Mars Exploration Rover Opportunity Research Articles

Precise pose estimation of the NASA Mars 2020 Perseverance rover through a stereo‐vision‐based approach

AbstractVisual Odometry (VO) is a fundamental technique to enhance the navigation capabilities of planetary exploration rovers. By processing the images acquired during the motion, VO methods provide estimates of the relative position and attitude between navigation steps with the detection and tracking of two‐dimensional (2D) image keypoints. This method allows one to mitigate trajectory inconsistencies associated with slippage conditions resulting from dead‐reckoning techniques. We present here an independent analysis of the high‐resolution stereo images of the NASA Mars 2020 Perseverance rover to retrieve its accurate localization on sols 65, 66, 72, and 120. The stereo pairs are processed by using a 3D‐to‐3D stereo‐VO approach that is based on consolidated techniques and accounts for the main nonlinear optical effects characterizing real cameras. The algorithm is first validated through the analysis of rectified stereo images acquired by the NASA Mars Exploration Rover Opportunity, and then applied to the determination of Perseverance's path. The results suggest that our reconstructed path is consistent with the telemetered trajectory, which was directly retrieved onboard the rover's system. The estimated pose is in full agreement with the archived rover's position and attitude after short navigation steps. Significant differences (~10–30 cm) between our reconstructed and telemetered trajectories are observed when Perseverance traveled distances larger than 1 m between the acquisition of stereo pairs.

“My battery is low and it's getting dark”

The Mars Exploration Rover Opportunity operated on Mars from 2004 until it was disabled by a dust storm in 2018. Its demise was declared in February 2019 after months of unsuccessful recontact attempts by scientists at the National Aeronautics and Space Administration (NASA). This announcement sparked a global outpouring of grief that demonstrated people understood and related to the robot in a notably human-like manner. In short, it had been given a collectively understood persona. This paper presents a study of 100 digital postcards created by users on a NASA website that demonstrate the ways in which people expressed love, grief, hope, and thanks for Opportunity’s fourteen years of operation on another planet. In presenting this case study, the paper argues that certain personas are collective achievements. This is especially likely to occur for robots and other inanimate objects which have no centrally controlled or developed persona. The paper is situated within existing persona studies literature to extend and stretch the definition of persona studies and therefore expand the field in productive ways to incorporate the study of non-human personas.

Geology and Geochemistry of Noachian Bedrock and Alteration Events, Meridiani Planum, Mars: MER Opportunity Observations

AbstractWe have used Mars Exploration Rover Opportunity data to investigate the origin and alteration of lithic types along the western rim of Noachian‐aged Endeavour crater on Meridiani Planum. Two geologic units are identified along the rim: the Shoemaker and Matijevic formations. The Shoemaker formation consists of two types of polymict impact breccia: clast‐rich with coarser clasts in upper units; clast‐poor with smaller clasts in lower units. Comparisons with terrestrial craters show that the lower units represent more distal ejecta from at least two earlier impacts, and the upper units are proximal ejecta from Endeavour crater. Both are mixtures of target rocks of basaltic composition with subtle compositional variations caused by differences in post‐impact alteration. The Matijevic formation and lower Shoemaker units represent pre‐Endeavour geology, which we equate with the regional Noachian subdued cratered unit. An alteration style unique to these rocks is formation of smectite and Si‐ and Al‐rich vein‐like structures crosscutting outcrops. Post‐Endeavour alteration is dominated by sulfate formation. Rim‐crossing fracture zones include regions of alteration that produced Mg‐sulfates as a dominant phase, plausibly closely associated in time with the Endeavour impact. Calcium‐sulfate vein formation occurred over extended time, including before the Endeavour impact and after the Endeavour rim had been substantially degraded, likely after deposition of the Burns formation that surrounds and embays the rim. Differences in Mg, Ca and Cl concentrations on rock surfaces and interiors indicate that mobilization of salts by transient water has occurred recently and may be ongoing.

