Young gullies and their relationships to the dust-ice mantle on Mars

Posted by Jan Raack, Institut für Planetologie, WWU Münster, Germany

Image 1: Smooth appearing atmospherically derived dust-ice mantle on a south-west facing mountain slope. The flow direction of the gullies is from north to south. The gullies only erode the dust-ice mantle; the underlying bedrock was not substantially eroded. A modified dust-ice mantle  indicates as viscous flow features(black arrows) are visible at the termini of the aprons. Subscene of CTX-image P05_003170_1331_XI_46S050W

Image 1: Smooth appearing atmospherically derived dust-ice mantle on a south-west facing mountain slope. The flow direction of the gullies is from north to south. The gullies only erode the dust-ice mantle; the underlying bedrock was not substantially eroded. A modified dust-ice mantle indicates as viscous flow features(black arrows) are visible at the termini of the aprons. Subscene of CTX-image P05_003170_1331_XI_46S050W

Gullies are erosional-depositional landforms consisting of a source area (alcove), channel and apron. They occur primarily on mountain slopes and on crater walls on Mars. Morphologic attributes such as braided channels, point bars, and cut banks in many gullies suggest that fluvial processes were involved in their formation. The most plausible agent to form gullies is liquid H2O (groundwater seepage, melting of near surface ice and snow, or melting of a dust-ice layer on the surface). Alternative gully formation processes on Mars include the sublimation of CO2 or dry granular flows. Gullies have a wide range of ages and age determinations by crater size-frequency distribution measurements (a method used in planetary science to date surfaces via the size and frequency of impact craters) show that gullies on Mars were active in the past few million years. Read the full post »


Closed (hydrostatic) pingos on Earth and possibly Mars

Post by Drs. Richard Soare, Susan Conway and Peter Grindrod

Closed-system (hydrostatic) pingos (CSPs) are perenially ice-cored (non-glacial) mounds formed primarily by the near-surface injection of pore water. Their shape ranges from circular and sub-circular to elongate and their size varies from a few to hundreds of metres in diameter. Some of them reach tens of metres in height (see Figs. 1a,b).

Image 1 Plan view of a thermokarst lake/closed-system pingo assemblage that lies 6 km sw of Tuktoyaktuk on the coast of the Beaufort Sea in northern Canada (690,26’,34” N, 1330,01’,52” W). Ibyuk Pingo, at the right, is ~48 m high; Split Pingo, at the centre, is ~38 m high. Both pingos display irregular cavities at their summits. These are markers of mound degradation. Image A27917- 35-1993, courtesy of the National Air Photo Library, Ottawa, all rights reserved. Arrow indicates approximate viewing direction of part b. b. Ground view of Split Pingo (at the right) and Ibyuk Pingo (at the left) from the Beaufort Sea. Note the slope-side cracks that radiate from the summit cavities. They too are markers of mound degradation. Image, courtesy of R. Soare.

Image 1 Plan view of a thermokarst lake/closed-system pingo assemblage that lies 6 km sw of Tuktoyaktuk on the coast of the Beaufort Sea in northern Canada (690,26’,34” N, 1330,01’,52” W). Ibyuk Pingo, at the right, is ~48 m high; Split Pingo, at the centre, is ~38 m high. Both pingos display irregular cavities at their summits. These are markers of mound degradation. Image A27917- 35-1993, courtesy of the National Air Photo Library, Ottawa, all rights reserved. Arrow indicates approximate viewing direction of part b. b. Ground view of Split Pingo (at the right) and Ibyuk Pingo (at the left) from the Beaufort Sea. Note the slope-side cracks that radiate from the summit cavities. They too are markers of mound degradation. Image, courtesy of R. Soare.

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Unexpected variety among small inner satellites of Saturn

Post by Peter Thomas, Cornell University, Ithaca, New York

 Small satellites (< 150 km mean radius) usually resemble potatoes. Their irregular shapes are formed by a history of impact cratering without the benefit of internally-driven processes of volcanism, tectonics, or atmospheric effects (Castillo-Rogez et al., 2012).  During its 9 years orbiting Saturn, the Cassini spacecraft has shown that the small satellites orbiting close to Saturn have a variety of shapes, most of which deviate from the expected familiar battered potato appearance.  These objects are likely dominated by water ice as determined from mean densities and spectroscopy (Thomas et al., 2010; Buratti et al. 2010).  Satellites within rings have equatorial ridges (Charnoz et al. 2007; Porco et al., 2007).  Others, such as Janus and Epimetheus, the “co-orbitals” are almost lunar-like in appearance, close to the expected potato variety.

