Polar Processes in the Antarctic Dry Valleys and Insights to Understanding Mars
The recognition of groups of climate-related landforms has led to the definition of well known morphogenetic regions on Earth, each defined in terms of mean annual temperature and precipitation. A byproduct of this classification scheme is the recognition of specific equilibrium landforms, i.e., those geomorphic features that are produced in equilibrium with prevailing climate conditions. The Antarctic Dry Valleys (ADV), one of the most Mars-like regions on Earth, can be subdivided into three microclimate zones: a coastal thaw zone, an inland mixed zone, and a stable upland zone; zones are defined on the basis of summertime measurements of atmospheric temperature, soil moisture, and relative humidity. The areal distribution of each zone has been maintained over million-year time scales. Subtle variations in climate parameters across each zone result in considerable differences in the distribution and morphology of: 1) macroscale features (e.g., slopes and gullies); 2) mesoscale features (e.g., polygons, including ice-wedge, sand-wedge, and sublimation-type polygons, as well as viscous-flow features, including solifluction lobes, gelifluction lobes, and debris-covered glaciers); and 3) microscale features (e.g., rock-weathering processes/features, including salt weathering, wind erosion, and surface pitting). At each scale, the ADV landforms resemble closely several Martian counterparts observed in Viking and Odyssey-scale imagery (macroscale), MGS MOC and MRO HiRise image data (mesoscale), and Viking Lander-Pathfinder-Phoenix scale-image data (microscale). Some equilibrium landforms of the ADV, such as sublimation polygons, indicate the presence of extensive near-surface ice, and the identification of similar landforms on Mars may also provide a basis for detecting the location of shallow ice there. The extreme hyper-aridity of both Mars and the ADV has focused attention on the importance of salts and brines on soil development, phase transitions from liquid water to water ice, and ultimately, on process geomorphology and landscape evolution at a range of scales. Understanding the role of ADV salts in creating duricrusts and subsurface salt-cemented horizons may shed light on the effectiveness of Martian salts in altering the rate and style of landscape evolution, in modulating the influx and outflux of vapor in Martian soils, and in assessing the distribution and longevity (including capability to produce geomorphic landforms) of near- surface water in very specific locales on the Martian surface.
A Comparison Between the High-Altitude Dry Valleys of Antarctica and the Phoenix Landing Site on Mars
Introduction: As part of the International Polar Year, a project was organized to study the Antarctic Dry Valley
(ADV) soils and ice in support of the Phoenix Mission to the Martian arctic. Mars is drier and colder than any
Antarctic location in the current epoch, but does undergo radical variations in its climate as the obliquity and
eccentricity of its orbit changes (Laskar et al, 2004). Therefore, knowledge of the analog environments on the
Earth may aid in interpreting the Martian conditions over time. The Phoenix mission was proposed to
investigate the ice discovered by the Odyssey instruments and landed inside the arctic circle at 68 deg latitude.
The goals of the mission are described by Smith et al. (2008). Sample collection and analysis: Fourteen pits
were dug at twelve different sites from near sea level at Lake Fryxell in Taylor Valley, a wet environment during
summer months, to University Valley near 1700 m where temperatures rarely exceed the melting point. These
samples were collected and frozen using sterile procedures so that contamination would not be an issue. The
samples are now being analyzed for their mineral, chemical, microscopic and biological properties. In
particular, analysis by instruments similar to those carried by the Phoenix mission is paramount for comparing
with Martian results. Besides the Phoenix-type instruments, a full suite of laboratory instrumentation is also
used to determine the complete range of properties outside those obtainable by Phoenix. Interpretation: At
University Valley, the valley walls are composed of dolorite and sandstone (Marchant and Head, 2007). The
sandstone is known to contain endoliths and sheds these layers into the valley so that the expectation is that
the surface layers of the soil should have a higher organic content than the underlying soil. On Mars we are
finding a Ca-carbonate controlled soil with a Ph of about 8 that contains a small amount of salt and about 2%
perchlorate. Perchlorate is known on Earth to provide energy for a variety of microbes through a redox couple
with various partners. But Mars would not be inhabitable now because the water activity level is very low and
temperatures are too cold. However, over the last few millions years the obliquity has exceeded 30ç numerous
times, at tilts beyond this tipping point the ice cap is no longer stable and conditions become much wetter and
warmer. This may be a period when the carbonates are created with CO2 dissolving in thin films of liquid water
and creating a weak acid that leaches Ca from the volcanic soil. In the upper ADV, the ice is kept near a
temperature of -10çC yet the water activity is near 0.9 and the water vapor pressure may be enough to support
a small community of microbes. Water is only available in thin films and various salts are available. The
detailed analysis of these soils will be reported on at the conference and compared with the soils of the
Martian arctic. References: J. A. Laskar et al. (2004) Icarus 170, 343-364. D. R. Marchant and J. W. Head III
(2007) Icarus 192, 187-222. P. H. Smith et al. (2008) J. Geophys. Res. 113, Doi:10.1029/2008JE003089.