MARSWRF Prediction of Entry Descent Landing Profiles: Applications to Mars Exploration

AbstractIn this paper we use the Mars implementation of the Planet Weather Research and Forecasting model, MarsWRF, to simulate the Entry, Descent and Landing (EDL) vertical profiles from six past missions: Pathfinder, Mars Exploration Rovers Opportunity and Spirit, Phoenix, Mars Science Laboratory Curiosity rover, and ExoMars 2016 (Schiaparelli), and compare the results with observed data. In order to investigate the sensitivity of the model predictions to the atmospheric dust distribution, MarsWRF is run with two prescribed dust scenarios. It is concluded that the MarsWRF EDL predictions can be used for guidance into the design and planning stage of future missions to the planet, as it generally captures the observed EDL profiles, although it has a tendency to underestimate the temperature and overestimate the density for heights above 15 km. This could be attributed to an incorrect representation of the observed dust loading. We have used the model to predict the EDL conditions that may be encountered by two future missions: ExoMars 2020 and Mars 2020. When run for Oxia Planum and Jezero Crater for the expected landing time, MarsWRF predicts a large sensitivity to the dust loading in particular for the horizontal wind speed above 10‐15 km with maximum differences of up to ±30 m/s for the former and ±15 m/s for the latter site. For both sites, the best time for EDL, that is, when the wind speed is generally the weakest with smaller shifts in direction, is predicted to be in the late morning and early afternoon.

A Systematic Method for Classifying and Grouping Late Noachian and Early Hesperian Rock Targets Analyzed by the Mars Exploration Rover Opportunity at Endeavour Crater, Mars

AbstractThe Mars rover Opportunity has collected in situ compositional data with the Alpha Particle X‐ray Spectrometer at almost 500 sites. To analyze these data, hierarchical clustering analysis and an error‐weighted similarity index are applied to a subset of 57 APXS target compositions and selected Martian meteorites. Hierarchical clustering provides a rapid first approximation of compositional relationships, whereas the error‐weighted similarity index provides an in‐depth and quantifiable comparison of individual composition pairs. These analyses are combined into a statistical grouping model that provides insight into lithologic relationships and is critically informed by examination of Panoramic Camera and Microscopic Imager images. Major lithologies are (1) the Burns formation sulfate sandstones; (2) Shoemaker impact breccias (Endeavour crater ejecta/rim deposits); (3) the morphologically distinct Grasberg formation, associated with Endeavour crater rim deposits; (4) the Matijevic formation, an exposure interpreted to be Endeavour crater target rocks; and (5) erratics or other rocks that do not cluster with groups 1–4. The Grasberg formation is more similar to the Shoemaker formation than any other formation, and thus likely incorporated eroded Shoemaker material. The lowest Shoemaker member (Copper Cliff breccia) may contain material from the preimpact Matijevic formation. The Matijevic formation is the most chemically distinct formation and is most similar to the volcanic erratic rock “Marquette Island.” Clustering and similarity index values also show that regolith breccia Martian meteorites (represented by the NWA 7475/7034 paired meteorites) are similar in bulk composition to Mars surface materials at Meridiani, especially the Matijevic formation.

High-Precision Heading Determination Based on the Sun for Mars Rover

Since the American Mars Exploration Rover Opportunity landed on Mars in 2004, it has travelled more than 40 km, and heading-determination technology based on its sun sensor has played an important role in safe driving of the rover. A high-precision heading-determination method will always play a significant role in the rover’s autonomous navigation system, and the precision of the measured heading strongly affects the navigation results. In order to improve the heading precision to the 1-arcminute level, this paper puts forward a novel calibration algorithm for solving the comparable distortion of large-field sun sensor by introducing an antisymmetric matrix. The sun sensor and inclinometer alignment model are then described in detail to maintain a high-precision horizon datum, and a strict sun image centroid-extraction algorithm combining subpixel edge detection with circle or ellipse fitting is presented. A prototype comprising a sun sensor, electronic inclinometer, and chip-scale atomic clock is developed for testing the algorithms, models, and methods presented in this paper. Three field tests were conducted in different months during 2017. The results show that the precision of the heading determination reaches 0.28–0.97′ (1σ) and the centroid error of the sun image and the sun elevation are major factors that affect the heading precision.

