Mars Odyssey Thermal Emission Imaging Research Articles

Insight Into Formation Processes of Layered Ejecta Craters on Mars From Thermophysical Observations

AbstractUnderstanding the morphological characteristics of craters that are indicative of their formation environment can provide insight into surface geology. Layered ejecta (LE) craters, found on Mars and some other planetary bodies, have been hypothesized to have formed as a result of either interaction with subsurface volatiles (volatile fluidization model) and/or with the atmosphere (atmospheric entrainment model). Formation of LE craters by either model should result in different grain size distributions throughout the ejecta deposit. Using thermal inertia to infer surface properties, we investigated LE craters and their ejecta deposits in an effort to distinguish between possible LE formation processes on Mars. We used thermophysical properties of crater ejecta to determine grain size distribution, to model horizontal mixtures and vertical layering, and to identify materials present within the ejecta. We assessed the thermal properties of 50 uniformly sampled LE craters using Mars Odyssey Thermal Emission Imaging System (THEMIS) and Mars Global Surveyor Thermal Emission Spectrometer (TES) data. Our THEMIS analysis identifies 12 craters with grain size distributions consistent with the volatile fluidization model, 3 craters that have characteristics potentially associated with either model, and 22 craters that do not exhibit characteristics matching either model. Our TES analysis identifies 11 craters with characteristics consistent with the volatile fluidization model and 8 craters that are consistent with the atmospheric entrainment model. While some observations of grain size distributions provide evidence for either or both models, there is not overwhelming support for either model, potentially due to uncertainties of derived thermal inertia data.

Investigating Sources of Spectral Olivine Enrichments in Martian Bedrock Plains Using Diurnal Emissivity Changes in THEMIS Multispectral Images

AbstractWe investigate spectral olivine detections in the Noachian cratered highlands that are spatially associated with flat bedrock exposures. Strong olivine detections were previously attributed to relatively high (∼10%–15%) modal abundances of olivine in the bedrock, and then later hypothesized to instead originate from a patchy cover of olivine‐rich sediment formed from erosional lag deposits and mineral‐specific comminution/transport. We test these hypotheses by developing a new technique to partially separate the spectral signals of bedrock and unconsolidated surficial sediment. It uses the differing thermophysical properties of sand and indurated materials, which change the relative contributions of these materials to the emitted spectrum over the diurnal cycle. We use multispectral Mars Odyssey Thermal Emission Imaging System (THEMIS) observations collected in the mid‐afternoon and early evening to apply this technique to eight Terra Sabaea bedrock plains and the Nili Fossae olivine‐carbonate plain. Significant changes in spectral shape arising from compositional differences between bedrock and sediment cover are observed in four bedrock plains. Where these differences are observed, the spectral changes are consistent decreased olivine abundance in the sediment fraction, rather than increased as previously hypothesized. Our results indicate that bedrock materials in the Terra Sabaea region are olivine‐rich in composition, likely indicating a pyroclastic origin for these materials.

Thermophysical and Compositional Analyses of Dunes at Hargraves Crater, Mars

Abstract We analyze thermal emission spectra using the 2001 Mars Odyssey Thermal Emission Imaging System and the Mars Global Surveyor Thermal Emission Spectrometer to characterize grain size and mineralogical composition of dunes at Hargraves crater, Mars. Thermal inertia and bulk composition of the dunes were compared to inferred provenances from the thermal infrared response of surface constituent materials. We use a Markov Chain Monte Carlo technique to estimate the bulk amount of mineralogy contributed by each inferred provenance to the dune field composition. An average thermal inertia value of 238 ± 17 Jm−2 K−1 s−0.5 was found for the dunes, corresponding to a surface composed of an average effective grain size of ∼391 ± 172 μm. This effective particle size suggests the presence of mostly medium sand-sized materials mixed with fine and coarse grain sands. The dunes are likely composed of a weakly indurated surface mixed with unconsolidated materials. Compositional analysis specifies that the dunes are composed of a mixture of feldspar, olivine, pyroxene, and relatively low bulk-silica content. Dune materials were likely derived from physical weathering, especially aeolian erosion, predominantly from the crater ejecta unit at the crater, mixed with a small amount from the crater floor and crater rim and wall lithologies—indicating that the dune materials were likely sourced locally.

