Martian Terrain Research Articles

Fractal analysis of drainage basins on Mars

We used statistical properties of drainage networks on Mars as a measure of martian landscape morphology and an indicator of landscape evolution processes. We utilize the Mars Orbiter Laser Altimeter (MOLA) data to construct digital elevation maps (DEMs) of several, mostly ancient, martian terrains. Drainage basins and channel networks are computationally extracted from DEMs and their structures are analyzed and compared to drainage networks extracted from terrestrial and lunar DEMs. We show that martian networks are self‐affine statistical fractals with planar properties similar to terrestrial networks, but vertical properties similar to lunar networks. The uniformity of martian drainage density is between those for terrestrial and lunar landscapes. Our results are consistent with the roughening of ancient martian terrains by combination of rainfall‐fed erosion and impacts, although roughening by other fluvial processes cannot be excluded. The notion of sustained rainfall in recent Mars history is inconsistent with our findings.

Results of the Imager for Mars Pathfinder windsock experiment

The Imager for Mars Pathfinder (IMP) windsock experiment measured wind speeds at three heights within 1.2 m of the Martian surface during Pathfinder landed operations. These wind data allowed direct measurement of near‐surface wind profiles on Mars for the first time, including determination of aerodynamic roughness length and wind friction speeds. Winds were light during periods of windsock imaging, but data from the strongest breezes indicate aerodynamic roughness length of 3 cm at the landing site, with wind friction speeds reaching 1 m/s. Maximum wind friction speeds were about half of the threshold‐of‐motion friction speeds predicted for loose, fine‐grained materials on smooth Martian terrain and about one third of the threshold‐of‐motion friction speeds predicted for the same size particles over terrain with aerodynamic roughness of 3 cm. Consistent with this, and suggesting that low wind speeds prevailed when the windsock array was not imaged and/or no particles were available for aeolian transport, no wind‐related changes to the surface during mission operations have been recognized. The aerodynamic roughness length reported here implies that proposed deflation of fine particles around the landing site, or activation of duneforms seen by IMP and Sojourner, would require wind speeds >28 m/s at the Pathfinder top windsock height (or >31 m/s at the equivalent Viking wind sensor height of 1.6 m) and wind speeds >45 m/s above 10 m. These wind speeds would cause rock abrasion if a supply of durable particles were available for saltation. Previous analyses indicate that the Pathfinder landing site probably is rockier and rougher than many other plains units on Mars, so aerodynamic roughness length elsewhere probably is less than the 3‐cm value reported for the Pathfinder site.

“Pathological” Martian craters: Evidence for a transient obliteration event?

— We have detected three unusual, low-relief circular features, 1.2 to 2.1 km in diameter, in the northwest Noachis highlands, which may be craters that have undergone isostatic deformation. They may shed light on the existence, nature, and timing of suspected widespread Martian erosion/obliteration events, and offer clues to a type of Martian terrain softening. In the surrounding area, we find an anomalous deficiency of craters in the 3–11 km diameter range and evidence that larger, older craters have undergone relief softening and infill. We discuss three different hypotheses to explain these features, two of which involve Martian ice. This region may have undergone a transient event in which a near-surface permafrost layer (several hundred meters deep) underwent partial melting or softening. This would allow relaxation of kilometer-scale craters and softening of larger craters. Crater data presented here suggest that this event happened some time in mid-Martian history. Whether the event was regional or related to global-scale events is uncertain, though it may represent a class of events that also happened in other Martian areas.

Planetary protection program for Mars 94/96 mission

Mars surface in-situ exploration started in 1975 with the American VIKING mission. Two probes landed on the northern hemisphere and provided, for the first time, detailed information on the martian terrain, atmosphere and meteorology. The current goal is to undertake larger surface investigations and many projects are being planned by the major Space Agencies with this objective. Among these projects, the Mars 94/96 mission will make a major contributor toward generating significant information about the martian surface on a large scale. Since the beginning of the Solar System exploration, planets where life could exist have been subject to planetary protection requirements. Those requirements accord with the COSPAR Policy and have two main goals: • - the protection of the planetary environment from influence or contamination by terrestrial microorganisms • - the protection of life science, and particularly of life detection experiments searching extra-terrestrial life, and not life carried by probes and spacecrafts As the conditions for life and survival for terrestrial microorganisms in the Mars environment became known, COSPAR recommendations were updated /1/. This paper will describe the decontamination requirements which will be applied for the MARS 94/96 mission, the techniques and the procedures which are and will be used to realize and control the decontamination of probes and spacecrafts.

