Viking Images Research Articles

Thermal and albedo mapping of the polar regions of Mars using Viking thermal mapper observations: 1. North polar region

We present the first maps of the apparent thermal inertia and albedo of the north polar region of Mars. The observations used to create these maps were acquired by the infrared thermal mapper (IRTM) instruments on the two Viking orbiters over a 50‐day period in 1978 during the Martian early northern summer season. The maps cover the region from 60°N to the north pole at a spatial resolution of 1/2° of latitude. The analysis and interpretation of these maps is aided by the results of a one‐dimensional radiative convective model, which is used to calculate diurnal variations in surface and atmospheric temperatures, and brightness temperatures at the top of the atmosphere for a wide range of assumptions concerning aerosol optical properties and aerosol optical depths. The results of these calculations show that the effects of the Martian atmosphere on remote determinations of surface thermal inertia are more significant than have been indicated in previous studies. The maps of apparent thermal inertia and albedo show a great deal of spatial structure that is well correlated with surface features. The north residual polar cap has a very high apparent thermal inertia, and is interpreted to contain dense, coarse‐grained, or solid water ice that extends from within 2 mm of the surface to depths of at least l m below the surface. Detached, bright water ice deposits surrounding the residual cap also have very high apparent thermal inertias, and are interpreted to have similar properties. Polar layered deposits surrounding the north residual cap also have high apparent thermal inertias, and are also interpreted to contain near‐surface water ice. Mariner 9 images of the north residual cap obtained in 1972 show much less bright water frost coverage than Viking images obtained three Mars years later in 1978, and it is suggested that layered deposits may be actively forming in these areas over interannual timescales. Dark transverse dune deposits adjacent to the north residual cap have relatively low apparent thermal inertias, as do arcuate scarp regions within the polar layered deposits that appear to be major sources of polar dune material. The apparent thermal inertias of these north polar dune deposits are significantly lower than those of intracrater dune deposits at lower latitudes. The north polar dunes are interpreted to be composed of dark unconsolidated material that is being eroded from the layered deposits and transported away from the pole by saltation. The region poleward of 60°N contains no large low thermal inertia regions, which is interpreted as evidence that atmospheric dust is not accumulating in the north polar region under present climatic conditions.

"White Rock": An eroded Martian lacustrine deposit(?)

The existence and location of ancient lake sites and sediments have important implications for Martian paleoclimate and exobiology. White Rock, an enigmatic crater interior deposit, may be the eroded remnant of such a lacustrine deposit. Stereogrammetric analysis of newly processed Viking images allows better determination of the dimensions of White Rock (12.5 x 15 km, thickness 180 to 540 m, volume ∼40 km 3 ), reveals differences in erosion patterns that may reflect differences in depositional environment, and allows the identification in or on the crater wall of a possible source region of the high-albedo White Rock material. If White Rock is the remnant of a once-larger deposit, then open- system circulation may have been required to deliver the required quantity of evaporites.

Geographic asymmetries of the Viking auroral distribution: Implications for ionospheric coordinate systems

Viking images of the auroral distribution have been used to investigate the relevance of various ionospheric coordinate systems. An important aspect of the large‐scale auroral shape is its dependence on the asymmetries of the Earth's internal field. Model predictions of where the aurora occurs, using the equatorial plane's volume current density, agree with observations and imply that the internal field plays a more important role than generally believed. Historically, the belief that the internal field has only small effects seems to stem from the widespread use of the corrected geomagnetic and invariant coordinate systems. These systems involve the mapping of field lines and have advantages in statistical studies and comparisons; less sophisticated systems such as the eccentric dipole coordinate system should be used in individual studies and in studies involving the differentiation or integration of some observational parameters. Observations of the auroral distribution are given to illustrate the universal time, tilt angle, and Kp variability in different coordinate systems and demonstrate that the dominant variability of the aurora is due to internal field asymmetries. A new set of coordinate systems are briefly developed as examples of how to incorporate external field models into studies of auroral images. It is proposed that one of these coordinate systems can be used as a test of how well an external field model can match observed auroral distributions.

