We use Thermal Emission Imaging System (THEMIS) data to identify and characterize the global distribution of distinct materials interpreted to contain chloride salts on the Martian surface. ...Previously mapped global geochemical and physical properties are used in concert with thermophysical and morphological observations to assess the materials' local and regional characteristics. The results of our survey have expanded the characterization of the materials from ∼200 to ∼640 distinct sites dispersed throughout low‐albedo Noachian‐ and Hesperian‐aged terrains. Our survey also shows that the materials are detected in locally thermophysically distinct terrains and display a range of morphologies. Topography indicates that the majority of the materials occur in local lows, although crosscutting relationships indicate that some sites are located in “geologic windows” implying that the materials may be older than the terrains in which they are situated. Once exposed, the materials appear to undergo erosion, which may be the reason we do not observe large laterally extensive materials at the surface. The materials are predominantly local in nature, yet their prevalence across the southern highlands suggests that they represent one or more globally ubiquitous processes. We consider a number of formation hypotheses but find that most observations are consistent with formation via ponding of surface runoff or groundwater upwelling, although efflorescence and hydrothermal activity may also be possible in some locales. The materials' inferred ages suggest that the conditions that enabled the deposition of the materials persisted for up to 1 billion years.
We used spectral indexing and linear deconvolution to compare thermal infrared emission spectra of Fo91, Fo68, Fo53, Fo39, Fo18, and Fo1 olivine samples to Mars Global Surveyor Thermal Emission ...Spectrometer (TES) data over low‐albedo regions of Mars. The Fo91, Fo68, Fo53, and Fo39 spectral end‐members were confidently identified on Mars, a range of compositions wider than inferred from Martian meteorites. Small (less than hundreds of square kilometers) occurrences of the Fo91 spectral end‐member are present in the rims of the Argyre and Hellas impact basins and may represent Martian mantle materials. The Fo68 spectral end‐member is common throughout the highlands, chasmata, outflow channels, and Nili Fossae region. The Fo53 spectral end‐member occurs in eastern Syrtis Major, the Nili Fossae region, and smooth‐floored craters of the highlands. Although less abundant than Fo68 and Fo53, the distribution of the Fo39 spectral end‐member suggests that some olivine on Mars is more Fe‐rich than olivine in Martian meteorites. Global maps of olivine show that (1) materials containing 10–20% of olivine are common in the southern highlands of Mars, (2) olivine is most common near the topographic dichotomy boundary, and (3) olivine becomes uncommon near the poles suggesting that it may be influenced by topography and/or latitude (climate). Olivine is found in early Noachian to Amazonian terrains, some of which may be coeval with phyllosilicate and sulfate deposits detected by OMEGA implying that any early Noachian wet period of Mars' climate history may have been globally inhomogeneous or insufficient to weather the olivine that remains today.
•The meteorology is controlled by interacting circulations and dynamical instabilities from the planetary scale down to the microscale.•The northern winter season is unique; the air mass in the ...crater mixes with external crater air due to the breaking of large amplitude mountain waves.•At other seasons, the mixing between the air in the floor of Gale Crater and air external to the crater may be more limited.•It is difficult to reconcile the putative methane detection with the Gale Crater circulation.
Numerical modeling results from the Mars Regional Atmospheric Modeling System are used to interpret the landed meteorological data from the Rover Environmental Monitoring Station onboard the Mars Science Laboratory rover Curiosity. In order to characterize seasonal changes throughout the Martian year, simulations are conducted at Ls 0, 90, 180 and 270. Two additional simulations at Ls 225 and 315 are explored to better understand the unique meteorological setting centered on Ls 270. The synergistic combination of model and observations reveals a complex meteorological environment within the crater. Seasonal planetary circulations, the thermal tide, slope flows along the topographic dichotomy, mesoscale waves, slope flows along the crater slopes and Mt. Sharp, and turbulent motions all interact in nonlinear ways to produce the observed weather. Ls 270 is shown to be an anomalous season when air within and outside the crater is well mixed by strong, flushing northerly flow and large amplitude, breaking mountain waves. At other seasons, the air in the crater is more isolated from the surrounding environment. The potential impact of the partially isolated crater air mass on the dust, water, noncondensable and methane cycles is also considered. In contrast to previous studies, the large amplitude diurnal pressure signal is attributed primarily to necessary hydrostatic adjustments associated with topography of different elevations, with contributions of less than 25% to the diurnal amplitude from the crater circulation itself. The crater circulation is shown to induce a suppressed boundary layer.
