Exploring Gusev Crater with spirit: Review of science objectives and testable hypotheses

Gusev Crater was selected as the landing site for the Mars Exploration Rover (MER) Spirit mission. Located at the outlet of Ma'adim Vallis and 250 km south of the volcano Apollinaris Patera, Gusev is an outstanding site to achieve the goals of the MER mission. The crater could have collected sediments from a variety of sources during its 3.9 Ga history, including fluvial, lacustrine, volcanic, glacial, impact, regional and local aeolian, and global air falls. It is a unique site to investigate the past history of water on Mars, climate and geological changes, and the potential habitability of the planet, which are central science objectives of the MER mission. Because of its complex history and potential diversity, Gusev will allow the testing of a large spectrum of hypotheses with the complete suite of MER instruments. Evidence consistent with long-lived lake episodes exist in the landing ellipse area. They might offer a unique opportunity to study, for the first time, Martian aqueous sediments and minerals formed in situ in their geological context. We review the geological history and diversity of the landing site, the science hypotheses that can be tested during the MER mission, and the relevance of Gusev to the MER mission objectives and payload

Discrete Element Modeling of the Grading- and Shape-Dependent Behavior of Granular Materials

Granular materials, such as sand, biomass particles, and pharmaceutical pills, are widespread in nature, industrial systems, and our daily life. Fundamentally, the bulk mechanical behavior of such materials is governed by the physical and morphological features of and the interactions among constituent particles at the microscopic scale. From a modeling standpoint, the particle-based discrete element method (DEM) has emerged as the most prevalent numerical tool to model and study the behavior of granular materials and the systems they form. A critical step towards an accurate and predictive DEM model is to incorporate those physical and morphological features (e.g., particle size, shape, and deformability) pertaining to the constituent particles. The main objective of this dissertation is to approach an accurate characterization and modeling of the grading- and shape-dependent behavior of granular materials by developing DEM models that incorporate realistic physical and morphological features of granular particles. Revolving around this objective, three studies are presented: image-based particle reconstruction and morphology characterization, grading and shape-dependent shearing behavior of rigid-particle systems, and granular flow of deformable irregular particles. The first study presents a machine learning and level-set based framework to re- construct granular particles and to characterize particle morphology from X-ray computed tomography (X-ray CT) imaging of realistic granular materials. Images containing detailed microstructure information of a granular material are obtained using the X-ray CT tech- nique. Approaches such as the watershed method in two dimensions (2D) and the combined machine learning and level set method in three dimensions (3D) are then utilized and implemented to segment X-ray CT images and to numerically reconstruct individual particles in the granular material. Based on the realistic particle shapes, particle morphology is characterized by descriptors including aspect ratio, roundness, circularity (2D) or sphericity (3D). The particle shapes or morphology provide important constraints to develop DEM models with particle physical and morphological features conforming to the specific granular material of interest. In the second study, DEM models incorporated with realistic particle sizes and shapes are developed and applied to study the shearing behavior of sandy soils. The particle sizes and shapes are obtained from realistic samples of JSC-1A Martian regolith simulant. Irregular-shape particles are represented by rigid clumps based on the domain overlapping filling method. The effects of particle shape irregularity on the shearing behavior of granular materials are investigated through direct shear tests, along with the comparisons from spherical particles with or without rolling resistance. The micro-mechanisms of shape irregularity contributing to the shear resistance are identified. The last study investigates the effects of particle deformability (e.g., compression, deflection or torsion), together with particle sizes and shapes, on the granular flow of flexible granular materials. A bonded-sphere DEM model is implemented with the capability of embodying various particle sizes and irregular shapes, as well as capturing particle deformability. This approach is then applied to simulate and study the behavior of flexible granular materials in cyclic compression and hopper flow tests. The effects of particle size, shape and deformability on the bulk mechanical behavior are investigated on the basis of the DEM simulation results. The importance of particle deformability to the DEM simulations of flexible granular materials is demonstrated

