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All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Preliminary geologic mapping near the Nilosyrtis Mensae, Mars

Virtually the entire map area is mantled by an irregular deposit of material that is apparently fine-grained and erodible. It is also extremely young, as there is not a single crater larger than 1 km in the map area that was emplaced atop the mantle. Knobs abound in the study area; many are presumably caused by the mantling of pre-existing topography. In many cases the older knob of the core is exposed. Many such knob cores are surrounded by small scarplets; it is not yet clear whether the scarplets are the eroded edges of mantle beds that at one time draped over the knob core and have been subsequently exposed by erosion, or whether they are eroded versions of lobate debris aprons. Many craters in the study area contain concentric crater fill, which may indicate downslope movement of volatile-rich materials or repeated cycles of aeolian gradation.

Williams, Steven H.↗
NASA NTRS1993

The roughness of the Martian surface: A scale dependent model

In the coming decade, several lander missions to Mars are planned (e.g., MESUR Pathfinder, MESUR). One of the dangers facing planners of these missions is the rough topography observed at both Viking Lander sites. Both landing sites are ubiquitously covered with meter-scale boulders. Objects of this size pose obvious threats to soft landers, especially at Mars where the distance from Earth causes prohibitive time lags between the transmission of commands and feedback from the spacecraft. An obvious solution is to scout for a 'smooth' site prior to the landing. However, the best resolutions realizable on current and future missions (i.e., Mars Observer) are on the order of several meters. Even at this scale, boulders of 1-2 meters in size are unresolvable. Additionally, the amount of time and spacecraft resources required to search even a small area of the planet are unrealistic given other mission objectives. An alternative is to determine the 'roughness' of the surface at a subpixel scale using bidirectional reflectance observations. Much larger areas of the planet can be searched, and much of the search can easily be automated. The morphology of the martian plains observed by the Viking Landers is physically simple. The surface is covered with a layer (approximately flat lying) of aeolian sediment from which numerous outcrops of bedrock and boulders protrude. This morphology, while simple, will be difficult to characterize from orbit using traditional bidirectional reflectance models for two reasons. First, modeling the surface as facets with Gaussian or exponential slope distributions is not realistic given the morphology described above. Second, the roughness parameter is an 'average' of the roughness at scales ranging from the wavelength of light being scattered to the pixel size of the observation. Thus, there is no definite scale of roughness that can be extracted from the Hapke roughness parameter. Using the concepts of geometric and boolean models developed by several workers, we have developed a model for the bidirectional reflectance of a surface morphology comparable to that observed at the Viking Lander sites.

Shepard, M. K.↗
NASA NTRS2024

Sampling the Margin Unit of Jezero Crater, Mars for Future Mars Sample Return

Mars 2020 Perseverance rover is currently exploring Jezero crater, which contains an ancient lake-delta system with a high potential for past habitability. One of Perseverance’s primary science goals is to collect a set of scientifically return-worthy samples for return to Earth (Mars Sample Return; MSR). Between February 2021 and December 2023, Perseverance has sealed 23 tubes containing 20 rock cores, 2 regolith samples and one atmosphere sample. All rock and regolith samples are accompanied by a set of observations (Sample Threshold Observation Protocol, the STOP List) performed on abrasion patches or regolith near each sample collection site. These observations are documented in the Initial Reports and the Sample Dossier (https://pds-geosciences.wustl.edu/missions/mars2020/returned_sample_science.htm). Here we provide an overview of the samples collected during the Margin campaign. The Margin unit is situated interior and adjacent to the western crater rim and exhibits a strong carbonate signal from orbital reflectance spectroscopy. Stratigraphically the unit lies beneath the previously explored curvilinear and blocky units of the fan top and is therefore older than those units. Based on its position near the crater rim and the strong carbonate detections it has been proposed to be a shoreline deposit with possible lacustrine carbonates. Alternative hypotheses include pyroclastic, fluviolacustrine and aeolian deposits. Based on rover observations a lacustrine shoreline deposit seems most likely. The planning of the Margin campaign took place during the summer of 2023, and 3-5 samples were baselined to be collected. Exploration of the Margin unit began in September 2023 and so far, two samples have been collected: the Pelican Point core at the Hans Amundsen Memorial Workspace in the Mandu Wall region , and the Lefroy Bay core at Lake Newell in the Turquoise Bay region (Fig. 1). The associated abrasion patches are Amherst Point (Pelican Point) and Bills Bay (Lefroy Bay) . Mandu Wall is interpreted to be stratigraphically lower than Turquoise Bay based on topography.