Image 1: Best available view of Helene. N1687119756, UV3 filter, phase = 97°, sub-spacecraft point is 2.7°N, 124.8°W.  North is down in this presentation.  Taken June 18, 2011.

Image 1: Best available view of Helene. N1687119756, UV3 filter, phase = 97°, sub-spacecraft point is 2.7°N, 124.8°W. North is down in this presentation. Taken June 18, 2011.

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Cryo-volcanic “Mount Doom” on Titan

Post by Rosaly LopesRandy Kirk,  and Mary Bourke,

Jet Propulsion Laboratory, California Institute of Technology, California, USA.
US Geological Survey, Astrogeology Science Center, Flagstaff, Arizona, USA.
Geography, Trinity College, Dublin, Ireland.

Data from the Cassini mission have revealed that Titan is a planetary body where the interior, the surface, and atmospheric processes interact to create and modify landforms (Loppes et al, 2010). In terms of recent surface processes, Titan is one of the most earth-like bodies in our solar system. Landforms include the largest area of aeolian dunefields in our solar system (e.g., Radebaugh et al., 2008), lakes (e.g., Stofan et al., 2006), fluvial channels (e.g., Langhans et al., 2012), mountains (e.g., Radebaugh et al., 2007), and features that have been interpreted as volcanic (e.g., Lopes et al., 2007).

Image 1: The  RADAR (SAR) images in black and white over a false-color mosaic of VIMS data.  The globe at upper left shows the location of the map on Titan (arrow). The white lines show the approximate boundaries of the perspective view in Image 2.

Image 1: The RADAR (SAR) images in black and white over a false-color mosaic of VIMS data. The globe at upper left shows the location of the map on Titan (arrow). The white lines show the approximate boundaries of the perspective view in Image 2.

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Dry ice gone wild: araneiform on Mars

Post by Dr. Candice Hansen and  Dr. Mary Bourke,

Planetary Science Institute, Tucson, Arizona, 85705

Geography, Trinity College, Dublin, Ireland

Every year, Mars’ polar regions are covered by a seasonal layer of CO2 ice (dry ice).  We are just beginning to understand the important role this volatile plays as an active agent of geomorphic change on Mars. The HiRISE camera on the Mars Reconnaissance Orbiter has been used to study sublimation activity in the spring for 3 Mars years.  C hannel features often organised in radial patterns were noted and known informally as “spiders”, more formally as “araneiform terrain” (Image 1).  They are tens to hundreds of m wide, with individual channels measuring several meters wide. Estimates of depth are in the order of ~ 2 m, decreasing with distance from the center of the araneform. Thin channels widen and deepen as they converge. Where they drape pre-existing topography, the channels are larger in the uphill direction suggesting they were eroded by pressurised fluid (Hansen et al, 2010).

Image 1: Subset of HiRISE Image   ESP_011420_0930 locatedf at  87.0°S / 127.27°E.  A variety of patterns of channels have been carved in the surface and are conformally-coated with seasonal ice.  At the time this image was taken, L s = 184.3 (southern spring), the sun had just started peeking above the horizon and the scene is covered with the seasonal ice cap, ~1m thick.  Araneiform channels in this image are 1-2 m deep and ~3-5 m wide.  The image is 1 km across.

Image 1: Subset of HiRISE Image ESP_011420_0930 locatedf at 87.0°S / 127.27°E. A variety of patterns of channels have been carved in the surface and are conformally-coated with seasonal ice. At the time this image was taken, L s = 184.3 (southern spring), the sun had just started peeking above the horizon and the scene is covered with the seasonal ice cap, ~1m thick. Araneiform channels in this image are 1-2 m deep and ~3-5 m wide. The image is 1 km across.

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Young volcanism on Mercury

Post by Carolyn Ernst, Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA.

Prior to 2008, less than half of Mercury’s surface had been imaged at close range, during the flybys of Mariner 10 in the mid-1970s. The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft completed three flybys of the planet in 2008 and 2009 on its way to insertion into orbit about Mercury on 18 March 2010 and viewed most of the planet’s surface that had never before been seen by a spacecraft. These MESSENGER images have helped to confirm some Mariner-10-based hypotheses and have elicited new science questions to be investigated.


Image 1: Narrow-angle camera mosaic of Rachmaninoff basin, 290 km in diameter, as seen during MESSENGER’s third Mercury flyby on 29 September 2009. Orthographic projection, ~ 440 m/pixel, centered at ~28ºN, 58ºE. MESSENGER images 0162744128 and 0162744150, credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.