Trajectories of land surface evolution in polygonal tundra

In the past three decades, an abrupt acceleration in the thaw of ice wedges has spurred rapid surface deformation (i.e., thermokarst) in polygonal tundra landscapes spanning the Arctic. The ensuing conversion of low-centered polygons (LCPs) and flat terrain into high-centered polygons (HCPs) has profound impacts on regional hydrology and carbon fluxes between the soil and atmosphere. However, pathways of ice wedge degradation and the stability of the deformed terrain are uncertain, complicating efforts to project feedbacks on global climate change. In this dissertation, I explore trajectories of surface deformation in ice wedge polygons, using a combination of calibration-constrained numerical experiments, remote sensing, and machine learning. In the first two chapters, numerical simulations of the soil hydrologic and thermal regimes reveal that, relative to terrain unaffected by thermokarst, the permafrost beneath HCPs tends to be well-buffered against climate extremes, promoting landscape stability. Ice wedges at HCP boundaries are less vulnerable to thaw during warm summers, reinforcing prior field-based observations that thermokarst is typically a self-arresting process. Simultaneously, the cooling of thermokarst-affected ice wedges in winter tends to be inhibited by snow accumulation in degraded troughs, reducing the likelihood of renewed ice wedge cracking and restoration of LCP microtopography. Overall, these results indicate that the microtopography of polygons already affected by thermokarst will likely remain stable over the next century. In the second half of this dissertation, a novel machine-learning-based tool is introduced for delineating and measuring the microtopography associated with ice wedge polygons in high-resolution digital elevation models. The tool is used to map polygonal geomorphology across ~1,000 km² of tundra south of Prudhoe Bay, Alaska, visualizing in unprecedented detail the heterogeneous extent to which thermokarst has affected a modern polygonal landscape. This map of polygonal geomorphology provides useful context for upscaling point- to plot-scale observations of gas exchange in ice wedge polygons to landscape-scale estimates of carbon fluxes. It also provides an extensive baseline dataset for quantifying contemporary rates of land surface deformation, through future surveys at the site.Geological Science

The deposition and alteration history of the northeast Syrtis Major layered sulfates

Ancient stratigraphy on Isidis Basin's western margin records the history of water on early Mars. Noachian units are overlain by layered, basaltic composition sedimentary rocks that are enriched in polyhydrated sulfates and capped by more resistant units. The layered sulfates—uniquely exposed at northeast Syrtis Major—comprise a sedimentary sequence up to 600 m thick that has undergone a multistage history of deposition, alteration, and erosion. Siliciclastic sediments enriched in polyhydrated sulfates are bedded at meter scale and were deposited on slopes up to 10°, embaying and thinning against preexisting Noachian highlands around the Isidis Basin rim. The layered sulfates were modified by volume loss fracturing during diagenesis. Resultant fractures hosted channelized flow and jarosite mineral precipitation to form resistant ridges upon erosion. The structural form of the layered sulfates is consistent with packages of sediment fallen from either atmospheric or aqueous suspension; coupling with substantial diagenetic volume loss may favor deepwater basin sedimentation. After formation, the layered sulfates were capped by a “smooth capping unit” and then eroded to form paleovalleys. Hesperian Syrtis Major lavas were channelized by this paleotopography, capping it in some places and filling it in others. Later fluvial features and phyllosilicate‐bearing lacustrine deposits, sharing a regional base level of ∼−2,300 m, were superimposed on the sulfate‐lava stratigraphy. The layered sulfates suggest surface bodies of water and active groundwater upwelling during the Noachian‐Hesperian transition. The northeast Syrtis Major stratigraphy records at least four distinct phases of surface and subsurface aqueous activity spanning from late Noachian to early Amazonian time

First Landing Site/Exploration Zone Workshop for Human Mission to the Surface of Mars : October 27–30, 2015, Houston, Texas

The purpose of this workshop is to identify and discuss candidate locations where humans could land, live, and work on the martian surface.Organizer, Lunar and Planetary Institute, Universities Space Research Association, National Aeronautics and Space Administration ; Co-Chairs, Human Landing Sites Study Steering Committee, Benjamin Bussey, National Aeronautics and Space Administration, Richard Davis, National Aeronautics and Space Administratio

Reports of planetary geology program, 1977-1978

A compilation of abstracts of reports which summarizes work conducted by Planetary Geology Principal Investigators and their associates is presented. Full reports of these abstracts were presented to the annual meeting of Planetary Geology Principal Investigators and their associates at the Universtiy of Arizona, Tucson, Arizona, May 31, June 1 and 2, 1978

Characterization of Impactite Clay Minerals with Implications for Mars Geologic Context and Mars Sample Return