Mars sample return↗
NASA NTRS2018

Reworking and Diagenesis of Martian Soil: Pathway to Murray Formation Sediments?

In Gale crater, the Curiosity Mars rover has climbed over 300 meters of the Murray formation from the base of the Pahrump Hills to the crest of Vera Rubin Ridge. We discuss the possibility that fine-grained mudstone of the Murray formation is a diagenetic product of sediments with a chemical and mineralogical composition similar to present-day martian soil. Typical (low Ca-sulfate) Murray samples have Na2O, Al2O3, SiO2, SO3, TiO2 and FeOT concentrations within 10% (relative) of average martian soil. These oxides constitute ~85% of each sample. The Al/Si and Ti/Si ratios of Murray samples are comparable to average martian soil but distinct from other martian geologic units. Percentage difference in P2O5, Cl, K2O, Cr2O3, MnO, Ni, Zn, Br, and Ge between soil and Murray samples generally exceed 10%, but these elements and oxides amount to less than 4% of the samples. These constituents are highly variable in Murray mudstone and may reflect mobility in fluid interactions. Large discrepancies in MgO and CaO with ~50% lower concentrations in the Murray samples (~2% absolute differences) are indicative of open-system alteration if the Murray mudstone originated from soil-like material. Mineralogically, martian soil is dominated by plagioclase feldspar, pyroxenes, and olivine with minor hematite, magnetite, and Ca-sulfate. In comparison, Murray samples generally have less feldspar and pyroxene, little to no olivine, more iron oxides and Ca-sulfates, and Fe-containing phyllosilicates. If Murray mudstone originated from a Mars soil composition, aqueous alteration could have converted olivine and pyroxenes to iron oxides and phyllosilicates. Intermixed or zoned plagioclase feldspars could have lost a larger portion of calcic constituents, consistent with susceptibility to weathering, resulting in a change from ~An55 (soil) to ~An40 (Murray). This alteration could be consistent with the major element chemistry, including the small decrease in MgO and CaO. A subsequent influx of minor/trace elements and Ca-sulfate, e.g. from groundwater, would be required. In this diagenetic scenario, the bulk of the alteration would have been nearly isochemical, suggesting limited mineral segregation and aqueous alteration during transport from the drainage basin or a significant direct aeolian contribution to the Murray sediments.

Yen, Albert S.↗
NASA NTRS1993

Modern shelf ice, equatorial Aeolis Quadrangle, Mars

As part of a detailed study of the geological and geomorphological evolution of Aeolis Quadrangle, I have encountered evidence suggesting that near surface ice exists at low latitudes and was formed by partial or complete freezing of an inland sea. The area of interest is centered at approximately -2 deg, 196 deg. As seen in a suite of Viking Orbiter frames obtained at a range of approximately 600 km, the plains surface at this location is very lightly cratered or uncratered, and it is thus of late Amazonian age. Extant topographic data indicate that the Amazonian plains at this location occupy a trough whose surface lies at least 1000 m below the Mars datum. A reasonable hypothesis is that quite recent surface water releases, perhaps associated with final evolution of large 'outflow chasms' to the south, but possibly from other source areas, filled this trough, that ice floes formed almost immediately, and that either grounded ice or an ice-covered sea still persists. A reasonable hypothesis is that quite recent surface water releases, perhaps associated with final evolution of large 'outflow chasms' to the south, but possibly from other source areas, filled this trough, that ice floes formed almost immediately, and that either grounded ice or an ice-covered sea still persists. In either case, the thin (a few meters at most) high albedo, low thermal inertia cover of aeolian materials was instrumental in allowing ice preservation, and at least the lower portions of this dust cover may be cemented by water ice. Detailed mapping using Viking stereopairs and quantitative comparisons to terrestrial shelf ice geometries are underway.

