The Surface of Mars
TL;DR: Mariner 6 and 7 pictures show that craters are the dominant landform on Mars and that their occurrence is not correlated uniquely with latitude, elevation, or albedo markings.
Abstract: Mariner 6 and 7 pictures show that craters are the dominant landform on Mars and that their occurrence is not correlated uniquely with latitude, elevation, or albedo markings. Two distinct morphological classes are recognized: small bowl-shaped and large flat-bottomed. The former show little evidence of modifications, whereas the latter appear generally more modified than hmar upland craters of comparable size. A regional maria/uplands dichotomy like the moon has not yet been recognized on Mars. Crater modification on Mars has involved much greater horizontal redistribution of material than in the lunar uplands. It is possible that there are erosional processes only infrequently active. Analysis of the natures and fluxes of bodies that have probably impacted the moon and Mars leads to the likelihood that most of the large flat-bottomed craters on Mars have survived from the final phases of planetary accretion. Significant crater modification, however, has taken place more recently on Mars. Inasmuch as the present small bowl-shaped craters evidence little modification, the postaccretion crater-modification process on Mars may have been primarily episodic rather than continuous. The size-frequency distribution of impacting bodies that produced the present small Martian bowl-shaped craters differs from that responsible for post-mare primary impacts on the moon by a marked deficiency of large bodies. Survival of crater topography from the end of planetary accretion would make any hypothetical earthlike phase with primitive oceans there unlikely. The traditional view of Mars as an earthlike planetary neighbor in terms of its surface history is not supported by the picture data.
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TL;DR: The Mars Orbiter Laser Altimeter (MOLA) has been used to measure the topography, surface roughness, and 1.064-μm reflectivity of Mars and the heights of volatile and dust clouds as mentioned in this paper.
Abstract: The Mars Orbiter Laser Altimeter (MOLA), an instrument on the Mars Global Surveyor spacecraft, has measured the topography, surface roughness, and 1.064-μm reflectivity of Mars and the heights of volatile and dust clouds. This paper discusses the function of the MOLA instrument and the acquisition, processing, and correction of observations to produce global data sets. The altimeter measurements have been converted to both gridded and spherical harmonic models for the topography and shape of Mars that have vertical and radial accuracies of ~1 m with respect to the planet's center of mass. The current global topographic grid has a resolution of 1/64° in latitude × 1/32° in longitude (1 × 2 km^2 at the equator). Reconstruction of the locations of incident laser pulses on the Martian surface appears to be at the 100-m spatial accuracy level and results in 2 orders of magnitude improvement in the global geodetic grid of Mars. Global maps of optical pulse width indicative of 100-m-scale surface roughness and 1.064-μm reflectivity with an accuracy of 5% have also been obtained.
1,542 citations
TL;DR: Gullies within the walls of a very small number of impact craters, south polar pits, and two of the larger martian valleys display geomorphic features that can be explained by processes associated with groundwater seepage and surface runoff.
Abstract: Relatively young landforms on Mars, seen in high-resolution images acquired by the Mars Global Surveyor Mars Orbiter Camera since March 1999, suggest the presence of sources of liquid water at shallow depths beneath the martian surface. Found at middle and high martian latitudes (particularly in the southern hemisphere), gullies within the walls of a very small number of impact craters, south polar pits, and two of the larger martian valleys display geomorphic features that can be explained by processes associated with groundwater seepage and surface runoff. The relative youth of the landforms is indicated by the superposition of the gullies on otherwise geologically young surfaces and by the absence of superimposed landforms or cross-cutting features, including impact craters, small polygons, and eolian dunes. The limited size and geographic distribution of the features argue for constrained source reservoirs.
1,008 citations
TL;DR: The Noachian period was characterized by high rates of impact, valley formation, weathering, and erosion all dropped precipitously but volcanism continued at a relatively high average rate throughout the Hesperian, resulting in the resurfacing of at least 30% of the planet.
578 citations
Cites background from "The Surface of Mars"
...Going from the upper Noachian into the Hesperian, valleys with sapping characteristics may become more common and surface runoff characteristics less common (Harrison and Grimm, 2005; Carr, 2006)....
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...The geomorphic evidence for lakes and rivers (Carr, 2006; Fassett and Head, 2008a) the widespread presence of phyllosilicates in Noachian terrains (Bibring et al., 2006; Murchie et al., 2008), the evidence for groundwater movement and surface water at Meridiani (Grotzinger et al., 2005a,b), and…...
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...Precipitation followed by surface runoff, coupled with infiltration and groundwater seepage must have occurred at least episodically in the Noachian (Craddock and Howard, 2002; Irwin and Howard, 2002; Hynek and Phillips 2003; Stepinski and O'Hara, 2003; Howard et al., 2005a,b; Carr, 2006)....
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...The geomorphic evidence for lakes and rivers (Carr, 2006; Fassett and Head, 2008a) the widespread presence of phyllosilicates in...
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...Possibly the oldest geologic event recorded in the configuration of the surface is formation of the global dichotomy (McGill and Squyres, 1991; Nimmo and Tanaka, 2005; Carr, 2006)....
