Calibrating mars orbiter laser altimeter pulse widths at mars science laboratory candidate landing sites

Accurate estimates of surface roughness allow quantitative comparisons between planetary terrains. These comparisons enable us to improve our understanding of commonly occurring surface processes, and develop a more complete analysis of candidate landing and roving sites. A (secondary) science goal of the Mars Orbiter Laser Altimeter was to map surface roughness within the laser footprint using the backscatter pulse-widths of individual pulses, at finer scales than can be derived from the elevation profiles. On arrival at the surface, these pulses are thought to have diverged to between 70 and 170 m, corresponding to surface roughness estimates at 35 and 70 m baselines respectively; however, the true baseline and relationship remains unknown. This work compares the Mars Orbiter Laser Altimeter pulse-widths to surface roughness estimates at various baselines from high-resolution digital terrain models at the final four candidate landing sites of Mars Science Laboratory. The objective was to determine the true baseline at which surface roughness can be estimated, and the relationship between surface roughness and the pulse-widths, to improve the reliability of current global surface roughness estimates from pulse-width maps. The results seem to indicate that pulse-widths from individual shots are an unreliable indicator of surface roughness, and instead, the pulse-widths should be downsampled to indicate regional roughness, with the Slope-Corrected pulse-width dataset performing best. Where Rough Patches are spatially large compared to the footprint of the pulse, pulse-widths can be used as an indicator of surface roughness at baselines of 150 to 300 m; where these patches are spatially small, as observed at Mawrth Vallis, pulse-widths show no correlation to surface roughness. This suggests that a more complex relationship exists, with varying correlations observed, which appear dependent on the distribution of roughness across the sites

PLZF Controls the Expression of a Limited Number of Genes Essential for NKT Cell Function

Natural killer (NKT) T cells exhibit tissue distribution, surface phenotype, and functional responses that are strikingly different from those of conventional T cells. The transcription factor PLZF is responsible for most of these properties, as its ectopic expression in conventional T cells is sufficient to confer to them an NKT-like phenotype. The molecular program downstream of PLZF, however, is largely unexplored. Here we report that PLZF regulates the expression of a surprisingly small set of genes, many with known immune functions. This includes several established components of the NKT cell developmental program. Expression of the transcriptional regulators Id2, previously shown to be required for iNKT cell survival in the liver and c-Maf, which shapes the NKT cytokine profile, was compromised in PLZF-deficient cells. Ectopic expression of c-Maf complemented the cells’ defect in producing IL-4 and IL-10. PLZF also induced a program of cell surface receptors which shape the NKT cell’s response to external stimuli, including the costimulatory receptor ICOS and the cytokine receptors IL12rb1 and IL18r1. As an ensemble, the known functions of the molecules whose expression is affected by PLZF explain many defects observed in $PLZF^{−/−}$ NKT cells

Near-tropical subsurface ice on Mars

Near-surface perennial water ice on Mars has been previously inferred down to latitudes of about 45{\deg} and could result from either water vapor diffusion through the regolith under current conditions or previous ice ages precipitations. In this paper we show that at latitudes as low as 25{\deg} in the southern hemisphere buried water ice in the shallow (< 1 m) subsurface is required to explain the observed surface distribution of seasonal CO2 frost on pole facing slopes. This result shows that possible remnants of the last ice age, as well as water that will be needed for the future exploration of Mars, are accessible significantly closer to the equator than previously thought, where mild conditions for both robotic and human exploration lie

Global surface slopes and roughness of the Moon from the Lunar Orbiter Laser Altimeter

The acquisition of new global elevation data from the Lunar Orbiter Laser Altimeter, carried on the Lunar Reconnaissance Orbiter, permits quantification of the surface roughness properties of the Moon at unprecedented scales and resolution. We map lunar surface roughness using a range of parameters: median absolute slope, both directional (along-track) and bidirectional (in two dimensions); median differential slope; and Hurst exponent, over baselines ranging from ~17 m to ~2.7 km. We find that the lunar highlands and the mare plains show vastly different roughness properties, with subtler variations within mare and highlands. Most of the surface exhibits fractal-like behavior, with a single or two different Hurst exponents over the given baseline range; when a transition exists, it typically occurs near the 1 km baseline, indicating a significant characteristic spatial scale for competing surface processes. The Hurst exponent is high within the lunar highlands, with a median value of 0.95, and lower in the maria (with a median value of 0.76). The median differential slope is a powerful tool for discriminating between roughness units and is useful in characterizing, among other things, the ejecta surrounding large basins, particularly Orientale, as well as the ray systems surrounding young, Copernican-age craters. In addition, it allows a quantitative exploration on mare surfaces of the evolution of surface roughness with age

Cloud Formation and Water Transport on Mars after Major Outflow Events

The triggering of a robust water cycle on Mars might have been caused by the gigantic flooding events evidenced by outflow channels. We use the Ames Mars General Circulation Model (MGCM) to test this hypothesis, studying how these presumably abrupt eruptions of water might have affected the climate of Mars in the past. We model where the water ultimately went as part of a transient atmospheric water cycle, to answer questions including: (1) Can sudden introductions of large amounts of water on the Martian surface lead to a new equilibrated water cycle? (2) What are the roles of water vapor and water ice clouds to sudden changes in the water cycle on Mars? (3) How are radiative feedbacks involved with this? (4) What is the ultimate fate of the outflow water? (5) Can we tie certain geological features to outflow water redistributed by the atmosphere

T cell receptor–instructed αβ versus γδ lineage commitment revealed by single-cell analysis

