Structural analysis of sulfate vein networks in Gale crater (Mars)

The Curiosity rover's campaign in the Gale crater on Mars provides a large set of close-up images of sedimentary formations outcrops displaying a variety of diagenetic features such as light-toned veins, nodules and raised ridges. Through 2D and 3D analyses of Mastcam images we herein reconstruct the vein network of a sample area and estimated the stress field. Assessment of the spatial distribution of light-toned veins shows that the basin infillings, after burial and consolidation, experienced a sub-vertical compression and lateral extension coupled with fluid overpressure and cracking. Overall, rock failure and light-toned veins formations could have been generated by an overload produced by infilling material within the basin

Evidence of Titan's Climate History from Evaporite Distribution

Water-ice-poor, 5-$\mu$m-bright material on Saturn's moon Titan has previously been geomorphologically identified as evaporitic. Here we present a global distribution of the occurrences of the 5-$\mu$m-bright spectral unit, identified with Cassini's Visual Infrared Mapping Spectrometer (VIMS) and examined with RADAR when possible. We explore the possibility that each of these occurrences are evaporite deposits. The 5-$\mu$m-bright material covers 1\% of Titan's surface and is not limited to the poles (the only regions with extensive, long-lived surface liquid). We find the greatest areal concentration to be in the equatorial basins Tui Regio and Hotei Regio. Our interpretations, based on the correlation between 5-$\mu$m-bright material and lakebeds, imply that there was enough liquid present at some time to create the observed 5-$\mu$m-bright material. We address the climate implications surrounding a lack of evaporitic material at the south polar basins: if the south pole basins were filled at some point in the past, then where is the evaporite

Potentially active regions on Titan: New processing of Cassini/VIMS data

The Cassini Visual and Infrared Mapping Spectrometer (VIMS) obtained data of Titan's surface from flybys performed during the last seven years. In the 0.8-5.2 µm range, these spectro-imaging data showed that the surface consists of a multivariable geological terrain hosting complex geological processes. The data from the seven narrow methane spectral "windows" centered at 0.93, 1.08, 1.27, 1.59, 2.03, 2.8 and 5 µm provide some information on the lower atmospheric context and the surface parameters that we want to determine. Atmospheric scattering and absorption need to be clearly evaluated before we can extract the surface properties. We apply here a statistical method [1, 2] and a radiative transfer method [3, 1] on three potentially "active" regions on Titan, i.e. regions possibly subject to change over time (in brightness and/or in color etc) [4]: Tui Regio (20°S, 130°W) [5], a 1,500-km long flow-like figure, Hotei Regio (26°S, 78°W) [6], a 700-km wide volcanic-like terrain, and Sotra Facula (15°S, 42°W) [7], a 235-km in diameter area. With our method of Principal Component Analysis (PCA) we have managed to isolate specific regions of distinct and diverse chemical composition. We have tested this method on the previously studied Sinlap crater [8], delimitating compositional heterogeneous areas compatible with the published conclusions by Le Mouélic et al. (2008). Our follow-up method focuses on retrieving the surface albedo of the three areas and of the surrounding terrains with different spectral response by applying a radiative transfer (RT) code. We have used as input most of the Cassini HASI and DISR measurements, as well as new methane absorption coefficients [9], which are important to evaluate the atmospheric contribution and to allow us to better constrain the real surface alterations, by comparing the spectra of these regions. By superposing these results onto the PCA maps, we can correlate composition and morphology. As a test case, we used our RT code to verify the varying brightness of Hotei Regio reported by other investigators based on models lacking proper simulation of the atmospheric absorption [10]. Even though we have used exactly the same dataset, we did not detect any significant surface albedo variations over time; this led us to revise the definition of "active" regions: even if these regions have not visually changed over the course of the Cassini mission, the determination of the chemical composition and the correlation with the morphological structures [11] observed in these areas do not rule out that past and/or ongoing cryovolcanic processes are still a possible interpretation. [1] Solomonidou, A. et al. (2011). Potentially active regions on Titan: New processing of Cassini/VIMS data. In preparation. [2] Stephan, K. et al. (2008). Reduction of instrument-dependent noise in hyperspectral image data using the principal component analysis: Applications to Galileo NIMS data. Planetary and Space Science 56, 406-419. [3] Hirtzig, M. et al. (2011). Applications of a new methane linelist to Cassini/VIMS spectra of Titan in the 1.28-5.2 µm range . In preparation. [4] Wall, s. D. et al. (2009). Cassini RADAR images at Hotei Arcus and western Xanadu, Titan: Evidence for geologically recent cryovolcanic activity. Journal of Geophysical Research 36, L04203, [5] Barnes, J.W. et al. (2006). Cassini observations of flow-like features in western Tui Regio, Titan. Geophysical Research Letters 33, L16204. [6] Soderblom, L.A. et al. (2009). The geology of Hotei Regio, Titan: Correlation of Cassini VIMS and RADAR. Icarus 204, 610-618. [7] Lopes, R.M.C. et al. (2010). Distribution and interplay of geologic processes on Titan from Cassini radar data. Icarus 205, 540-558. [8] Le Mouélic et al. (2008). Mapping and interpretation of Sinlap crater on Titan using Cassini VIMS and RADAR data. Journal of Geophysical Research 113, E04003. [9] Campargue, A. et al. (2011). An empirical line list for methane at 80 K and 296 K in the 1.26-1.71 µm region for planetary investigations. Application to Titan. Icarus. Submitted. [10] Nelson, R. et al (2009). Saturn's Titan: Surface change, ammonia, and implications for atmospheric and tectonic activity. Icarus 199, 429-441. [11] Solomonidou, A. et al. (2011). Possible morphotectonic features on Titan and their origin. Planetary and Space Science. Submitted