Aqueous geochemistry on early Mars

A geochemical cycle model is presented for the interaction between the atmosphere, hydrosphere, and regolith of Mars. It was developed to study how this interaction might have produced the present Martian environment from a primitive Martian environment much like that of the primitive Earth. The model is a simple system, consisting of an unweathered starting material (calcium-bearing and magnesium-bearing silicates), a CO 2 atmosphere, an ocean of water in contact with both the atmosphere and the unweathering starting material, and both calcite and dolomite precipitates. Several interesting points arise from this model. A 1-bar CO 2; atmosphere can be removed by carbonate precipitation alone in about half a billion years. This is roughly fifty times longer than earlier estimates, which were not based on time-varying models ( Fanale et al., 1982; Carr, 1986; Pollack et al., 1987). One of the chief problems in Martian geology has been how to explain the large number and wide variety of surface features that were apparently formed by aqueous erosion. This longer atmospheric lifetime may be enough to explain the large number of channels seen on older Martian terrain. If the atmosphere started out with more than 1 bar of CO 2, it would take correspondingly longer to remove it. If there should be no other means to remove CO 2 from the atmosphere, this long time constant would indicate that the atmosphere could never have contained more than a few bars of CO 2, or else there would still be remnants present today. The increase in alkalinity of the ocean as the atmosphere disappears, even without the effects of reduction in the amount of water available, indicates that evaporite deposits may have formed on Mars. If these deposits are still present, they may even yet contain some liquid water.

The use of mineral crystals as bio-markers in the search for life on Mars

Photographs that depict presumed fluvial features on the martian surface have led geologists to hypothesize that water flowed across the early martian terrain. From this, it has been further hypothesized that the surface and atmospheric conditions on early Mars were similar to those on early Earth. Because the oldest fossil evidence of life on Earth dates back to this early period, at least 3.5 billion years ago /1/, the possibility exists that the early Martian environment could have also been conducive to the origin of life. To investigate this possibility, universal signatures or bio-markers indicative of past (or present) biological activity must be identified for use in the search for life on Mars. Several potentially applicable biomarkers have been identified and include: organics (e.g., specific classes of lipids and hopanes), suites of specific inorganic and organic compounds, as well as the isotopic ratios of C, N, and S /2/. Unfortunately, all of these biomarkers may be biologic or abiotic origin; these origins are often difficult to distinguish. Thus, the discovery of any one of these compounds alone is not a bio-marker. Because minerals produced under biologic control have distinctive crystallographies, morphologies, and isotopic ratios that are distinguishable from abiotically produced minerals with the same chemical composition, and are stable through geologic time, we propose the use of minerals resulting from biologically controlled mineralization processes as bio-markers.

The oblique impact hypothesis and relative probabilities of lunar and Martian meteorites

The author has previously suggested that shergottites and possibly other SNC meteorites were launched from the Martian surface by the oblique impact of large meteoroids. This hypothesis is further evaluated in the context of the subsequent discovery of a lunar meteorite. The oblique impact hypothesis is consistent with observations concerning the lunar and putative Martian meteorites. Oblique impacts are comparatively rare, consistent with the observation that ejecta from only one lunar event and one or two putative Martian events have been recognized. The hypothesis is also consistent with the observation of ejecta from a volatile‐poor object, the moon, as well as the probable existence of ejecta from a more volatile‐enriched object, Mars. Furthermore, in spite of the comparative rarity of oblique impacts, there exists at least one candidate source crater for the lunar meteorite in the lunar highlands adjacent to a source of the VLT basalt fragment discovered in it. There also exist at least two candidate source craters on Martian terrain of appropriate age to be the source terrain of the SNC meteorites. The candidate source craters are of appropriate size to be representative of events that have contributed to the current inventory of a continuous background of space stored lunar and Martian ejecta. Finally, it is shown that within calculational uncertainties and the current poorly known fall statistics of lunar and probable Martian meteorites, the oblique impact hypothesis gives a satisfactory explanation of the relative abundances of lunar, Martian, and other meteorites. These results support the oblique‐impact‐on‐Mars origin of SNC meteorites and give a satisfactory explanation for the occurrence of a lunar meteorite.