αβ and γδ T cell lineages develop in the thymus from a common precursor. It is unclear at which stage of development commitment to these lineages takes place and in which way T cell receptor signaling contributes to the process. Recently, it was demonstrated that strong TCR signals favor γδ lineage development, whereas weaker TCR signals promote αβ lineage fate. Two models have been proposed to explain these results. The first model suggests that commitment occurs after TCR expression and TCR signaling directly instructs lymphocytes to adopt one or the other lineage fate. The second model suggests that commitment occurs before TCR expression and that TCR signaling merely confirms the lineage choice. By tracing the fate of single T cell precursors, this study shows that there is no commitment to either the αβ or γδ lineage before TCR expression and that modulation of TCR signaling in progeny of a single TCR-expressing cell changes lineage commitment

Water ice at low to midlatitudes on Mars

In this paper, we analyze water ice occurrences at the surface of Mars using near-infrared observations, and we study their distribution with a climate model. Latitudes between 45{\deg}S and 50{\deg}N are considered. Data from the Observatoire pour la Min\'eralogie, l'Eau, les Glaces et l'Actitit\'e and the Compact Reconnaissance Imaging Spectrometer for Mars are used to assess the presence of surface water ice as a function of location and season. A modeling approach combining the 1-D and 3-D versions of the General Circulation Model of the Laboratoire de M\'et\'eorologie Dynamique de Jussieu is developed and successfully compared to observations. Ice deposits 2-200 \mu m thick are observed during the day on pole facing slopes in local fall, winter and early spring. Ice extends down to 13{\deg} latitude in the Southern Hemisphere but is restricted to latitudes higher than 32{\deg} in the north. On a given slope, the pattern of ice observations at the surface is mainly controlled by the global variability of atmospheric water (precipitation and vapor), with local ground properties playing a lower role. Only seasonal surface ice is observed: no exposed patches of perennial ground ice have been detected. Surface seasonal ice is however sensitive to subsurface properties: the results presented in this study are consistent with the recent discovery of low latitude subsurface ice obtained through the analysis of CO2 frost

Negative selection, not receptor editing, is a physiological response of autoreactive thymocytes

Antigen receptor editing—a process of secondary rearrangements of antigen receptor genes in autoreactive lymphocytes—is a well-established tolerance mechanism in B cells, whereas its role in T cells remains controversial. Here, we investigated this issue using a novel Tcra knock-in locus, which ensured appropriate timing of TCRα expression and allowed secondary rearrangements. Under these conditions the only response to self-antigen that could be unambiguously identified was negative selection of CD4/CD8 double positive thymocytes. No evidence could be obtained for antigen-induced TCR editing, whereas replacement of the transgenic TCRα chain by ongoing gene rearrangement occurred in some cells irrespective of the presence or absence of self-antigen

Megafans as Hydrous Environments

The mesoscale sedimentary environment known as the megafan, is a low-angle, partial cone of fluvial sediment generated where a river enters an unconfined basin where it begins the process of avulsing over wide areas. In shifting to different positions, the river lays down a partial cone of sediment and establishes a characteristic radial pattern of paleo courses. The apparent paucity of sedimentary bodies obviously tied to martian outflow channels may also relate to the difficulty of recognition due to their sheer size and featurelessness. However, the existence of megafans on Mars is being examined now that their ubiquity and characteristics on Earth are better understood. Accordingly we suggest two likely candidates on Mars: Maja Valles fluvial cone and Amazonis Planitia fluvial sedimentary bodies. Two cryptic examples from Amazonis Planitia may be important for understanding subsurface hydrous accumulation. For at least some of its history, discharges from Mangala Valles likely resulted in megafans. Distances from the end of Mangala Valles to the northern (low) margin of the planitia are very large, a fact that has suggested that fluvial emplacement was unlikely. However, the megafan model shows that long megafan radii are indeed feasible. It has been suggested further that discharge from Labou Vallis (8.5S 154.5W) must have led to fluvial sedimentation in the planitia. We suggest that during locally non-lacustrine/ocean phases, this sedimentation would have occurred in the form of megafans. However, the megafan model shows that long megafan radii are indeed feasible. It has been suggested further that discharge from Labou Vallis (8.5S 154.5W) must have led to fluvial sedimentation in the planitia. We suggest that during locally non-lacustrine/ocean phases, this sedimentation would have occurred in the form of megafans. Megafans emanating from Marte, Mangala and Labou valles have probably contributed to hydrous near-subsurface environments--in their distal reaches, i.e. along the northern, eastern and southeastern margins of Amazonis Planitia at various times. Following a new terrestrial analog, we conclude groundwater has at times accumulated preferentially beneath distal slopes of the Maja Valles feature, and along the northern, eastern and southeastern margins of Amazonis Planitia

Mass wasting triggered by seasonal CO₂ sublimation under Martian atmospheric conditions: Laboratory experiments

Sublimation is a recognized process by which planetary landscapes can be modified. However, interpretation of whether sublimation is involved in downslope movements on Mars and other bodies is restricted by a lack of empirical data to constrain this mechanism of sediment transport and its influence on landform morphology. Here we present the first set of laboratory experiments under Martian atmospheric conditions which demonstrate that the sublimation of CO2 ice from within the sediment body can trigger failure of unconsolidated, regolith slopes and can measurably alter the landscape. Previous theoretical studies required CO2 slab ice for movements, but we find that only frost is required. Hence, sediment transport by CO2 sublimation could be more widely applicable (in space and time) on Mars than previously thought. This supports recent work suggesting CO2 sublimation could be responsible for recent modification in Martian gullies