Brakenridge, G. R.↗
DOE OSTI2022

The Curiosity Rover's Exploration of Glen Torridon, Gale Crater, Mars: An Overview of the Campaign and Scientific Results

The Mars Science Laboratory rover, Curiosity, explored the clay mineral-bearing Glen Torridon region for 1 Martian year between January 2019 and January 2021, including a short campaign onto the Greenheugh pediment. The Glen Torridon campaign sought to characterize the geology of the area, seek evidence of habitable environments, and document the onset of a potentially global climatic transition during the Hesperian era. Curiosity roved 5 km in total throughout Glen Torridon, from the Vera Rubin ridge to the northern margin of the Greenheugh pediment. Curiosity acquired samples from 11 drill holes during this campaign and conducted the first Martian thermochemolytic-based organics detection experiment with the Sample Analysis at Mars instrument suite. The lowest elevations within Glen Torridon represent a continuation of lacustrine Murray formation deposits, but overlying widespread cross bedded sandstones indicate an interval of more energetic fluvial environments and prompted the definition of a new stratigraphic formation in the Mount Sharp group called the Carolyn Shoemaker formation. Glen Torridon hosts abundant phyllosilicates yet remains compositionally and mineralogically comparable to the rest of the Mount Sharp group. Glen Torridon samples have a great diversity and abundance of sulfur-bearing organic molecules, which are consistent with the presence of ancient refractory organic matter. The Glen Torridon region experienced heterogeneous diagenesis, with the most striking alteration occurring just below the Siccar Point unconformity at the Greenheugh pediment. Results from the pediment campaign show that the capping sandstone formed within the Stimson Hesperian aeolian sand sea that experienced seasonal variations in wind direction.

58 GEOSCIENCES↗
NASA NTRS2022

The Curiosity Rover’s Exploration of Glen Torridon, Gale Crater, Mars: An Overview of the Campaign and Scientific Results

The Mars Science Laboratory rover, Curiosity, explored the clay mineral-bearing Glen Torridon region for 1 Martian year between January 2019 and January 2021, including a short campaign onto the Greenheugh pediment. The Glen Torridon campaign sought to characterize the geology of the area, seek evidence of habitable environments, and document the onset of a potentially global climatic transition during the Hesperian era. Curiosity roved 5 km in total throughout Glen Torridon, from the Vera Rubin ridge to the northern margin of the Greenheugh pediment. Curiosity acquired samples from 11 drill holes during this campaign and conducted the first Martian thermochemolytic-based organics detection experiment with the Sample Analysis at Mars instrument suite. The lowest elevations within Glen Torridon represent a continuation of lacustrine Murray formation deposits, but overlying widespread cross bedded sandstones indicate an interval of more energetic fluvial environments and prompted the definition of a new stratigraphic formation in the Mount Sharp group called the Carolyn Shoemaker formation. Glen Torridon hosts abundant phyllosilicates yet remains compositionally and mineralogically comparable to the rest of the Mount Sharp group. Glen Torridon samples have a great diversity and abundance of sulfur-bearing organic molecules, which are consistent with the presence of ancient refractory organic matter. The Glen Torridon region experienced heterogeneous diagenesis, with the most striking alteration occurring just below the Siccar Point unconformity at the Greenheugh pediment. Results from the pediment campaign show that the capping sandstone formed within the Stimson Hesperian aeolian sand sea that experienced seasonal variations in wind direction.

Kristen A Bennett↗
NASA NTRS2010

Geomorphic Mapping of MTMS -20022 and -20017

Geomorphic mapping at 1:500,000 scale within three quadrangles in Margaritifer Terra, Mars, is nearing completion (Fig. 1) [e.g., 1 - 4]. This region was previously studied [5-9] because of the combination of geomorphic processes that have shaped its surface, and the current mapping has revealed details that were not visible in Viking Orbiter images used by those previous studies. The large Uzboi- Holden-Ladon-Margaritifer megaoutflow system has shaped the western part of Margaritifer Terra (Fig. 1), and flow in the Samara and Paran -Loire valley systems merged with UHLM in MTM -15022 [3]. The area in MTMs -20022 and -20017 has also been shaped by many impact craters, including an outer ring of Ladon basin and the relatively young Jones crater. Fluvial erosion associated with Loire Valles and Samara Valles and their tributaries has influenced much of the surface, and many areas are covered by resurfacing deposits (possibly fluvial, volcanic, and/or aeolian). MTMs -20022 and -20017 include Jones crater, the confluence of Himera Valles and Samara Valles, and a significant portion of Loire Valles (Fig. 1). One of the main objectives of this mapping is to determine the relative timing of fluvial activity and impact cratering, specifically the impact that created Jones.