Geological Analysis of Martian Rover‐Derived Digital Outcrop Models Using the 3‐D Visualization Tool, Planetary Robotics 3‐D Viewer—PRo3D

AbstractPanoramic camera systems on robots exploring the surface of Mars are used to collect images of terrain and rock outcrops which they encounter along their traverse. Image mosaics from these cameras are essential in mapping the surface geology and selecting locations for analysis by other instruments on the rover's payload. 2‐D images do not truly portray the depth of field of features within an image, nor their 3‐D geometry. This paper describes a new 3‐D visualization software tool for geological analysis of Martian rover‐derived Digital Outcrop Models created using photogrammetric processing of stereo‐images using the Planetary Robotics Vision Processing tool developed for 3‐D vision processing of ExoMars PanCam and Mars 2020 Mastcam‐Z data. Digital Outcrop Models are rendered in real time in the Planetary Robotics 3‐D Viewer PRo3D, allowing scientists to roam outcrops as in a terrestrial field campaign. Digitization of point, line, and polyline features is used for measuring the physical dimensions of geological features and communicating interpretations. Dip and strike of bedding and fractures is measured by digitizing a polyline along the contact or fracture trace, through which a best fit plane is plotted. The attitude of this plane is calculated in the software. Here we apply these tools to analysis of sedimentary rock outcrops and quantification of the geometry of fracture systems encountered by the science teams of NASA's Mars Exploration Rover Opportunity and Mars Science Laboratory rover Curiosity. We show the benefits PRo3D allows for visualization and collection of geological interpretations and analyses from rover‐derived stereo‐images.

Young, small-scale surface features in Meridiani Planum, Mars: A possible signature of recent transient liquid and gas emissions

Enigmatic small-scale (<1 m) depositional and erosional features found in basaltic sands partly covering bedrock exposures, imaged at several locations in the equatorial Meridiani Planum region by the Mars Exploration Rover Opportunity, may be evidence of previously unrecognized, geologically young (or even contemporary) Martian surface processes. Leveed fissures appear to have formed by venting from beneath; possible explanations include aeolian blowholes near crater margins, volcanic fumarole activity, or gas/vapour escape resulting from the decomposition of small pockets of ground ice, methane clathrates or hydrated sulphate minerals. Some leveed fissures cross-cut and are therefore younger than aeolian ripples thought to have last been active c. 50,000 years ago. Erosional gutters are sharply defined and fresh-looking, internally terraced, sometimes are deeper near one end, and in one case seem to give way to small depositional fans downslope; they have the appearance of having been formed by liquid flow rather than by wind erosion. There is evidence elsewhere that contemporary ground-ice thaw and consequent transient surface run-off may occur occasionally under present conditions at low, near-equatorial latitudes on Mars; short-lived (even for just a few minutes) meltwater emission and flow at the surface could form gutters before evaporating. Further possibilities are the decomposition of buried pockets of methane clathrates (which theoretical considerations suggest might be present and stable even in equatorial regions) giving rise to both methane gas venting and transient surface water, or the release of liquid brines by decomposition of hydrated magnesium sulphate minerals or deliquescence of perchlorates. Dry granular flow mechanisms proposed as explanations for Recurring Slope Lineae seem inadequate to explain the morphologies of leveed fissures and gutters.

