Morphometric and Geomorphologic Mapping of Landforms in Gorgonum and Atlantis Basins, Mars
Mapping an extraterrestrial planet that has had a complex evolution remains a challenge for planetary scientists. Advance in imagery spatial resolution and DEM datasets availability make possible better representation of landforms in a GIS environment. Two main issues referring to the current geologic mapping procedures are debated here. First, the geologic mapping approach a priori assigned the Noachian boundaries to the small-scale processes (fluvial resurfacing, reduced-flux impact craters) that acted more recently, and did so without a clear justification. Second, the observed texture on higher resolution THEMIS imagery cannot be associated only with the Noachian (e.g. heavy meteoric bombardment) and Hesperian processes in the area of study, so as the resolution of observation increases, more recent erosional and depositional processes are visible. Morphometric mapping approach is to use DEM (digital elevation model) data to delineate erosional and depositional morphologies based on extraction of their relative elevation. Then, a geomorphologic map of Gorgonum and Atlantis basins has been compiled by identifying and correlating the landforms that present genetic linkages and similar morphometric and morphologic attributes. The geomorphologic map is compared with the USGS map, highlighting similarities and differences, as well as the implications thereof.
Detection and identification of ground ice types in periglacial environments: implication for Martian life
Near-subsurface hydrogen gamma-ray and neutron fluxes measured by gamma-ray spectrometer aboard Mars Odyssey combined with the recent findings by Phoenix Lander in the northern Martian plains and radar data from the Mars Reconnaissance Orbiter are highly indicative of the presence of thick bodies of massive ground ice in the permanently frozen Martian subsurface. These large ice bodies not only offer an in situ resource to support human exploration, but may also contain evidence of ancient life. On Earth, various geomorphological landforms in periglacial regions can be indicative of the presence of massive ground ice bodies. These landforms can be divided into two main categories: those associated with the aggradation of permafrost, which includes polygonal patterned ground and ice-cored mounds (palsa, pingo, lacolith); and those associated with the degradation of permafrost, which include thaw lakes, ice wedge thermokarst terrain and thaw slumps. These features, detectable by remote sensing techniques, provide initial insights into the type (pore, wedge, segregated, intrusive, glacial, snowbank, etc.) and amount of ground ice that may be preserved in the permafrost. In this study, the various types of ground ice associated with these landforms and approaches (i.e., ice crystallography, stable isotope geochemistry, gas composition) used to determine the nature and origin of the ground ice are discussed. Of the various techniques that can discriminate between ground ice formed by firn (snow) densification or freezing of liquid water, the gas composition of air entrapped in the ice can provide additional insights into physical and biological processes operating in the subsurface, a key component for astrobiology. Overall, this study should help to identify which region to prioritize as targets for future missions with the objective of finding ancient signature of life on Mars.
Testing the Snowpack Hypothesis for Gully Formation on Mars: Utilization of the Antarctic Dry Valleys (ADV) as a Terrestrial Analog
The identification of young gullies on Mars suggests that small amounts of liquid water has flowed across the martian surface during the recent climatic regime, which otherwise has been considered to have been cold and extremely dry. Research into the martian gullies suggest that water flow may have been sourced from the melting of surface/near-surface snow and ice deposits, concurrent with periods of higher obliquity. However, numerous questions remain regarding the origin of the water source, the volume and duration of flow, and the specific mechanisms of gully erosion. We undertook research into gully formation in the McMurdo Dry Valleys of Antarctica (ADV), a hyper-arid cold polar desert that is considered a close terrestrial analog to current Martian conditions. Our research identified two water sources in gully formation: 1) perennial snow/ice deposits within the gully alcoves and 2) annual accumulations of windblown snow trapped within the channels themselves. The melt produced by each source was found to be a function of the local microclimatic conditions, lithology, slope steepness, slope aspect (especially in relation to incident solar radiation), and elevation. Variation in seasonal and inter-annual gully activity was recorded. Of prime importance is the volume of snow accumulation at the onset of the austral summer. We classified and mapped a range of meso-scale features (m to 10s of m scale) within and adjacent to gullies that can be compared to landforms identifiable within ~25 cm/pixel HiRISE images of Mars; the latter help constrain gully formation processes and potential levels of recent activity on Mars. Our findings demonstrate that gully erosion can take place in an extremely dry region characterized by below freezing mean summer temperatures and low precipitation. On Mars, meltwater for gullies may have originated from a variety of ice-rich surficial deposits including: windblown snow deposits, the latitude dependant mantling units and near-surface ground ice. These results also underline the significance of snowmelt as a source of water for both ADV hydrological systems and ecosystems.
