The location of the Opportunity landing site was determined to better than 10-m absolute accuracy from analyses of radio tracking data. We determined Rover locations during traverses with an error as ...small as several centimeters using engineering telemetry and overlapping images. Topographic profiles generated from rover data show that the plains are very smooth from meter- to centimeter-length scales, consistent with analyses of orbital observations. Solar cell output decreased because of the deposition of airborne dust on the panels. The lack of dust-covered surfaces on Meridiani Planum indicates that high velocity winds must remove this material on a continuing basis. The low mechanical strength of the evaporitic rocks as determined from grinding experiments, and the abundance of coarse-grained surface particles argue for differential erosion of Meridiani Planum.
The precise location and relative elevation of Spirit during its traverses from the Columbia Memorial station to Bonneville crater were determined with bundle-adjusted retrievals from rover wheel ...turns, suspension and tilt angles, and overlapping images. Physical properties experiments show a decrease of 0.2% per Mars solar day in solar cell output resulting from deposition of airborne dust, cohesive soil-like deposits in plains and hollows, bright and dark rock coatings, and relatively weak volcanic rocks of basaltic composition. Volcanic, impact, aeolian, and water-related processes produced the encountered landforms and materials.
Carbonate minerals have been detected in Jezero crater, an ancient lake basin that is the landing site of the Mars 2020 Perseverance rover, and within the regional olivine‐bearing (ROB) unit in the ...Nili Fossae region surrounding this crater. It has been suggested that some carbonates in the margin fractured unit, a rock unit within Jezero crater, formed in a fluviolacustrine environment, which would be conducive to preservation of biosignatures from paleolake‐inhabiting lifeforms. Here, we show that carbonate‐bearing rocks within and outside of Jezero crater have the same range of visible‐to‐near‐infrared carbonate absorption strengths, carbonate absorption band positions, thermal inertias, and morphologies. Thicknesses of exposed carbonate‐bearing rock cross‐sections in Jezero crater are ∼75–90 m thicker than typical ROB unit cross‐sections in the Nili Fossae region, but have similar thicknesses to ROB unit exposures in Libya Montes. These similarities in carbonate properties within and outside of Jezero crater is consistent with a shared origin for all of the carbonates in the Nili Fossae region. Carbonate absorption minima positions indicate that both Mg‐ and more Fe‐rich carbonates are present in the Nili Fossae region, consistent with the expected products of olivine carbonation. These estimated carbonate chemistries are similar to those in martian meteorites and the Comanche carbonates investigated by the Spirit rover in Columbia Hills. Our results indicate that hydrothermal alteration is the most likely formation mechanism for non‐deltaic carbonates within and outside of Jezero crater.
Plain Language Summary
Spacecraft orbiting Mars can measure the composition of rocks that make up its surface. Understanding rock composition allows us to interpret past environmental conditions on Mars, including their likelihood to be habitable. Using data acquired from orbit, researchers have found carbonate minerals in Jezero crater and the surrounding region—called the Nili Fossae region. Jezero crater is the landing site of NASA's Mars 2020 Perseverance rover and once contained a lake. The discovery of carbonates is exciting because on Earth they sometimes form in habitable environments and preserve fossils. In this study, we used all available high resolution orbital datasets to look at similarities and differences between carbonate‐bearing rocks within and outside of Jezero crater. We found that carbonate‐bearing rocks within and outside of Jezero crater have similar orbital properties, implying that they formed by the same processes. We found that the range in chemistries (magnesium‐rich vs. iron‐rich) for carbonates within and outside of Jezero crater is similar to carbonate chemistries found in martian meteorites and by other rovers on Mars. The carbonates within and outside of Jezero crater could have formed by the same water‐rock interactions that formed carbonates discovered in martian meteorites and by other rovers on Mars.