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TL;DR: The Antarctic Dry Valleys (ADV) is a hyper-arid, cold-polar desert region as mentioned in this paper, which contains a suite of landforms at macro-, meso-, and microscales that closely resemble those occurring on the martian surface.
371 citations
Cites background from "The Surface of Mars"
...ods of the climate history of Mars (e.g., Bibring et al., 2006; Carr, 2006)....
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TL;DR: A preliminary study of the means to produce Atacama perchlorate to help shed light on the origin of Martian perchlorates has been conducted in this paper, using a 1-D photochemical model.
Abstract: [1] Isotopic studies indicate that natural perchlorate is produced on Earth in arid environments by the oxidation of chlorine species through pathways involving ozone or its photochemical products With this analogy, we propose that the arid environment on Mars may have given rise to perchlorate through the action of atmospheric oxidants A variety of hypothetical pathways can be proposed including photochemical reactions, electrostatic discharge, and gas-solid reactions Because perchlorate-rich deposits in the Atacama desert are closest in abundance to perchlorate measured at NASA's Phoenix Lander site, we made a preliminary study of the means to produce Atacama perchlorate to help shed light on the origin of Martian perchlorate We investigated gas phase pathways using a 1-D photochemical model We found that perchlorate can be produced in sufficient quantities to explain the abundance of perchlorate in the Atacama from a proposed gas phase oxidation of chlorine volatiles to perchloric acid The feasibility of gas phase production for the Atacama provides justification for future investigations of gas phase photochemistry as a possible source for Martian perchlorate
253 citations
Cites background from "The Surface of Mars"
...Evidence from aqueous alteration minerals and fluvially eroded geological features suggests that different climate regimes and atmospheric conditions occurred during the Noachian before 3.7 Ga and the Hesperian era, which terminated 2.9–3.3 Ga [Carr, 1996, 2006; Hartmann and Neukum, 2001]....
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References
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TL;DR: Signer and Suess as discussed by the authors brought together and evaluated all significant evidence on the origin of meteorites, and showed that the absence of a Widmanstatten pattern in meteorites with > 16% Ni cannot be attributed to high pressures, but to supercooling or an unusually fast cooling rate for these meteorites.
Abstract: This paper attempts to bring together and evaluate all significant evidence on the origin of meteorites. The iron meteorites seem to have formed at low pressures. Laboratory evidence shows that the absence of a Widmanstatten pattern in meteorites with > 16% Ni cannot be attributed to high pressures, but to supercooling or an unusually fast cooling rate for these meteorites, which prevented the development of a pattern. The presence of tridymite in the Steinbach siderophyre provides further, direct proof that the Widmanstatten pattern can form at pressures less than 3 kb. Neither diamond, nor cliftonite, nor cohenite are reliable pressure indicators in meteorites. Diamonds were formed by shock while cliftonite may have been derived from a cubic carbide such as Fe4C. Cohenite is apparently stabilized by kinetic rather than thermodynamic factors. Several lines of evidence suggest that the irons come from more than one parent body, perhaps as many as four. The frequency of pallasites is perfectly consistent with an origin in the transition zone between core and mantle of the parent body. “Hybrid” meteorites such as Brenham are not necessarily derived from the metal-silicate interface, but probably resulted from dendrite growth in the solidifying melt. Ordinary chondrites definitely are equilibrium assemblages rather than chance conglomerates. According to the best available evidence, Prior's rules seem to be valid. The metal particles in chondrites differentiated into kamacite and taenite in their present location, rather than in a remote earlier environment. Trace element abundances in ordinary and carbonaceous chondrites suggest that these meteorites accreted from two types of matter: an undepleted fraction that separated from its complement of gases at low temperatures, and a depleted fraction that lost its gases at high temperatures. These two fractions of primitive meteoritic matter are tentatively identified with the matrix and chondrules-plus-metal, respectively. New restrictive limits are placed on the iron-silicate fractionation in chondrites. No direct evolutionary path exists that connects the currently accepted solar abundances of Fe and Ni and the observed Fe/Si and Ni/Si ratios in chondrites. Apparently the solar abundance of iron is in error. The iron-silicate fractionation seems to have occurred while chondritic matter was in a more strongly reduced state than its present one. The U-He and K-Ar ages of hypersthene chondrites are systematically shorter than those of bronzite chondrites. Short ages are correlated with shock effects, and it seems that the hypersthene chondrites suffered reheating and partial-to-complete outgassing 0.4 AE ago. The cosmic-ray exposure ages of all classes of meteorites cluster distinctly, indicating that the meteorites were produced in a few discrete major collisions rather than by a quasi-continuum of smaller ones. The dates of the principal breakups are: irons, 0.6 and 0.9 AE; aubrites, 45 m.y.; bronzite chondrites, 4 m.y.; hypersthene chondrites, 0.025, 3, 7–13, and 16–31 m.y. All four clusters of hypersthene chondrites show evidence of severe outgassing 0.4 AE ago, which implies that most or all hypersthene chondrites come from the same parent body. As already noted by Signer and Suess, two distinct types of primordial gas occur in meteorites. Differentiated meteorites always contain unfractionated gas, while relatively undifferentiated meteorites contain fractionated gas. The former component is invariably