The relationship of periodic structures in auroral luminosity in the afternoon sector of ULF pulsations

Preliminary studies of Viking imager data by Lui et al, [1987] have revealed the presence, on occasion, of bright auroral structures periodically arrayed along the auroral oval in the post noon quadrant. It was suggested that these auroral forms reflect the action of a Kelvin‐Helmholtz instability. In this paper we report the results of such a study of periodically arrayed auroral structures with concurrent ULF pulsations. Assuming a common origin of the two phenomena to be the Kelvin‐Helmholtz instability, we make quantitative estimates of some key physical properties of the source region for the ULF and auroral disturbances. We further report the observation of a westward traveling surge in the vicinity of 18 MLT, and argue on the basis of the mapping factor from the ionosphere to the magnetotail why surges closer to midnight do not appear to exhibit a significant westward propagation velocity.

Modeling the growth phase of a substorm using the Tsyganenko Model and multi‐spacecraft observations: CDAW‐9

The CDAW‐9 Event C focused upon the early part of 3 May 1986 when a large substorm onset occurred at 0111 UT. By modifying the Tsyganenko 1989 magnetic field model, we construct a model in which the near‐Earth current systems are enhanced with time to describe the observed development of the tail magnetic field during the growth phase. The cross‐tail current intensity and the thickness of the current sheet are determined by comparison with three spacecraft in the near‐Earth tail. The location of the auroral bulge as recorded by the Viking imager is mapped to the equatorial current sheet. The degree of chaotization of the thermal electrons is estimated, and the consequences to the tail stability towards ion tearing are discussed. We conclude that the mapping of the brightening region in the auroral oval corresponds to the regions in the tail where the current sheet may be unstable towards ion tearing.

Distribution of auroral surges in the evening sector

Over the past decades a large statistical data base has been gathered consisting of both ground‐based magnetometer and all‐sky camera records from which researchers have inferred the distribution of substorm expansive phase events across the nighttime sector. Almost without exception, the activity distribution has been based on single station data acquired over periods of years. However, to truly establish the occurrence frequency of substorm expansive phase events, it is necessary to view the entire nighttime sector instantaneously in the light of evidence which shows that more than one expansive phase disturbance can be in progress across the broad expanse of the evening sector. In this paper we study the distribution of regions of localized auroral luminosity in the poleward portion of the evening sector auroral oval using images in the ultraviolet portion of the auroral spectrum acquired by the Viking satellite over 9 months in 1986. We find that auroral surge activity peaks in the hour before local magnetic midnight, with the probability of detecting a surge steadily decreasing to 10% of the probability of finding a surge in the hour prior to midnight as one moves westward towards 1900 MLT. We show that our conclusion is not dependent on the threshold chosen for surge identification over a reasonable portion of the intensity range covered by the Viking imager. We further show that for the interval of several months near sunspot minimum in 1986 there is better than a 90% chance that no surge will be detected in a 1‐hour range of magnetic local time if one were to sample that segment of the auroral oval at any arbitrary time. However, if there is one surge to be detected along the auroral oval, there is better than a 50% probability that there will be more than one surge existent at that instant. This confirms that several surges may coexist along the poleward edge of the oval during periods of activity which are sufficiently high so as to feature at least one surge. Finally, we identify long‐lived surge forms and, for these cases, find that during their lifetimes the surges do not propagate significantly away from their point of origin.

Analysis of substorm expansion and surge development

We have used simultaneous magnetogram, radar, and Viking imager data from evening local time to study several substorm expansion phase onsets and an expansion phase auroral surge that formed near the radar field of view. At the onsets, auroral brightenings developed within the region of the electric field gradient of the Harang discontinuity, and if not already present, a westward electrojet began poleward of the eastward electrojet. Immediately following onsets, the poleward boundary of the westward electrojet moved poleward along with the poleward boundary of the aurora; however, no consistent motion of the Harang discontinuity was found in the ionosphere. The auroral surge formed along the poleward boundary of the westward electrojet (and of the aurora). We argue that the distortion of the poleward boundary of the aurora associated with the surge was a manifestation of a distortion of the separatrix between open and closed magnetic field lines, the distortion being caused by the field‐aligned currents within the head of the surge. We suggest that rapid surge development may result from a tapping of the westward electrojet current at the surge head. We also suggest that the separatrix distortion could lead to the escape of trapped plasma sheet particles along open field lines in the tail.