Thermophysical Properties and Surface Heterogeneity of Landing Sites on Mars From Overlapping Thermal Emission Imaging System (THEMIS) Observations

AbstractOrbitally derived thermal inertia (TI) values of surfaces allow for remote interpretation of rock and sediment physical characteristics. The evolving local times of the Mars Odyssey Thermal Emission Imaging System (THEMIS) mission have enabled surface temperature data collection over multiple seasons and local times over ∼9 Mars years (MY). We utilize this higher temporal resolution data set to separate TI values of individual materials within THEMIS pixels (100 m sampling). In this study, we focus on geologic units within Gusev, Gale, and Jezero crater landing sites to determine their respective TI and ground‐truth our methods. We use the KRC model to predict temperatures for a range of homogeneous and two‐component thermophysical mixing scenarios (laterally and vertically heterogeneous), and compare those to THEMIS brightness temperatures. The Gusev and Gale crater results are consistent with rover‐based evaluations, indurated or clast‐covered sands. The best‐fit scenarios along the Jezero crater volcanic floor unit show low to moderate TI values representative of coarse sediment, volcaniclastic, or pyroclastic rocks. The light toned unit and western fan deposits both indicate sands and a moderate TI component; we interpret this as heavy fracturing within the rock. Difficulties in modeling some THEMIS temperatures are attributed to daily weather effects, local atmospheric dust variability, and real surface changes over time (e.g., dust deposition and removal); we also observe that some temperature observations lead to non‐unique modeled physical solutions. Nevertheless, these methods can still rule out a significant range of material properties and provide meaningful geologic information about Mars’ surface.

Thermophysical Properties of Martian Fluvial Sinuous Ridges: Inferences on “Inverted Channel” Induration Agent

AbstractIn denuded landscapes, terrestrial inverted fluvial landforms are preferentially preserved due to their greater resistance to erosion from clast armoring, lava infilling, or cementation. These induration agents have differing material properties that should influence the thermal response of the surface. Using thermal inertia derived from 2001 Mars Odyssey Thermal Emission Imaging System (THEMIS) data, we find that the thermophysical contrast for 20 large “inverted channels” on Mars is comparable or elevated in comparison to nearby well‐indurated materials. The fluvial sinuous ridge (FSR) thermal signature, together with regional geology and morphology attributes, leads us to disfavor clast armoring as an induration agent for most Martian FSRs. The available evidence is consistent with cementation as the most likely induration agent for FSRs, although lava infilling is a plausible explanation especially for instances of nearby volcanic edifices. FSR cementation, probably by near‐surface solute‐rich groundwater, extends aqueous processes beyond the period of widespread fluvial activity. Future work on the temporal response of the surfaces of inverted channels has the potential to further test the inferred induration mechanism and potentially constrain the grain size distribution.

The albedo of Mars: Six Mars years of observations from Pancam on the Mars Exploration Rovers and comparisons to MOC, CTX and HiRISE

The Mars Exploration Rovers (MER) Spirit and Opportunity have systematically used their Panoramic Camera (Pancam) instruments to estimate the Lambert albedo of the surface across their traverses in Gusev crater and Meridiani Planum. The 360˚ “albedo pan” observations acquired with Pancam's broadband (739 ± 338 nm) L1 filter allow for quantitative estimates of the overall surface albedo and measurements of individual surface features. As of November 2016, over nearly six Mars years of the MER mission, Spirit acquired 20 albedo pans (over 7,730 m of traverse distance) and Opportunity acquired 117 albedo pans (over 42,368 m of traverse distance). For Spirit, this comprises the rover's complete dataset. The ranges of Pancam-derived albedos at Gusev crater (0.14–0.24) and at Meridiani Planum (0.11–0.22, with one anomalously high measurement of 0.27 during the July 2007 global dust storm) are consistent with large-scale albedos of the sites as previously determined by the Viking Orbiter Infrared Thermal Mapper (IRTM), Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES), MGS Mars Orbiter Camera (MOC), Mars Odyssey Thermal Emission Imaging System (THEMIS), Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) and MRO Mars Color Imager (MARCI) instruments. Through comparisons with atmospheric opacity measurements, temporal changes in Pancam albedo values provide insights into interactions between the Martian surface and atmosphere. Pancam observations are also used to “ground truth” measurements from orbit and validate radiometric calibrations, and we present comparisons across the full rover traverses to MOC, CTX, and MRO High Resolution Imaging Science Experiment (HiRISE) data. Albedo averages from the same regions observed by Pancam and all three orbital instruments generally agree to within ± 15%. The few instances found where cross-instrument comparisons exceed the estimated instrument calibration uncertainties can be attributed to atmospheric effects and/or differences in viewing geometries.

