Hydrated silicate minerals on Mars observed by the Mars Reconnaissance Orbiter CRISM instrument.

Phyllosilicates, a class of hydrous mineral first definitively identified on Mars by the OMEGA (Observatoire pour la Mineralogie, L'Eau, les Glaces et l'Activitié) instrument, preserve a record of the interaction of water with rocks on Mars. Global mapping showed that phyllosilicates are widespread but are apparently restricted to ancient terrains and a relatively narrow range of mineralogy (Fe/Mg and Al smectite clays). This was interpreted to indicate that phyllosilicate formation occurred during the Noachian (the earliest geological era of Mars), and that the conditions necessary for phyllosilicate formation (moderate to high pH and high water activity) were specific to surface environments during the earliest era of Mars's history. Here we report results from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) of phyllosilicate-rich regions. We expand the diversity of phyllosilicate mineralogy with the identification of kaolinite, chlorite and illite or muscovite, and a new class of hydrated silicate (hydrated silica). We observe diverse Fe/Mg-OH phyllosilicates and find that smectites such as nontronite and saponite are the most common, but chlorites are also present in some locations. Stratigraphic relationships in the Nili Fossae region show olivine-rich materials overlying phyllosilicate-bearing units, indicating the cessation of aqueous alteration before emplacement of the olivine-bearing unit. Hundreds of detections of Fe/Mg phyllosilicate in rims, ejecta and central peaks of craters in the southern highland Noachian cratered terrain indicate excavation of altered crust from depth. We also find phyllosilicate in sedimentary deposits clearly laid by water. These results point to a rich diversity of Noachian environments conducive to habitability.

Planetary science: bedrock formation at Meridiani Planum.

The Mars Exploration Rover Opportunity discovered sulphate-rich sedimentary rocks at Meridiani Planum on Mars, which are interpreted by McCollom and Hynek as altered volcanic rocks. However, their conclusions are derived from an incorrect representation of our depositional model, which is upheld by more recent Rover data. We contend that all the available data still support an aeolian and aqueous sedimentary origin for Meridiani bedrock.

Canyon Wall and Floor Debris Deposits in Aeolis Mons, Mars.

Aeolis Mons (informally, Mount Sharp) exhibits a number of canyons, including Gediz and Sakarya Valles. Poorly sorted debris deposits are evident on both canyon floors and connect with debris extending down the walls for canyon segments that cut through sulphate-bearing strata. On the floor of Gediz Vallis, debris overfills a central channel and merges with a massive debris ridge located at the canyon terminus. One wall-based debris ridge is evident. In comparison, the floor of Sakarya Vallis exhibits a complex array of debris deposits. Debris deposits on wall segments within Sakarya Vallis are mainly contained within chutes that extend downhill from scarps. Lateral debris ridges are also evident on chute margins. We interpret the debris deposits in the two canyons to be a consequence of one or more late-stage hydrogeomorphic events that increased the probability of landslides, assembled and channelized debris on the canyon floors, and moved materials down-canyon. The highly soluble nature of the sulphate-bearing rocks likely contributed to enhanced debris generation by concurrent aqueous weathering to produce blocky regolith for transport downslope by fluvial activity and landslides, including some landslides that became debris flows. Subsequent wind erosion in Gediz Vallis removed most of the debris deposits within that canyon and partially eroded the deposits within Sakarya Vallis. The enhanced wind erosion within Gediz Vallis was a consequence of the canyon's alignment with prevailing slope winds.

Assessment of Mars Exploration Rover landing site predictions.

Comprehensive analyses of remote sensing data during the three-year effort to select the Mars Exploration Rover landing sites at Gusev crater and at Meridiani Planum correctly predicted the atmospheric density profile during entry and descent and the safe and trafficable surfaces explored by the two rovers. The Gusev crater site was correctly predicted to be a low-relief surface that was less rocky than the Viking landing sites but comparably dusty. A dark, low-albedo, flat plain composed of basaltic sand and haematite with very few rocks was expected and found at Meridiani Planum. These results argue that future efforts to select safe landing sites based on existing and acquired remote sensing data will be successful. In contrast, geological interpretations of the sites based on remote sensing data were less certain and less successful, which emphasizes the inherent ambiguities in understanding surface geology from remotely sensed data and the uncertainty in predicting exactly what materials will be available for study at a landing site.

Phyllosilicates on Mars and implications for early martian climate.