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Climbing and Falling Sand Dunes in Valles Marineris, Mars

Post by Matt Chojnacki, Devon Burr and Jeff Moersch, Earth and Planetary Sciences Department and Planetary Geosciences Institute, University of Tennessee Knoxville, USA

Aeolian transport of sand-sized particles on planetary surfaces is both enhanced and inhibited by the presence of topography.  Mountainous topography at all length scales significantly affects dune location, size, shape, and orientation [Pye and Tsoar, 1990].   The surface of Mars has both abundant sand dune populations and substantial topographic relief.  Perhaps the best example of the relationship between topography and relief is the ancient rift valleys of Valles Marineris, with over ~21,000 km2 of dune fields found within the ~10 km deep rift system [Chojnacki and Moersch, 2009].  This system of interconnected-chasms, provides natural sinks where wind blown sediment can accumulate.  Additionally, the substantial relief and the resulting atmospheric pressure gradient significantly influence the regional meteorology [Rafkin and Michaels, 2003].

Dune fields in Valles Marineris can be broadly divided into two classes: floor- and wall-related dune fields.  The “wall dunes” class dune fields are interpreted as climbing and falling dunes [Chojnacki et al., 2010].  On Earth, climbing dunes are formed when migrating dunes encounter and ascend a substantial slope or cliff (>10°), where there is no major wind flow blockage [Pye and Tsoar, 1990].  Falling dunes, found on the downwind side of large topographic highs, are formed by unidirectional down slope winds and gravity [Greeley and Iversen, 1985].

Climbing Dunes of Valles Marineris:

Image 1

Image 1: Oblique southward perspective views of Melas Chasma climbing dunes using a CTX Camera image (P16_007245_1648) over HRSC elevation (H0334). The white arrows indicate slip faces and are consistent with upslope transport. Vertical exaggeration is 2x.

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Water tracks on Earth and Mars

Post by Joe Levy, Department of Geological Sciences, University of Texas, Austin, Texas, USA

  Water tracks are zones of enhanced soil moisture that route shallow groundwater downslope in permafrost regions. Water tracks form in the active layer (the seasonally thawed portion of the permafrost) where melt water derived from snow-melt, ground ice melt, and exotic processes like salt deliquescence, concentrates in broad depressions in the ice table (the part of the permafrost that remains frozen) and flows downhill. Water tracks darken and lengthen during the summer melt season, and freeze-dry in winter, rendering them nearly undetectable from late fall to early spring.

Image 1. Quickbird satellite image of a water track in the vicinity of Lake Hoare, McMurdo Dry Valleys, Antarctica. Near-surface groundwater flows downhill from the top of the image towards the ice-covered pond at the bottom. Portion of Quickbird image orthowv02_10dec222046120-p1bs-103001000825e900_u08ns4326.

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Mercury’s Mighty Valles

Post by Dr. Paul K. Byrne, Carnegie Institution of Washington, USA

 Channel-like landforms termed “valles” (sing. “vallis”) have been observed on the Moon, Mars, and Venus, and recent results from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission show that the innermost planet hosts its own brand of valles, too. Resembling the broad outflow channels on Mars and Venus, five shallow, linear depressions form a channelized network at high latitudes in Mercury’s northern hemisphere. These valles are situated adjacent to expansive northern volcanic plains that cover some 6% of the planet’s surface, and likely conducted voluminous, low-viscosity lavas from these plains southward.

Image 1: This vallis has the steep sides, smooth floors, and erosional residuals characteristic of Mercury’s broad valles, and likely channeled lavas from left to right across the image. The image has a field of view of ca. 150 km. The 57°N parallel and 115°E meridian are shown, and Kofi basin is labeled. The image is a portion of MESSENGER’s Mercury Dual Imaging System (MDIS) global monochrome basemap, which has a resolution of 250 meters per pixel.

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Geomorphic activity on asteroid Vesta

Post by Prof. Dr. Ralf Jaumann and Dr. Mary C. Bourke,

German Aerospace Center, Berlin, Germany. 

Department of Geography, Trinity College Dublin, Ireland.

The NASA Dawn spacecraft was launched in September 2007 to characterize the conditions and processes of the solar system’s earliest epoch by investigating in detail two of the largest protoplanets remaining intact since their formation. Ceres and Vesta reside in the extensive zone between Mars and Jupiter together with many other smaller bodies, called the asteroid belt. Each has followed a very different evolutionary path constrained by the diversity of processes that operated during the first few million years of solar system evolution. The Dawn mission entered orbit around Vesta on 16 July 2011 for a one-year exploration and left orbit on 5 September 2012 heading towards Ceres.

Image A. A composite digital terrain model, and high resolution albedo mosaic and imbedded color channels of three cratres on the surface of Vesta. The image is composed of many individual photographs taken between October and December 2011 by Dawn’s framing camera during the high-altitude mapping orbit, at about 680 kilometers above Vesta’s surface. The image is centered on ~ 13° north latitude and ~ 195° eastern longitude. South is to the top of the image. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.

