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Recent robotic missions to Mars have offered new insights into the extent, diversity and habitability of the Martian sedimentary rock record. Since the Curiosity rover landed in Gale crater in August 2012, the Mars Science Laboratory Science Team has explored the origins and habitability of ancient fluvial, deltaic, lacustrine and aeolian deposits preserved within the crater. This study describes the sedimentology of a ca 13 m thick succession named the Pahrump Hills member of the Murray formation, the first thick fine‐grained deposit discovered in situ on Mars. This work evaluates the depositional processes responsible for its formation and reconstructs its palaeoenvironmental setting. The Pahrump Hills succession can be sub‐divided into four distinct sedimentary facies: (i) thinly laminated mudstone; (ii) low‐angle cross‐stratified mudstone; (iii) cross‐stratified sandstone; and (iv) thickly laminated mudstone–sandstone. The very fine grain size of the mudstone facies and abundant millimetre‐scale and sub‐millimetre‐scale laminations exhibiting quasi‐uniform thickness throughout the Pahrump Hills succession are most consistent with lacustrine deposition. Low‐angle geometric discordances in the mudstone facies are interpreted as ‘scour and drape’ structures and suggest the action of currents, such as those associated with hyperpycnal river‐generated plumes plunging into a lake. Observation of an overall upward coarsening in grain size and thickening of laminae throughout the Pahrump Hills succession is consistent with deposition from basinward progradation of a fluvial‐deltaic system derived from the northern crater rim into the Gale crater lake. Palaeohydraulic modelling constrains the salinity of the ancient lake in Gale crater: assuming river sediment concentrations typical of floods on Earth, plunging river plumes and sedimentary structures like those observed at Pahrump Hills would have required lake densities near freshwater to form. The depositional model for the Pahrump Hills member presented here implies the presence of an ancient sustained, habitable freshwater lake in Gale crater for at least ca 10^3 to 10^7 Earth years.

The Alpha Particle X-ray Spectrometer (APXS) onboard the Mars rover Curiosity conducts high-precision in situ chemical measurements of rocks and regolith. Target surfaces are not always flat and thus can pose issues for interpretations that assume such. Here, we investigate when variable target relief is an important effect to consider for APXS targets. We provide operational recommendations on how to most efficiently study targets of significant changes in surface relief with the rover-arm-mounted APXS and Mars Hand Lens Imager camera. Additionally, we deconvolve the chemistry of heterogeneous targets of significant vertical relief encountered along Curiosity's traverse, providing the chemical composition of visible endmembers in the process. Specifically, presented here are the deconvolved endmember compositions of two recent targets. The first is a manganese-rich, calcium-rich, and zinc-rich dark-toned vein at Garden City that is chemically and visually unique compared with the intermixed light-toned Ca-sulfate-dominated vein. The other target is a weathered Mg-sulfate-rich nodule that is unique compared with a previously encountered nodule that had significant nickel enrichment. The distinctly different chemistry both at Garden City and with the Mg-sulfate-rich nodules along the traverse provides further evidence for either multiple fluid events or an evolving fluid on the surface of ancient Mars. Copyright © 2017 John Wiley & Sons, Ltd.

The Curiosity rover observed high Mn abundances (>25 wt % MnO) in fracture-filling materials that crosscut sandstones in the Kimberley region of Gale crater, Mars. The correlation between Mn and trace metal abundances plus the lack of correlation between Mn and elements such as S, Cl, and C, reveals that these deposits are Mn oxides rather than evaporites or other salts. On Earth, environments that concentrate Mn and deposit Mn minerals require water and highly oxidizing conditions; hence, these findings suggest that similar processes occurred on Mars. Based on the strong association between Mn-oxide deposition and evolving atmospheric dioxygen levels on Earth, the presence of these Mn phases on Mars suggests that there was more abundant molecular oxygen within the atmosphere and some groundwaters of ancient Mars than in the present day.