Williams, K. K.↗
NASA NTRSDate not supplied

Recent Mineralogical Discoveries in Gale Crater, Mars from the CheMin XRD Instrument, Demonstrating a Watery Past

Curiosity landed in Gale crater August 2012 and has traversed (~27 km) sedimentary rocks that comprise a ~5 km-high mound, informally known as Mount Sharp, to investigate depositional/diagenetic environments and potential habitability. VSWIR spectra revealed the lowermost slopes of Mount Sharp contain mineral assemblages that are indicative of water-rock interactions (1-3), with sulfate-bearing units overlying phyllosilicate-bearing units. This mineralogical succession may mark the beginning of the transition from a relatively wet/warm to a very dry/cold Mars (e.g., 1, 4). Thirty-four powdered rock samples have been analyzed by the CheMin XRD instrument and mineralogical results from the first 6 years of the mission are reviewed in [5]. Here we describe the mineralogical diversity observed over the most recent 4 years. Sediments in the Vera Rubin Ridge (VRR) and Glen Torridon (GT) region were deposited in a lacustrine-fluvial environment and are syndepositional. The mineralogy suggests post-depositional fluid-rock interaction. Differences in mineralogy could have been the result of silica-poor, briny groundwater that destabilized smectite and precipitated hematite in VRR [6]. Other hypotheses include lake water-groundwater mixing or diagenesis driven by deeply sourced fluids altering smectite to precipitate hematite and amorphous silica. Preserved bedforms in the clay-sulfate transition region indicate a change from lacustrine-fluvial to aeolian depositional environments. Mineralogical changes include the identification of goethite along with the disappearance of phyllosilicate. The absence of crystalline Mg-sulfate in drilled samples from this transition region may mean that: 1) Sulfates are concentrated in secondary concretions not sampled by Curiosity’s drill, or 2) Sulfate components are either X-ray amorphous or if crystalline, became amorphous in the relatively low-humidity environment of the rover. Continued exploration of sulfate-rich rocks will elucidate this environmental transition above the phyllosilicate-rich sediments.

V M Tu↗
NASA NTRS1992

Martian surface simulations

Current scenarios for a Mars landing involve the extensive analysis of the surface near the landing site. Pinpoint landing, for example, requires a detailed mapping of the area from orbit for landmark identification and landing site selection, and the use by the lander of its own imaging data to recognize these landmarks and to guide itself safely to the surface. Hazard avoidance requires sufficient orbital imaging to ensure that safe landing sites exist, with the lander using its sensory data to find one of them. Once on the surface, a rover must be able to avoid or surmount obstacles, travel across surfaces with varying compositions and slopes, and navigate to a desired destination. Computer simulated Martian surfaces are being constructed to aid in the development of these exploration technologies. These surface simulations attempt to mimic the specific geologic episodes that built the surface, such as cratering, lava flows, and aeolian activity. Each episode takes a preexisting surface as a starting point, alters it in some way, and stores the new surface for further processing. This modular construction makes it possible for new processes to be included without altering existing software.

Gaskell, R. W.↗
NASA NTRS2020

Monitoring of Dust Devil Tracks Around the InSight Landing Site, Mars, and Comparison With In Situ Atmospheric Data

The NASA InSight mission on Mars is a unique opportunity to study atmospheric processes both from orbit and in situ observations. We use post-landing high-resolution satellite images to monitor dust devil activity during the first 8 months of the mission. We perform mapping and semiautomatic detection of newly formed dust devil tracks and analyze their characteristics (sizes, azimuths, distances, and directions of motion).We find a large number of tracks appearing shortly after landing, followed by a significant decrease of activity during late winter, then a progressive increase during early spring. New tracks are characterized by dark linear, to slightly curvilinear, traces ranging from a few to more than 10 m wide. Tracks are oriented in the ambient wind direction, according to measurements made by InSight's meteorological sensors. The systematic analysis of dust devil tracks is useful to have a better understanding of atmospheric and aeolian activity around InSight.