Seasonal Atmospheric Argon Variability Measured in the Equatorial Region of Mars by the Mars Exploration Rover Alpha Particle X‐Ray Spectrometers: Evidence for an Annual Argon‐Enriched Front

AbstractThe Mars Exploration Rover Opportunity (MER‐B) has been exploring the surface of Mars since landing in 2004. Its Alpha Particle X‐ray Spectrometer (APXS) is primarily used to interrogate the chemical composition of rocks and soil samples in situ. Additionally, the APXS has measured the atmosphere of Mars with a regular cadence, monitoring the change in relative atmospheric argon density. Atmospheric measurements with the MER‐B APXS span over six Mars years providing an unprecedented level of statistics for careful study of the ubiquitous APXS spectral background. Several models were applied to high‐frequency long‐duration Spirit rover atmospheric APXS measurements. The most stable model with the least uncertainty was applied to the MER‐B data set. Seasonal variation of 10–15% in equatorial atmospheric argon density was observed ‐ in agreement with existing literature and global climate models. Unseen in previous work and global climate models, an abrupt deviation from the model‐predicted annual mixing ratio was measured by the MER‐B APXS around Ls 150. The sharp change, ~10% over 10° Ls, provides strong evidence for a northward migrating front, enriched in argon, sourced from the south pole at the end of southern winter. A similar weaker front is possibly observed around Ls 325, sourced from the northern polar region.

Retrieval of Compositional End‐Members From Mars Exploration Rover Opportunity Observations in a Soil‐Filled Fracture in Marathon Valley, Endeavour Crater Rim

AbstractThe Opportunity rover investigated a gentle swale on the rim of Endeavour crater called Marathon Valley where a series of bright planar outcrops are cut into polygons by fractures. A wheel scuff performed on one of the soil‐filled fracture zones revealed the presence of three end‐members identified on the basis of Pancam multispectral imaging observations covering ~0.4 to 1 μm: red and dark pebbles, and a bright soil clod. Multiple overlapping Alpha Particle X‐ray Spectrometer (APXS) measurements were collected on three targets within the scuff zone. The field of view of each APXS measurement contained various proportions of the Pancam‐based end‐members. Application of a log maximum likelihood method for retrieving the composition of the end‐members using the 10 APXS measurements shows that the dark pebble end‐member is compositionally similar to average Mars soil, with slightly elevated S and Fe. In contrast, the red pebble end‐member exhibits enrichments in Al and Si and is depleted in Fe and Mg relative to average Mars soil. The soil clod end‐member is enriched in Mg, S, and Ni. Thermodynamic modeling of the soil clod end‐member composition indicates a dominance of sulfate minerals. We hypothesize that acidic fluids in fractures leached and oxidized the basaltic host rock, forming the red pebbles, and then evaporated to leave behind sulfate‐cemented soil.

Surface-based 3D measurements of small aeolian bedforms on Mars and implications for estimating ExoMars rover traversability hazards

Recent aeolian bedforms comprising loose sand are common on the martian surface and provide a mobility hazard to Mars rovers. The ExoMars rover will launch in 2020 to one of two candidate sites: Mawrth Vallis or Oxia Planum. Both sites contain numerous aeolian bedforms with simple ripple-like morphologies. The larger examples are ‘Transverse Aeolian Ridges’ (TARs), which stereo imaging analyses have shown to be a few metres high and up to a few tens of metres across. Where they occur, TARs therefore present a serious, but recognized and avoidable, rover mobility hazard. There also exists a population of smaller bedforms of similar morphology, but it is unknown whether these bedforms will be traversable by the ExoMars rover. We informally refer to these bedforms as “mini-TARs”, as they are about an order of magnitude smaller than most TARs observed to date. They are more abundant than TARs in the Oxia Planum site, and can be pervasive in areas. The aim of this paper is to estimate the heights of these features, which are too small to measured using High Resolution Imaging Science Experiment (HiRISE) Digital Elevation Models (DEMs), from orbital data alone. Thereby, we aim to increase our knowledge of the hazards in the proposed ExoMars landing sites. We propose a methodology to infer the height of these mini-TARs based on comparisons with similar features observed by previous Mars rovers. We use rover-based stereo imaging from the NASA Mars Exploration Rover (MER) Opportunity and PRo3D software, a 3D visualisation and analysis tool, to measure the size and height of mini-TARs in the Meridiani Planum region of Mars. These are good analogues for the smaller bedforms at the ExoMars rover candidate landing sites. We show that bedform height scales linearly with length (as measured across the bedform, perpendicular to the crest ridge) with a ratio of about 1:15. We also measured the lengths of many of the smaller aeolian bedforms in the ExoMars rover Oxia Planum candidate landing site, and find that they are similar to those of the Meridiani Planum mini-TARs. Assuming that the Oxia Planum bedforms have the same length/height ratio as the MER Opportunity mini-TARs, we combine these data to provide a probabilistic method of inferring the heights of bedforms at the Oxia Planum site. These data can then be used to explore the likely traversability of this site. For example, our method suggests that most of the bedforms studied in Oxia Planum have ridge crests higher than 15 cm, but lower than 25 cm. Hence, if the tallest bedforms the ExoMars rover will be able to safely cross are only 15 cm high, then the Oxia Planum sites studied here contain mostly impassable bedforms. However, if the rover can safely traverse 25 cm high bedforms, then most bedforms here will be smaller than this threshold. As an additional outcome, our results show that the mini-TARs have length/height ratios similar to TARs in general. Hence, these bedforms could probably be classified simply as “small TARs”, rather than forming a discrete population or sub-type of aeolian bedforms.

