ALBERT

Description: One of the major Mars discoveries of recent years is the existence of recurring slope lineae (RSL), which suggests that liquid water occurs on or near the surface of Mars today. These dark and narrow features emerge from steep, rocky exposures and incrementally grow, fade, and reform on a seasonal basis and are detected in images from the High Resolution Imaging Science Experiment camera. RSL are known to occur at scattered midlatitude and equatorial sites with little spatial connection to one another. One major exception is the steep, low-albedo slopes of Melas and Coprates Chasmata, in Valles Marineris where RSL are detected among diverse geologic surfaces (e.g., bedrock and talus) and landforms (e.g., inselbergs and landslides). New images show topographic changes including sediment deposition on active RSL slopes. Midwall locations in Coprates and Melas appear to have more areally extensively abundant RSL and related fans as compared with other RSL sites found on Mars. Water budget estimates for regional RSL are on the order of 10 5 to 10 6  m 3 of fluid, for depths of 10 to 100 mm, and suggest that a significant amount of near-surface water might be present. Many RSL are concentrated near local topographic highs, such as ridge crests or peaks, which is challenging to explain via groundwater or ice without a recharge mechanism. Collectively, results provide additional support for the notion that significant amounts of near-surface water can be found on Mars today and suggest that a widespread mechanism, possibly related to the atmosphere, is recharging RSL sources.

Description: [1]  There is ample evidence of both ancient and long-lasting fluvial activity and chemical alteration in the Libya Montes region south of Isidis Basin. The region hosts Noachian to Amazonian aged surface rocks with extensive outcrops of olivine- and pyroxene-bearing material. Libya Montes also features surface outcrops and/or deposits hosting Fe/Mg-smectite, Fe/Mg-smectite mixed with carbonate and/or other Fe/Mg-rich phyllosilicates, and Al-smectite. These units likely formed through chemical alteration connected with hydrothermal activity resulting from the formation of the Isidis Basin and/or the pervasive fluvial activity throughout this region. The morphology and stratigraphy of the aqueous and mafic minerals are described using High Resolution Imaging Science Experiment and High Resolution Stereo Camera derived digital terrain models. Analyses of the Compact Reconnaissance Imaging Spectrometer for Mars spectra show variations in the chemistry of the Fe/Mg-smectite from nontronite-like exposures with spectral features near 2.29 and 2.4 µm more consistent with Fe 3+ 2 OH groups in the mineral structure, and saponite-like outcrops with spectral features near 2.31 and 2.38 µm characteristic of Mg 2+ 3 OH groups. These Fe/Mg-smectite bearing materials also have bands near 1.9 µm due to H 2 O and near 2.5 µm that could be due to the smectite, other phyllosilicates, and carbonates. All regions exhibiting carbonate features near 3.4–3.5 µm also have features consistent with the presence of olivine and Fe/Mg-smectite, indicating that the carbonate signatures occur in rocks likely containing a mixture of these minerals. The Al-smectite-bearing rocks have bands near 1.41, 1.91, and 2.19 µm that are more consistent with beidellite than other Al-phyllosilicates, indicating a higher-temperature or diagenetically processed origin for this material. Our interpretation of the geologic history of this region is that ancient Noachian basaltic crustal materials experienced extensive aqueous alteration at the time of the Isidis impact, during which the montes were also formed, followed by emplacement of a rough olivine-rich lava or melt, and finally the smooth pyroxene-bearing caprock unit.

Description: [1]  We have measured the bidirectional reflectance of analogs of dry, wet and frozen Martian soils over a wide range of phase angles in the visible spectral range. All samples were produced from two geologic samples: the standard JSC Mars-1 soil simulant and Hawaiian basaltic sand. In a first step, experiments were conducted with the dry samples to investigate the effects of surface texture. Comparisons with results independently obtained by different teams with similar samples showed a satisfying reproducibility of the photometric measurements as well as a noticeable influence of surface textures resulting from different sample preparation procedures. In a second step, water was introduced to produce wet and frozen samples and their photometry investigated. Optical microscope images of the samples provided information about their micro-texture. Liquid water, even in relatively low amount, resulted in the disappearance of the backscattering peak and the appearance of a forward scattering peak whose intensity increases with the amount of water. Specular reflections only appeared when water was present in an amount large enough to allow water to form a film at the surface of the sample. Icy samples showed a wide variability of photometric properties depending on the physical properties of the water ice. We discuss the implications of these measurements in terms of the expected photometric behavior of the Martian surface, from equatorial to circum-polar regions. In particular, we propose some simple photometric criteria to improve the identification of wet and/or icy soils from multiple observations under different geometries.

