained for all but Ma'adim Vallis. We find that all 4 valley systems have higher inertias than their surroundings, consistent with previous thermal studies of Martian channels. We conclude that the higher inertia is likely due to some intrinsic difference associated with the channel floors, rather than due only to dark aeolian deposits as suggested by some previous studies. Our conclusion is based largely upon the localized nature of the dark deposits in contrast with the thermal homogeneity of the channel floors. Thus, these channels and valleys show an uncommon (for Mars) connection between morphology and inertia.
Betts, B. H.↗
Thermal studies of Martian channels and valleys using Termoskan data: New results
The Termoskan instrument onboard the Phobos '88 spacecraft acquired the highest-spatial-resolution thermal data ever obtained for Mars. Included in the thermal images are 2 km/pixel midday observations of several major channel and valley systems, including significant portions of Shalbatana Vallis, Ravi Vallis, Al-Qahira Vallis, Ma'adim Vallis, the channel connecting Valles Marineris with Hydraotes Chaos, and channel material in Eos Chasma. Termoskan also observed small portions of the southern beginnings of Simud, Tiu, and Ares Valles and some channel material in Gangis Chasma. Simultaneous broad band visible data were obtained for all but Ma'adim Vallis. We find that most of the channels and valleys have higher inertias than their surroundings, consistent with Viking IRTM-based thermal studies of Martian channels. We see for the first time that thermal inertia boundaries closely match all flat channel floor boundaries. Combining Termoskan thermal data, relative observations from Termoskan visible channel data, Viking absolute bolometric albedos, and a thermal model of the Mars surface, we have derived lower bounds on channel thermal inertias. Lower bounds on typical channel thermal inertias range from 8.4 to 12.5 (10(exp -3) cal cm(exp -2) s(exp -1/2)K(exp -1)) (352 to 523 in SI units). Lower bounds on inertia differences with the surrounding heavily cratered plains range from 1.1 to 3.5 (46 to 147 in SI units). Atmospheric and geometric effects are not sufficient to cause the inertia enhancements. We agree with previous researchers that localized, dark, high inertia areas within channels are likely eolian in nature. However, the Temloskan data show that eolian deposits do not fill the channels, nor are they responsible for the overall thermal inertia enhancement. Thermal homogeneity and strong correlation of thermal boundaries with the channel floor boundaries lead us to favor noneolian overall explanations.
Betts, B. H.↗
Thermally distinct ejecta blankets from Martian craters
The study of ejecta blankets on Mars gives information about the Martian surface, subsurface, geologic history, atmospheric history, and impact process. In Feb. and Mar. 1989, the Termoskan instrument on board the Phobos 1988 spacecraft of the USSR acquired the highest spatial resolution thermal data ever obtained for Mars, ranging in the resolution from 300 meters to 3 km per pixel. Termoskan simultaneously obtained broad band visible channel data. The data covers a large portion of the equatorial region from 30 degrees S latitude to 6 degrees N latitude. Utilizing the data set we have discovered tens of craters with thermal infrared distinct ejecta (TIDE) in the equatorial regions of Mars. In order to look for correlations within the data, we have compiled a database which currently consists of 110 craters in an area rich in TIDE's and geologic unit variations. For each crater, we include morphologic information from Barlow's Catalog of Large Martian Impact Craters in addition to geographic, geologic, and physical information and Termoskan thermal infrared and visible data.
Betts, B. H.↗
Mariner 9 observations of the south polar cap of Mars - Evidence for residual CO2 frost
The first spacecraft observations of the south residual polar cap of Mars were obtained by the Mariner 9 orbiter during the Martian southern summer season, 1971-1972. Analyses of Viking orbiter observations obtained 3 Mars years later have shown that residual carbon dioxide frost was present at the south polar cap in 1977. In this study, Mariner 9 infrared interferometer spectrometer spectra and television camera images are used in conjuction with multispectral thermal emission models to constrain the temperatures of dark bare ground and bright frost regions within the south residual cap. The results provide strong evidence that carbon dioxide frost was present throughout the summer season despite the fact that the residual frost deposits observed by Mariner 9 were less extensive than those observed by Viking.
Paige, D. A.↗
Television observations of Mercury by Mariner 10
The morphology and optical properties of the surface of Mercury resemble those of the Moon in remarkable detail, recording a very similar sequence of events; chemical and mineralogical similarity of the outer layers is implied. Mercury is probably a differentiated planet with an iron-rich core. Differentiation is inferred to have occurred very early. No evidence of atmospheric modification of any landform is found. Large-scale scarps and ridges unlike lunar or Martian features may reflect a unique period of planetary compression near the end of heavy bombardment, perhaps related to contraction of the core.
Murray, B. C.↗
Preliminary imaging results from the second Mercury encounter
The second Mercury encounter has resulted in the acquisition of about 360 pictures of the south polar regions which provide a reliable cartographic and geologic tie between the two sides of the planet photographed on the first encounter. Stereoscopic coverage of large areas of the southern hemisphere was obtained by combining Mercury 1 and 2 pictures taken at different viewing angles. The south polar regions consist of heavily cratered terrain and intercrater plains interspersed with patches of smooth plains. No large areas of smooth plains similar to those surrounding Caloris occur in the south polar regions. No new types of terrain have been recognized, but lobate scarps are common. The second largest basin seen by Mariner 10 has been confirmed on the new photography. At high solar elevations the surface displays an abundance of rays and rayed craters.