The recent identification of large deposits of sulphates by remote sensing and in situ observations has been considered evidence of the past presence of liquid water on Mars. Here we report the unambiguous detection of diverse phyllosilicates, a family of aqueous alteration products, on the basis of observations by the OMEGA imaging spectrometer on board the Mars Express spacecraft. These minerals are mainly associated with Noachian outcrops, which is consistent with an early active hydrological system, sustaining the long-term contact of igneous minerals with liquid water. We infer that the two main families of hydrated alteration products detected-phyllosilicates and sulphates--result from different formation processes. These occurred during two distinct climatic episodes: an early Noachian Mars, resulting in the formation of hydrated silicates, followed by a more acidic environment, in which sulphates formed.

Synergistic Ground and Orbital Observations of Iron Oxides on Mt. Sharp and Vera Rubin Ridge.

Visible/short-wave infrared spectral data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) show absorptions attributed to hematite at Vera Rubin ridge (VRR), a topographic feature on northwest Mt. Sharp. The goals of this study are to determine why absorptions caused by ferric iron are strongly visible from orbit at VRR and to improve interpretation of CRISM data throughout lower Mt. Sharp. These goals are achieved by analyzing coordinated CRISM and in situ spectral data along the Curiosity Mars rover's traverse. VRR bedrock within areas that have the deepest ferric absorptions in CRISM data also has the deepest ferric absorptions measured in situ. This suggests strong ferric absorptions are visible from orbit at VRR because of the unique spectral properties of VRR bedrock. Dust and mixing with basaltic sand additionally inhibit the ability to measure ferric absorptions in bedrock stratigraphically below VRR from orbit. There are two implications of these findings: (1) Ferric absorptions in CRISM data initially dismissed as noise could be real, and ferric phases are more widespread in lower Mt. Sharp than previously reported. (2) Patches with the deepest ferric absorptions in CRISM data are, like VRR, reflective of deeper absorptions in the bedrock. One model to explain this spectral variability is late-stage diagenetic fluids that changed the grain size of ferric phases, deepening absorptions. Curiosity's experience highlights the strengths of using CRISM data for spectral absorptions and associated mineral detections and the caveats in using these data for geologic interpretations and strategic path planning tools.

Evidence for a Diagenetic Origin of Vera Rubin Ridge, Gale Crater, Mars: Summary and Synthesis of Curiosity's Exploration Campaign.

This paper provides an overview of the Curiosity rover's exploration at Vera Rubin ridge (VRR) and summarizes the science results. VRR is a distinct geomorphic feature on lower Aeolis Mons (informally known as Mount Sharp) that was identified in orbital data based on its distinct texture, topographic expression, and association with a hematite spectral signature. Curiosity conducted extensive remote sensing observations, acquired data on dozens of contact science targets, and drilled three outcrop samples from the ridge, as well as one outcrop sample immediately below the ridge. Our observations indicate that strata composing VRR were deposited in a predominantly lacustrine setting and are part of the Murray formation. The rocks within the ridge are chemically in family with underlying Murray formation strata. Red hematite is dispersed throughout much of the VRR bedrock, and this is the source of the orbital spectral detection. Gray hematite is also present in isolated, gray-colored patches concentrated toward the upper elevations of VRR, and these gray patches also contain small, dark Fe-rich nodules. We propose that VRR formed when diagenetic event(s) preferentially hardened rocks, which were subsequently eroded into a ridge by wind. Diagenesis also led to enhanced crystallization and/or cementation that deepened the ferric-related spectral absorptions on the ridge, which helped make them readily distinguishable from orbit. Results add to existing evidence of protracted aqueous environments at Gale crater and give new insight into how diagenesis shaped Mars' rock record.

Mars global surveyor mission: overview and status.

The Mars Global Surveyor (MGS) spacecraft achieved a 45-hour elliptical orbit at Mars on 11 September 1997 after an 11-month cruise from Earth. The mission is acquiring high-quality global observations of the martian surface and atmosphere and of its magnetic and gravitational fields. These observations will continue for one martian year.

Magellan: initial analysis of venus surface modification.

Initial Magellan observations reveal a planet with high dielectric constant materials exposed preferentially in elevated regions with high slopes, ejecta deposits extending up to 1000 kilometers to the west of several impact craters, windblown deposits and features in areas where there are both obstacles and a source of particulate material, and evidence for slow, steady degradation by atmosphere-surface interactions and mass movements.

Three Mars years: viking lander 1 imaging observations.