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Sturzstroms on Saturn’s Moon Iapetus.

Post by Kelsi Singer. Ph.D Candidate, Earth and Planetary Sciences, Washington University, USA.

A typical landslide runs out less than two times its drop height whereas a long-runout landslide can extend 20-30 times the height it dropped from. Long-runout landslides (sturzstroms) are found across the Solar System.  They have been observed primarily on Earth (Image 1) and Mars, but also on Venus, and Jupiter’s moons Io and Callisto.

Image 1: An example of a long-runout landslide on Earth is the Blackhawk landslide in the Lucerne Valley, California. This landslide travelled ~8 km. Image Source USGS

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Lava temperatures determine flow composition on Earth and Io.

Post by Robert Wright, and Mary C. Bourke,

Hawaii Institute of Geophysics and Planetology, University of Hawaii at Manoa, US.

Department of Geography, Trinity College, Dublin, Ireland.

Image 1: A Giant plume from Io’s Tvashtar volcano composed of a sequence of five images taken by NASA’s New Horizons probe on March 1st 2007, over the course of eight minutes from 23:50 UT. The plume is 330 km high, though only its uppermost half is visible in this image, as its source lies over the moon’s limb on its far side. Image source from NASA.

The temperature at which active lava is erupted correlates well with the composition of the lava.  Mafic lavas may be up to 200-330 degrees celsius hotter than felsic lavas. The range of temperatures observed on active lava surfaces can also be used to determine the style with which the lava is erupted (i.e. as aa or pahoehoe lava flows, as lava lakes, or as lava domes). This is possible because the ease with which the crust is fractured depends on the volumetric flux of lava and its rheology (Image 2). As a result, lava bodies that fracture their cool crusts more easily (like aa flows) have hotter temperature distributions than those that fracture their upper surfaces less readily (such as viscous lava domes). Read the full post »

Surface Monitoring of the “Greeley Dune Field” in Endeavour Crater, Meridiani Planum, Mars.

Post by Dr Matthew Chojnacki

Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN

The 2011 arrival of the Mars Exploration Rover Opportunity at the western rim of Endeavour crater (Cape York) provided an excellent opportunity to look for aeolian dune activity over a multi-season time span (Figs. 1 & 2) and compare them to the decade-long orbital observations documented at that site (Chojnacki et al., 2011). Here are some of the first images from a dedicated Pancam campaign to monitor these dunes and to document any aeolian surface changes (also see Chojnacki et al., 2012).

Image 1

Image 1. HiRISE (McEwen et al. 2007) image PSP_005779_1775 of Endeavour crater’s western dune field. Inset shows a CTX (Malin et al. 2007) mosaic with the dune field’s location relative to Cape York and the Opportunity rover.

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Glass-rich sand dunes and plains suggest Ice-magma interactions on Mars

Post by Briony Horgan,

Postdoctoral Fellow, School of Earth and Space Exploration, Arizona State University, USA

Several large, overlapping basins dominate the northern hemisphere of Mars, and are collectively termed the northern lowlands. This ancient basin has been infilled by sediments and hosts some of the darkest terrains on the planet. A new spectral investigation of these dark terrains has revealed that they are almost entirely composed of iron-bearing glass. This is the first detection of glass on Mars, as most other martian surfaces exhibit a typical basaltic composition with abundant olivine and pyroxene. In total, glass-rich materials cover nearly ten million square kilometers in the northern lowlands (Horgan and Bell, 2012).

Image 1

Image 1 Caption: The prime meridian of Mars from Hubble. The large dark region in the northern hemisphere (Acidalia Planitia) is approximately 5 million square kilometers in area. The north polar cap and encircling north polar sand sea can also be seen at the top of the image (NASA/Lee/Bell/Wolff)

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Surface dissolution on Titan and Earth: Ontario Lacus and the Etosha Pan (Namibia) .

Post by Thomas Cornet, Olivier Bourgeois, Stephane Le Mouelic et al.,

Laboratoire de Planétologie et Géodynamique de Nantes, , Université de Nantes, UMR 6112, CNRS, Nantes, France.

Titan, Saturn’s major moon, possesses hydrocarbon lakes and seas in the polar regions [Stofan et al., 2007, Hayes et al., 2008]. Among these, Ontario Lacus (72°S, 180°E, Image 1) is the largest in the south (235 km-long, 75 km-wide). So far it is interpreted as a liquid-covered lake in Titan’s southern hemisphere because of its dark appearance in Cassini image data [Barnes et al., 2009; Turtle et al., 2009; Hayes et al., 2010; Wall et al. 2010], the identification of liquid ethane in its interior [Brown et al., 2008] and the smoothness of its surface [Wye et al., 2009].