C. Perrin↗
NASA NTRS2018

Potential High Priority Subaerial Environments for Mars Sample Return

Subaerial environments of interest for Mars Sample Return include surface or near-surface sites not covered by a body of water, but having direct access to water from precipitation, snow melt, or ambient-temperature groundwater. This includes soils, wetlands, ephemeral ponds, cold springs, and periglacial/glacial environments, with paleosol profiles as a high priority collection site. Such soils can be topped by aqueously deposited sediments and precipitates from wetlands, ephemeral ponds, and springs. The composition and morphology of paleosols preserve evidence of past climate, aqueous conditions, and life. Key topics addressed by samples collected from subaerial environments include: 1) Constrain the duration of interaction with liquid water by investigating a weathering profile from the surface to unaltered parent material. 2) Assess the characteristics of past liquid water, and how it has changed through time. 3) Investigate weathered materials such as soils, paleosols, sediments, weathering rinds or rock coatings to assess past climate. 4) Examine characteristics of past aeolian and atmospheric processes.

Source record↗
NASA NTRS1998

Deep Basalt Aquifers in Orcus Patera, Elysium Basin Mars: Perspectives for Exobiology Exploration

Direct indicators of shorelines, spillways, and terraces allowed to determine the extent of the Elysium Paleolake between the contour-lines 1000 and 500 m below the Martian datum. The Elysium Paleolake is bordered north by Orcus Patera (14N/181W), which lies west of the Tartarus Montes and Tartarus Colles. The Orcus Patera displays an ellipse-shaped collapsed caldera of 360-km long and 100-km wide. Viking topographic data show that the bottom of the caldera is located at 2500 below the Martian datum, and surrounded by a steep-walled ram art which crest is located at about 0 m elevation. Considering the localization of Orcus Patera in the Elysium paleolake, its altimetry, and the magmatic origin of this caldera, we propose the existence of a paleolake in Orcus Patera generated (a) by juvenile water from magma during the Noachian period, and (b) by intermittent influx of the Elysium Basin from Hesperian to Amazonian. Results are encouraging to consider this site as a potential high-energy source environment for microbial communities. are circumscribed by a 50-km wide lava field mapped as Noachian material. The structure of Orcus Patera represents the record of material erupted from a magmatic reservoir. The caldera is enclosed by steep inner walls (25% measured from topographic data), values which could be in agreement with the presence of a deep magmatic reservoir, as suggested by the typology of Crumpler et.al. The depth of the caldera might be due to the collapse of the magma reservoir, and the release of gases accompanying the magma thermal evolution. Origins of water for the paleolake(s): The water that generated a paleolake in Orcus Patera may have come from two origins: (1) Juvenile water: Plescia and Crips estimated a magma H20 content by weight between 0.5% and 1.5% using for the first value a comparison with terrestrial basalt, and for the second values from a Martian meteorite. The amount of H20 can be estimated by the volume of erupted lava, and the lava content of the caldera. In this study, we adopt a water content of 1%. The total volume of magma that has been contained in the caldera, and the volume of lava contained in the observed lava field is about 110 x 10(exp 6) cubic km, that gives a total volume of 1.10 x 10(exp 6) cubic km of water. The juvenile water expelled by the overpressure within the magma chamber