The Mutch Memorial Station (Viking Lander 1) on Mars acquired imaging and meteorological data over a period of 2245 martian days (3:3 martian years). This article discusses the deposition and erosion of thin deposits (ten to hundreds of micrometers) of bright red dust associated with global dust storms, and the removal of centimeter amounts of material in selected areas during a dust storm late in the third winter. Atmospheric pressure data acquired during the period of intense erosion imply that baroclinic disturbances and strong diurnal solar tidal heating combined to produce strong winds. Erosion occurred principally in areas where soil cohesion was reduced by earlier surface sampler activities. Except for redistribution of thin layers of materials, the surface appears to be remarkably stable, perhaps because of cohesion of the undisturbed surface material.

Viking magnetic properties investigation: further results.

The amounts of magnetic particles held on the reference test chart and backhoe magnets on lander 2 and lander 1 are comparable, indicating the presence of an estimated 3 to 7 percent by weight of relatively pure, strongly magnetic particles in the soil at the lander 2 sampling site. Preliminary spectrophotometric analysis of the material held on the backhoe magnets on lander 1 indicates that its reflectance characteristics are indistinguishable from material within a sampling trench with which it has been compared. The material on the RTC magnet shows a different spectrum, but it is suspected that the difference is the result of a reflectance contribution from the magnesium metal covering on the magnet. It is argued that the results indicate the presence, now or originally, of magnetite, which may be titaniferous.

An overview of venus geology.

The Magellan spacecraft is producing comprehensive image and altimetry data for the planet Venus. Initial geologic mapping of the planet reveals a surface dominated by volcanic plains and characterized by extensive volcanism and tectonic deformation. Geologic and geomorphologic units include plains terrains, tectonic terrains, and surficial material units. Understanding the origin of these units and the relation between them is an ongoing task of the Magellan team.

Impact craters on venus: initial analysis from magellan.

Magellan radar images of 15 percent of the planet show 135 craters of probable impact origin. Craters more than 15 km across tend to contain central peaks, multiple central peaks, and peak rings. Many craters smaller than 15 km exhibit multiple floors or appear in clusters; these phenomena are attributed to atmospheric breakup of incoming meteoroids. Additionally, the atmosphere appears to have prevented the formation of primary impact craters smaller than about 3 km and produced a deficiency in the number of craters smaller than about 25 km across. Ejecta is found at greater distances than that predicted by simple ballistic emplacement, and the distal ends of some ejecta deposits are lobate. These characteristics may represent surface flows of material initially entrained in the atmosphere. Many craters are surrounded by zones of low radar albedo whose origin may have been deformation of the surface by the shock or pressure wave associated with the incoming meteoroid. Craters are absent from several large areas such as a 5 million square kilometer region around Sappho Patera, where the most likely explanation for the dearth of craters is volcanic resurfacing. There is apparently a spectrum of surface ages on Venus ranging approximately from 0 to 800 million years, and therefore Venus must be a geologically active planet.

One Mars year: viking lander imaging observations.

Throughout the complete Mars year during which they have been on the planet, the imaging systems aboard the two Viking landers have documented a variety of surface changes. Surface condensates, consisting of both solid H(2)O and CO(2), formed at the Viking 2 lander site during the winter. Additional observations suggest that surface erosion rates due to dust redistribution may be substantially less than those predicted on the basis of pre-Viking observations. The Viking 1 lander will continue to acquire and transmit a predetermined sequence of imaging and meteorology data as long as it is operative.

Fine particles on Mars: observations with the viking 1 lander cameras.

Drifts of fine-grained sediment are present in the vicinity of the Viking 1 lander. Many drifts occur in the lees of large boulders. Morphologic analysis indicates that the last dynamic event was one of general deflation for at least some drifts. Particle cohesion implies that there is a distinct small-particle upturn in the threshold velocity-particle size curve; the apparent absence of the most easily moved particles (150 micrometers in diameter) may be due to their preferential transport to other regions or their preferential collisional destruction. A twilight rescan with lander cameras indicates a substantial amount of red dust with mean radius on the order of 1 micrometer in the atmosphere.

The surface of Mars: the view from the viking 2 lander.

