Intra-Annual Variations of the Martian Swiss Cheese Terrain

Journal of Geophysical Research, 2011

1] We use data from the High Resolution Imaging Science Experiment (HiRISE) camera and the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) imaging spectrometer onboard the Mars Reconnaissance Orbiter to follow the evolution of the appearance and composition of 12 regions of the south polar layered deposits from spring to summer time. We distinguish three steps in the evolution of the volatile layer: a decrease of both CO 2 band strength and albedo until Ls = 190°-210°, a significant increase in both until Ls = 240°-260°and finally a rapid decrease until the complete defrosting of the ground. In contrast, the water ice band displays a more monotonic decrease. Analysis of HiRISE color images acquired simultaneously with CRISM data allows a plausible interpretation of this evolution. In early springtime (Ls < 200°), intense jet activity results in deposition of fans of large mineral grains and a wide spatial distribution of fine grains. The small-scale topography controls the presence and location of the jets by allowing more solar energy to be collected on slopes. Grains from the dust fans warm and sink through the CO 2 layer, resulting in a bluish color at the locations of the fans around Ls = 190°-210°. As the atmosphere warms up, the surface of the ice layer sublimes and releases dust and water, resulting in its brightening. The last phase of the process consists in a progressive defrosting resulting in a patchwork of frozen and unfrozen areas.

Scientific Reports

Carbon dioxide is Mars' primary atmospheric constituent and is an active driver of Martian surface evolution. CO 2 ice sublimation mechanisms have been proposed for a host of features that form in the contemporary Martian climate. However, there has been very little experimental work or quantitative modelling to test the validity of these hypotheses. Here we present the results of the first laboratory experiments undertaken to investigate if the interaction between sublimating CO 2 ice blocks and a warm, porous, mobile regolith can generate features similar in morphology to those forming on Martian dunes today. We find that CO 2 sublimation can mobilise grains to form (i) pits and (ii) furrows. We have documented new detached pits at the termini of linear gullies on Martian dunes. Based on their geomorphic similarity to the features observed in our laboratory experiments, and on scaling arguments, we propose a new hypothesis that detached pits are formed by the impact of granular jets generated by sublimating CO 2. We also study the erosion patterns formed underneath a sublimating block of CO 2 ice and demonstrate that these resemble furrow patterns on Mars, suggesting similar formation mechanisms. The Martian atmosphere, which is comprised of over 95% CO 2 1 , interacts seasonally with the planetary surface. As temperatures fall between late autumn and early winter, a CO 2 deposit covers the surface 2 in thicknesses ranging from around a metre in the polar regions 1,3 to a few millimetres towards the equator 4. The distribution of this dry ice is governed primarily by solar insolation 5. In the early spring, as insolation increases, the dry ice begins to sublimate. This process is now recognised as an important agent in the formation of contemporary surface features on Mars. These features include the dendritic araneiform terrain of the south polar cryptic region 6-8 , linear gullies, their associated pits 9,10 , and sand furrows 11. In this study we focus on linear gully pits and sand furrows; both active features which are observed to form and evolve on dunes under the current Martian climate. These features have no Earth analogues and the specific mechanisms responsible for their formation have yet to be fully understood and quantified. Furrows Furrows are shallow (~0.25 m) and narrow (~1.5 m) negative relief 11,12 , features which are observed on over 95% of the northern polar dunes 11 and are also found between 40°S and 72°S 13. Their network patterns range from rectilinear, to dendritic and radial, tributary and distributary and their planforms can be linear or sinuous 12 (Fig. 1), though it is unclear what factors control this variety of patterns. Appearing to "defy gravity", furrows extend upslope and transect existing aeolian ripples, and so while their patterns may resemble those eroded by fluvial activity on Earth, gravity-driven processes are unlikely to form them 12. Furrow Formation Hypotheses. Furrows frequently form after the appearance of polygonal cracks in CO 2 ice. This led Bourke 12 to hypothesise that they were caused by cryoventing; that is, basal sublimation of CO 2 and consequent erosion. This is similar to Kieffer's model for the dark spots and fans in the southern hemisphere 14 , but applied in the context of dunes. The cryoventing model proposes that in the spring, gas pressures increase at