Description: ABSTRACT Schmidt-hammer exposure-age dating (SHD) was applied to the problem of dating the diachronous surfaces of five distal river-bank boulder ramparts deposited by snow avalanches plunging into the Jostedøla and Sprongdøla rivers in the Jostedalsbreen region of southern Norway. Approaches to local high-precision linear age calibration, which controlled in different ways for boulder roundness, were developed. The mean age (SHD mean ) and the maximum age (SHD max ) of surface boulders were estimated for whole ramparts, crests and distal fringes. Interpretation was further assisted by reference to R-value distributions. SHD mean ages (with 95% confidence intervals) ranged from 520 ± 270 years to 5375 ± 965 years, whereas SHD max ages (expected to be exceeded by 〈5% of surface boulders) ranged from 675 to 9065 years. SHD ages from the Jostedøla ramparts tended to be older than those associated with the Sprongdøla, rampart crests were younger than the respective distal fringes, and use of relatively rounded boulders yielded more consistent SHD ages than angular boulders. The SHD mean ages indicate differences in recent levels of snow-avalanche activity between ramparts and provide insights into rampart dynamics as boulders are deposited on rampart crests and, in smaller numbers, on the distal fringes. SHD max ages provide minimum age estimates of rampart age (i.e. the time elapsed since the ramparts began to form) and suggest that at least some of the ramparts have been developing since the early Holocene. This article is protected by copyright. All rights reserved.

Description: We have analysed high-spatial-resolution and high-temporal-resolution temperature measurements of the active lava lake at Erta'Ale volcano, Ethiopia, to derive requirements for measuring eruption temperatures at Io's volcanoes. Lava lakes are particularly attractive targets because they are persistent in activity and large, often with ongoing lava fountain activity that exposes lava at near-eruption temperature. Using infrared thermography, we find that extracting useful temperature estimates from remote-sensing data requires (a) high spatial resolution to isolate lava fountains from adjacent cooler lava and (b) rapid acquisition of multi-color data. Because existing spacecraft data of Io's volcanoes do not meet these criteria, it is particularly important to design future instruments so that they will be able to collect such data. Near-simultaneous data at more than two relatively short wavelengths (shorter than 1 μm) are needed to constrain eruption temperatures. Resolving parts of the lava lake or fountains that are near the eruption temperature is also essential, and we provide a rough estimate of the required image scale.

Description: The Cassini Imaging Science Subsystem has observed Titan for ∼1/4 Titan year, and we report here the first evidence of seasonal shifts in preferred locations of tropospheric methane clouds. South-polar convective cloud activity, common in late southern summer, has become rare. North-polar and northern mid-latitude clouds appeared during the approach to the northern spring equinox in August 2009. Recent observations have shown extensive cloud systems at low latitudes. In contrast, southern mid-latitude and subtropical clouds have appeared sporadically throughout the mission, exhibiting little seasonality to date. These differences in behavior suggest that Titan's clouds, and thus its general circulation, are influenced by both the rapid temperature response of a low-thermal-inertia surface and the much longer radiative timescale of Titan's cold thick troposphere. North-polar clouds are often seen near lakes and seas, suggesting that local increases in methane concentration and/or lifting generated by surface roughness gradients may promote cloud formation.

