Decades of speculation about a warmer, wetter Mars climate in the planet's first billion years postulate a denser CO₂ -rich atmosphere than at present. Such an atmosphere should have led to the ...formation of outcrops rich in carbonate minerals, for which evidence has been sparse. Using the Mars Exploration Rover Spirit, we have now identified outcrops rich in magnesium-iron carbonate (16 to 34 weight percent) in the Columbia Hills of Gusev crater. Its composition approximates the average composition of the carbonate globules in martian meteorite ALH 84001. The Gusev carbonate probably precipitated from carbonate-bearing solutions under hydrothermal conditions at near-neutral pH in association with volcanic activity during the Noachian era.
The Meridiani Planum region of Mars has been identified as a region of past aqueous activity by a combination of orbital and in situ observations that revealed evidence for sulfate‐rich dirty ...evaporites formed in a playa setting. We investigate the hydrology and sedimentary record of this area using global and regional hydrological models in which groundwater flow is driven by a combination of precipitation, evaporation, and the surface topography. Groundwater evaporation results in evaporite precipitation and cementation of aeolian sediments, allowing the accumulation of deposits of substantial thickness, which then affect the subsequent patterns of groundwater flow. Hydrological activity is initially predicted to be isolated to the deepest craters and depressions, primarily within the Arabia Terra region surrounding Meridiani. As these depressions fill with sediments, the groundwater upwelling spreads laterally across broad regions of Arabia Terra, including Meridiani Planum, as well as regional topographic lows such as the northern lowlands and large impact basins. The model predictions are borne out by observations of large intracrater deposits, inverted valley networks, finely layered deposits, spectral evidence for hydrated sulfates, and pedestal craters that preserve the remnants of a much larger deposit that once covered much of Arabia Terra. The results suggest that the inferred playa at Meridiani was part of a regionally extensive zone of groundwater upwelling. This hydrological cycle requires that conditions in the late Noachian to early Hesperian must have been conducive to the existence of liquid water at the surface throughout much of the low latitudes of Mars.
New impact craters at five sites in the martian mid-latitudes excavated material from depths of decimeters that has a brightness and color indicative of water ice. Near-infrared spectra of the ...largest example confirm this composition, and repeated imaging showed fading over several months, as expected for sublimating ice. Thermal models of one site show that millimeters of sublimation occurred during this fading period, indicating clean ice rather than ice in soil pores. Our derived ice-table depths are consistent with models using higher long-term average atmospheric water vapor content than present values. Craters at most of these sites may have excavated completely through this clean ice, probing the ice table to previously unsampled depths of meters and revealing substantial heterogeneity in the vertical distribution of the ice itself.
We present a new high-resolution map of thermal inertia derived from observations of planetary brightness temperature by the Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) obtained ...during the entire MGS primary mapping mission. Complete seasonal coverage provides a nearly global view of Mars, including the polar regions, at a spatial resolution of approximately 3 km. Our map of nighttime thermal-bolometer-based thermal inertia covers approximately 60% of the surface between 80° S and 80° N latitudes. We confirm the global pattern of high and low thermal inertia seen in lower resolution mapping efforts and provide greater detail concerning a third surface unit with intermediate values of both thermal inertia and albedo first identified by Mellon et al. 2000, Icarus 148, 437–455. Several smaller regional units with distinct characteristics are observed. Most notably, a unit of low thermal inertia (
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) and low-to-intermediate albedo (0.09–0.22) dominates the region polewards of 65° S. We consider possible causes for these characteristics and conclude that a low-density mantle formed by desiccation of a previously ice-rich near-surface layer is the most likely explanation for the observed thermophysical properties. Global comparison of thermal inertia and elevation shows that high and low thermal inertia values can be found over a broad range of elevation, with only low values (30–
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) occurring at the highest elevations and the highest values occurring only at lower elevations. However, the lowest values (
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) are found only at lower elevations, implying that the distribution of low thermal inertia material is not solely controlled by atmospheric pressure and the trapping of fines at high elevations. A new estimate of thermal inertia for the Viking and Pathfinder landing sites helps establish an important link between surface characteristics observed in situ and those derived from remote-sensing data.