associated with shock effects, and seems to have been derived from the solar wind. The latter component is correlated with other volatiles and seems to be a truly primitive constituent of meteoritic matter. Isotopic anomalies in the fractionated gas suggest that meteoritic matter was irradiated with ⩾ 1017 protons/cm2 at a very early stage of its history. There is very little doubt that most, if not all, meteorites come from the asteroid belt rather than from the moon. The orbits and geocentric velocities of stony meteorites resemble those of the Apollo asteroids (most of which are former members of the asteroid belt that have strayed into terrestrial space), but disagree strongly with the calculated orbits and velocities for lunar ejecta. Opik's conclusions about the difficulty of accelerating lunar debris to escape velocity represent a further argument against a lunar origin of stony meteorites. The most likely parent bodies of the meteorites are the 34 asteroids which cross the orbit of Mars. Collisional debris from these objects will remain in Mars-crossing orbits, and perturbations by Mars will inject some fraction of this material into terrestrial space. Most of the Mars asteroids, comprising 98% of the mass and 92% of the cross-section, belong to three Hirayama families (Phocaea, Desiderata, and Aethra), and an additional, previously unrecognized family. These families were apparently produced by disruption of parent asteroids ca. 104, 105, and 46 km in diameter. The size distribution and light curves of asteroids indicate that the larger asteroids are original accretions, rather than collision fragments. There is no reason to believe that the meteorites ever resided in bodies larger than Ceres (d = 770 km). Various theories on the origin of the meteorites are critically reviewed in the light of the preceding evidence. Wood's theory, which postulates a high-temperature and a low-temperature variety of primordial matter, is in best accord with the evidence. Apparently the asteroids accreted from varying proportions of these two types of material, and were then heated by extinct radioactivity produced in the early irradiation.
699 citations
"The Surface of Mars" refers background or methods in this paper
...Martian impact fluxes were entirely asteroidal and used a previous estimate by Anders [1964] of asteroidal fluxes at Mars higher by a factor of 25....
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...Martian impact fluxes were entirely asteroidal and used a previous estimate by Anders [1964] of asteroidal fluxes at Mars higher by a factor of 25. This factor of 25 is probably grossly overestimated, as indicated by a variety of reasons. First, Wetherill [1968] has shown by dynamical arguments that the probability of Mars being impacted by an asteroidal object whose orbit was perturbed by Mars is very low....
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...Studies of the chemical nature and cosmic-ray exposure ages of terrestrial meteorite falls [Anders, 1964] suggest that as many as 5 to 20...
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...This was first attempted by Anders and Arnold [1965]. A more complete analysis was performed by Hartmann [1966] using Mariner 4 crater counts....
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TL;DR: Generalization of Oepik theory of planetary bodies collision to include case where orbits of both colliding bodies are ellipses is discussed in this paper, where the authors propose a generalization to include the case where the collision point is an ellipsis.
Abstract: Generalization of Oepik theory of planetary bodies collision to include case where orbits of both colliding bodies are ellipses
328 citations
TL;DR: Upper Martian atmosphere UV emission spectrum observation noting carbon dioxide photoionization, ion fluorescent scattering and photon/electron dissociative excitation as discussed by the authors, showing that carbon dioxide photos are photoionized.
Abstract: Upper Martian atmosphere UV emission spectrum observation noting carbon dioxide photoionization, ion fluorescent scattering and photon/electron dissociative excitation
252 citations
TL;DR: A base surge, first identified at the Bikini thermonuclear undersea explosion, is a ring-shaped basal cloud that sweeps outward as a density flow from the base of a vertical explosion column.
Abstract: A base surge, first identified at the Bikini thermonuclear undersea explosion, is a ring-shaped basal cloud that sweeps outward as a density flow from the base of a vertical explosion column. Base surges are also common in shallow underground test explosions and are formed by expanding gases which first vent vertically and then with continued expansion rush over the crater lip (represented by a large solitary wave in an underwater explosion), tear ejecta from it, and feed a gas-charged density flow, which is the surge cloud. This horizontally moving cloud commonly has an initial velocity of more than 50 meters per second and can carry clastic material many kilometers. Base surges are a common feature of many recent shallow, submarine and phreatic volcanic eruptions. They transport ash, mud, lapilli, and blocks with great velocity and commonly sandblast and knock down trees and houses, coat the blast side with mud, and deposit ejecta at distances beyond the limits of throw-out trajectories. Close to the eruption center, the base surge can erode radial channels and deposit material with dune-type bedding.
230 citations
TL;DR: In the absence of juvenile liquid water, condensation of water vapor to ice and subsequent melting of ice are the only means of producing liquid water on the martian surface because the evaporation rate is so high that the available heat sources cannot melt pure ice.
Abstract: In the absence of juvenile liquid water, condensation of water vapor to ice and subsequent melting of ice are the only means of producing liquid water on the martian surface. However, the evaporation rate is so high that the available heat sources cannot melt pure ice. Liquid water is therefore limited to concentrated solutions of strongly deliquescent salts.
219 citations