Description: Chemical, mineralogic, and lithologic ground truth was acquired for the first time on Mars in terrain units mapped using orbital Mars Reconnaissance Orbiter's High Resolution Imaging Science Experiment (MRO HiRISE) image data. Examination of several dozen outcrops shows that Mars is geologically complex at meter length scales, the record of its geologic history is well exposed, stratigraphic units may be identified and correlated across significant areas on the ground, and outcrops and geologic relationships between materials may be analyzed with techniques commonly employed in terrestrial field geology. Despite their burial during the course of Martian geologic time by widespread epiclastic materials, mobile fines, and fall deposits, the selective exhumation of deep and well-preserved geologic units has exposed undisturbed outcrops, stratigraphic sections, and structural information much as they are preserved and exposed on Earth. A rich geologic record awaits skilled future field investigators on Mars. The correlation of ground observations and orbital images enables construction of a corresponding geologic reconnaissance map. Most of the outcrops visited are interpreted to be pyroclastic, impactite, and epiclastic deposits overlying an unexposed substrate, probably related to a modified Gusev crater central peak. Fluids have altered chemistry and mineralogy of these protoliths in degrees that vary substantially within the same map unit. Examination of the rocks exposed above and below the major unconformity between the plains lavas and the Columbia Hills directly confirms the general conclusion from remote sensing in previous studies over past years that the early history of Mars was a time of more intense deposition and modification of the surface. Although the availability of fluids and the chemical and mineral activity declined from this early period, significant later volcanism and fluid convection enabled additional, if localized, chemical activity.

Description: The depth/diameter ratio for new meter- to decameter-scale martian craters formed in the last ~20 years averages 0.23, only slightly deeper than that expected for simple primary craters on rocky surfaces. Large variations in d/D between impact sites indicate that differences between the sites such as target material properties, impact velocity, angle, and physical state of the bolide(s) are important in determining the depth of small craters in the strength regime. On the Moon, the d/D of random fresh small craters with similar diameters averages only 0.10, indicating that either the majority of them are unrecognized secondaries, or some proportion are degraded primaries. Older craters such as these may be shallower due to erosional infilling, which is probably not linear over time but more effective over recently-disturbed and steeper surfaces, processes that are not yet acting on the new martian craters. Brand new meter- to decameter-scale craters such as the martian ones studied here are statistically easily distinguishable as primaries, but the origins of older craters of the same size, such as the lunar ones in this study, are ambiguous.

Description: The brain is an ever-changing organ that encodes memories and directs behavior. Neuroanatomical studies have revealed structural plasticity of neural architecture, and advances in gene expression technology and epigenetics have demonstrated new mechanisms underlying the brain's dynamic nature. Stressful experiences challenge the plasticity of the brain, and prolonged exposure to environmental stress redefines the normative transcriptional profile of both neurons and glia, and can lead to the onset of mental illness. A more thorough understanding of normal and abnormal gene expression is needed to define the diseased brain and improve current treatments for psychiatric disorders. The efforts to describe gene expression networks have been bolstered by microarray and RNA-sequencing technologies. The heterogeneity of neural cell populations and their unique microenvironments, coupled with broad ranging interconnectivity, makes resolving this complexity exceedingly challenging and requires the combined efforts of single cell and systems level expression profiling to identify targets for therapeutic intervention. Transcriptional profiling techniques are revealing novel mechanisms underlying stress-induced neuroplasticity and yielding new insights into mood disorders. The image illustrates how the same stressor produces unique transcriptional profiles depending on the stress history of the mouse, highlighting how past experiences can alter cellular reactivity in certain dynamic brain regions.

Description: [1]  The properties of granular material have an important effect on surface landforms and processes. Recently it has been suggested that material properties called dynamic and static angle of repose vary with gravitational acceleration, which would have a significant effect on many planetary surface processes such as crater collapse and gully formation. In order to test that hypothesis we measured lee slopes of active aeolian sand dunes on Mars using HiRISE DTMs (Digital Terrain Model). We examined dune fields in Nili Patera, Herschel Crater and Gale Crater. Our measurements showed the dynamic angles of repose for the sands in these areas are 33-34° in the first region, and 30-31° in the other two. These results fall within the 30° to 35° window for the dynamic angles of repose for terrestrial dunes with similar flow depths and grain properties and thus show that this angle does not significantly vary with decreasing gravity.