The formation of gullies on Mars today

A decade of high-resolution monitoring has revealed extensive activity in fresh Martian gullies. Flows within the gullies are diverse: they can be relatively light, neutral or dark, colourful or bland, and range from superficial deposits to 10 m-scale topographic changes. We observed erosion and transport of material within gullies, new terraces, freshly eroded channel segments, migrating sinuous curves, channel abandonment, and lobate deposits. We also observed early stages of gully initiation, demonstrating that these processes are not merely modifying pre-existing land-forms. The timing of activity closely correlates with the presence of seasonal CO2 frost, so the current changes must be part of ongoing gully formation that is driven largely by its presence. We suggest that the cumulative effect of many flows erodes alcoves and channels, and builds lobate aprons, with no involvement of liquid water. Instead, flows may be fluidized by sublimation of entrained CO2 ice or other mechanisms. The frequent activity is likely to have erased any features dating from high-obliquity periods, so fresh gully geomorphology at middle and high latitudes is not evidence for past liquid water. CO2 ice-driven processes may have been important throughout Martian geological history and their deposits could exist in the rock record, perhaps resembling debris-flow sediments.Mars Data Analysis Program [NNH13AV85I]; Mars Reconnaissance Orbiter HiRISE project12 month embargo; published 27 November 2017This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

The NASA Roadmap to Ocean Worlds

In this article, we summarize the work of the NASA Outer Planets Assessment Group (OPAG) Roadmaps to Ocean Worlds (ROW) group. The aim of this group is to assemble the scientific framework that will guide the exploration of ocean worlds, and to identify and prioritize science objectives for ocean worlds over the next several decades. The overarching goal of an Ocean Worlds exploration program as defined by ROW is to identify ocean worlds, characterize their oceans, evaluate their habitability, search for life, and ultimately understand any life we find. The ROW team supports the creation of an exploration program that studies the full spectrum of ocean worlds, that is, not just the exploration of known ocean worlds such as Europa but candidate ocean worlds such as Triton as well. The ROW team finds that the confirmed ocean worlds Enceladus, Titan, and Europa are the highest priority bodies to target in the near term to address ROW goals. Triton is the highest priority candidate ocean world to target in the near term. A major finding of this study is that, to map out a coherent Ocean Worlds Program, significant input is required from studies here on Earth; rigorous Research and Analysis studies are called for to enable some future ocean worlds missions to be thoughtfully planned and undertaken. A second finding is that progress needs to be made in the area of collaborations between Earth ocean scientists and extraterrestrial ocean scientists

Modeling Aeolian Dune and Dune Field Evolution

sand hops and bounces -see the dunes grow, run, collide -form the field's pattern.Aeolian sand dune morphologies and sizes are strongly connected to the environmental context and physical processes active since dune formation. As such, the patterns and measurable features found within dunes and dune fields can be interpreted as records of environmental conditions. Using mathematical models of dune and dune field evolution, it should be possible to quantitatively predict dune field dynamics from current conditions or to determine past field conditions based on present-day observations.In this dissertation, we focus on the construction and quantitative analysis of a continuum dune evolution model. We then apply this model towards interpretation of the formative history of terrestrial and martian dunes and dune fields. Our first aim is to identify the controls for the characteristic lengthscales seen in patterned dune fields. Variations in sand flux, binary dune interactions, and topography are evaluated with respect to evolution of individual dunes. Through the use of both quantitative and qualitative multiscale models, these results are then extended to determine the role such processes may play in (de)stabilization of the dune field. We find that sand flux variations and topography generally destabilize dune fields, while dune collisions can yield more similarly-sized dunes. We construct and apply a phenomenological macroscale dune evolution model to then quantitatively demonstrate how dune collisions cause a dune field to evolve into a set of uniformly-sized dunes. Our second goal is to investigate the influence of reversing winds and polar processes in relation to dune slope and morphology. Using numerical experiments, we investigate possible causes of distinctive morphologies seen in Antarctic and martian polar dunes. Finally, we discuss possible model extensions and needed observations that will enable the inclusion of more realistic physical environments in the dune and dune field evolution models.By elucidating the qualitative and quantitative connections between environmental conditions, physical processes, and resultant dune and dune field morphologies, this research furthers our ability to interpret spacecraft images of dune fields, and to use present-day observations to improve our understanding of past terrestrial and martian environments

Modeling aeolian dune and dune field evolution

Aeolian sand dune morphologies and sizes are strongly connected to the environmental context and physical processes active since dune formation. As such, the patterns and measurable features found within dunes and dune fields can be interpreted as records of environmental conditions. Using mathematical models of dune and dune field evolution, it should be possible to quantitatively predict dune field dynamics from current conditions or to determine past field conditions based on present-day observations. In this dissertation, we focus on the construction and quantitative analysis of a continuum dune evolution model. We then apply this model towards interpretation of the formative history of terrestrial and martian dunes and dune fields. Our first aim is to identify the controls for the characteristic lengthscales seen in patterned dune fields. Variations in sand flux, binary dune interactions, and topography are evaluated with respect to evolution of individual dunes. Through the use of both quantitative and qualitative multiscale models, these results are then extended to determine the role such processes may play in (de)stabilization of the dune field. We find that sand flux variations and topography generally destabilize dune fields, while dune collisions can yield more similarly-sized dunes. We construct and apply a phenomenological macroscale dune evolution model to then quantitatively demonstrate how dune collisions cause a dune field to evolve into a set of uniformly-sized dunes. Our second goal is to investigate the influence of reversing winds and polar processes in relation to dune slope and morphology. Using numerical experiments, we investigate possible causes of distinctive morphologies seen in Antarctic and martian polar dunes. Finally, we discuss possible model extensions and needed observations that will enable the inclusion of more realistic physical environments in the dune and dune field evolution models. By elucidating the qualitative and quantitative connections between environmental conditions, physical processes, and resultant dune and dune field morphologies, this research furthers our ability to interpret spacecraft images of dune fields, and to use present-day observations to improve our understanding of past terrestrial and martian environments

Martian active gully studies and what they imply about present and recent surface processes

International audienc

Aeolian Processes and Landforms Across the Solar System: Science and Technology Requirements for the Next Decade

Aeolian processes and phenomena have sculpted landscapes and influenced planetary climate states across the Solar System, including planetary bodies with transient atmospheres. This white paper highlights the need for a planetary aeolian goals-and-objectives document that is inclusive of multiple planetary bodies, processes, and phenomen

Aeolian Processes and Landforms Across the Solar System: Science and Technology Requirements for the Next Decade

Aeolian processes and phenomena have sculpted landscapes and influenced planetary climate states across the Solar System, including planetary bodies with transient atmospheres. This white paper highlights the need for a planetary aeolian goals-and-objectives document that is inclusive of multiple planetary bodies, processes, and phenomen