Image 1

Image 1: Ontario Lacus (Titan) and the Etosha Pan (Namibia) as surface dissolution morphologies under arid climates. Credits: Envisat ASAR, data provided by the European Space Agency ©ESA 2009, ESA ®; Cassini RADAR, data provided by JPL/NASA. Link to high resolution image

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The effect of gravity on granular flows

Post by Dr. Maarten G. Kleinhans River and delta morphodynamics research group, University of Utrecht, The Netherlands.


Image 1

Image 1: Subscene of HRSC image presented in Kleinhans et al. (2010) showing an oblique view on a classic bed load-dominated Gilbert delta with a subaqueous lee slope at an angle of about 30°. Delta is about 5 km wide.

Granular materials avalanche when a static angle of repose is exceeded and freeze at a dynamic angle of repose. Such avalanches occur subaerially on steep hillslopes (Image 2), aeolian dunes and subaqueously at the lee side of deltas (Image 1). The angle varies from 25° for smooth spherical particles to 45° for rough angular particles. Noncohesive granular materials are found in many contexts, from kitchen to industry and nature. The angle of repose is an empirical friction parameter that is essential in models of numerous phenomena involving granular material, most of them actually occur at slopes much lower than the angle of repose. The angle of repose is therefore relevant for many geomorphological phenomena. Read the full post »

Latitudinal-dependent Surface Runoff on Titan

Post by Dr Mirjam Langhans, Istituto di Astrofisica Spaziale e Fisica Cosmica – INAF, Roma, Italy

Saturn‘s largest moon Titan is one of only a few bodies in the Solar System with an active volatile cycle. Besides Earth, only ancient Mars is supposed to have hosted a water cycle. Titan‘s volatile cycle is based on methane (CH4), occurring in liquid and gaseous state given Titan‘s environmental conditions (e.g. Flasar 1983, Lorenz & Lunine 2005). Despite the different volatiles involved, similar atmospheric processes occur on Titan and Earth, such as the formation of clouds and precipitation .

Following the action of the methane cycle, surface runoff and the incision of linear valleys take place. As a result, fluvial landscapes evolved on Titan, analog to those on Earth (e.g. Tomasko et al. 2005; Perron et al. 2006, Lorenz et al. 2008, Langhans et al. 2012).

Image 1

Image 1: Cassini-Radar-SAR image shows a dendritic valley network at high northern latitudes of Titan, ending in Kraken Mare, captured by radar-SAR (Radar-SAR T28, April 10, 2007). The image is centered at 280°W, 78°N.

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Moraines Left by Carbon Dioxide Glaciers on Mars

Post by Dr. Mikhail Kreslavsky1 and Prof. James Head2

1Assistant Research Planetary Scientist, UC Santa Cruz, USA. 2Planetary geosciences group, Brown University, Providence, Rhode Island, USA.

On Earth, cold-based glaciers (glaciers deforming internally, without basal melting and basal sliding) are found in the coldest environments (e.g., Antarctica, Marchant et al., 1993). Unlike the majority of glaciers, cold-based glaciers do not scour their substrate and leave pre-glacier topography unaffected. When cold-based glaciers advance and then dynamically stabilize (the ice flow is balanced by frontal ice ablation); debris carried forward by the glacier drops out at the glacial fronts as sublimation of the ice occurs; the dropped material produces so-called drop moraines.

In three locations at high northern latitudes of Mars, overlapping small ridges of arcuate planforms associated with slopes were interpreted as drop moraines left by extinct cold-based glaciers (Garvin et al., 2006; Kreslavsky and Head, 2011). Image 1 shows one of these locations, where a presumable glacier was formed at south-eastern part of an impact crater rim. The shapes of the extinct glacial lobes around the central peak of the crater suggest a few hundred meters thickness of the glacier.

Image 1

Image 1: Unnamed impact crater in the Northern Lowlands on Mars at 70.3oN, 266.5oE with loop-shaped ridges interpreted as drop moraines created by carbon dioxide glaciers. Image captured by Context Camera onboard Mars Reconnaissance Orbiter, image number T01_000876_2505 Illumination is from lower left.