Antarctic Analogs to Lobate Debris Aprons and Lineated Valley Fill on Mars: Insights Into Processes of Formation and Evolution
Lobate debris aprons (LDA) and lineated valley fill (LVF) have been known to characterize the mid-latitude regions of Mars since initially documented in Viking images; their flow-like character suggested that deposition of ice in pore-spaces within talus caused lubrication and flow during an earlier climatic regime. Uncertain has been the detailed structure and texture of LDA/LVF, the relationships between them, their direction of flow, the origin and abundance of the lubricating agent, and their exact mode of origin (e.g., ice-assisted rock creep, ice- rich landslides, rock glaciers, debris-covered glaciers). We use new insights provided by cold-based terrestrial glacial analogs in the Mars-like Antarctic Dry Valleys to show that debris-covered glaciers offer a compelling analog for lobate debris aprons on Mars. We analyze new High-Resolution Stereo Camera (HRSC) images and topography data for Mars, in conjunction with a range of other post-Viking data sets, to assess the characteristics of LDA/LVF in the northern mid-latitudes of Mars. We find evidence that the characteristics and flow patterns of the LDA and LVF are most consistent with Late Amazonian debris-covered glacial valley landsystems. The broad distribution and integrated characteristics of the LDA/LVF systems suggest that earlier in the Amazonian, climatic conditions were such that significant snow and ice accumulated on mid- latitude plateaus and in valleys, producing integrated glacial landsystems, the remnants of which are preserved today beneath residual sublimation tills derived from adjacent valley walls. Atmospheric general circulation models suggest that these climatic conditions occurred when Mars was at a spin-axis obliquity of ~35°, and the atmosphere was relatively dusty. Glacial flow modeling under these conditions produces patterns similar to those documented in the LDA/LVF, and SHARAD radar data suggests that significant amounts of ice remain sequestered below the sublimation lag today. These hypotheses are being tested with MRO SHARAD (SHallow RADar) data and significant quantities of buried ice are being found. We describe further ongoing detailed studies of the terrestrial debris-covered glacial analog as a basis for a more detailed understanding of the features on Mars.
A Perchlorate Brine Lubricated Deformable Bed Could Facilitate Flow of the North Polar Cap of Mars: Possible Mechanism for Water Table Recharge
The discovery of substantial amounts of magnesium and/or calcium perchlorate hydrate by Phoenix' "Wet Chemistry Lab" (WCL) (Hecht et al., 2009) in the soil of Polar Mars opens some unexpected doors for moving liquid water around at temperatures as low as -68C. In its fully hydrated form with 8 water molecules attached to each magnesium perchlorate, the salt water mixture has a high density (~ 1980 kgm /cubic meter)(Besley and Bottomley,1969) and a freezing point of - 69 C (Pestova et al., 2005). This perchlorate is very deliquescent and gives off heat as it melts ice. About 1.7 gram of ice can be 'melted' by 1 gm of pure magnesium perchlorate (Besley and Bottomley , 1969). If the 1% perchlorate is typical of polar soils and if 5% of the Northern Permanent Ice Cap is soil then the perchorate, makes up about 1/2000 the of the ice cap. Given the average thickness of the ice cap is about 2000 meters this suggests there enough perchorate in the ice cap to generate about 2m of salty water at the bed. Because of its density the perclorate salty water would pool and make the bed into a perchorate sludge that could be mobilized and deformed by the overburden of ice. The deformation of mobile beds is a well known phenomenon on some terrestrial glaciers presently and was thought to have played a major role during the Wisconsinan ice age . The perchorate sludge would be deformed and moved outwards possibly resulting its reintroduction to the periglacial environment for re-use. Having a deliquescent basal salt sludge, whose melting point is -69 C would mean that the ice cap could slide on its deformable bed, while the ice itself was still very cold and stiff . This possibility has been modeled with a 2D time varying model . The model preserves the scarp/trough features and allows flow. The model isochrones resemble better those found by SHARAD. The ice cap has long been thought of as a possible re- charge area for the deep water return flow (Clifford, 1987), but the low basal temperatures even under the deepest part of the cap seemed to preclude liquid water. But there could be brine at the bed. The model suggests that most of the time there would be a peripheral frozen basal ring under the cap and that basal brines might thus be dammed and accumulate at the bed analogous to the subglacial lakes under Antarctic. The freezing isotherm for liquid water return flow to the hypothetical ground water system is then raised from ~0 to -69 C. M.H. Hecht, S. P. Kounaves, R. C. Quinn, S. J. West, S. M. M Young, D. W. Ming, D.C. Catling, B. C. Clark, P. H. Smith. Invited and submitted 2009. Detection of perchlorate and the soluble chemistry of martian soil: Findings from the Phoenix Mars Lander. Science. Pestova O. N.,Myund L.A.,Khripun M.K. and A.V. Prigaro. 2005. Polythermal study of systems M(ClO4)2-H2O (M2+=Mg2+, Ca2+, Sr2+, Ba2+). Russian Journal of Applied Chemistry , Vol.78.No.3,pp409- 413. Clifford S.M. 1987. Polar basal melting on Mars. JGR. Vol 92,No. B9. pp9135-9152. Besley L. M. and G.A. Bottomley. 1969. The water vapour equilibria over magnesium perchlorate hydrates. Journal of Chemical Thermodynamics. 1, pp13-19.