charged with desolved water-vapor may have moved into the crust. The decrease in overburden pressure led to bubble formation. The ascent of these bubbles generated a pressurization of the magma, which was sufficient to fracture the overlaying magma layer, (2) Water from Elysium paleolake. During the Amazonian, the rise of the Elysium paleolake level generated an overspilling that supplied the caldera with water. The southern portion of the crest shows a deep gap 12-km wide at -1500 m elevation, locating the gap between 500 to 1000 in below the assumed water of Elysium paleolake, thus facilitating the influx of Elysium paleolake water into Orcus Patera. Bathymetric calculations give a floor area of 25,500 sq km at -2000 m elevation, and a water volume of 42,000 cubic km, with a lake-level at -1500 m. A substantial amount of water may have percolated through the fractured lava, and part of the volume may have overspilled the northern crest of Orcus Patera to debouch in the Tartarus Montes region. We envision the formation of a subsurface aqueous environment in basaltic rocks at the contact of the two water-source origins, possibly the percolating surface lake water, and more likely the juvenile water. Similarly to terrestrial calderas, Orcus Patera might be surrounded by ring-fractures caused by the collapse of the magma chamber that followed the release of gases. These ring-fractures may have been covered later by sedimentation in the caldera (lacustrine, aeolian, and volcanic), and by mass wasting. The detumescence of the magma in the caldera, and the vesiculation of the juvenile water may have operated simultaneously. Comparatively to terrestrial melts, Martian iron-rich melts are denser. This greater density implies greater effusion rates (eight-times terrestrial values), and larger fissuration widths (two-times terrestrial ones). With increasing vesiculation of magma, the bubbles interact with one-another because there are of similar pressure. They make a magma froth at the contact with the caldera surface, and on the walls of the fractures. In the saturated magma, froth, where the volume ratio of gases-to-liquid is about 4:1, the bubbles form a huge surface area of interconnected spaces. Bubbles near the caldera surface disrupt the magma, and fragmentation takes place, which moves downward through the magma column. On Earth, the bubbles are likely to grow between 1 and 50 mm in diameter due to the difference between the magma surface tension, and the bubble supersaturation pressure. The Martian low-pressure at surface level is likely to accelerate the expansion of the bubbles, and increase their final diameter and number, creating more voids in the magma. The strong magma froth with enclosed juvenile water bubbles interconnected with exsolved gas bubbles constitute a potential geothermal environment for geochemical energy production from basalt and water that does not require excessive temperatures. This process can start at +20C. Similar types of environments have been shown on Earth as potential energy sources for microbial metabolism, and could have provided deep aqueous basaltic niches for possible Martian microorganisms, even geologically recently. During the Amazonian, combination of volcanism and water activity still existed on Mars. Moreover, this type of potential niches open ways for investigation of possible oases of extinct or extant life, not only on paleolakes, and surface hydrothermalism spring areas, but also all large systems of fossae, which combine hydrologic and volcanic activities, and which provide an energy source, and an underground shelter to prevent surface UV bombardment. Additional information contained in the original.