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Weathering profiles on Earth and Mars

Post by Anne Gaudin, University Nantes, CNRS, Laboratoire LPGN, France

On Earth, weathering profiles that have developed in ultramafic rocks under tropical climate show a mineralogical transition between a Fe, Mg-rich smectite zone and an Al-rich kaolinite-bearing zone (e.g. Colin et al., 1990; Gaudin et al., 2005; Yongue-Fouateu et al., 2009). This evolution is due to an intense leaching of Mg2+ cations during the weathering process. The Murrin Murrin (MM) site is an example of such a profile located in the Archean Eastern Yilgarn Craton, in Western Australia. The MM profile is developed in serpentinized peridotite massifs over a 40 m thick sequence (Image 1) and shows three zones: serpentinized peridotites at the bottom, immediately overlain by Fe/Mg-bearing smectites and then Al-bearing phyllosilicates (kaolinite) mixed with iron hydroxides.

Image 1

Image 1: Weathering profile at the Murrin Murrin site which is currently mined for nickel, located in Western Australia (121º53’41’’E, 28º44’51’’S) (Gaudin et al., 2011).

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Evaporites on Titan

Post by Jason W. Barnes, Assistant Professor of Physics, University of Idaho

Evaporites form on planetary surfaces when dissolved chemical solids precipitate out of saturated solution as their liquid solvent evaporates. Until recently theywere known to exist on only two planets: Earth and Mars. On Earth there are a variety of evaporite constituents including carbonates (CaCO3), sulfates (CaSO4), and halides (NaCl), progressing in order of increasing solubility.  NASA’s rover Opportunity discovered evaporitic deposits on Mars that are primarily composed of sulfates — different from Earth’s due to a highly acidic formation environment.

A third planetary instance of evaporite has now been discovered in an exotic location:  Saturn’s moon Titan.  Being so far from the Sun, Titan has a low surface temperature of 90°K (-183°C), just warmer than liquid nitrogen.  Hence all of Titan’s water is permanently frozen.  However methane on Titan plays the same role that water does on Earth and Mars. Titan has methane clouds, methane rain, methane rivers, and methane lakes and seas (Image of the Month, March 2010).

Therefore the evaporites on Titan have an unusual nature relative to those on rocky planets.  Instead of water being the solvent, on Titan the solvent is methane.  And instead of salts being the solute, on Titan organic molecules derived from ultraviolet photolysis of methane dissolve in rain, surface, and ground liquid.  Those organics precipitate out of lakes when the liquid methane solute evaporates, becoming evaporite.

Image 1

Image 1: Cassini VIMS/RADAR hybrid image of filled and dry lakes south of Titan’s methane sea Ligeia Mare. The brightness of the image is determined by synthetic aperture radar which indicates roughness, and the colors by Cassini’s Visual and Infrared Mapping Spectrometer indicate composition. Some of the small lakes in the image are filled (cyan arrows). Other lakes show lacustrine morphology, but no evidence for liquids. Some of those dry lakes have the same composition as the surrounding terrain, but others show evaporites in bright orange.

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The periglacial landscape of Utopia Planitia, Mars

Post by Antoine Séjourné, Univ. Paris-Sud XI, CNRS, Laboratoire IDES, France

On Earth, periglacial regions underlined by continuous and ice-rich permafrost are found in areas of Northern Canada and Siberia These areas are very sensitive to abrupt climate-changes (Murton, 2001). The ice-rich permafrost has a unique assemblage of landforms, some of which are signatures of climate change (Image 1).

On Earth one example are the thermokarst lakes that have resulted from extensive thawing of permafrost following global warming during the Holocene (Czudek and Demek, 1970).  Freeze-thaw cycles of the permafrost produce ice-wedge polygons (Washburn, 1973). Localized melting of ice-wedges at the junction of the polygons induces the formation of small ponds of surface water (Washburn, 1973).

Image 1

Image 1: Assemblage of periglacial landforms in Canada (aerial photo 2009 A. Séjourné)

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Inflated Lava Flows on Earth and Mars

Post by Dr. W. Brent Garry1, Dr. Jacob E. Bleacher2, Dr. James R. Zimbelman3, and Dr. Larry S. Crumpler4

  1. Planetary Science Institute, Tucson, AZ, 85719, USA
  2. Planetary Geodynamics Laboratory, Code 698, NASA Goddard Space Flight Center, Greenbelt, MD, 20771, USA
  3. Center for Earth and Planetary Studies, Smithsonian Institution, National Air and Space Museum, Washington, DC, 20013, USA
  4. New Mexico Museum of Natural History and Science, Albuquerque, NM, 87104, USA

In volcanology, we are traditionally taught about basaltic lava flows advancing as toes of pāhoehoe or as channeled ‘a‘ā flows.  However, under the right emplacement conditions, some basaltic sheet flows will inflate (thicken) from only a few centimeters or meters to almost 20 meters in height.  This process occurs when lateral advancement of the flow is inhibited and liquid lava is injected underneath the solid crust of stalled sections of the flow field, causing the crust to uplift over an expanding liquid core.  The study of inflated lava flows on Earth reveals distinctive morphologic features related to this process including tumuli, inflated sheet lobes (Image 1), squeeze ups, and inflation-rise pits [1,2].  The McCartys lava flow (Image 2) is a 48-km-long, basaltic lava flow in El Malpais National Monument, near Grants, New Mexico that exhibits many of the complex morphologic features related to the process of lava flow inflation.  By studying the morphologic features that are characteristic of inflated lava flows on Earth, we can begin to identify this style of lava flow on other planetary bodies, including the Moon and Mars [3,4,5].