Well‐preserved low thermal inertia ejecta deposits surrounding young secondary impact craters on Mars

AbstractFollowing the most recent updates to the Mars Odyssey Thermal Emission Imaging System daytime and nighttime infrared global mosaics, a colorized global map was produced that combines the thermophysical information from the nighttime infrared global mosaic with the morphologic context of the daytime infrared global mosaic. During the validation of this map, large numbers of low thermal inertia ejecta deposits surrounding small young impact craters were observed. A near‐global survey (60°N–60°S) identified 4024 of these low thermal inertia ejecta deposits, which were then categorized based on their apparent state of degradation. Mapping their locations revealed that they occur almost exclusively in regions with intermediate‐to‐high thermal inertias, with distinct clusters in northern Terra Sirenum, Solis Planum, and southwestern Daedalia Planum. High‐Resolution Imaging Science Experiment images show that the thermophysically distinct facies of the deposits are well correlated with the estimated average ejecta grain sizes, which decrease with radial distance from the crater. Comparisons with recent primary impact craters and secondary impact craters surrounding Zunil Crater show that the low thermal inertia ejecta deposits very closely resemble the secondary craters, but not the primary craters. We conclude that the low thermal inertia ejecta deposits are secondary impact crater ejecta deposits, many of which originated from the rayed crater primary impact events, and are both well preserved and easily identifiable due to the absence of dust cover and aeolian modification that would otherwise reduce the thermal contrast between the ejecta facies and the surrounding terrain.

Comparison of the mineral composition of the sediment found in two Mars dunefields: Ogygis Undae and Gale crater – three distinct endmembers identified

The composition of two dune fields, Ogygis Undae and the NE–SW trending dune field in Gale crater (the “Bagnold Dune Field” and “Western Dune Field”), were analyzed using thermal emission spectra from the Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) and the Mars Odyssey Thermal Emission Imaging System (THEMIS). The Gale crater dune field was used as a baseline as other orbital compositional analyses have been conducted, and in situ sampling results will soon be available.Results from unmixing thermal emission spectra showed a spatial variation between feldspar mineral abundances and pyroxene mineral abundances in Ogygis Undae. Other datasets, including nighttime thermal inertia values, also showed variation throughout the dune field. One explanation proposed for this variation is a bimodal distribution of two sand populations. This distribution is seen in some terrestrial dune fields.The two dune fields varied in both mineral types present and in uniformity of composition. These differences point to different source lithologies and different distances travelled from source material. Examining these differences further will allow for a greater understanding of aeolian processes on Mars.

Constraints on the composition and particle size of chloride salt‐bearing deposits on Mars

AbstractChloride salt‐bearing deposits on Mars were discovered using the Mars Odyssey Thermal Emission Imaging System (THEMIS) and have been characterized by both mid‐infrared (MIR) and visible‐to‐near‐infrared (VNIR) remote sensing instruments. The chloride salt‐bearing deposits exhibit a blue slope at MIR wavelengths and a featureless red slope at VNIR wavelengths. These deposits also lack strong 3 µm bands in VNIR spectra, indicating that they are desiccated compared to the surrounding regolith. The lack of VNIR spectral features suggests that an anhydrous chloride salt, the most likely of which is halite, is responsible for the observed spectral slope. In this work, we use laboratory spectra and a hybrid T‐matrix/Hapke light scattering model to constrain the particle sizes and salt abundances of the Martian chloride salt‐bearing deposits. Our work shows that the two broad spectral classes of these deposits observed by THEMIS can be explained by a difference in the particle size of the admixed silicate regolith. In all cases, chloride salt abundances of 10–25% are required to match the THEMIS data. The chloride salt abundances determined in this work suggest deposition in a lacustrine/playa setting or in association with late‐stage groundwater upwelling.