Amazonian chemical weathering rate derived from stony meteorite finds at Meridiani Planum on Mars.

Spacecraft exploring Mars such as the Mars Exploration Rovers Spirit and Opportunity, as well as the Mars Science Laboratory or Curiosity rover, have accumulated evidence for wet and habitable conditions on early Mars more than 3 billion years ago. Current conditions, by contrast, are cold, extremely arid and seemingly inhospitable. To evaluate exactly how dry today's environment is, it is important to understand the ongoing current weathering processes. Here we present chemical weathering rates determined for Mars. We use the oxidation of iron in stony meteorites investigated by the Mars Exploration Rover Opportunity at Meridiani Planum. Their maximum exposure age is constrained by the formation of Victoria crater and their minimum age by erosion of the meteorites. The chemical weathering rates thus derived are ∼1 to 4 orders of magnitude slower than that of similar meteorites found in Antarctica where the slowest rates are observed on Earth.

Interannual perturbations of the Martian surface heat flow by atmospheric dust opacity variations

AbstractThe InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission will perform the first Martian in situ heat flow measurement by deploying the Heat Flow and Physical Properties Package (HP3) onto the Martian surface. In order to estimate the heat flow coming from the planetary interior, HP3 will measure the local subsurface thermal gradient as well as the local thermal conductivity to a depth of up to 5 m. From these measurements, local heat flow can be determined, but this will in general differ from the heat flow emanating from the planetary interior due to atmosphere‐induced perturbations. Here we quantify heat flow perturbation induced by dust loading of the Martian atmosphere using dust opacity data obtained by the Mars Exploration Rover Opportunity. Dust opacity data span the time period between Mars year (MY) 27 and MY 32, thus incorporating the global dust storm event of MY 28 as a signal. We consider two end‐member cases for the regolith thermal conductivity and find that the background planetary heat flow is superposed by atmosphere‐induced perturbations of less than 1.5 mW m−2 at depths below 2 m if regolith thermal conductivity is low and around 0.025 W m−1 K−1 on average. If thermal conductivity is high and around 0.05 W m−1 K−1 on average, perturbations are less than 2.5 mW m−2 at depths below 3 m. Overall, the influence of interannual variability on subsurface heat flow is found to be moderate following a global dust storm. Considerably smaller perturbations are introduced by regional dust storms, which are of shorter duration and smaller magnitude.