Geomorphology, 2021

Extensive evidence of landform-scale martian geomorphic changes has been acquired in the last decade, and the number and range of examples of surface activity have increased as more high-resolution imagery has been acquired. Within the present-day Mars climate, wind and frost/ice are the dominant drivers, resulting in large avalanches of material down icy, rocky, or sandy slopes; sediment transport leading to many scales of aeolian bedforms and erosion; pits of various forms and patterned ground; and substrate material carved out from under subliming ice slabs. Due to the ability to collect correlated observations of surface activity and new landforms with relevant environmental conditions with spacecraft on or around Mars, studies of martian geomorphologic activity are uniquely positioned to directly test surface-atmosphere interaction and landform formation/evolution models outside of Earth. In this paper, we outline currently observed and interpreted surface activity occurring within the modern Mars environment, and tie this activity to wind, seasonal surface CO2 frost/ice, sublimation of subsurface water ice, and/or gravity drivers. Open questions regarding these processes are outlined, and then measurements needed for answering these questions are identified. In the final sections, we discuss how many of these martian processes and landforms may provide useful analogs for conditions and processes active on other planetary surfaces, with an emphasis on those that stretch the bounds of terrestrial-based models or that lack terrestrial analogs. In these ways, modern Mars presents a natural and powerful comparative planetology base case for studies of Solar System surface processes, beyond or instead of Earth.

Journal of Geophysical Research, 2003

1] The surfaces of the Martian north and south polar residual caps are marked by unusual ice features: Dark spiralesque troughs up to 1 km deep, 10 km wide, and 300 km long appear on both ice caps, and circular pits that make up the ''Swiss cheese'' terrain appear on the south polar cap. Both types of features are of interest to researchers as a potential means of understanding ice composition and flow rates. Some glaciers of the McMurdo dry valleys have surface features unknown elsewhere on terrestrial glaciers, including canyons over 6 km long, 100 m wide, and tens of meters deep and basins up to 100 m across. High sublimation, dust accumulation, and very little melting is key to their origin. These processes and ice landforms are suggested as terrestrial analogs for the sublimation behavior of Martian ice caps, where dust accumulation and sublimation are significant but surface melting is absent. We have developed a solar radiation model of canyon formation and have applied it to the Martian polar caps. The modeled processes do well to describe direct and reflected radiation within V grooves, a process that may be significant in the development of the spiral troughs and Swiss cheese terrain. The model fails to reproduce the low observed slopes of the Martian troughs. The grooves are too shallow, with opening angles of $165°compared with model predictions of $90°. The reason for the failure may be that we have not included creep closure, which should flatten their slopes.

Nature, 2006

The seasonal polar ice caps of Mars are composed mainly of CO 2 ice 1,2 . A region of low (<30%) albedo has been observed within the south seasonal cap during early to mid-spring 3,4 . The low temperature of this 'cryptic region' has been attributed to a clear slab of nearly pure CO 2 ice, with the low albedo resulting from absorption by the underlying surface 4 . Here we report nearinfrared imaging spectroscopy of the south seasonal cap. The deep and broad CO 2 absorption bands that are expected in the near-infrared with a thick transparent slab of CO 2 ice are not observed. Models of the observed spectra indicate that the low albedo results from extensive dust contamination close to the surface of a CO 2 ice layer, which could be linked to atmospheric circulation patterns 5,6 . The strength of the CO 2 absorption increases after mid-spring, so part of the dust is either carried away or buried more deeply in the ice layer during the CO 2 ice sublimation process.

Journal of Geophysical Research, 2005

1] The record of recent climate change on Mars is encoded in the polar layered deposits within the north polar cap. Individual Mars Orbiter Camera (MOC) images of exposed layer sequences in cliffs and troughs provide the equivalent of high resolution ''cores'' through many sections in the upper part of the north polar layered terrain. In order to decode this record it is necessary 1) to quantitatively characterize the layers in individual ''cores'' and 2) to assess possible correlations between ''cores'' in vertical layered deposit sequences across the cap. We use two techniques commonly employed in paleoceanography for the study of deep-sea sediment cores on Earth to establish the characteristics of layers in individual cores (Fourier analysis) and to determine the correlation between cores (curve-shape matching algorithms). Application to ''cores'' (vertical sections) of the north polar layered terrain on Mars reveals several fundamental properties of north polar cap stratigraphy: 1) Fourier analysis of the layer vertical sequences reveals a characteristic and repetitive wavelength of $30 m thickness throughout the upper part (Zone 1) of all sequences analyzed. 2) Application of curveshape matching algorithms demonstrates that layers correlate across at least three quarters of the cap ($6 Â 10 5 km 2 ) in the 13 images analyzed to date. 3) Assessment of geometric relationships shows that layers are not horizontal, but rather have an apparent dip of approximately 0.5 degrees. We interpret these results as follows: 1) The fundamental $30 m signal is interpreted as a climate signal that may correspond to a 51 kyr insolation cycle.