Distribution of auroral precipitation at midnight during a magnetic storm

On the night of November 4, 1986, a very complex precipitation pattern was observed by Viking in the magnetic midnight sector over Scandinavia and Svalbard. The pass took place during a magnetic storm, and during substorm recovery phase. Going from north to south, the satellite first encountered a plasma region of BPS‐type (name derived from boundary plasma sheet) and then a region of CPS type (derived from central plasma sheet). Then, however, a new region of BPS‐type was traversed. The quite intense, most equatorward aurora corresponded to a plasma region which was not of ordinary CPS type but contained sharp quasi‐monoenergetic peaks. The high‐latitude midnight sector was totally dominated by eastward convection. The Harang discontinuity had passed northern Scandinavia the first time as early as 17 to 20 MLT, more than three hours before the Viking pass. It is suggested that the particle precipitation pattern and the general shape of the aurora as observed by the Viking imager can be explained in a natural way by the convection pattern. The northernmost BPS‐ and CPS‐type regions originated in the morningside convection cell, while the more equatorward population of BPS type had drifted in from the eveningside. The interpretation is supported by ground‐based measurements by EISCAT and magnetometers.

The configuration of the auroral distribution for interplanetary magnetic field Bz northward: 1. IMF Bx and By dependencies as observed by the Viking satellite

Viking images obtained throughout 1986 have been utilized in combination with IMP 8 satellite measurements of the interplanetary magnetic fields (IMF) to determine typical northern hemisphere auroral distributions for a variety of IMF Bz positive conditions. Varying By has an effect which is consistent with expected results. That is, By positive implies high‐latitude auroral arcs in the dusk sector while negative By gives dawn sector polar arcs. A new result gives significant importance to the Bx component of the IMF. Bx toward the Sun (By = 0) gives polar arcs on both dawn and dusk with comparatively weak UV emissions. With Bx away from the Sun (By = 0) a single Sun‐aligned morning sector polar arc dominates the auroral distribution. Azimuthal angle changes to the IMF of only 45° seem to affect the global auroral distribution with time scales of less than 2–3 hours. Poleward boundaries of the aurora were found to have a strong dependence on the IMF azimuthal angle which varied according to the magnetic local time investigated.

Magnitude of a catastrophic flood event at Kasei Valles, Mars

Research Article| September 01, 1990 Magnitude of a catastrophic flood event at Kasei Valles, Mars Mark S. Robinson; Mark S. Robinson 1Hawaii Institute of Geophysics, Planetary Geoscience Division, 2525 Correa Road, Honolulu, Hawaii 96822 Search for other works by this author on: GSW Google Scholar Kenneth L. Tanaka Kenneth L. Tanaka 2U.S. Geological Survey, 2255 North Gemini Drive, Flagstaff, Arizona 86001 Search for other works by this author on: GSW Google Scholar Geology (1990) 18 (9): 902–905. https://doi.org/10.1130/0091-7613(1990)018<0902:MOACFE>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Mark S. Robinson, Kenneth L. Tanaka; Magnitude of a catastrophic flood event at Kasei Valles, Mars. Geology 1990;; 18 (9): 902–905. doi: https://doi.org/10.1130/0091-7613(1990)018<0902:MOACFE>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Kasei Valles compose an enormous outflow-channel system on Mars. The upper part of the channel system is typically less than 1 km deep and descends from Echus Chasma about 1 km over a distance of 1000 km; it then splits into north and south channels. On the basis of a stereomodel of Viking images, we have measured the geometry of a steep, constricted reach of the north channel that drops 900 m in only 100 km. A late-stage flood is hypothesized to have scoured the channel. If we assume that channel striations indicate water levels, then the flood had a minimum cross-sectional area of 3.12 x 107 m2 (the putative flood had a width of 83 km, an average depth of 374 m, and maximum depth of 1280 m). These channel measurements suggest that flood velocities ranged from 32 to 75 m⋅s-1 and that discharge was greater than 1 km3⋅s-1, values larger than those calculated for any other flood event on Mars or Earth. The flood maintained supercritical flow and caused intense erosion in this area, scouring a 350-m-deep megapothole. The source of the flood water may have been a temporary lake in Echus Chasma, a deep canyon formed in association with tectonism at Valles Marineris. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Auroral bright spots on the dayside oval