A Revised Stratigraphical Ordering of Glacial and Periglacial Processes in Utopia Planitia, Mars
Recent modeling of Martian meteorological conditions during and following times of high obliquity suggests that an icy mantle could have been emplaced in western Utopia Planitia by atmospheric deposition during the late Amazonian period. Astapus Colles (ABa) is a late Amazonian geological unit (Tanaka et al. 2005) - located in this hypothesised area of accumulation - that comprises an icy mantle tens of metres thick. For the most part, this unit drapes three desiccated geological units: 1. the early Amazonian Vastitas Borealis interior unit (ABvi); 2. to a lesser degree, the early Amazonian Vastitas Borealis marginal unit (ABvm); and, 3. the early to late Hesperian Utopia Planitia plains unit (HBu2). Numerous landforms whose morphology, size and geological characteristics are consistent with formation by glacial (gp) and periglacial processes (pp) have been identified in the region, i.e. concentric and geometrically undifferentiated crater-fill (gp), lobate crater-wall flows (gp), intra-crater (sub-kilometre) stratified mounds (gp), scalloped terrains (pp), small-sized polygonal patterned-ground (pp) and polygon-junction pits (pp). Most researchers have assumed that these landforms, despite being the products of disparate formation processes, occur within the same geological unit, the ABa. We use HiRISE (High Resolution Image Science Experiment, Mars Reconnaissance Orbiter) imagery to identify the stratigraphical separation of the two landscape types and show that periglacial landscape development has occurred in the geological units that underlie and predate the ABa, not in the ABa itself (Soare et al. 2009). Moreover, mapping of the periglacial landscape suggests that the landscape extends well beyond the perimeter of the ABa and could be the result of "wet" cold-climate processes. These processes involve intermittently stable liquid-water at or near the surface, saturation of the near-surface regolith and numerous freeze-thaw cycles. We also propose that these processes modified the near-surface regional regolith to tens of metres of depth, significantly enough to warrant the identification of this horizon as a separate and heretofore unidentified pre-glacial and "wet" geological unit. The ABa overlies this unit, is relatively youthful (perhaps having formed in conjunction with the most recent periods of high obliquity) and was formed principally by "dry" cold-climate processes. These processes comprise accumulation (by atmospheric deposition) and ablation (by sublimation).
Periglacial and Glacial Modification of Impact Ejecta Deposits in Utopia Planitia
In this study, we explore the relationship between impact crater ejecta morphologies and target properties in the middle latitudes of Utopia Planitia using Mars Orbiter Camera (MOC), Thermal Emission Imaging System (THEMIS), and High Resolution Imaging Science Experiment (HiRISE) imagery. This study forms part of a larger ongoing collaborative investigation of impact and periglacial landforms in Utopia Planitia . Our investigations show that many craters in this region possess a unit with a characteristic smooth texture, typically present around the rim. At first glance this unit may appear to be a second or third layer of ejecta, which would lead to the classification of a crater as a double or multiple layered ejecta structure . However, in several instances, cross-cutting relationships with the grooved ballistic ejecta and the presence of polygons and thermokarst depressions - interpreted elsewhere in the northern plains as indicative of ground ice - indicate that this unit is actually an ice-rich mantle. These structures can, therefore, be classified as single layered ejecta structures with an ice-rich mantle superposed on the ejecta blanket. At several sites, we have also observed glacier-like flow lobes on the perimeter of ejecta blankets. Thus, great care should be taken when making regional or global interpretations of large datasets without attention to the geomorphology of individual craters. This also has implications for estimating ejecta thickness and volume based on MOLA data. Refs:  Soare R. J. et al. 2008. Thermokarst lakes and ponds on Mars in the very recent (late Amazonian) past, EPSL, 272, 382-393.  Barlow N. G. et al. 2000. Standardizing the nomenclature of Martian impact crater ejecta morphologies. JGR, 105, 26733-26738.