Esperance: Multiple episodes of aqueous alteration involving fracture fills and coatings at Matijevic Hill, Mars

In the search for evidence of past aqueous activity by the Mars Exploration Rover Opportunity, fracture-filling veins and rock coatings are prime candidates for exploration. At one location within a segment of remaining rim material surrounding Endeavour Crater, a set of “boxwork” fractures in an outcrop called Esperance are filled by a bright, hydrated, and highly siliceous (SiO2 ~ 66 wt%) material, which has overall a montmorillonite-like chemical composition. This material is partially covered by patches of a thin, dark coating that is sulfate-rich (SO3 ~ 21 wt%) but also contains significant levels of Si, Fe, Ca, and Mg. The simultaneous presence of abundant S, Si, and Fe indicates significant mineralogical complexity within the coating. This combination of vein and coating compositions is unlike previous analyses on Mars. Both materials are heterogeneously eroded, presumably by eolian abrasion. The evidence indicates at least two separate episodes of solute precipitation from aqueous fluids at this location, possibly widely separated in time. In addition to the implications for multiple episodes of alteration at the surface of the planet, aqueous chemical environments such as these would have been habitable at the time of their formation and are also favorable for preservation of organic material.

Spectral and chemical characterization of jarosite in a palaeolacustrine depositional environment in Warkalli Formation in Kerala, South India and its implications

Coastal cliffs fringing the Arabian Sea near Varkala exhibits the Warkalli Formation of the Tertiary sequence of Kerala, South India, with well-marked occurrence of jarosite associated with other hydrous mineral phases of phyllosilicate family in a palaeo-lacustrine depositional environment. Sandy phyllosilicates dominate the mineral assemblage, but jarosite occurs as a prominent secondary phase formed during acid-sulphate alteration of iron sulphide in this area. Here, we discuss about the potentiality of spectroscopic techniques to identify the possible mineral phases in the collected samples. The samples from the coastal cliffs have been characterized by hyperspectral analysis (VIS-NIR-SWIR), X-ray Diffraction (XRD), Fourier Transform Infra-red Reflectance (FTIR), Electron Probe Microanalysis (EPMA) and Laser Raman spectroscopy. The spectral and chemical analyses have confirmed the jarosite as natrojarosite and phyllosilicate as kaolinite. Other accessory phases have also been identified through XRD. FTIR spectroscopy has played a major role in identifying the major hydrous bonds between the minerals. VIS-NIR-SWIR spectra show several optimum spectral features at 910nm, 1470nm, 1849–1864nm (in the form of a doublet), 1940nm and 2270nm, which could be utilised to locate jarosite in the remotely-sensed data. X-ray diffraction peaks helped in the identification of maximum number of minerals (kaolinite, smectite, quartz, feldspar, pyrite, marcasite and hematite) and the variation in jarosite content in the samples. We propose the formation of jarosite in the region by a seasonal, local and temporary development of acidic conditions. Abundance of organic matter in a fluvio-lacustrine environment has developed anaerobic conditions by removing available oxygen through decomposition of organic matter containing sulphur compounds. The sulphur thus liberated combines with hydrogen from water to develop acidic conditions and resulted in the formation of jarosite. The occurrence of jarosite in Warkalli Formation suggests on and off supply of water during diagenesis. Jarosite has been detected as a prominent deposit in several regions on Mars by Mars Exploration rover Opportunity and Mars Reconnaissance Orbiter-Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). This study of jarosite formation in terrestrial environment will influence our understanding on the mineral precipitation, diagenesis and hydration processes on Mars. Additionally, it also shows the importance of spectroscopic techniques like Raman spectrometry to be used in future missions to Mars to further validate the results of orbital spectroscopy.

Rockster: Onboard Rock Segmentation Through Edge Regrouping

To perform more complex space exploration activities with limited human intervention, an intelligent system must be able not only to sense its environment, but also to interpret the sensory data it acquires. Rock Segmentation Through Edge Regrouping is an autonomous perception algorithm for scientific analysis that is deployed on Mars. It conducts onboard analysis of images collected by the Mars Exploration Rover Opportunity and provides a list of closed rock contours to the Autonomous Exploration for Gathering Increased Science software module, which then prioritizes the identified rocks for subsequent targeting based on preferences expressed by scientists. Rock Segmentation Through Edge Regrouping processes images in 600–900 s on the MER RAD6000 flight processor, clocked to operate at 20 million instructions per second, with a guaranteed high-water memory footprint of less than 4 megabytes of RAM. In all runs on Mars with rocks or outcrop present, the top 10 returned targets have been valid rocks or outcrop with one exception, which was a dark patch of soil. In several runs in which there were no rocks present, the algorithm correctly returned no detections. A nearly integer-only parallel version of the algorithm has been demonstrated on a Tilera TILE64 multicore processor.