Global auroral images from the ultraviolet imager on the Viking spacecraft are used to investigate spatially periodic bright spots on the dayside auroral oval that resemble beads on a string. The newly achieved temporal resolution of 1 min. or less in monitoring worldwide auroral distributions by the Viking imager contributes significantly to the capability of observing this phenomenon. It is found that these are frequently seen in the 1400–1600 MLT sector. The series of bright spots are not, however, limited to this unique local time sector, since they are seen to extend into the prenoon sector on some occasions. They occur often during substorm intervals but are also seen unaccompanied by substorm activities in the nightside. There is neither a consistent north‐south nor east‐west direction of motion for all the dayside bright spots observed so far. Our observation of the time scales for the transient intensifications of bright spots and the lack of consistent directions of their motion are consistent with the characteristics expected from the suggestion that these bright spots are related to the Kelvin‐Helmholtz instability occurring within the magnetosphere.

HDO in the Martian atmosphere: Implications for the abundance of crustal water

The physical and chemical processes that lead to the preferential escape of hydrogen over deuterium in the Martian atmosphere are studied in detail using a one-dimensional photochemical model. Comparison of our theory with recent observations of HDO suggests that, averaged over the planet, Mars contains 0.2 m of crustal water that is exchangeable with the atmosphere. Our estimate is considerably lower than recent estimates of subsurface water on Mars based on geomorphological analysis of Viking images. The estimate can be reconciled if only a small fraction of crustal water can exchange with the atmosphere.

Nature and origin of materials exposed in the Oxia Palus-Western Arabia-Sinus Meridiani region, Mars

Mars Observer will map physical, elemental, and mineralogical properties of surface materials. A key to understanding the regional variations in crustal composition will be the extent to which in situ debris produced from bedrock can be separated from laterally mixed eolian sediments. Viking Orbiter image and thermal data covering equatorial cratered terrain in western Arabia, eastern Oxia, and Sinuses Sabaeus and Meridiani were evaluated to test whether local materials related to bedrock could be identified, characterized, and mapped. Crater obliteration models imply that kilometers of debris have been produced locally, although obliteration rates for the past few billion years have been less than 8 × 10 −3 μm/year. Fluvial and eolian landforms clearly indicate lateral transport and mixing of tens of meters of debris. Six sets of calibrated violet, green, and red Viking images covering the study area were mosaicked and examined in combination with block abundance and fine component inertias from IRTM data. Three major color/ thermal units can be discerned: bright red dust storm deposits; brown materials that are probably indurated; and dark, less red materials that are probably composed of lithic fragments in the medium sand size range. The unit boundaries are independent of bedrock geology and erosional landforms. The brightest red material apparently mixes with each of the darker units. The presence of dark splotches, streaks, and dunes associated with large craters in Oxia indicates that the dark, less red material is also mobile. The surficial units exposed over the ∼6 × 10 6-km 2 study area are therefore likely to represent mixed eolian deposits, predominantly decoupled from the underlying bedrock. Unraveling the mixtures and assignment of components to local bedrock origins will be a major challenge for Mars Observer.

Global albedo variations on Mars: Implications for active aeolian transport, deposition, and erosion