Geomorphological significance of Ontario Lacus on Titan: Integrated interpretation of Cassini VIMS, ISS and RADAR data and comparison with the Etosha Pan (Namibia)

International audienceOntario Lacus is the largest lake of the whole southern hemisphere of Titan, Saturn's major moon. It has been imaged twice by each of the Cassini imaging systems (Imaging Science Subsystem (ISS) in 2004 and 2005, Visual and Infrared Mapping Spectrometer (VIMS) in 2007 and 2009 and Radar in 2009 and 2010). In this study, we take advantage of each imaging dataset to establish a global survey of Ontario Lacus' environment from 2005 to 2010. We perform a geomorphological mapping and interpretation of Ontario Lacus, mainly based on a joint analysis of VIMS and Radar SAR datasets, along with the T49 altimetric profile acquired in December 2008. The morphologies observed on Ontario Lacus are compared to landforms of a semi-arid terrestrial analog, which closely resembles Titan's lakes: the pans of the Etosha Basin, located in Namibia. From this comparison, we infer that Ontario Lacus is an extremely flat depression where liquids, only located in the darkest areas in the Radar data, cover topographic lows where the "alkanofer" would raise above the depression floor. The rest of the depression appears rather as a muddy flat surface likely composed of a thick coating of photon-absorbing materials, explaining its still rather dark appearance in the infrared and radar data. We also determined whether surface changes occurred during the 5 years time interval between 2005 and 2010. We found that the depression contour is constant at the resolution of ISS and VIMS data, both being consistent with the depression contour derived from the Radar data. Our interpretation, in which the liquids are located only in some parts of Ontario Lacus, agrees with the lack of significant change of the depression contour between 2007 (and 2005 with more uncertainties) and 2010

Singular regional brightening events on Titan as seen by Cassini/VIMS

Titan, the largest satellite of Saturn, is the only satellite in the solar system with a dense atmosphere. The close and continuous observations of Titan by the Cassini spacecraft, in orbit around Saturn since July 2004, bring us evidences that Titan tropo-sphere and low stratosphere experience an exotic, but complete meteorological cycle similar to the Earth hy-drological cycle, with hydrocarbons evaporation, con-densation in clouds, and rainfall. Cassini monitoring campaigns also demonstrate that Titan’s cloud cover-age and climate vary with latitude. Titan’s tropics, with globally weak meteorological activity and widespread dune fields, seem to be slightly more arid than the poles, where extensive and numerous liquid reservoirs and sustained cloud activity were discovered. Only a few tropospheric clouds have been observed at Titan’s tropics during the southern summer [2-4]. As equinox was approaching (in August 2009), they oc-curred more frequently and appeared to grow in strength and size [5-7]