Atypical pit craters on Mars: New insights from THEMIS, CTX, and HiRISE observations

AbstractMore than 100 pit craters in the Tharsis region of Mars exhibit morphologies, diameters, and thermal behaviors that diverge from the much larger bowl‐shaped pit craters that occur in most regions across Mars. These Atypical Pit Craters (APCs) generally have sharp and distinct rims, vertical or overhanging walls that extend down to their floors, surface diameters of ~50–350 m, and high depth to diameter (d/D) ratios that are usually greater than 0.3 (which is an upper range value for impacts and bowl‐shaped pit craters) and can exceed values of 1.8. Observations by the Mars Odyssey Thermal Emission Imaging System (THEMIS) show that APC floor temperatures are warmer at night and fluctuate with much lower diurnal amplitudes than nearby surfaces or adjacent bowl‐shaped pit craters. Kīlauea volcano, Hawai'i, hosts pit craters that formed through subsurface collapse into active volcanic dikes, resulting in pits that can appear morphologically analogous to either APCs or bowl‐shaped pit craters. Partially drained dikes are sometimes exposed within the lower walls and floors of these terrestrial APC analogs and can form extensive cave systems with unique microclimates. Similar caves in Martian pit craters are of great interest for astrobiology. This study uses new observations by the Mars Reconnaissance Orbiter High Resolution Imaging Science Experiment (HiRISE) and Context Camera to refine previous work where seven APCs were described from lower resolution THEMIS visible wavelength observations. Here we identify locations of 115 APCs, map their distribution across the Tharsis region, characterize their internal morphologies with high‐resolution observations, and discuss possible formation mechanisms.

Long-term variability of CO2and O in the Mars upper atmosphere from MRO radio science data

We estimate the annual variability of CO2 and O partial density using approximately 6 years of Mars Reconnaissance Orbiter (MRO) radio science data from August 2006 to January 2012, which cover three full Martian years (from the northern hemisphere summer of 28 to the northern hemisphere summer of 31). These two elements are the dominant species at the MRO periapsis altitude, constituting about 70–80% of the total density. We report the recovered annual cycle of CO2 and the annual and seasonal cycle of O in the upper atmosphere. Although no other observations are available at those altitudes, our results are in good agreement with the density measurements of the Mars Express Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars, which uses stellar occultations between 60 and 130 km to determine the CO2 variability, and with the Mars Global Reference Atmospheric Model 2010 for the O annual and seasonal variabilities. Furthermore, the updated model provides more reasonable MRO drag coefficients (CD), which are estimated to absorb mismodeling in the atmospheric density prediction. The higher content of dust in the atmosphere due to dust storms increases the density, so the CDs should compensate for this effect. The correlation between the drag coefficient and the dust optical depth, measured by the Mars Odyssey Thermal Emission Imaging System (THEMIS) instrument, increases from 0.4 to 0.8 with the a priori and adjusted models, respectively. The trend of CDs not only confirms a substantial improvement in the prediction of the atmospheric density with the updated model but also provides useful information for local dust storms, near MRO periapsis, that cannot be measured by the opacity level since THEMIS does not always sample the southern hemisphere evenly.

Thermal and near‐infrared analyses of central peaks of Martian impact craters: Evidence for a heterogeneous Martian crust

AbstractCentral peaks of impact craters contain materials exhumed from depth, and therefore, investigation of these materials provides clues to subsurface geology and mineralogy. A global spectral survey of central peaks of Martian impact craters between 10 and 200 km diameter was completed using Mars Odyssey Thermal Emission Imaging System (THEMIS) data. Twenty‐six central peaks with distinctive spectral signatures from surrounding plains were identified and characterized with thermal infrared and visible/near‐infrared data. The distribution of spectrally distinct central peaks (SDCPs) shows some degree of regional clustering, with most craters found in western Noachis Terra, Tyrrhena Terra, within the northern rim of Hellas Basin, and fewer in the northern lowlands. With the exception of four craters in western Noachis Terra, SDCPs contain only one spectrally distinct unit at THEMIS resolution (100 m/pixel). The maximum number of spectrally distinct units observed was three, in Jones and Ostrov craters. The western Noachis Terra SDCPs may expose crustal stratigraphies of multiple igneous compositions or impact materials from Argyre. In the highlands, most SDCP units are consistent with enrichments in olivine or pyroxene relative to surrounding plains, suggesting olivine and pyroxene basaltic lithologies; few are olivine and pyroxene poor. No spatial trend in spectrally derived compositions of SDCPs was observed. Three SDCPs contain THEMIS signatures consistent with high abundances of phyllosilicates, which may contain the most phyllosilicate‐rich lithologies found in central peak‐associated materials globally.