Simulations of Mars Rover Traverses Zhou, Feng; Arvidson, Raymond E.; Bennett, Keith ...
Journal of field robotics,
01/2014, Volume:
31, Issue:
1
Journal Article
Peer reviewed
Artemis (Adams‐based Rover Terramechanics and Mobility Interaction Simulator) is a software tool developed to simulate rigid‐wheel planetary rover traverses across natural terrain surfaces. It is ...based on mechanically realistic rover models and the use of classical terramechanics expressions to model spatially variable wheel‐soil and wheel‐bedrock properties. Artemis's capabilities and limitations for the Mars Exploration Rovers (Spirit and Opportunity) were explored using single‐wheel laboratory‐based tests, rover field tests at the Jet Propulsion Laboratory Mars Yard, and tests on bedrock and dune sand surfaces in the Mojave Desert. Artemis was then used to provide physical insight into the high soil sinkage and slippage encountered by Opportunity while crossing an aeolian ripple on the Meridiani plains and high motor currents encountered while driving on a tilted bedrock surface at Cape York on the rim of Endeavour Crater. Artemis will continue to evolve and is intended to be used on a continuing basis as a tool to help evaluate mobility issues over candidate Opportunity and the Mars Science Laboratory Curiosity rover drive paths, in addition to retrieval of terrain properties by the iterative registration of model and actual drive results.
NASA's Phoenix mission, which landed on the northern plains of Mars in 2008, returned evidence of the perchlorate anion distributed evenly throughout the soil column at the landing site. Here, we use ...spectral data from Phoenix's Surface Stereo Imager to map the distribution of perchlorate salts at the Phoenix landing site, and find that perchlorate salt has been locally concentrated into subsurface patches, similar to salt patches that result from aqueous dissolution and redistribution on Earth. We propose that thin films of liquid water are responsible for translocating perchlorate from the surface to the subsurface, and for concentrating it in patches. The thin films are interpreted to result from melting of minor ice covers related to seasonal and long‐term obliquity cycles.
After landing in Gale Crater on August 6, 2012, the Mars Science Laboratory Curiosity rover traveled across regolith‐covered, rock‐strewn plains that transitioned into terrains that have been ...variably eroded, with valleys partially filled with windblown sands, and intervening plateaus capped by well‐cemented sandstones that have been fractured and shaped by wind into outcrops with numerous sharp rock surfaces. Wheel punctures and tears caused by sharp rocks while traversing the plateaus led to directing the rover to traverse in valleys where sands would cushion wheel loads. This required driving across a megaripple (windblown, sand‐sized deposit covered by coarser grains) that straddles a narrow gap and several extensive megaripple deposits that accumulated in low portions of valleys. Traverses across megaripple deposits led to mobility difficulties, with sinkage values up to approximately 30% of the 0.50 m wheel diameter, resultant high compaction resistances, and rover‐based slip up to 77%. Analysis of imaging and engineering data collected during traverses across megaripples for the first 710 sols (Mars days) of the mission, laboratory‐based single‐wheel soil experiments, full‐scale rover tests at the Dumont Dunes, Mojave Desert, California, and numerical simulations show that a combination of material properties and megaripple geometries explain the high wheel sinkage and slip events. Extensive megaripple deposits have subsequently been avoided and instead traverses have been implemented across terrains covered with regolith or thin windblown sand covers and megaripples separated by bedrock exposures.