Observations at 0.3–3.0 μm by the Viking infrared thermal mapper have been used to determine the temporal and spatial variations of the albedo of the Martian surface and atmosphere. These data were collected into 1° × 1° latitude, longitude bins, for local times of 6–10 H, 10–14 H, and 14–18 H (24 H equals 1 Martian day), and for 10° Ls bins throughout the Viking mission. The major variations in albedo were associated with the two global dust storms of 1977, The first storm began near Ls 205°, and the second storm began between Ls 273.5° and 274.0°, consistent with Viking imaging and thermal observations. For optically thick atmospheric dust, the observed albedo was 0.37–0.40. Over all regions the atmosphere cleared substantially between the two storms, with many southern hemisphere regions returning to their prestorm albedos. In general, the northern hemisphere atmosphere had a higher dust content throughout the storm phase, and retained dust longer during the decay phases, than the southern hemisphere. Southern hemisphere dark regions were not measurably brighter following the global storms, suggesting little net deposition of dust. In contrast, the northern hemisphere dark regions of Syrtis Major and Acidalia Planitia were measurably brighter following the storm, indicating the deposition of ∼7–45 μm of dust per year. These surfaces subsequently darkened over the following months, returning to prestorm albedo values prior to the next dust storm season. The material raised from these surfaces, and atmospheric dust observed locally over several other dark regions during the clear periods, may account for the general dust haze observed throughout the year. It appears that dust is also deposited in bright, low‐inertia regions, where it remains. The albedo data suggest active dust transport into the north, with net deposition in the bright, low‐inertia regions. This south‐to‐north transport of dust during global storms is consistent with atmospheric circulation models, which predict the presence of cross‐equatorial Hadley circulation during this season. Because of the close connection between dust transport and atmospheric circulation at present, it is possible that under reversed conditions of north‐to‐south circulation during epochs when the maximum solar heating occurs in the north, the current deposits would be eroded and transported back to the south. This continual reworking of an active, surface dust layer would therefore not require substantial erosion of the surface to account for the high level of aeolian erosion and transport observed at present.

North‐south structures in the midnight sector auroras as viewed by the Viking imager

During auroral substorms, active auroras involving field‐aligned electric fields appear at the poleward border of the auroral oval. Equatorward of these active discrete auroras, a diffuse region of luminosity develops which often features imbedded localized structures which can have distinctively north‐south orientations. In this paper we study the behaviour of such longitudinally confined northsouth oriented auroral arc structures which may turn on and off sporadically during the substorm lifetime. In particular, we show observations which suggest that these structures may be the projection on the ionosphere of the drift paths of energetic electrons as they drift from the magnetotail into the more dipolar inner magnetosphere. Our results suggest that injection of auroral particles into the central plasma sheet occurs in quite localized regions over lengthy periods of time. The injected particles drift earthward in the central plasma sheet where those electrons with pitch angles close to the loss cone are sporadically caused to precipitate into the ionosphere causing the fingers of luminosity. North‐south aligned structures near the equatorward edge of the oval are believed to represent precipitation of a spatially localized population of energetic electrons for which the westward convective drift velocity in the evening sector nearly balances the eastward gradient and curvature drift velocity thus leading to purely earthward convective drift of the energetic electrons.

Linear volcanic features at Alba Patera, Mars ‐ PRobable spatter ridges

A number of extensive linear constructional features occur on the north and east flanks of Alba Patera. They are found in a 150‐km‐wide zone and comprise aligned ridge elements that are locally associated with short volcanic flows. They are among the youngest volcanic features in the region and are believed to be Martian analogs of terrestrial spatter ridges. On the basis of measurements made on Viking images, it appears that active volcanic fissures on Mars were larger than their terrestrial counterparts.

The stratigraphy of Mars

A detailed planetwide stratigraphy for Mars has been developed from global mapping based on Viking images and crater counting of geologic units. The original Noachian, Hesperian, and Amazonian Systems are divided into eight series corresponding to stratigraphic referents. Characteristic crater densities and material referents of each series are (1) Lower Noachian [N(16)] (number of craters &gt; 16 km in diameter per 106 km2) &gt; 200] basement material; (2) Middle Noachian [N(16) = 100–200] cratered terrain material; (3) Upper Noachian [N(16) = 25–100; N(5) = 200–400] intercrater plains material; (4) Lower Hesperian [N(5) = 125–200] ridged plains material; (5) Upper Hesperian [N(5) = 67–125; N(2) = 400–750] complex plains material; (6) Lower Amazonian [N(2) = 150–400] smooth plains material in southern Acidalia Planitia; (7) Middle Amazonian [N(2) = 40–150] lava flows in Amazonis Planitia; and (8) Upper Amazonian [N(2) &lt; 40] flood‐plain material in southern Elysium Planitia. Correlations between various crater size‐frequency distributions of highland materials on the moon and Mars suggest that rocks of the Middle Noachian Series are about 3.92–3.85 b.y. old. Stratigraphic ages compiled for units and features of various origins show that volcanism, tectonism, and meteorite bombardment have generally decreased through Mars' geologic history. In recent time, surficial processes have dominated the formation and modification of rock units. The overall stratigraphy of Mars is complex, however, because of temporal and spatial variations in geologic activity.