New observations of martian southern mid-latitude recurring slope lineae (RSL) imply formation by freshwater subsurface flows

Southern mid-latitude (SML) recurring slope lineae (RSL) are narrow (0.5–5m) dark albedo features that emanate from bedrock and incrementally lengthen down steep slopes that preferentially face the equator. We observe that SML RSL begin lengthening prior to southern summer at a solar longitude (Ls) of 245°±11° when Mars Global Surveyor Thermal Emission Spectrometer (TES)-derived near-maximum surface temperatures are 296±5K and Mars Reconnaissance Orbiter Mars Climate Sounder (MCS) – and Mars Odyssey Thermal Emission Imaging System (THEMIS)-derived mid-afternoon surface temperatures are >273K. SML RSL continue to lengthen for 104±38 sols with an average near-maximum surface temperature of 298±5K. The SML RSL then stop lengthening at Ls=314°±12° when mid-afternoon surface temperatures drop below 273K. They remain dark for another 116±41 sols (until Ls=16°±14°) as surface temperatures continue to fall. Although the RSL recharge mechanism remains unknown, our observation that the vast majority of RSL lengthen only when mid-afternoon surface temperatures are >273K supports the hypothesis that they are formed by shallow subsurface liquid water flows without significant freezing-point depression. The number and length of RSL at multiple sites increased dramatically following the Mars Year 28 globe-encircling dust storm. We interpret this increase to be due to warmer subsurface temperatures created by a dust-laden greenhouse effect that may be unique to the southern mid-latitudes near Ls=270°. Therefore SML RSL flow is quite sensitive to ground temperature and may only occur under favorable orbital parameters when mean insolation during the RSL lengthening season is above that of the current southern mid-latitude mean insolation value. This value is currently at a peak that has not been attained for the last ∼100ka. Meanwhile, the RSL-poor northern mid-latitude mean insolation is near a minimum and has a value 27% lower than the southern value. If SML RSL are indeed formed by shallow subsurface freshwater flows, then they may be some of the best locations on Mars to explore for extant life.

Thermal behavior and ice-table depth within the north polar erg of Mars

We fully resolve a long-standing thermal discrepancy concerning the north polar erg of Mars. Several recent studies have shown that the erg’s thermal properties are consistent with normal basaltic sand overlying shallow ground ice or ice-cemented sand. Our findings bolster that conclusion by thoroughly characterizing the thermal behavior of the erg, demonstrating that other likely forms of physical heterogeneity play only a minor role, and obviating the need to invoke exotic materials. Thermal inertia as calculated from orbital temperature observations of the dunes has previously been found to be more consistent with dust-sized materials than with sand. Since theory and laboratory data show that dunes will only form out of sand-sized particles, exotic sand-sized agglomerations of dust have been invoked to explain the low values of thermal inertia. However, the polar dunes exhibit the same darker appearance and color as that of dunes found elsewhere on the planet that have thermal inertia consistent with normal sand-sized basaltic grains, whereas Martian dust deposits are generally lighter and redder. The alternative explanation for the discrepancy as a thermal effect of a shallow ice table is supported by our analysis of observations from the Mars Global Surveyor Thermal Emission Spectrometer and the Mars Odyssey Thermal Emission Imaging System and by forward modeling of physical heterogeneity. In addition, our results exclude a uniform composition of dark dust-sized materials, and they show that the thermal effects of the dune slopes and bright interdune materials evident in high-resolution images cannot account for the erg’s thermal behavior.