The reststrahlen features in thermal infrared, or vibrational, spectra of Mg-Fe olivines ((Mg,Fe)
2SiO
4) exhibit trends in position, strength, and number of features that are diagnostic of the ...relative proportions of the Mg and Fe cations in the minerals. Although band positions move to lower wavenumbers (longer wavelengths) across the forsterite–fayalite compositional binary in a generally linear manner, specific feature shifts in transmittance data are described best by two linear fits with a break in slope near Fo
70. The break in slope may be accompanied by an offset as well; both traits are attributed to structural changes in olivine brought about by distortion of the crystal lattice by Fe. Reflectance and emissivity spectra exhibit similar trends in band position with composition, and all three types of data demonstrate that some olivine band strengths change across the Mg–Fe solid solution series and also are diagnostic of composition. Olivines have been identified in a wide array of thermal infrared spectra of planetary materials and have been interpreted as being present on the surfaces of Mercury, the Moon, Mars, and a number of asteroids based on the analysis of thermal infrared spectra. New linear least squares models of the emissivity spectra of olivine-bearing Martian meteorites enable a preliminary estimation of the accuracy with which quantitative estimates of olivine abundance and solid solution composition can be derived from the spectra of mixtures.
Almahata Sitta (AhS), an anomalous polymict ureilite, is the first meteorite observed to originate from a spectrally classified asteroid (2008 TC3). However, correlating properties of the meteorite ...with those of the asteroid is not straightforward because the AhS stones are diverse types. Of those studied prior to this work, 70–80% are ureilites (achondrites) and 20–30% are various types of chondrites. Asteroid 2008 TC3 was a heterogeneous breccia that disintegrated in the atmosphere, with its clasts landing on Earth as individual stones and most of its mass lost. We describe AhS 91A and AhS 671, which are the first AhS stones to show contacts between ureilitic and chondritic materials and provide direct information about the structure and composition of asteroid 2008 TC3. AhS 91A and AhS 671 are friable breccias, consisting of a C1 lithology that encloses rounded to angular clasts (<10 μm to 3 mm) of olivine, pyroxenes, plagioclase, graphite, and metal‐sulfide, as well as chondrules (~130–600 μm) and chondrule fragments. The C1 material consists of fine‐grained phyllosilicates (serpentine and saponite) and amorphous material, magnetite, breunnerite, dolomite, fayalitic olivine (Fo 28‐42), an unidentified Ca‐rich silicate phase, Fe,Ni sulfides, and minor Ca‐phosphate and ilmenite. It has similarities to CI1 but shows evidence of heterogeneous thermal metamorphism. Its bulk oxygen isotope composition (δ18O = 13.53‰, δ17O = 8.93‰) is unlike that of any known chondrite, but similar to compositions of several CC‐like clasts in typical polymict ureilites. Its Cr isotope composition is unlike that of any known meteorite. The enclosed clasts and chondrules do not belong to the C1 lithology. The olivine (Fo 75‐88), pyroxenes (pigeonite of Wo ~10 and orthopyroxene of Wo ~4.6), plagioclase, graphite, and some metal‐sulfide are ureilitic, based on mineral compositions, textures, and oxygen isotope compositions, and represent at least six distinct ureilitic lithologies. The chondrules are probably derived from type 3 OC and/or CC, based on mineral and oxygen isotope compositions. Some of the metal‐sulfide clasts are derived from EC. AhS 91A and AhS 671 are plausible representatives of the bulk of the asteroid that was lost. Reflectance spectra of AhS 91A are dark (reflectance ~0.04–0.05) and relatively featureless in VNIR, and have an ~2.7 μm absorption band due to OH− in phyllosilicates. Spectral modeling, using mixtures of laboratory VNIR reflectance spectra of AhS stones to fit the