Loss of fine-scale surface texture in Viking orbiter inages and implications for the inferred distribution of Debris Mantles

The absence of fine-scale surface features in Viking Orbiter images must be interpreted with caution. A reduction in contrast due to the presence of atmospheric haze will preferentially obscure small features. Two sets of images of the same region, taken with similar viewing geometry but under different atmospheric conditions, allow us to demonstrate that a single scattering model quantitatively accounts for the effects of the atmosphere. Craters five to seven times the size of the camera picture element should be resolved in Viking Orbiter images if the atmosphere is clear. When atmospheric haze effects dominate, larger craters are obscured and crater size-frequency distributions appear to be depleted in small-sized craters in a predictable way. Twelve crater size-frequency counts in the northern hemisphere behave in the manner predicted for hazy conditions. Their characteristics also follow the pattern of increasing atmospheric opacity with latitude in spring and summer deduced from other measurements of cloudiness. Loss of surface resolution due to the nearly ubiquitous atmospheric obscuration in the northern mid to high latitudes makes it difficult to assesst, with existing images, the validity of suggestions that fine-scale surface features have been preferentially degraded by surface processes. However, the atmosphere in the southern mid and high latitudes is relatively clear during autumn and winter, and a preliminary review of existing image data suggests that features with sizes down to five to seven picture elements can be detected in this region. No evidence for a recent circumpolar debris mantle can be found in the southern hemisphere data. Because the smallest craters that can be resolved in Viking images are several tens of meters in diameter, we cannot rule out the occurrence of debris deposits less than a few tens of meters thick, regardless of atmospheric clarity.

Global geologic mapping of Mars: The western equatorial region

Global geologic mapping of Mars was originally accomplished following acquisition of orbital spacecraft images from the Mariner 9 mission. The mapping program represented a joint enterprise by the U.S. Geological Survey and other planetary scientists from universities in the United States and Europe. Many of the Mariner photographs had low resolution or poor albedo contrast caused by atmospheric haze and high-sun angles. Some of the early geologic maps reflect these deficiencies in their poor discrimination and subdivision of rock units. New geologic maps made from higher resolution and better quality Viking images also represent a cooperative effort, by geologists from the U.S. Geological Survey, Arizona State University, and the University of London. This second series of global maps consists of three parts: 1) western equatorial region, 2) eastern equatorial region, and 3) north and south polar regions. These maps, at 1:15 million scale, show more than 60 individual rock-stratigraphic units assigned to three Martian time-stratigraphic systems. The first completed map of the series covers the western equatorial region of Mars. Accompanying the map is a description of the sequence and distribution of major tectonic, volcanic, and fluvial episodes as recorded in the stratigraphic record.

Martian rampart crater ejecta: Experiments and analysis of melt-water interaction

Viking images of Martian craters with rampart-bordered ejecta deposits reveal distinct impact ejecta morphology when compared to that associated with similar-sized craters on the Moon and Mercury. Topographic control of distribution, lobate and terraced margins, cross-cutting relationships, and multiple stratigraphic units are evidence for ejecta emplacement by surface flowage. It is suggested that target water explosively vaporized during impact alters initial ballistic trajectories of ejecta and produces surging flow emplacement. The dispersal of particulates during a series of controlled steam explosions generated by interaction of a thermite melt with water has been experimentally modeled. Preliminary results indicate that the mass ratio of water to melt and confining pressure control the degree of melt fragmentation (ejecta particle size) and the energy and mode of melt-ejecta dispersal. Study of terrestrial, lobate, volcanic ejecta produced by steam-blast explosions reveals that particle size and vapor to clast volume ratio are primary parameters characterizing the emplacement mechanism and deposit morphology. Martian crater ramparts are formed when ejecta surges lose fluidizing vapors and transported particles are deposited en masse. This deposition results from flow yield strength increasing above shear stress due to interparticle friction.