Icarus, 2000

As the planet's principal cold traps, the martian polar regions have accumulated extensive mantles of ice and dust that cover individual areas of ∼10 6 km 2 and total as much as 3-4 km thick. From the scarcity of superposed craters on their surface, these layered deposits are thought to be comparatively young-preserving a record of the seasonal and climatic cycling of atmospheric CO 2 , H 2 O, and dust over the past ∼10 5 -10 8 years. For this reason, the martian polar deposits may serve as a Rosetta Stone for understanding the geologic and climatic history of the planet-documenting variations in insolation (due to quasiperiodic oscillations in the planet's obliquity and orbital elements), volatile mass balance, atmospheric composition, dust storm activity, volcanic eruptions, large impacts, catastrophic floods, solar luminosity, supernovae, and perhaps even a record of microbial life. Beyond their scientific value, the polar regions may soon prove important for another reason-providing a valuable and accessible reservoir of water to support the long-term human exploration of Mars. In this paper we assess the current state of Mars polar research, identify the key questions that motivate the exploration of the polar regions, discuss the extent to which current missions will address these questions, and speculate about what additional capabilities and investigations may be required to address the issues that remain outstanding. FIG. 1. (a) Color mosaic digital image map (polar projection) of the north polar deposits (Vistitas Borealis) showing the ground track of the MOLA topographic profile in (b) (USGS CD-ROM VO 2001). The most notable features of the deposits are the white perennial ice cap (which overlies several kilometers of layered terrain), the dark troughs that spiral outward from the pole, several large erosional reentrants along the periphery of the deposits (the largest of which, Chasma Boreale, nearly bisects the perennial ice cap), and the polar erg-a dark band of dunes that encircle the cap. (b) MOLA topographic profile of the north polar cap obtained on MGS Pass 404 (Zuber et al. 1998). The ground track of the profile crosses directly over the north pole and provides a measure of the height of the northern ice cap above the surrounding plains. The MGS spacecraft was pointing about 50 • off-nadir for this profile (provided by MOLA Science Team).

Annual Review of Environment and Resources, 2014

Almost 20 years ago, the first CO2 capture and storage (CCS) project began injecting CO2 into a deep geological formation in an offshore aquifer. Relevant science has advanced in areas such as chemical engineering, geophysics, and social psychology. Governments have generously funded demonstrations. As a result, a handful of industrial-scale CCS projects are currently injecting about 15 megatons of CO2 underground annually that contribute to climate change mitigation. However, CCS is struggling to gain a foothold in the set of options for dealing with climate change. This review explores why and discusses critical conditions for CCS to emerge as a viable mitigation option. Explanations for this struggle include the absence of government action on climate change, economic crisis–induced low carbon prices, public skepticism, increasing costs, and advances in other options including renewables and shale gas. Climate change action is identified as a critical condition for progress in CC...

IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, 1990

This report describes the Chippe system, gives some background previous work and describes several sample design runs of the system. Also presented are the sources of the design tradeoffs used by Chippe, an overview of the internal design model, and experiences using the system.

Mesolithic Miscellany, 2023

During excavations in 2017, several pits with cremated human remains were found at the Laarakker in Haps, Land of Cuijk municipality (province of Noord-Brabant), in the southern part of the Netherlands. In addition to cremated remains and charcoal, one of the pits contained charred hazel nutshells and burnt flint artefacts. With an age of around 10,000 years the Haps cremation is the oldest known grave in the Netherlands. The cremation is part of an extensive Mesolithic landscape. The grave and its contents were investigated by a team of specialists; the results of this research are presented in this contribution.