The Mars Hand Lens Imager (MAHLI) is a 2-megapixel, color camera with resolution as high as 13.9 µm pixel−1. MAHLI has operated successfully on the Martian surface for over 1150 Martian days (sols) aboard the Mars Science Laboratory (MSL) rover, Curiosity. During that time MAHLI acquired images to support science and science-enabling activities, including rock and outcrop textural analysis; sand characterization to further the understanding of global sand properties and processes; support of other instrument observations; sample extraction site documentation; range-finding for arm and instrument placement; rover hardware and instrument monitoring and safety; terrain assessment; landscape geomorphology; and support of rover robotic arm commissioning. Operation of the instrument has demonstrated that imaging fully illuminated, dust-free targets yields the best results, with complementary information obtained from shadowed images. The light-emitting diodes (LEDs) allow satisfactory night imaging but do not improve daytime shadowed imaging. MAHLI's combination of fine-scale, science-driven resolution, RGB color, the ability to focus over a large range of distances, and relatively large field of view (FOV), have maximized the return of science and science-enabling observations given the MSL mission architecture and constraints.

The Alpha Particle X-Ray Spectrometer (APXS) determines the chemical composition of Martian rocks and soils on-board both active National Aeronautics and Space Administration (NASA) rovers using X-ray emission spectroscopy through complementary particle-induced X-ray emission (PIXE) and X-ray fluorescence (XRF) excitation methods. A single APXS spectrum represents the sum of the signals from within the instrument's field of view (FOV). In the past, features smaller than the FOV have been investigated through repeated measurements with stepwise lateral offsets. These lateral offsets allow for empirically extracting, through elemental correlations, distinct compositions of different features. Here, we present a novel analytical method for deconvolving the endmember chemistry of visually distinct components through oversampling and the integrated analysis of the elemental data and supporting images. We discuss specifically the method's application to three targets investigated by the Mars Science Laboratory rover Curiosity during its traverse, as well as the added information that can be gained from this method in the future. Copyright © 2016 John Wiley & Sons, Ltd.

Ancient lake system at Gale crater Since 2012, the Curiosity rover has been diligently studying rocky outcrops on Mars, looking for clues about past water, climate, and habitability. Grotzinger et al. describe the analysis of a huge section of sedimentary rocks near Gale crater, where Mount Sharp now stands (see the Perspective by Chan). The features within these sediments are reminiscent of delta, stream, and lake deposits on Earth. Although individual lakes were probably transient, it is likely that there was enough water to fill in low-lying depressions such as impact craters for up to 10,000 years. Wind-driven erosion removed many of these deposits, creating Mount Sharp. Science , this issue p. 10.1126/science.aac7575 , see also p. 167

We combine the results of orbitally-derived morphologic and thermal inertia data with in situ observations of abundance, size, morphologic characteristics, and distribution of pebble- to cobble-sized clasts along the Curiosity rover traverse. Our goals are to characterize rock sources and transport history, and improve our ability to predict upcoming terrain. There are ten clast types, with nine types interpreted as sedimentary rocks. Only Type 3 clasts had morphologies indicative of significant wear through transport; thus, most clast types are indicative of nearby outcrops or prior presence of laterally extensive sedimentary rock layers, consistent with the erosional landscape. A minor component may reflect impact delivery of more distant material. Types 1 and 4 are heavily-cemented sandstones, likely associated with a “caprock” layer. Types 5 and 6 (and possibly 7) are pebble-rich sandstones, with varying amounts of cement leading to varying susceptibility to erosion/wear. Type 3 clasts are rounded pebbles likely transported and deposited alluvially, then worn out of pebbly sandstone/conglomerate. Types 9 and 10 are poorly-sorted sandstones, with Type 9 representing fragments of Square Top-type layers, and Type 10 deriving from basal or other Mt. Sharp layers. Types 2, 8 and 9 are considered exotics. There are few clear links between clast type and terrain surface roughness (particularly in identifying terrain that is challenging for the rover to navigate). Orbital data may provide a reasonable prediction of certain end-member terrains but the complex interplay between variables that contribute to surface characteristics makes discriminating between terrain types from orbital data problematic. Prediction would likely be improved through higher-resolution thermal inertia data., This research was supported by the Mars Science Laboratory Program through Malin Space Science Systems contract 08-0315 to R.A.Y. Work in Denmark was funded by the Danish Council for Independent Research/Natural Sciences (FNU grants 12-127126 and 11-107019) and the TICRA Foundation. Work in Germany was funded by the Deutsche Forschungsgemeinschaft (DFG grant GO 2288/1-1). V.E.H. was supported by the Mars Science Laboratory Participating Scientist Program (JPL subcontract 1449892).