Key Points
Carbonates within and outside of Jezero crater have similar spectra, thermal inertias, morphologies, and thicknesses
Carbonates within and outside of Jezero crater likely formed via the same processes
Hydrothermal alteration and evaporation are the most likely processes for carbonate formation within and outside of Jezero crater
Current maps of compositional variation across south polar ice exposures on Mars do not resolve the meter‐scales at which erosional processes are most active, ultimately limiting our understanding of ...how the deposits form and evolve and how they can be used to interpret long‐term climate records. In this study, we use k‐means clustering and random forest classification to identify and map a set of universal spectral endmembers across 167 high‐resolution observations acquired during southern summer by the Compact Reconnaissance Imaging Spectrometer for Mars. The 21 endmembers show distinct combinations and strengths of key infrared absorption features reflecting diverse mixtures of CO2 ice, H2O ice, and dust. The resulting compositional framework can be used to characterize the nature of both seasonal CO2 frost and the residual ices it overlies across a variety of terrains. Following the large dust event of Mars Year 28, the residual CO2‐ice deposits (RCD) were covered by an unusually thick or long‐lived deposit of seasonal frost. Within the RCD, low‐albedo material around erosional features display H2O ice absorptions consistent with exposures around the outer margins of the RCD. These peripheral water‐ice deposits show unexpected variation in CO2 ice and dust content. Most notably, regions within several km of the edge of the RCD display spectral contributions from CO2 ice even after seasonal frost has been removed. These results can inform investigations focused on the dynamics of seasonal CO2 deposition, the development of erosional morphologies, and the creation of climate records in south polar stratigraphy.
Plain Language Summary
Ice deposits near the south pole of Mars contain varied mixtures of CO2 ice, water ice, and dust. These mixtures influence interactions with solar heating and atmospheric cycling that affect the formation, evolution, and preservation of different ice deposits. However, ice composition in this region has not been mapped in sufficient detail to fully understand these dynamic processes. We used high‐resolution data gathered from an orbiting spectrometer that measured sunlight reflected from the surface. Through automated and manual techniques, we identified the most typical reflectance signatures in the data set and generated maps showing where those materials are located. These results reveal unprecedented detail in the nature of both seasonal (removed during summer) and residual (remaining on the surface throughout each year) ice deposits. The most compelling findings are that (a) increased seasonal CO2 ice thickness or retention appeared following a large dust storm, (b) residual CO2 ice is found to extend beyond the brightest deposits, and (c) water ice‐rich exposures reveal more varied CO2 ice and dust content than previously understood. The compositional framework provided by the study can help guide future investigations into a variety of processes that shape south polar ices and the climate records they preserve.
Key Points
One hundred sixty‐seven south polar observations by the Compact Reconnaissance Imaging Spectrometer for Mars images were mapped with a set of 21 spectral endmembers representing a range of CO2 ice, H2O ice, and dust mixtures
Seasonal CO2 ice cover was thicker or more prolonged in Mars Year 28, linking dust storms to cold‐trapping of CO2 on the bright residual ice
CO2 ice signatures extend beyond the bright residual ice and into surrounding material, even in late summer after seasonal frost removal
The investigation of hyperspectral data from the Mars Reconnaissance Orbiter Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) and the Observatoire pour la Minéralogie, L'Eau, les Glaces ...et l'Activitié (OMEGA) on Mars Express has revealed an increasingly diverse suite of minerals present on the Martian surface. A revised set of 60 spectral parameters derived from corrected spectral reflectance at key wavelengths in CRISM targeted observations and designed to capture the known diversity of surface mineralogy on Mars is presented here as “summary products.” Some of the summary products have strong heritage to OMEGA spectral parameter calculations; this paper also presents newly derived parameters that highlight locations with more recently discovered spectral signatures. Type locations for the diversity of currently identified mineral spectral signatures have been compiled into a library presented in this work. Our analysis indicates that the revised set of summary products captures the known spectral diversity of the surface, and successfully highlights and differentiates between locations with differing spectral signatures. The revised spectral parameter calculations and related products provide a useful tool for scientific interpretation and for future mission landing site selection and operations.