Image 1

Image 1. Geologist Dr. Jake Bleacher stands on the edge of a 12 meter high inflated sheet lobe in the McCartys lava flow, New Mexico. This inflated lobe continues in the foreground and extends in the distance along the left side of the photograph. Cracks, up to 8 meters deep, have formed along the margin of the lobe as the brittle crust had to accommodate for the inflation. The lower elevation unit seen in the central part of this photograph is formed from breakouts along the margin of this inflated sheet lobe and has a hummocky and swale surface texture. Photograph by W. Brent Garry. Full Size Image.

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Lunar Sinuous Rille

Post by Scott MestPlanetary Science Institute, Tucson, AZ 85719, USA.

Lunar sinuous rilles (German for ‘groove’) consist of long, narrow depressions in the lunar surface that meander in a curved path across the surface and morphologically resemble terrestrial fluvial channels (Image 1). Sinuous rilles are generally up to several kilometers wide and hundreds of kilometers in length. On the Moon, sinuous rilles are found within volcanic terrains such as the extensive lunar mare. Their morphology and association with volcanic deposits suggests that they are the remains of lava channels or collapsed lava tubes.

Image 1

Image 1: Part of LROC image M115429448L (resolution is 0.970 m/pixel) showing a close-up of a sinuous rille (arrows) that cuts through dark plains (p) and adjacent hilly (h) materials on the floor of Schrödinger.

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Tufa mounds on Earth and Mars

Post by Dr. Rogelio Linares1 and Dr. Alexis Rodríguez2,3

1Department of Geology- GATA, Autonomous University of Barcelona, Spain . 2 Planetary Science Institute, Tucson, AZ 85719, USA. 3State key Laboratory of Information Engineering on Surveying, Mapping and Remote Sensing, Wuhan University, China.

Tufa or travertine deposition at spring discharges often produce mounded landforms. They are one of the least understood calcareous landforms on Earth. Most documented mounds correspond to thermogene travertine. build-up associated with geothermal springs (where the carbon dioxide comes from thermally generated sources). See May 2009  image of the month. In contrast, work on meteogene mounds (where the carrier carbon dioxide originates in the soil and epigean atmosphere) are quite scarce (Linares et al, 2010).

Image 1

Image 1 (A) Shaded relief view of the Tremp Basin. (B) Geologic map of the study region in Isona area. (C) Electrical resistivity cross-sectional view of the central part of a tufa mound (inset in panel B). Note the cistern-like geometry of the pool facies and the overhanging upflow side of the rimstone. Number 1-2 respectively correspond to Rimstone and Rimstone with crescentic geometry.

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Fluvial flow triggered by impact events on Mars

Post by Andrea Jones, Lunar and Planetary Institute/NASA Goddard Space Flight Center

 In memory of our dear friend and colleague Dr. Elisabetta (Betty) Pierazzo

Hale crater is a 125×150 km impact crater located near the intersection of Uzboi Vallis and the northern rim of Argyre basin on Mars, at 35.7ºS, 323.6ºE. Hale is an unusual crater on Mars because it is modified by fluvial channels. The channels originate from the outer edges of Hale’s ejecta and extend as far as 460 km from the crater rim (Image 1). They are upto a few kilometers wide, exhibit a braided planform (Image 2), and had sufficient stream power to incise and transport the crater ejecta. Most of the channels are found to the south-southwest of Hale crater, on the northern slope of Argyre basin (Image 3).

Image 1

Image 1: Channels in the southeastern ejecta of Hale crater, Mars in a THEMIS daytime-infrared mosaic. The channels were likely carved with water mobilized by the Hale-forming impact event. White box is location of Image 2. North is up in all images.

Image 2

Image 2: Detailed view of fluvial channel flowing through crater ejecta. CTX image
Location is shown in Image 1.