Thermal contraction crack polygons on Earth and Mars: Classification, Distribution, and Implications for Recent Cold Desert Processes
The Antarctic Dry Valleys provide a unique natural laboratory in which to study thermal contraction crack polygons forming under a range of cold desert temperature, soil moisture, and ice stability conditions. Past work has shown that morphological variation in polygon form can serve as an indicator of varying concentrations of subsurface ice and microclimate conditions. Applying a similar scientific approach to martian polygons, we here describe polygon morphology using HiRISE image data and assess the potential role and thermal state of liquid water/ice in the development of small-scale (<25 m diameter) thermal contraction crack polygons. Thermal contraction crack polygons are shown to be ubiquitous in the martian latitude- dependent mantle. The distribution of polygon morphological groups is found to be broadly zonal, and to be approximately symmetrical in both the northern and southern hemispheres, suggesting climatic controls on morphology (similar to microclimate controls on polygon morphology observed on Earth). The preponderance of high-centered polygons, morphologically similar to terrestrial sublimation polygons, strongly argues for near-surface ice exceeding available pore space in martian polygonally-patterned surfaces. Complex polygons with both high and low center morphologies are interpreted to indicate an advanced state of modification by differential sublimation, consistent with recent climate conditions favoring net ice loss over accumulation. All observed polygon morphological classes, with the exception of gully-polygon systems can form from processes that do not require the presence of liquid water (e.g., thermal contraction cracking and differential sublimation), suggesting that ice-wedge polygons may be extremely rare on Mars. Polygons in the northern hemisphere are found to follow a correlation between latitude and age: equatorward polygons are the oldest (1.3 My) and transition to younger (50-100 ky) high-latitude polygons, suggesting that the recent martian hydrological cycle has been dominated by solid-vapor phase transitions and not by widespread thermokarst formation.
Morphological Variation of Polygonal Terrain Within Scalloped Depressions, Utopia Planitia, Mars
A variety of landforms observed in the Utopia Planitia region of Mars suggests the existence of water ice in the shallow subsurface. Two landforms in particular are particularly suggestive of ground ice processes in the region: (i) 'polygonal terrain', interconnected troughs in the ground often associated with the presence of subsurface ice deposits on both Earth and Mars, and; (ii) 'scalloped terrain', landscape depressions thought to be caused by surface deflation resulting from ice loss through sublimation. The appearance of the polygonal terrain networks found in and near scalloped terrain can vary greatly. For example, a variety of previous studies have noted that polygons within the scallops tend to be smaller and differently shaped than those on the upper surrounding plains. However, an objective numerical classification of these polygonal networks has yet to be developed. Through the use of statistical analysis, categories of polygonal networks can be identified and grouped according to their overall network geometries. The primary goal of this work was to develop such a classification scheme for polygonal terrain found in conjunction with scalloped depressions. Specifically, the objectives were to: (i) apply a particular analytical method (Spatial Point Pattern Analysis: 'SPPA') to develop categories of polygonal morphologies found in the region; (ii) examine the spatial relationship between the different polygon types and their position with respect to scalloped depressions, and; (iii) use the relationship outlined in (ii) to develop a conceptual model of scalloped terrain evolution. All HiRISE imagery within the area 40-50N and 80-100E were inspected for the presence of polygonal and scalloped terrain. Images were spatially georeferenced in a GIS and polygon trough intersections were manually identified and digitized. The x- y coordinates of these intersections were then exported and used to perform the SPPA. Of the 30 locations imaged, 29 displayed polygonal terrain while 22 contained scalloped depressions in various stages of formation. In photos where polygons and scallops are both found, the polygons appear to develop along a continuum. Three categories of polygonal morphologies were identified, with SPPA results revealing end- member geometries characterized by (i) large irregular networks on the upper surrounding plains with median trough intersection spacings of >25m and a primarily random spatial distribution (Type 'UtP1'), and; (ii) small networks on the scallops' scarp faces with median intersection spacings of <5m and a primarily regular spatial distribution (Type 'UtP3'). Moreover, it appears that each category of polygonal terrain is associated with a particular stage of scallop development: UtP1 dominates landscapes unmodified by degradation, UtP2 is associated with early-stage depression, and UtP3 appears only after extensive scallop evolution has taken place. As a result, we suggest that the appearance of the scallops may result from two separate processes: (i) large-scale gentle subsidence caused by generalized ground-ice sublimation, and; (ii) enhanced modification caused by localized interaction with near-surface ground ice. In summary, this work demonstrates that the analysis of polygonal terrain geometry may lead to a more complete interpretation of the role that ground ice has played in shaping the landscape of Mars during the recent past.