Key Points
A revised set of 60 CRISM summary products captures Mars' spectral diversity
A library of 30 surface type spectra identified using CRISM is presented
New “browse products” demonstrate surface spectral variability
A previously unidentified artifact has been found in Compact Reconnaissance Imaging Spectrometer for Mars targeted I/F data. It exists in a small fraction (<0.05%) of pixels within 90% of images ...investigated and occurs in regions of high spectral/spatial variance. This artifact mimics real mineral absorptions in width and depth and occurs most often at 1.9 and 2.1 μm, thus interfering in the search for some mineral phases, including alunite, kieserite, serpentine, and perchlorate. A filtering step in the data processing pipeline, between radiance and I/F versions of the data, convolves narrow artifacts (“spikes”) with real atmospheric absorptions in these wavelength regions to create spurious absorption‐like features. The majority of previous orbital detections of alunite, kieserite, and serpentine we investigated can be confirmed using radiance and raw data, but few to none of the perchlorate detections reported in published literature remain robust over the 1.0‐ to 2.65‐μm wavelength range.
Plain Language Summary
Many minerals can be identified with remote sensing data by their characteristic absorptions in visible‐shortwave infrared data. This type of data has allowed geological interpretation of much of Mars' surface, using satellite‐based observation. We have discovered an issue with the Compact Reconnaissance Imaging Spectrometer for Mars instrument's data processing pipeline. In ~ <0.05% of pixels in almost all images, noise in the data is smoothed in such a way that it mimics real mineral absorptions, falsely making it look as though certain minerals are present on Mars' surface. The vast majority of previously identified minerals are still confirmed after accounting for the artifact, but some to all perchlorate detections and a few serpentine detections were not confirmed, suggesting that the artifact created false detections. This means concentrated regions of perchlorate may not occur on Mars and so may not be available to generate possibly habitable salty liquid water at very cold temperatures.
Key Points
A filtering step in conversion to I/F can cause few‐pixel artifacts in high variance regions of a CRISM image cube
Orbital detections of perchlorate and some serpentine on Mars may not be robust, instead caused by the newly discovered artifact
Few‐pixel mineral detections using visible‐shortwave infrared reflectance spectroscopy should be confirmed with radiance data
Over 100 Martian gully sites were analyzed using orbital data collected by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) and High Resolution Imaging Science Experiment on the Mars ...Reconnaissance Orbiter (MRO). Most gullies are spectrally indistinct from their surroundings, due to mantling by dust. Where spectral information on gully sediments was obtained, a variety of mineralogies were identified. Their relationship to the source rock suggests that gully‐forming processes transported underlying material downslope. There is no evidence for specific compositions being more likely to be associated with gullies or with the formation of hydrated minerals in situ as a result of recent liquid water activity. Seasonal CO2 and H2O frosts were observed in gullies at middle to high latitudes, consistent with seasonal frost‐driven processes playing important roles in the evolution of gullies. Our results do not clearly indicate a role for long‐lived liquid water in gully formation and evolution.
Key Points
CRISM images provide new constraints on the formation of Martian gullies
Seasonal frost‐driven processes play greater role in middle‐latitude/high‐latitude gullies
Gully mineralogies do not require in situ liquid water‐rock interactions
Multispectral mapping data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) provide a unique opportunity to characterize south polar ice deposits at higher spectral sampling, ...spatial resolution, or spatiotemporal coverage than previous work. This new perspective can help constrain the nature and distribution of different mixtures of CO2 ice, H2O ice, and dust that influence the formation, evolution, and preservation of Mars climate records. We processed 1,103 CRISM observations spanning the southern summer of six Mars Years (MYs) through a combination of k‐means clustering and random forest classification. Using a set of 12 spectral endmembers directly tied to previous work with high‐resolution CRISM targeted data, we made a series of temporally restricted mosaics showing surface spectral variation over time. The mosaics show the effects of the MY 28 dust storm on the removal of the seasonal CO2 ice cap that year and reveal how this process differed from the years that followed. A mosaic showing residual ice surfaces displays broad agreement with previous compositional maps while resolving new details in the distribution of H2O ice‐rich material around the periphery of the bright CO2 ice cap. By showing how surface composition varies across a broad swath of the south polar region through time, the endmember set and classified mosaics produced in this work can provide critical context for future studies of the dynamic processes that shape south polar ice deposits.