Desiccation cracks provide evidence of lake drying on Mars, Sutton Island member, Murray formation, Gale Crater

Mars Science Laboratory (MSL) Curiosity rover data are used to describe the morphology of desiccation cracks observed in ancient lacustrine strata at Gale crater, Mars, and to interpret their paleoenvironmental setting. The desiccation cracks indicate subaerial exposure of lacustrine facies in the Sutton Island member of the Murray formation. In association with ripple cross-stratification and possible eolian cross-bedding, these facies indicate a transition from longer-lived perennial lakes recorded by older strata to younger lakes characterized by intermittent exposure. The transition from perennial to episodically exposed lacustrine environments provides evidence for local to regional climate change that can help constrain Mars climate models

The SuperCam Remote Sensing Instrument Suite for Mars 2020

International audienceThe Mars 2020 rover, essentially a structural twin of MSL, is being built to a) characterize the geology and history of a new landing site on Mars, b) find and characterize ancient habitable environments, c) cache samples for eventual return to Earth, and d) demonstrate in-situ production of oxygen needed for human exploration. Remote-sensing instrumentation is needed to support the first three of these goals [1]. The SuperCam instrument meets these needs with a range of instrumentation including the highest-resolution remote imaging on the rover, two different techniques for determining mineralogy , and one technique to provide elemental compositions. All of these techniques are co-boresighted, providing rapid comprehensive characterization. In addition, for targets within 7 meters of the rover the laser shock waves brush away the dust, providing cleaner surfaces for analysis. SuperCam will use an advanced version of the AEGIS robotic target selection software

Manganese-Iron Phosphate Nodules at the Groken Site, Gale Crater, Mars

The MSL Curiosity rover investigated dark, Mn-P-enriched nodules in shallow lacustrine/fluvial sediments at the Groken site in Glen Torridon, Gale Crater, Mars. Applying all relevant information from the rover, the nodules are interpreted as pseudomorphs after original crystals of vivianite, (Fe2+,Mn2+)3(PO4)2·8H2O, that cemented the sediment soon after deposition. The nodules appear to have flat faces and linear boundaries and stand above the surrounding siltstone. ChemCam LIBS (laser-induced breakdown spectrometry) shows that the nodules have MnO abundances approximately twenty times those of the surrounding siltstone matrix, contain little CaO, and have SiO2 and Al2O3 abundances similar to those of the siltstone. A deconvolution of APXS analyses of nodule-bearing targets, interpreted here as representing the nodules’ non-silicate components, shows high concentrations of MnO, P2O5, and FeO and a molar ratio P/Mn = 2. Visible to near-infrared reflectance of the nodules (by ChemCam passive and Mastcam multispectral) is dark and relatively flat, consistent with a mixture of host siltstone, hematite, and a dark spectrally bland material (like pyrolusite, MnO2). A drill sample at the site is shown to contain minimal nodule material, implying that analyses by the CheMin and SAM instruments do not constrain the nodules’ mineralogy or composition. The fact that the nodules contain P and Mn in a small molar integer ratio, P/Mn = 2, suggests that the nodules contained a stoichiometric Mn-phosphate mineral, in which Fe did (i.e., could) not substitute for Mn. The most likely such minerals are laueite and strunzite, (Fe2+,Mn2+)3(PO4)2·8H2O and –6H2O, respectively, which occur on Earth as alteration products of other Mn-bearing phosphates including vivianite. Vivianite is a common primary and diagenetic precipitate from low-oxygen, P-enriched waters. Calculated phase equilibria show Mn-bearing vivianite could be replaced by laueite or strunzite and then by hematite plus pyrolusite as the system became more oxidizing and acidic. These data suggest that the nodules originated as vivianite, forming as euhedral crystals in the sediment, enclosing sediment grains as they grew. After formation, the nodules were oxidized—first to laueite/strunzite yielding the diagnostic P/Mn ratio, and then to hematite plus an undefined Mn oxy-hydroxide (like pyrolusite). The limited occurrence of these Mn-Fe-P nodules, both in space and time (i.e., stratigraphic position), suggests a local control on their origin. By terrestrial analogies, it is possible that the nodules precipitated near a spring or seep of Mn-rich water, generated during alteration of olivine in the underlying sediments