Context of ancient aqueous environments on Mars from in situ geologic mapping at Endeavour Crater

AbstractUsing the Mars Exploration Rover Opportunity, we have compiled one of the first field geologic maps on Mars while traversing the Noachian terrain along the rim of the 22 km diameter Endeavour Crater (Latitude −2°16′33″, Longitude −5°10′51″). In situ mapping of the petrographic, elemental, structural, and stratigraphic characteristics of outcrops and rocks distinguishes four mappable bedrock lithologic units. Three of these rock units predate the surrounding Burns formation sulfate‐rich sandstones and one, the Matijevic Formation, represents conditions on early Mars predating the formation of Endeavour Crater. The stratigraphy assembled from these observations includes several geologic unconformities. The differences in lithologic units across these unconformities record changes in the character and intensity of the Martian aqueous environment over geologic time. Water circulated through fractures in the oldest rocks over periods long enough that texturally and elementally significant alteration occurred in fracture walls. These oldest pre‐Endeavour rocks and their network of mineralized and altered fractures were preserved by burial beneath impact ejecta and were subsequently exhumed and exposed. The alteration along joints in the oldest rocks and the mineralized veins and concentrations of trace metals in overlying lithologic units is direct evidence that copious volumes of mineralized and/or hydrothermal fluids circulated through the early Martian crust. The wide range in intensity of structural and chemical modification from outcrop to outcrop along the crater rim shows that the ejecta of large (&gt;8 km in diameter) impact craters is complex. These results imply that geologic complexity is to be anticipated in other areas of Mars where cratering has been a fundamental process in the local and regional geology and mineralogy.

Opportunity Rover's image analysis: Microbialites on Mars?

The Mars Exploration Rover Opportunity investigated plains at Meridiani Planum, where laminated sedimentary rocks are present. The Opportunity rover’s Athena morphological investigation showed microstructures organized in intertwined filaments of microspherules: a texture we have also found on samples of terrestrial (biogenic) stromatolites and other microbialites. We performed a quantitative image analysis to compare images (n=45) of microbialites with the images (n=30) photographed by the rover (corresponding, approximately, to 25,000/15,000 microstructures). Contours were extracted and morphometric indexes were obtained: geometric and algorithmic complexities, entropy, tortuosity, minimum and maximum diameters. Terrestrial and Martian textures present a multifractal aspect. Mean values and confidence intervals from the Martian images overlapped perfectly with those from the terrestrial samples. The probability of this occurring by chance is 1/2 8 , less than p<0.004. Terrestrial abiogenic pseudostromatolites showed a simple fractal structure and different morphometric values from those of the terrestrial biogenic stromatolite images or Martian images with a less ordered texture (p<0.001). Our work shows the presumptive evidence of microbialites in the Martian outcroppings: i.e., the presence of unicellular life on the ancient Mars.

Late Amazonian aeolian features, gradation, wind regimes, and Sediment State in the Vicinity of the Mars Exploration Rover Opportunity, Meridiani Planum, Mars