A primary objective of the Phoenix mission was to examine the characteristics of high latitude ground ice on Mars. We report observations of ground ice, its depth distribution and stability ...characteristics, and examine its origins and history. High latitude ground ice was explored through a dozen trench complexes and landing thruster pits, over a range of polygon morphological provinces. Shallow ground ice was found to be abundant under a layer of relatively loose ice‐free soil with a mean depth of 4.6 cm, which varied by more than 10x from trench to trench. These variations can be attributed mainly to slope effects and thermal inertia variations in the overburden soil affecting ground temperatures. The presence of ice at this depth is consistent with vapor‐diffusive equilibrium with respect to a mean atmospheric water content of 3.4 × 1019 m−3, consistent with the present‐day climate. Significant ice heterogeneity was observed, with two major forms: ice‐cemented soil and relatively pure light toned ice. Ice‐cemented soils, which comprised about 90% of the icy material exposed by trenching, are best explained as vapor deposited pore ice in a matrix supported porous soil. Light toned ice deposits represent a minority of the subsurface and are thought to consist of relatively thin near surface deposits. The origin of these relatively pure ice deposits appears most consistent with the formation of excess ice by soil ice segregation, such as would occur by thin film migration and the formation of ice lenses, needle ice, or similar ice structures.
The missions that have operated on the surface of Mars acquired data that complement observations acquired from orbit and provide information that would not have been acquired without surface ...measurements. Data from the Viking Landers demonstrated that soils have basaltic compositions, containing minor amounts of salts and one or more strong oxidants. Pathfinder with its rover confirmed that the distal portion of Ares Vallis is the site of flood‐deposited boulders. Spirit found evidence for hydrothermal deposits surrounding the Home Plate volcanoclastic feature. Opportunity discovered that the hematite signature on Meridiani Planum as seen from orbit is due to hematitic concretions concentrated on the surface as winds eroded sulfate‐rich sandstones that dominate the Burns formation. The sandstones originated as playa muds that were subsequently reworked by wind and rising groundwater. Opportunity also found evidence on the rim of the Noachian Endurance Crater for smectites, with extensive leaching along fractures. Curiosity acquired data at the base of Mount Sharp in Gale Crater that allows reconstruction of a sustained fluvial‐deltaic‐lacustrine system prograding into the crater. Smectites and low concentrations of chlorinated hydrocarbons have been identified in the lacustrine deposits. Phoenix, landing above the Arctic Circle, found icy soils, along with low concentrations of perchlorate salt. Perchlorate is considered to be a strong candidate for the oxidant found by the Viking Landers. It is also a freezing point depressant and may play a role in allowing brines to exist at and beneath the surface in more modern periods of time on Mars.
Key Point
Landed mission data indicate sustained surface and subsurface waters in Martian past
Martian aqueous mineral deposits have been examined and characterized using data acquired during Mars Reconnaissance Orbiter's (MRO) primary science phase, including Compact Reconnaissance Imaging ...Spectrometer for Mars hyperspectral images covering the 0.4–3.9 μm wavelength range, coordinated with higher–spatial resolution HiRISE and Context Imager images. MRO's new high‐resolution measurements, combined with earlier data from Thermal Emission Spectrometer; Thermal Emission Imaging System; and Observatoire pour la Minéralogie, L'Eau, les Glaces et l'Activitié on Mars Express, indicate that aqueous minerals are both diverse and widespread on the Martian surface. The aqueous minerals occur in 9–10 classes of deposits characterized by distinct mineral assemblages, morphologies, and geologic settings. Phyllosilicates occur in several settings: in compositionally layered blankets hundreds of meters thick, superposed on eroded Noachian terrains; in lower layers of intracrater depositional fans; in layers with potential chlorides in sediments on intercrater plains; and as thousands of deep exposures in craters and escarpments. Carbonate‐bearing rocks form a thin unit surrounding the Isidis basin. Hydrated silica occurs with hydrated sulfates in thin stratified deposits surrounding Valles Marineris. Hydrated sulfates also occur together with crystalline ferric minerals in thick, layered deposits in Terra Meridiani and in Valles Marineris and together with kaolinite in deposits that partially infill some highland craters. In this paper we describe each of the classes of deposits, review hypotheses for their origins, identify new questions posed by existing measurements, and consider their implications for ancient habitable environments. On the basis of current data, two to five classes of Noachian‐aged deposits containing phyllosilicates and carbonates may have formed in aqueous environments with pH and water activities suitable for life.
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