Using THEMIS data to resolve the discrepancy between CRISM/OMEGA and TES modeled phyllosilicate abundance in Mawrth Vallis

We explore the effects of spatial resolution on the detectability of phyllosilicates in the thermal infrared dataset from the Mars Global Surveyor Thermal Emission Spectrometer (TES). Data from the Mars Odyssey THermal Emission Imaging System (THEMIS) instrument is used to resolve spatial resolution driven discrepancies between detection of phyllosilicates in the infrared and visible/near-infrared wavelength range. The 100-m/pixel spatial resolution offered by THEMIS, even with its limited spectral resolution, significantly improves the likelihood of phyllosilicate detection. Furthermore, spectral unit mapping techniques provide the first phyllosilicate abundance maps of the Mawrth Vallis phyllosilicate-bearing units, which indicate phyllosilicate abundances of >50% with heterogeneous spatial distributions. Derived abundances are used to evaluate the proposed formation mechanisms for phyllosilicates in this region and are found to be consistent with intermediate weathering of mafic primary material.

Wet Mars implications of revised scaling calculations for Evros Vallis

In this paper we report the results of our investigation of Evros Vallis, a martian late Noachian dendritic valley network centered at ∼12°E, 12°S. The study area is located SSW of Schiaparelli and SE relative to Meridiani Planum. After establishment of the valley system, the region underwent extensive erosion and tectonic activity, which partly obliterated and modified Evros Vallis's original features. We used Mars Global Surveyor Mars Orbiter Laser Altimeter, Mars Odyssey Thermal Emission Imaging System, and Mars Express High Resolution Stereo Camera imagery and altimetry data to carry out observations and morphometric analysis of the system, and applied network scaling parameters to our measurements of valley widths, slopes, lengths and drainage areas. We obtained the following results: (a) Hack's law exponent n=1.02; (b) width–area scaling exponent b=0.21; and (c) slope–area scaling exponent θ=0.23. These values are different from those previously derived from analysis of the eastern extent of the valley system. We found that network scaling is not applicable to the investigation of Evros Vallis, a conclusion that may be relevant also to other martian network valleys. The concave-up 790 km-long profile of the main valley suggests that a classic equilibrium status was reached. Our findings are in agreement with models of a warmer and wetter martian climate at the end of the Noachian.

Mosaicking of global planetary image datasets: 1. Techniques and data processing for Thermal Emission Imaging System (THEMIS) multi-spectral data

[1] The mosaicking of global planetary data sets allows for the examination of local, regional, and global scale processes on all planetary bodies. Processing techniques that allow us and other users to crate mosaics of tens of thousands of images are documented along with the associated errors introduced by each image-processing algorithm. These techniques (e.g., non-uniformity correction, running contrast stretches, line and row correlated noise removal, and random noise removal) were originally developed for the 2001 Mars Odyssey Thermal Emission Imaging System (THEMIS) infrared multispectral imager data but can be adapted and applied to other data sets by the alteration of input parameters. The techniques for mosaicking planetary image data sets (e.g., image registration, blending, and normalization) are also presented along with the generation of qualitative and quantitative products. These techniques are then applied to generate THEMIS daytime and nighttime infrared, Viking, Context Imager (CTX), and Mars Orbiter Camera (MOC) visible mosaics using a variety of input and output types at a variety of scales. By creating mosaics of the same area using different data sets such as those that illustrate compositional diversity, thermophysical properties, or small-scale morphology, it is possible to view the surface of the planet and geologic problems through many different perspectives. In addition to the techniques used to create large-scale seamless mosaics, we also present the THEMIS daytime and nighttime relative temperature global mosaics, which are the highest resolution (100m/pixel) global scale data sets available for Mars to date.

Impact‐induced overland fluid flow and channelized erosion at Lyot Crater, Mars

Lyot Crater is one of the youngest impact basins > 200 km in diameter on Mars. Although published hydrological models suggest that impact‐related groundwater release might have occurred at Lyot, no geomorphic evidence for such activity has been previously identified. Here, we use images acquired predominantly by the Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) and Mars Odyssey Thermal Emission Imaging Spectrometer (THEMIS) visible and infrared subsystems to document an extensive channeled scabland extending to the north, west, and east of Lyot, covering an area of ∼300,000 km2. The configuration and morphology suggests that the channel‐forming fluid was water derived from the target substrate and/or the surrounding terrain. Possible formation mechanisms are groundwater mobilization by seismic energy from the impact event and dewatering of the ejecta blanket.