Estimating Ice Wedge Geometry Using Near Surface Geophysical Methods
Polygonal features on Axel Heiberg Island and Devon Island in the Canadian High Arctic have diverse appearances and occur in a variety of surface materials. These features can be used as analogues for potentially similar features on Mars, including the polygonal features at the Phoenix landing site. Just as at other locations on Earth, not all of the polygonal surface features studied on Devon Island contain subsurface ice, so it is important to understand how surface characteristics may be used as a way to remotely predict the presence or absence of ice below the surface. In order to compare surface morphologies with locations of subsurface ice over larger areas than would be possible by drilling or trenching, ground penetrating radar (GPR) and capacity-coupled resistivity (CCR) data were collected along transects over a variety of polygonal features at several locations on Axel Heiberg and Devon Islands. The polygonal features studied on Axel Heiberg Island formed in fine grained sediments near the base of Crusoe Glacier and at a location in Strand Fjord. GPR data collected at 200 MHz using the GSSI SIR-300 controller suggested the presence of ice wedges beneath polygonal troughs with various surface morphologies, and CCR data collected with a Geometrics system confirmed the ice presence. Together, GPR and CCR data were used to map the distribution of subsurface ice beneath ice wedge polygons and in bodies of ground ice within the interiors of some polygons. The polygons on Devon Island are located in a drier environment and have different morphologies than those on Axel Heiberg Island. These polygons were formed in fine sediments near Thomas Lee Inlet east of the Haughton impact crater and in cobbles near Lake Orbiter north of the crater. At both of these locations, GPR data collected at 200 MHz and 400 MHz and CCR data reveal the geometry of wedge-shaped ice bodies beneath most of the polygon troughs, which allows for correlation of ice wedge width to the overlying polygon trough width. At the Lake Orbiter location, the GPR data show stratigraphy of several deposits that could indicate different episodes of glacial deposition. In fact, the GPR and CCR data suggest that ice wedges formed in a stratigraphically older layer that was later buried by a younger deposit. As the top of the permafrost moved upward into this younger deposit, a new ice wedge developed above the original. Investigations at this level of detail show the utility of using GPR and CCR together to reveal the spatial distribution of ground ice associated with surface polygons and other features that could indicate ground ice. Although the Phoenix lander discovered ice by trenching, it is unclear if and how that ice is related to the surface polygons. To fully understand whether a location on Mars (or another planetary body) has a significant amount of ice accessible from the surface, it will be necessary to deploy rover-mounted geophysical instruments to map the ice distribution. As part of developing those instruments, it is necessary to use terrestrial analogue environments such as those in the Canadian Arctic to improve the techniques required to interpret geophysical data of ground ice deposits.
Comparison of a Possible Ice-Rich Unit in the Hellas Basin with a Periglacial Landscape in Utopia Planitia, Northern Plains of Mars
As part of an ongoing study of periglacial processes in the northern plains of Mars, Soare et al.  characterized the morphology and distribution of thermokarst-like depressions, polygonal terrain, and crater- rim gullies in Utopia and western Elysium Planitiae (80-120° E, 40-55° N). These authors proposed a model for the formation of this landscape beginning with the late-Amazonian (<10 Myr) deposition of ice-rich materials caused by shifts in the obliquity of Mars' spin axis and followed by the initiation of periglacial processes as obliquity and surface temperatures reached their maxima. Extending this study to the southern hemisphere, we identify a region in the south-eastern region of the Hellas basin that features scalloped depressions (<20 m deep) and polygonal ground analogous to the possible periglacial features in Utopia and Elysium Planitiae. Although they contain landforms of similar morphology, there are several important differences between these landscapes: the Hellas unit covers a smaller area (~56-60° S, 62- 76° E) and is thinner than the Utopia unit; the Hellas unit occurs at higher latitudes, and; the Utopia unit contains features that are absent from the Hellas unit that are consistent with the late-Amazonian presence of liquid water . As both the origin of the ice-rich mantle and the initiation of periglacial processes in the Utopia unit have been linked with climatic processes [2,3], morphological differences between the features characterizing the Utopia and Hellas units are best explained by different climatic conditions. Based on a comparison between the Martian units and terrestrial perglacial landscapes, we suggest that the Hellas unit is consistent with dry (i.e., sublimation-based) periglacial activity (predominately thermokarst formation) whereas the Utopia unit is consistent with some degree of wet-based periglacial activity (i.e., melting and evaporation) as well as sublimation-related processes. Together, the Hellas and Utopia units are consistent with the late- Amazonian equator-ward migration of polar volatiles in both hemispheres and a climatic gradient leading to both wet and dry-based periglacial activity. Refs:  Soare et al. (2008), Thermokarst lakes and ponds on Mars in the very recent (late Amazonian) past, EPSL, V. 272, I. 1-2, p. 382-393.  Morgenstern, et al. (2007), Deposition and degradation of a volatile-rich layer in Utopia Planitia and implications for climate history on Mars, J. Geophys. Res., 112, E06010.  Boyce et al. (2003), Evidence for a thick mantle of volatile-rich materials in the Utopia basin, Mars, based on crater depth/diameter measurements, LPSC XXXIV, abstract 1967.