Grin, E. A.↗
NASA NTRS1998

Gale Crater: An Amazonian Impact Crater Lake at the Plateau/Plain Boundary

Gale is a 140-km diameter impact crater located at the plateau/plain boundary in the Aeolis Northeast subquadrangle of Mars (5S/223W). The crater is bordered in the northward direction by the Elysium Basin, and in eastward direction by Hesperian channels and the Aeolis Mensae 2. The crater displays a rim with two distinct erosion stages: (a) though eroded, the south rim of Gale has an apparent crest line visible from the north to the southwest (b) the west and northwest rims are characterized by a strong erosion that, in some places, partially destroyed the rampart, leaving remnant pits embayed in smooth-like deposits. The same type of deposits is observed north, outside Gale, it also borders the Aeolis Mensae, covers the bottom of the plateau scarp, and the crater floor. The central part of Gale shows a 6400 km2 subround and asymmetrical deposit: (a) the south part is composed of smooth material, (b) the north part shows spectacular terraces, streamlines, and channels. The transition between the two parts of the deposit is characterized by a scarp ranging from 200 to 2000 in high. The highest point of the scarp is at the center of the crater, and probably corresponds to a central peak. Gale crater does not show a major channel directly inflowing. However, several large fluvi systems are bordering the crater, and could be at the origin of the flooding of the crater, or have contributed to. One fluvial system is entering the crater by the southwest rim but cannot be accounted alone for the volume of sediment deposited in the crater. This channel erodes the crater floor deposit, and ends in a irregular-shaped and dark albedo feature. Gale crater shows the morphology of a crater filled during sedimentation episodes, and then eroded Part of the lower sediment deposition contained in Gale might be ancient and not only aqueous in origin. According to the regional geologic history, the sedimentary deposit could be a mixture of aeolian and pyroclastic material, and aqueous sedimentary material that can originate both from drainage of the regional subsurface aquifer, and/or from surface flood. The central deposit shows three main levels: (a) the current crater floor (north of Gale), (b) an ancient level about 200 rn higher (south of Gale), and (c) the massive terraced deposits. A crater statistics on the 15,400 kM2 area of the crater floor and deposit [3,41 gave: 259+/-112.4 craters, most of them partly embayed in the sedimentary deposit, and all inferior to 5-km diameter. For superimposed crater population only, the result is 194+/-112. The deduced relative ages ranges from Early to Middle Amazonian. The population of craters are comparable for the three levels, implying that the last sedimentation/erosion episode on Gale was recent and affected the whole crater. The streamlined morphology of the border of the deposit, the layering, the channels, and the terraces are compatible with a significant fluvio-lacustrine history of the site. Multiple levels may suggest different episodes, but the common statistical age of the three levels shows that the last episode involved the whole crater. The origin of the lake water in Gale may have varied in time. Three major contributions have been proposed: (a) the drainage of the regional underground aquifer by Gale crater over an area of 110-km radius around the crater which would have provided approximately 1,600 cubic km of water, (b), surface drainage entering Gale by the south and north rims. In the south, a 250-km long system originates in the cratered uplands in a Noachian crater material plain (Nc), and crosses Hesperian and Amazonian crater material plains (AHc) northward [1]. Several fluvial systems originate in the Aeolis Mensae, east of Gale. They may had two functions in time: to recharge, the underground aquifer in the region of Gale, and to supply surface water in the crater by overspilling the northern rim, and (c) surface floods that originated from the rising of the water level in the Elysium Basin. According to the Amazonian age of Gale's floor, and the erosion direction in the crater, a flood from Elysium Basin is the most likely event to explain the material observed in Gale, and the formation of the last lake. This last flood may have been important enough to flood the central deposit up to about 1400 m above the crater floor, leaving two islands (non stream lined features) at the center of the deposit. Terrace spacing suggests a regular drop of the lake level in time. Fractures in terraces perpendicular to the shoreline can be interpreted either as: (a) the result of the drainage systems during the waning of the lake, or (b) traces of the pressure of an ice-covered sheet associated with subglacial drainage. The presence of a lake of such volume during the Amazonian period is one more evidence that water was still active on Mars relatively recently. Gale crater offers the rare opportunity to unveil a key-period of the martian history. The Amazonian might proved not as cold and dry as previously thought. The presence of large lakes and basins (Elysium Basin is large as the Mediterranean Sea), reinforces the model of an extensive water activity during the Amazonian that has still to be understood in the context of an assumed cooling and drying planet. The sediments and rocks that were left of this period in Gale keep the record of the climatic conditions of the Amazonian and the clues that are missing to understand the climatic evolution of Mars. In addition, Gale crater presents the advantage to be located at the plateau/plain boundary, which has never been studied and contains information about the two main martian geological units. As a conclusion, we propose a table that summarizes the worthiness of a mission in Gale crater, and the expected science return relative to the objectives to be met by the Surveyor Program. Additional information contained in the original.

Cabrol, N. A.↗
NASA NTRS1998

Perennial Antarctic lake ice: an oasis for life in a polar desert

The permanent ice covers of Antarctic lakes in the McMurdo Dry Valleys develop liquid water inclusions in response to solar heating of internal aeolian-derived sediments. The ice sediment particles serve as nutrient (inorganic and organic)-enriched microzones for the establishment of a physiologically and ecologically complex microbial consortium capable of contemporaneous photosynthesis, nitrogen fixation, and decomposition. The consortium is capable of physically and chemically establishing and modifying a relatively nutrient- and organic matter-enriched microbial "oasis" embedded in the lake ice cover.