Global distribution of bedrock exposures on Mars using THEMIS high‐resolution thermal inertia

We investigate high thermal inertia surfaces using the Mars Odyssey Thermal Emission Imaging System (THEMIS) nighttime temperature images (100 m/pixel spatial sampling). For this study, we interpret any pixel in a THEMIS image with a thermal inertia over 1200 J m−2 K−1 s−1/2 as “bedrock” which represents either in situ rock exposures or rock‐dominated surfaces. Three distinct morphologies, ranked from most to least common, are associated with these high thermal inertia surfaces: (1) valley and crater walls associated with mass wasting and high surface slope angles; (2) floors of craters with diameters >25 km and containing melt or volcanics associated with larger, high‐energy impacts; and (3) intercrater surfaces with compositions significantly more mafic than the surrounding regolith. In general, bedrock instances on Mars occur as small exposures (less than several square kilometers) situated in lower‐albedo (<0.18), moderate to high thermal inertia (>350 J m−2 K−1 s−1/2), and relatively dust‐free (dust cover index <0.95) regions; however, there are instances that do not follow these generalizations. Most instances are concentrated in the southern highlands, with very few located at high latitudes (poleward of 45°N and 58°S), suggesting enhanced mechanical breakdown probably associated with permafrost. Overall, Mars has very little exposed bedrock with only 960 instances identified from 75°S to 75°N with likely <3500 km2 exposed, representing ≪1% of the total surface area. These data indicate that Mars has likely undergone large‐scale surface processing and reworking, both chemically and mechanically, either destroying or masking a majority of the bedrock exposures on the planet.

The Martian surface: composition, mineralogy, and physical properties

Dedication Acknowledgements Foreword Part I. Introduction and Historical Perspective: 1. Exploration of the Martian surface: 1992-2007 2. Historical context: the pre-MGS view of Mars' surface composition Part II. Elemental Composition: Orbital and In Situ Surface Measurements: Part II. A. Results and Interpretations from New In Situ APXS Measurements: 3. Martian surface chemistry: APXS results from the Pathfinder landing site 4. Mars exploration rovers - chemical composition by the APXS Part II. B. Results and Interpretations from New Orbital Elemental Measurements: 5. Elemental abundances determined via the Mars Odyssey GRS 6. Volatiles on Mars: scientific results from the Mars Odyssey Neutron Spectrometer Part III. Mineralogy and Remote Sensing of Rocks, Soil, Dust, and Ices: Part III. A. Visible to Near-IR Telescopic and Orbital Measurements: 7. Mineralogy of the Martian surface from Mars Express OMEGA Observations 8. Visible to near-IR multispectral orbital observations Part III. B. Mid-IR and Magnetic Orbital Measurements: 9. Global mineralogy mapped from the Mars Global Surveyor Thermal Emission Spectrometer 10. The compositional diversity and physical properties mapped from the Mars Odyssey Thermal Emission Imaging System 11. Mars' crustal magnetization: a window into the past Part III. C. Observations from Surface Landers/Rovers: 12. Multispectral imaging from Mars Pathfinder 13. Mars Exploration Rover Pancam multispectral imaging of rocks, soil, and dust at Gusev Crater and Meridiani Planum 14. The mineralogy of Gusev Crater and Meridiani Planum derived from the Miniature Thermal Emission Spectrometers on the Spirit and Opportunity Rovers 15. Iron mineralogy and aqueous alteration on Mars from the MER Moessbauer Spectrometers 16. Magnetic properties results from surface landers and rovers Part III. D: 17. Martian meteorites as crustal samples Part IV. Physical Properties of Surface Materials: 18. The thermal inertia of the surface of Mars 19. Physical properties of the Martian surface from spectrophotometric observations 20. In-situ observations of the physical properties of the Martian surface 21. Martian surface properties from joint analyses of orbital, Earth-based, and surface observations Part V. Synthesis: 22. Implications of the observed primary lithologies 23. Aqueous alteration on Mars 24. The sedimentary rock cycle of Mars 25. Implications for Martian polar processes 26. Astrobiological implications of Mars surface composition and properties Part VI: 27. Summary, upcoming missions, and new measurement needs Acronyms Index.