F‐type spectrum of the asteroid, suggests that 2008 TC3 consisted mainly of ureilitic and AhS 91A‐like materials, with as much as 40–70% of the latter, and <10% of OC, EC, and other meteorite types. The bulk density of AhS 91A (2.35 ± 0.05 g cm−3) is lower than bulk densities of other AhS stones, and closer to estimates for the asteroid (~1.7–2.2 g cm−3). Its porosity (36%) is near the low end of estimates for the asteroid (33–50%), suggesting significant macroporosity. The textures of AhS 91A and AhS 671 (finely comminuted clasts of disparate materials intimately mixed) support formation of 2008 TC3 in a regolith environment. AhS 91A and AhS 671 could represent a volume of regolith formed when a CC‐like body impacted into already well‐gardened ureilitic + impactor‐derived debris. AhS 91A bulk samples do not show a solar wind component, so they represent subsurface layers. AhS 91A has a lower cosmic ray exposure (CRE) age (~5–9 Ma) than previously studied AhS stones (11–22 Ma). The spread in CRE ages argues for irradiation in a regolith environment. AhS 91A and AhS 671 show that ureilitic asteroids could have detectable ~2.7 μm absorption bands.
A Global View of Martian Surface Compositions from MGS-TES Bandfield, Joshua L.; Hamilton, Victoria E.; Christensen, Philip R.
Science (American Association for the Advancement of Science),
03/2000, Volume:
287, Issue:
5458
Journal Article
Peer reviewed
Thermal Emission Spectrometer (TES) data from the Mars Global Surveyor (MGS) are used to determine compositions and distributions of martian low-albedo regions. Two surface spectral signatures are ...identified from low-albedo regions. Comparisons with spectra of terrestrial rock samples and deconvolution results indicate that the two compositions are a basaltic composition dominated by plagioclase feldspar and clinopyroxene and an andesitic composition dominated by plagioclase feldspar and volcanic glass. The distribution of the two compositions is split roughly along the planetary dichotomy. The basaltic composition is confined to older surfaces, and the more silicic composition is concentrated in the younger northern plains.
The stratigraphy and mineral heterogeneity of surface and crater‐exposed deposits in the southwestern portion of the Isidis Basin were investigated using spatial, spectral, visible, and ...thermophysical data sets from both the Mars Global Surveyor and Odyssey missions. Four THEMIS spectral surface units were identified progressing from the Libya Montes highlands to the inner lowland plains of Isidis Planitia. Lithologic determinations of these spectral units were made by linear deconvolution analysis of TES data. Olivine‐rich surface materials correlate with a well‐documented high‐thermal inertia unit. Based on spatial and stratigraphic relationships interpreted from both crater‐exposed and surface exposures, the olivine‐rich unit was determined to have formed subsequent to the Isidis Basin forming event. Morphology, occurrence, and linear deconvolution of this unit suggests that it may represent Noachian age to Hesperian age picritic lavas that erupted as early‐stage lavas originating from sources such as Syrtis Major, beneath Isidis, and as far as Tyrrhena Patera. These lavas are suggested to have partially filled the basin, based on crater‐exposed occurrences, and were subsequently buried by further evolved olivine‐poor lavas. Later, these lavas were exposed by erosion and subsequent impacts into the basin. Crater scaling suggests significant infilling of the basin by these lavas that may account for craters with very high d/D ratios and the well‐developed positive mass anomaly associated with the basin. This study also demonstrates that the remote sensing of impact craters, in conjunction with surface mapping, is a potent mapping tool for understanding stratigraphy and the petrogenesis of the Martian crust.
Identification of quartzofeldspathic materials on Mars Bandfield, Joshua L.; Hamilton, Victoria E.; Christensen, Philip R. ...