NASA Center ARC↗
NASA NTRS1993

Early Mars: A regional assessment of denudation chronology

Within the oldest highland units on Mars, the record of crater degradation indicates that fluvial resurfacing was responsible for modifying the Noachian through middle-Hesperian crater population. Based on crater frequency in the Noachian cratered terrain, age/elevation relations suggest that the highest exposures of Noachian dissected and plateau units became stabilized first, followed by successively lower units. In addition, studies of drainage networks indicate that the frequency of Noachian channels is greatest at high elevations. Together, these observations provide strong evidence of atmospheric involvement in volatile recycling. The long time period of crater modification also suggests that dendritic highland drainage was not simply the result of sapping by release of juvenile water, because the varied geologic units as well as the elevation dependence of stability ages makes it unlikely that subsurface recycling could provide a continuous supply of water for channel formation by sapping. While such geomorphic constraints on volatile history have been established by crater counts and stratigraphic relations using the 1:2M photomosaic series, photogeologic age relationships at the detailed level are needed to establish a specific chronology of erosion and sedimentation. Age relations for discrete erosional slopes and depositional basins will help refine ages of fluvial degradation, assess effectiveness of aeolian processes, and provide a regional chronology of fluvial events.

Maxwell, T. A.↗
NASA NTRS1994

Assessment of antipodal-impact terrains on Mars

The regions anitpodal to Mars' three largest impact basins, Hellas, Isidis, and Argyre, were assessed for evidence of impact-induced disrupted terrains. Photogeology and computer modeling using the Simplified Arbitrary Lagrangian Eulerian (SALE) finite element code suggest that such terrains could have been found by the Hellas impact. Maximum antipodal pressures are 1100 MPa for Hellas, 520 MPa for Isidis, and 150 MPa for Argyre. The results suggest that if antipodal fracturing were associated with later volcanism, then Alba Patera may be related to the Hellas event, as proposed by Peterson (1978). Alba Patera is a unique volcano in the solar system, being a shield volcano which emitted large volume lava flows. This volcanism could be the result of the focusing of seismic energy which created a fractured region that served as a volcanic conduit for the future release of large volumes of magma. No disrupted terrain features are observed antipodal to the Isidis or Argyre basins, although some of the old fractures in Noctis Labyrinthus could have originated in response to the Isidis impact, and later have been reactivated by the Tharsis tectonics assumed to have produced Noctis. If the lower calculated antipodal pressures for Argyre were capable of producing disrupted terrains, then the terrains have been covered subsequently by volcanic or aeolian material, or modified beyond recognition.

Williams, David A.↗
NASA NTRSDate not supplied

An Overview of SHERLOC Raman and Fluorescence Spectroscopy Results Obtained During Perseverance’s Green Zone Campaign at Jezero Crater, Mars

The Perseverance rover landed in Jezero crater, Mars, in February 2021. The field site was chosen because orbiter data provided evidence that the crater hosted an ancient (>2.7 Ga) fluvio-lacustrine environment. The Octavia E. Butler landing site is located ~1.9 km east of the erosional remnant of the Jezero river delta. Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) is an arm-mounted instrument that combines fluorescence and Raman spectroscopy with microscopic imaging to analyze geological materials in order to better understand the history of the environments recorded in the rocks within Jezero crater and to search for potential biosignatures. SHERLOC has two microscopic cameras, the Autofocus and Context Imager (ACI) and the Wide-Angle Topographic Sensor for Operations and eNgineering, (WATSON). These subsystems obtain high spatial resolution (10.1–100 µm/pixel) images to identify grain-scale structure and texture. SHERLOC spectroscopy enables high-sensitivity detection, characterization, and spatially-resolved correlation of trace organic materials. SHERLOC’s 248.6 nm deep UV laser generates a 100 µm-diameter spot. Photons generated by Raman scattering and fluorescence emission are collected and the spectra are downlinked to Earth for analysis. Knowledge of where the laser is pointed allows for mineral and compositional maps to be generated and overlain in ACI and WATSON images. Early spectroscopy observations focused on natural rock surfaces at targets named Nataani (sol 83), Bi_la_sana (sol 98) and Foux (sol 141). These surfaces included patches of aeolian dust that had settled upon the rocks. Perseverance’s abrasion tool is expected to become available in August 2021; it will grind to depths of 14 mm to remove dust and penetrate coatings and weathering rinds. This presentation will summarize major results from analysis of the rocks examined by SHERLOC during Perseverance’s first science and sample coring campaign (Green Zone Campaign).

Luther W Beegle↗