Abstract The 2° × 2° region surrounding the landing site and traverse of Mars Exploration Rover (MER) Opportunity is richly blanketed with several generations and classes of aeolian features, including coarse-grained ripples, large dark dunes (LDDs), transverse aeolian ridges (TARs), erosional scars, depositional wind streaks of two types, and a new class of wind streak comprised entirely of coarse-grained ripples. The extensive observation campaigns from orbiting spacecraft in support of the MER and 2016 ExoMars missions, as well as in situ data from Opportunity, have provided unprecedented coverage of the region, permitting further interpretation of the local aeolian history than is typically possible on Mars. We present an analysis of bedform construction, sediment-transporting wind patterns, crater gradation and resulting erosion rate, sand provenance, and sediment state resulting from surficial mapping and geomorphic backstripping of aeolian features. Coarse-grained ripples on the intercrater plains formed from local sediments, with induration and low wind speeds preventing them from migrating more than roughly one bedform wavelength from their source region. Limited migration and a likely local, planar sand source of plains bedforms suggests their provenance is previously-eroded layers within the underlying Burns Formation. Although the bedform stabilization process is different from that of Earth, these ripples appear to be analogous to coarse-grained ripples that form and quickly stabilize on the Argentinean Puna. Some small craters ( 15 km) responds differently to a regionally-uniform wind than that in smaller craters ( The preserved surface record from the Late Amazonian consists of four periods of bedform construction. (1) The oldest wind corresponds to putative east–west oriented bedforms on the plains, from which little information may be recovered. (2) Prior to ∼200 ka, an easterly wind created TARs, plains ripples, plains-like ripples on crater floors, and ripple streaks. (3) At some point between ∼50 and ∼200 ka, smaller bedforms with northeast-southwest oriented crestlines partially reworked both plains ripples and TARs, and small similarly-oriented bedforms accumulated in the floors of craters. (4) Finally, the present-day crestline orientations of LDDs and dark sand streaks are inconsistent with each of the older bedforms. Excluding the first wind regime, the remaining bedforms can be represented by an easterly wind gradually giving way to a relative strengthening of northwesterly and southeasterly winds. Based on observations, one possible scenario describing the sediment state of the plains alternated between transport-limited contemporaneous and lagged sediment influx (CLI TL ), during which bedforms are constructed, and relatively long periods (including the present-day) of availability-limited contemporaneous sediment influx (CI AL ).

Embedded clays and sulfates in Meridiani Planum, Mars

The area of Meridiani Planum on Mars became of particular interest after the detection of coarse-grained, gray hematite, which led to the choice of this region as final landing site for the Mars Exploration Rover Opportunity. Multiple additional minerals have since been detected in the region, both from orbit and in situ. The present paper reassesses in detail the mineralogy and geomorphology of the area (between 3.5°S to 6.5°N latitude and 8.0°W to 8.0°E longitude) using visible and near-infrared hyperspectral data, merged with high spatial resolution images into a Geographic Information System. Fe/Mg-rich phyllosilicates, as well as several types of sulfates are identified within the kilometer of sedimentary deposits constituting the etched terrains and the overlying hematite-rich plains. The mineralogical stratigraphy of the etched terrains is characterized by a sulfate-rich unit, enriched in Fe/Mg-rich clays in its uppermost part. This clay-rich horizon is capped by another sulfate-rich unit, of different composition, associated with hematite detections and constituting the material of the hematite plains unit. The clay-bearing unit, which directly underlies the hematite plains, may be exposed in the rim of Endeavour Crater and could correspond to the material that is currently being analyzed by Opportunity. Diverse landforms including karsts and pan features are observed at the surface of the hydrated etched terrains and indicate past surface water and potential groundwater aquifers. Our analysis reveals that both surficial water and groundwater processes are required to explain the diversity of morphologies and mineralogies observed in the area. Although orbital detections are consistent with the hematite and sulfate detections made in situ by Opportunity in the hematite plains, they also show the presence of a clay-rich horizon at depth, overlying another, thicker, possibly chemically distinct, sulfate-rich unit within the etched terrains. Therefore we conclude that the very acidic conditions that prevailed during the formation of the topmost sulfate-rich unit, as observed in Meridiani Planum and in the hematite plains by the rover Opportunity, are not representative of the entire history of the etched terrains. In contrast, most hydrated minerals in Meridiani Planum likely formed at more neutral pH, at the beginning of the Hesperian. The overall sulfate/clay/sulfate sequence is similar to the one observed in Gale Crater, the landing site of the Mars Science Laboratory rover.