Martian cratering revisited: Implications for early geologic evolution

Improved crater statistics from varied Martian terrains are compared to lunar crater populations. The distribution functions for the average Martian cratered terrain and the average lunar highlands over the diameter range 8–2000 km are quite similar. The Martian population is less dense by approximately 0.70 from 8 to 256 km diameter and diverges to proportionally lower densities at greater diameters. Crater densities on Martian “pure” terra give a lower limit to the Mars/Moon integrated crater flux of 0.75 since the last stabilization of the respective planetary crusts. The crater population >8 km diameter postdating the Martian northern plains is statistically indistinguishable from that population postdating the lunar maria. Monte Carlo simulations were performed to constrain plausible mechanisms of crater obliteration. The models demonstrate that if the crater density difference between the lunar and Martian terra has been due to resurfacing processes, random intercrater plains formation cannot be the sole process. If plains preferentially form in and obliterate larger craters, then the observed Martian distribution retains its “shape” as the crater density decreases. This result is consistent with the morphology of Martian intercrater plains.

Mutch memorial plaque unveiled

A plaque commemorating Thomas A. Mutch, former associate administrator of NASA's Office of Space Science, was unveiled in a ceremony at the National Air and Space Museum earlier this month. Mutch was lost while mountain climbing in the Himalayas in October (Eos, October 28, p. 693). The plaque will be affixed to the Viking 1 lander, renamed the Mutch Memorial Station, during a future Mars mission.A follow‐up Mars mission has been suggested for the 1990's, and although no funding is available now, there is talk, NASA says, of sending a roving spacecraft to Mars that would affix the plaque, scoop up some Martian terrain, and bring the sample back to earth. Until the plaque can be transported to Mars, it will remain at NASA headquarters in Washington, D.C.

A thermodynamical study of the Martian permafrost

An outstanding result of the Viking mission has been the detection of water vapor in the martian environment. The only possible reservoir for the water, where no evidence of surface frost has been detected, is the soil. Comparative morphologic analyses of periglacial terrestrial and martian terrains suggested that permafrost can play an important role in forming many surficial structures as the Valles Marineris landslides or the collapse structures in the volcanic region of Tharsis. In this paper a study of the thermodynamics which regulate the processes of thawing and freezing of the layers of permafrost on Mars has been carried out. The equation of the heat propagation has been solved under martian conditions both in the case of periodic variations of the surface temperature and in the case of an anomalous heating of the ground. Seasonal temperature variations do not allow survival of CO2 or clathrate permafrost down to a depth of 15 m. We have demonstrated the existence of a secular ‘active layer’ of about 100‐m depth.

Bistatic radar measurements of electrical properties of the Martian surface

The Viking lander-to-orbiter relay links make it possible to perform measurements of the electrical properties of the Martian surface by the bistatic technique. The electromagnetic signals radiated by the lander antenna at 381 MHz, in fact, reach the orbiter both directly and after reflection from the Martian terrain as the orbiter rises and sets with respect to the lander. The fading pattern of the signal intensity received at the orbiter therefore contains information on the reflection coefficient of the terrain and hence on the relative dielectric constant er and the conductivity σ in the vicinity of the lander. The signal amplitude's fading patterns collected with the Lander 1 to Orbiter 1 relay link were of good quality and led to the determination of εr = 3.3 ± 0.7 in the vicinity of Lander 1 (when the quasi-specular theory was used and σ was assumed to be between 10−3 and 1.0−5 mho/m). These electrical properties are similar to those of pumice and tuff. The dielectric constant of the surface near the Lander 2 site is estimated to be εr = 2.8–12.5.

Structure pattern analysis of the Noctis Labyrinthus-Valles Marineris regions of Mars

The Coprates and Phoenicis Lacus quadrangles of Mars contain the Valles Marineris, Noctis Labyrinthus, and Claritas Fossae areas, each of which shows distinctive structural patterns. Analyses of the structural trends seen within these quadrangles show four principal trend directions. The chronological relationships among these trends and their relation to the stratigraphy has been determined. It appears that the two oldest trends (essentially WSW/ENE and NNE/ SSW), on the basis of transection relations, are best defined in what have been mapped on stratigraphic criteria as older Martian terrains (troughed and furrowed and cratered terrains). Younger trends (WNW/ESE and N/S), also on the basis of transection relations, appear to be related to opening and widening of the canyon. These are present only in the younger stratigraphic units. A comparison between the structural pattern of the Valles Marineris region and that of the Eastern African Rift system at the same scale reveals regional similarities. These suggest that a common major process, lateral extensions in the crust, was involved in the formation of both features.