Journal of Geophysical Research - Planets,
October 2004, Volume:
109, Issue:
E10
Journal Article
Peer reviewed
Open access
A unique spectral component has been identified near and on the central peaks of two 30 km diameter craters in northern Syrtis Major. These exposures are clearly visible in Thermal Emission Imaging ...System (THEMIS) color radiance images as well as THEMIS and Thermal Emission Spectrometer (TES) surface emissivity data. Both TES and THEMIS data indicate the presence of increased 1050–1250 cm−1 (∼8–9.5 μm) absorption compared to the surrounding basaltic plains, and TES data also display other absorptions at 400, 470, and 800 cm−1 (∼25, 20, and 12 μm) consistent with the presence of quartz. Ratio and isolated central peak spectral unit spectra match laboratory emissivity spectra of granitoid rocks composed primarily of quartz and plagioclase feldspar. Deconvolution results also indicate that the surface contains quartz and feldspar in addition to a high‐Si glass and/or sheet silicate component. Because central peak materials are brought up from depth during the cratering event, the association of the quartzofeldspathic mineralogy with the central peaks of the craters indicates that the quartz‐bearing material was excavated from depth. The occurrence in the two adjacent craters may imply a granitoid pluton of considerable extent. A plausible formation mechanism for this relatively silicic material may be similar to that of terrestrial trondhjemites, which do not require plate tectonics. The rarity of the exposures implies that the process that formed the granitoid composition was probably not widespread. The presence of quartz‐bearing material on Mars indicates that mechanisms that produce highly differentiated magmas have been present and extends the diversity of surface compositions identified.
•Simulations of the meteorology of Gale crater with the Mars regional atmospheric modeling system compare favorably to the data recorded by the rover environmental monitoring station aboard the Mars ...Science Laboratory Curiosity Rover.•Simulations are conducted for periods covering Ls 0, 90, 180 and 270.•The model may be used to provide context for the observations and to elucidate the physics behind the variations of the observed meteorological parameters.
Air temperature, ground temperature, pressure, and wind speed and direction data obtained from the Rover Environmental Monitoring Station onboard the Mars Science Laboratory rover Curiosity are compared to data from the Mars Regional Atmospheric Modeling System. A full diurnal cycle at four different seasons (Ls 0, 90, 180 and 270) is investigated at the rover location within Gale crater, Mars. Model results are shown to be in good agreement with observations when considering the uncertainties in the observational data set. The good agreement provides justification for utilizing the model results to investigate the broader meteorological environment of the Gale crater region, which is described in the second, companion paper.
We studied visible to near‐infrared (VNIR, 0.35–2.5 μm) and middle infrared (MIR, 1800–250 cm−1, also called thermal infrared and vibrational) spectra of basaltic tephras from Mauna Kea volcano that ...were altered under ambient, hydrothermal (hydrolytic and acid sulfate), and dry heat conditions. Although models of MIR spectra of altered tephras generally produce fits whose quality is reduced compared to deconvolutions of primary lithologies, they successfully identify major alteration phases (cristobalite, oxide, phyllosilicate, and sulfate) except in palagonites. MIR spectra of the <45 μm fraction of all altered tephra samples exhibit an H2O peak at ∼1640 cm−1, but it cannot be used as an indicator of H2O content. This feature is present with band strengths >1% in spectra of the 500–1000 μm fraction only if phyllosilicates are present. Although Mauna Kea palagonitic tephra is considered a VNIR analog to Martian dust, comparison of MIR altered tephra spectra (<45 μm fraction) to dust spectra retrieved from Mars Global Surveyor and Mars Exploration Rover instruments do not provide good spectral matches. The best MIR match is a tephra that has a strong plagioclase feldspar transparency feature and was altered under dry, high‐temperature, oxidizing conditions. This sample is not a VNIR analog and is not a process analog, but it emphasizes the mineralogical importance of plagioclase feldspar in Martian dust. No single tephra is a good spectral analog across the VNIR and MIR. We found no evidence for substantial sulfates or phyllosilicates in Mini‐Thermal Emission Spectrometer (Mini‐TES) spectra from Gusev Crater.
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