Viking 2 lander began imaging the surface of Mars at Utopia Planitia on 3 September 1976. The surface is a boulder-strewn reddish desert cut by troughs that probably form a polygonal network. A plateau can be seen to the east of the spacecraft, which for the most probable lander location is approximately the direction of a tongue of ejecta from the crater Mie. Boulders at the lander 2 site are generally more vesicular than those near lander i. Fines at both lander sites appear to be very fine-grained and to be bound in a duricrust. The pinkish color of the sky, similar to that observed at the lander I site, indicates suspension of surface material. However, the atmospheric optical depth is less than that at the lander I site. After dissipation of a cloud of dust stirred during landing, no changes other than those stemming from sampling activities have been detected in the landscape. No signs of large organisms are apparent at either landing site.

Chemistry, mineralogy, and grain properties at Namib and High dunes, Bagnold dune field, Gale crater, Mars: A synthesis of Curiosity rover observations.

The Mars Science Laboratory Curiosity rover performed coordinated measurements to examine the textures and compositions of aeolian sands in the active Bagnold dune field. The Bagnold sands are rounded to subrounded, very fine to medium sized (~45-500 µm) with ≥6 distinct grain colors. In contrast to sands examined by Curiosity in a dust-covered, inactive bedform called Rocknest and soils at other landing sites, Bagnold sands are darker, less red, better sorted, have fewer silt-sized or smaller grains, and show no evidence for cohesion. Nevertheless, Bagnold mineralogy and Rocknest mineralogy are similar with plagioclase, olivine, and pyroxenes in similar proportions comprising >90% of crystalline phases, along with a substantial amorphous component (35% ± 15%). Yet Bagnold and Rocknest bulk chemistry differ. Bagnold sands are Si enriched relative to other soils at Gale crater, and H2O, S, and Cl are lower relative to all previously measured Martian soils and most Gale crater rocks. Mg, Ni, Fe, and Mn are enriched in the coarse-sieved fraction of Bagnold sands, corroborated by visible/near-infrared spectra that suggest enrichment of olivine. Collectively, patterns in major element chemistry and volatile release data indicate two distinctive volatile reservoirs in Martian soils: (1) amorphous components in the sand-sized fraction (represented by Bagnold) that are Si-enriched, hydroxylated alteration products and/or H2O- or OH-bearing impact or volcanic glasses and (2) amorphous components in the fine fraction (<40 µm; represented by Rocknest and other bright soils) that are Fe, S, and Cl enriched with low Si and adsorbed and structural H2O.

The stratigraphy and evolution of lower Mount Sharp from spectral, morphological, and thermophysical orbital data sets.

We have developed a refined geologic map and stratigraphy for lower Mount Sharp using coordinated analyses of new spectral, thermophysical, and morphologic orbital data products. The Mount Sharp group consists of seven relatively planar units delineated by differences in texture, mineralogy, and thermophysical properties. These units are (1-3) three spatially adjacent units in the Murray formation which contain a variety of secondary phases and are distinguishable by thermal inertia and albedo differences, (4) a phyllosilicate-bearing unit, (5) a hematite-capped ridge unit, (6) a unit associated with material having a strongly sloped spectral signature at visible near-infrared wavelengths, and (7) a layered sulfate unit. The Siccar Point group consists of the Stimson formation and two additional units that unconformably overlie the Mount Sharp group. All Siccar Point group units are distinguished by higher thermal inertia values and record a period of substantial deposition and exhumation that followed the deposition and exhumation of the Mount Sharp group. Several spatially extensive silica deposits associated with veins and fractures show that late-stage silica enrichment within lower Mount Sharp was pervasive. At least two laterally extensive hematitic deposits are present at different stratigraphic intervals, and both are geometrically conformable with lower Mount Sharp strata. The occurrence of hematite at multiple stratigraphic horizons suggests redox interfaces were widespread in space and/or in time, and future measurements by the Mars Science Laboratory Curiosity rover will provide further insights into the depositional settings of these and other mineral phases.

Deposition, exhumation, and paleoclimate of an ancient lake deposit, Gale crater, Mars.

The landforms of northern Gale crater on Mars expose thick sequences of sedimentary rocks. Based on images obtained by the Curiosity rover, we interpret these outcrops as evidence for past fluvial, deltaic, and lacustrine environments. Degradation of the crater wall and rim probably supplied these sediments, which advanced inward from the wall, infilling both the crater and an internal lake basin to a thickness of at least 75 meters. This intracrater lake system probably existed intermittently for thousands to millions of years, implying a relatively wet climate that supplied moisture to the crater rim and transported sediment via streams into the lake basin. The deposits in Gale crater were then exhumed, probably by wind-driven erosion, creating Aeolis Mons (Mount Sharp).