Plain Language Summary
At the south pole of Mars, different mixtures of CO2 ice, water ice, and dust on the surface influence interactions with the atmosphere. These influences affect how polar ice deposits are formed, how they change over time, and how they are preserved as records of past climates. Existing maps of ice and dust in the region have limitations in how accurately they can describe mixtures and how much detail they can show on the ground. Using data from an orbiting spectrometer that measures sunlight reflected from the surface, we made new maps that reveal important details not seen in previous work. For example, these maps show how surface composition changes through time, which can be used to study CO2 frost that forms on the surface every winter and is removed in the summer. We observe how a dust storm in 1 year affected the composition and/or thickness of seasonal frost compared with other years. The maps also reveal how composition varies in different permanent ice deposits. Compared to previous work, it is easier to see how CO2 ice and dust are mixed with water ice in enigmatic exposures that may be linked to the formation of new climate records.
Key Points
Variable mixtures of CO2 and H2O ice with dust are linked to the formation of south polar climate records
To better understand these mixtures, we mapped 12 endmembers across multispectral data spanning 6 south polar summers
We made a series of mosaics to explore compositional variation in both seasonal and residual ice deposits
Columbus crater in the Terra Sirenum region of the Martian southern highlands contains light‐toned layered deposits with interbedded sulfate and phyllosilicate minerals, a rare occurrence on Mars. ...Here we investigate in detail the morphology, thermophysical properties, mineralogy, and stratigraphy of these deposits; explore their regional context; and interpret the crater's aqueous history. Hydrated mineral‐bearing deposits occupy a discrete ring around the walls of Columbus crater and are also exposed beneath younger materials, possibly lava flows, on its floor. Widespread minerals identified in the crater include gypsum, polyhydrated and monohydrated Mg/Fe‐sulfates, and kaolinite; localized deposits consistent with montmorillonite, Fe/Mg‐phyllosilicates, jarosite, alunite, and crystalline ferric oxide or hydroxide are also detected. Thermal emission spectra suggest abundances of these minerals in the tens of percent range. Other craters in northwest Terra Sirenum also contain layered deposits and Al/Fe/Mg‐phyllosilicates, but sulfates have so far been found only in Columbus and Cross craters. The region's intercrater plains contain scattered exposures of Al‐phyllosilicates and one isolated mound with opaline silica, in addition to more common Fe/Mg‐phyllosilicates with chlorides. A Late Noachian age is estimated for the aqueous deposits in Columbus, coinciding with a period of inferred groundwater upwelling and evaporation, which (according to model results reported here) could have formed evaporites in Columbus and other craters in Terra Sirenum. Hypotheses for the origin of these deposits include groundwater cementation of crater‐filling sediments and/or direct precipitation from subaerial springs or in a deep (∼900 m) paleolake. Especially under the deep lake scenario, which we prefer, chemical gradients in Columbus crater may have created a habitable environment at this location on early Mars.
We present detailed stratigraphic and spectral analyses that focus on a region in northern Sinus Meridiani located between 1°N to 5°N latitude and 3°W to 1°E longitude. Several stratigraphically ...distinct units are defined and mapped using morphologic expression, spectral properties, and superposition relationships. Previously unreported exposures of hydrated sulfates and Fe/Mg smectites are identified using MRO CRISM and MEX OMEGA near‐infrared (1.0 to 2.5 μm) spectral reflectance observations. Layered deposits with monohydrated and polyhydrated sulfate spectral signatures that occur in association with a northeast‐southwest trending valley are reexamined using high‐resolution CRISM, HiRISE, and CTX images. Layers that are spectrally dominated by monohydrated and polyhydrated sulfates are intercalated. The observed compositional layering implies that multiple wetting events, brine recharge, or fluctuations in evaporation rate occurred. We infer that these hydrated sulfate‐bearing layers were unconformably deposited following the extensive erosion of preexisting layered sedimentary rocks and may postdate the formation of the sulfate‐ and hematite‐bearing unit analyzed by the MER Opportunity rover. Therefore, at least two episodes of deposition separated by an unconformity occurred. Fe/Mg phyllosilicates are detected in units that predate the sulfate‐ and hematite‐bearing unit. The presence of Fe/Mg smectite in older units indicates that the relatively low pH formation conditions inferred for the younger sulfate‐ and hematite‐bearing unit are not representative of the aqueous geochemical environment that prevailed during the formation and alteration of earlier materials. Sedimentary deposits indicative of a complex aqueous history that evolved over time are preserved in Sinus Meridiani, Mars.
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