Strom, R. G.↗
Surface history of Mercury - Implications for terrestrial planets
A plausible surface history of Mercury is presented which is suggested by Mariner 10 television pictures. Five periods are postulated which are delineated by successive variations in the modification of the surface by external and internal processes: accretion and differentiation, terminal heavy bombardment, formation of the Caloris basin, flooding of that basin and other areas, and light cratering accumulated on the smooth plains. Each period is described in detail; the overall history is compared with the surface histories of Venus, Mars, and the moon; and the implications of this history for earth are discussed. It is tentatively concluded that: Mercury is a differentiated planet most likely composed of a large iron core enclosed by a relatively thin silicate layer; heavy surface bombardment occurred about four billion years ago, which probably affected all the inner planets, and was followed by a period of volcanic activity; no surface modifications caused by tectonic, volcanic, or atmospheric processes took place after the volcanic period.
Murray, B. C.↗
Climatic variations on Mars. II - Evolution of carbon dioxide atmosphere and polar caps
The long-term variations in the atmospheric pressure and the polar cap temperature of Mars resulting from the obliquity oscillations are discussed. In performing these calculations, the assumption is made that the atmosphere is in equilibrium with perennial CO2 ice deposits at the north pole, as is proposed by Leighton and Murray (1966). If heat transport by the atmosphere is neglected, the temperature of CO2 ice at the poles ranges from about 130 K to about 160 K, the corresponding atmospheric pressure rising from a few tenths of a millibar to about 30 mbar, respectively. The neglect of atmospheric heat transport probably underestimates the peak pressure. Because the altitude of the south cap is about 2 km higher than that of the north cap, CO2 ice is unstable there and will migrate to the north cap at a rate of about 10 g/sq cm yr, the implication being that the south residual cap is water ice. A simplified model of the annual polar caps and pressure fluctuations is also presented.
Ward, W. R.↗
Mercury's surface - Preliminary description and interpretation from Mariner 10 pictures
The surface morphology and optical properties of Mercury resemble those of the moon in remarkable detail and record a very similar sequence of events. Chemical and mineralogical similarity of the outer layers of Mercury and the moon is implied; Mercury is probably a differentiated planet with a large iron-rich core. Differentiation is inferred to have occurred very early. No evidence of atmospheric modification of landforms has been found. Large-scale scarps and ridges unlike lunar or Martian features may reflect a unique period of planetary compression near the end of heavy bombardment by small planetesimals.
Murray, B. C.↗
Mariner 10 pictures of Mercury - First results
Mercury has a heavily cratered surface containing basins up to at least 1300 kilometers diameter flooded with mare-like material. Many features are closely similar to those on the moon, but significant structural differences exist. Major chemical differentiation before termination of accretion is implied.
Murray, B. C.↗
Venus - Atmospheric motion and structure from Mariner 10 pictures
The Mariner 10 television cameras imaged the planet Venus in the visible and near ultraviolet for a period of 8 days at resolutions ranging from 100 meters to 130 kilometers. The general pattern of the atmospheric circulation in the upper tropospheric/lower stratospheric region is displayed in the pictures. Atmospheric flow is symmetrical between north and south hemispheres. The equatorial motions are zonal (east-west) at approximately 100 meters per second, consistent with the previously inferred 4-day retrograde rotation. Angular velocity increases with latitude. The subsolar region, and the region downwind from it, show evidence of large-scale convection that persists in spite of the main zonal motion. Dynamical interaction between the zonal motion and the relatively stationary region of convection is evidenced by bowlike waves.
Murray, B. C.↗
Television observations of Mercury by Mariner 10
The morphology and optical properties of the surface of Mercury resemble that of the moon in remarkable detail, recording a very similar sequence of events; chemical and mineralogical similarity of the outer layers is implied. Mercury is probably a differentiated planet with an iron-rich core. Differentiation is inferred to have occurred very early. No evidence of atmospheric modification of any landform is found. Large-scale scarps and ridges unlike lunar or Martian features may reflect a unique period of planetary compression near the end of heavy bombardment, perhaps related to contraction of the core.
Murray, B. C.↗
Polar volatiles on Mars - Theory versus observation
Synthesis of the results of the Mariner 9 mission, as they pertain to polar volatiles, and comparison of them with a description of the solid-vapor equilibrium relations believed to be presently active on Mars. The discovery by Mariner 9 of extensive volcanic deposits on portions of the Martian surface suggests that the total amount of CO2 liberated to the surface probably exceeds that now present in the atmosphere. Thus excess CO2 in the solid form is to be expected in the polar areas. Although the simplified model of Leighton and Murray (1966), which predicts a permanent CO2 cap, has significant deficiencies both theoretically and observationally, the seasonal caps are composed of CO2, as predicted, excess CO2 is quite likely, and a permanent deposit of solid CO2 evidently is in equilibrium with atmospheric CO2. It is suggested that there must be a large reservoir of solid CO2 in gaseous equilibrium with the atmosphere, but buried immediately below the exposed residual water-ice cap. This reservoir is believed to be located near the north pole. The principal effect of such a reservoir is to average out annual and longer-term fluctuations in the polar heat balance.
Murray, B. C.↗