Geological processes, including impact cratering, are fundamental throughout rocky bodies in the solar system. Studies of terrestrial impact structures, like the Ries impact structure, Germany, have informed on impact cratering processes – e.g., early hot, hydrous degassing, autometamorphism, and recrystallization/devitrification of impact glass – and products – e.g., impact melt rocks and breccias comprised of clay minerals. Yet, clay minerals of authigenic impact origin remain understudied and their formation processes poorly-understood. This thesis details the characterization of impact-generated clay minerals at Ries, showing that compositionally diverse, abundant Al/Fe/Mg smectite clays formed through these processes in thin melt-bearing breccia deposits of the ejecta, as well as at depth. The inherent complexity of smectites – their formation, type, structure, and composition – makes their provenance difficult to discern; these factors may explain why impact-generated and altered materials, which comprise an appreciable volume and extent of Mars’ ancient Noachian crust, are not generally recognized as a source of the enigmatic clays that are ubiquitous in those regions. Clay minerals can provide a defining window into a planet’s geologic and climatic past as an indicator of water availability and geochemistry; the presence of clay minerals on Mars has been used to support the hypothesis of climatically “warm, wet” ancient conditions. Yet, climate modeling of Early Mars suggests that the likely nature of the climate was not conducive to long-term aqueous activity. We suggest that the omission of impact-generated materials in current models of Mars clay mineral formation leaves a fundamental gap in our understanding of Noachian crustal materials – materials that were continually recycled and completely transformed on a global scale over millennia on Mars. The opportunity to investigate clay-bearing impactites and strata-bound clay minerals will be presented to the upcoming NASA Mars 2020 and ESA ExoMars rovers; this thesis offers caution in assigning clay mineral provenance until samples are returned to Earth from these missions. We furthermore suggest a methodological approach to augment current rover-based exploration frameworks to characterize potential impact-origin. Discerning clay species and provenance – and acknowledging the implications of that provenance – is central to understanding the geologic context of Mars, and thus its past climatic conditions and habitability potential

Spatial variability of aircraft-measured surface energy fluxes in permafrost landscapes

Arctic ecosystems are undergoing a very rapid change due to global warming and their response to climate change has important implications for the global energy budget. Therefore, it is crucial to understand how energy fluxes in the Arctic will respond to any changes in climate related parameters. However, attribution of these responses is challenging because measured fluxes are the sum of multiple processes that respond differently to environmental factors. Here, we present the potential of environmental response functions for quantitatively linking energy flux observations over high latitude permafrost wetlands to environmental drivers in the flux footprints. We used the research aircraft POLAR 5 equipped with a turbulence probe and fast temperature and humidity sensors to measure turbulent energy fluxes along flight tracks across the Alaskan North Slope with the aim to extrapolate the airborne eddy covariance flux measurements from their specific footprint to the entire North Slope. After thorough data pre-processing, wavelet transforms are used to improve spatial discretization of flux observations in order to relate them to biophysically relevant surface properties in the flux footprint. Boosted regression trees are then employed to extract and quantify the functional relationships between the energy fluxes and environmental drivers. Finally, the resulting environmental response functions are used to extrapolate the sensible heat and water vapor exchange over spatio-temporally explicit grids of the Alaskan North Slope. Additionally, simulations from the Weather Research and Forecasting (WRF) model were used to explore the dynamics of the atmospheric boundary layer and to examine results of our extrapolation

Geo-Spatial Analysis in Hydrology

Geo-spatial analysis has become an essential component of hydrological studies to process and examine geo-spatial data such as hydrological variables (e.g., precipitation and discharge) and basin characteristics (e.g., DEM and land use land cover). The advancement of the data acquisition technique helps accumulate geo-spatial data with more extensive spatial coverage than traditional in-situ observations. The development of geo-spatial analytic methods is beneficial for the processing and analysis of multi-source data in a more efficient and reliable way for a variety of research and practical issues in hydrology. This book is a collection of the articles of a published Special Issue Geo-Spatial Analysis in Hydrology in the journal ISPRS International Journal of Geo-Information. The topics of the articles range from the improvement of geo-spatial analytic methods to the applications of geo-spatial analysis in emerging hydrological issues. The results of these articles show that traditional hydrological/hydraulic models coupled with geo-spatial techniques are a way to make streamflow simulations more efficient and reliable for flood-related decision making. Geo-spatial analysis based on more advanced methods and data is a reliable resolution to obtain high-resolution information for hydrological studies at fine spatial scale

MSATT: Mars Surface and Atmosphere Through Time

The papers published here are based on a workshop entitled "Mars: Past, Present, and Future: Results from the MSATT Program." MSATT (Mars Surface and Atmosphere Through Time) was the last of the Mars data analysis programs and functioned mainly through a series of focused workshops, the final one being held at the Lunar and Planetary Institute in Houston, Texas on November 15-17, 1993. The program began and ended with workshops that brought the entire MSATT community together. Here you will find papers that address the geology, mineralogy, and meteorology of Mars in an effort to assess how the surface and atmosphere of this fascinating planet have evolved over time. Could early Mars have been warmed by a brighter young sun instead of a massive greenhouse effect? Were glaciers and hydrological cycles part of Mars' relatively recent past, or was aeolian activity responsible for the putative glacial features? Do the SNCs come from a single source region, or is more than one site involved? And what really are the properties of Martian soils and what do they tell us about the weathering environment? Clearly, these are difficult questions, but progress toward answers can be found in this issue. Also contained in this issue are a mix of theoretical and observational papers that deal with the general circulation of the current atmosphere, the factors that drive it (dust properties), and the role it plays in controlling the current climate system