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Fracture fills and alteration on Mars

Post by Dr. James Wray, Cornell University

Recent missions to Mars have pursued a theme of “following the water,” with orbital and surface observations revealing locations where groundwater processes have affected rocks exposed at the modern surface.  Rock fractures or joints can act as conduits for subsurface fluids, which may precipitate fracture-filling minerals or alter pre-existing rocks along the fracture walls.  Both outcomes are evident in orbital images of sulfate-bearing layered rocks in Candor Chasma, part of the vast Valles Marineris canyon system near the Martian equator.  Joints in these layered rocks are surrounded by bright “halos” attributed to chemical bleaching by paleo-fluids, as observed in sedimentary rocks on Earth (Image 1).  Some joints in Candor Chasma also exhibit positive relief  (Okubo and McEwen, 2007), suggesting that fluids cemented the fracture walls and increased their resistance to subsequent erosion.  These ridged fractures would therefore represent another example of inverted topography on Mars.

Image 1

Image 1: Rocks bleached by fracture fluids on Mars and Earth. (a) Portion of HiRISE image TRA_000836_1740 in Candor Chasma, from Okubo and McEwen (2007). (b) Jurassic Entrada Sandstone, Salt Wash graben, southeast Utah (credit C. Okubo).

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Deformation of Sedimentary Rocks in Valles Marineris, Mars

Post by Dr. Joannah Metz, Shell Oil Company

 A large canyon system (up to 8 km deep) called Valles Marineris is located near the equator on Mars.  The relative timing between the formation of the Valles Marineris canyon system and various light-toned stratified deposits observed within the different chasmata remains an outstanding question for the geologic history of Mars (Malin and Edgett 2000; Okubo et al. 2008) .  Some of these stratified deposits have been deformed and understanding the mechanism(s) responsible for this deformation, both within and between chasmata, could provide insight into the relative timing of events within the Valles Marineris system (Metz et al. 2010).

Image 1

Image 1: Example of detached slabs from Melas Chasma. Subscene of CTX image P05_002828_1711

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Dry lake beds on Mars

Post by M. R. El Maarry, MaxPlanck Institut für Sonnensystemforschung, KatlenburgLindau, Germany

Polygons are some of the most common features at high latitudes on Mars and have been observed by both lander and orbiting spacecraft. They range in size from 2 m all the way up to 10 km and different formation mechanisms have been proposed that include thermal contraction, desiccation, volcanic, and tectonic processes (Buczkowski and McGill, 2002; Levy et al., 2009; Mangold, 2005; Marchant and Head, 2007; McGill and Hills, 1992; Yoshikawa, 2003).

Crater floor polygons have diameters ranging from 15 to 350 m (Image 1). Although, morphologically they resemble both terrestrial thermal contraction polygons and desiccation cracks, their size distribution is significantly larger than thermal contraction polygons that are ubiquitous in the Martian high latitudes.

Image 1

Image 1. Typical crater floor polygons. [A] CTX (a 6 meter/pixel camera onboard the Mars Reconnaissance Orbiter, P16_007372_2474).of a 14 km‐sized impact crater (location: 67.2°N, 47.8°E). [B] Close-up from the same image. Two distinct size groups can be seen: A large 70-350 m sized polygons with an average polygon diameter of 120 m and mainly orthogonal trough intersection, and a smaller group, not always present, ranging in size from 5 to 20 m. [C] High resolution HiRISE (a telescopic camera with an impressive 25 cm/pixel resolution onboard the same spacecraft as the CTX, PSP_007372_2247) sub-image for the same crater of a 100 m‐wide polygon with a 6-8 m-wide, frost‐filled troughs surrounding it. Secondary troughs within the larger features form polygons with an average diameter of 10 m. These embedded features are probably periglacial thermal contraction polygons.

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‘Bullseye’ dunes on Mars

Post by Dr. Lori Fenton, Carl Sagan Center SETI Institute, 189 Bernardo Ave., Suite 100, CA 94043

 Fields of dunes and sand sheets are common on Mars. The largest type of dune is made of dark sand, which is thought to be similar in composition to the mafic sands often found near volcanoes on Earth (such as the “black beaches” of Hawaii). As on Earth, aeolian dune fields accumulate where sand is deposited by the wind, typically in low-lying areas such as basins, canyons, and craters.

Image 1: Sub set of Context camera image B11_013963_1120 showing unusual-shaped intra-crater dunefield. The inset on the upper right shows the context of the image on colorized MOLA topography, showing the unnamed crater that contains the dune field. Note the small bright dust devil crossing the dark sand (red arrow). Many dust devil tracks cross the dune fields in the southern high latitudes, removing dust that has settled out of the atmosphere.

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Rock breakdown on Earth and Mars: Linking the visible signs to the processes responsible

Post by Professor Heather Viles, School of Geography, University of Oxford, UK.

Observations in arid and hyper-arid environments on Earth show a range of processes, often acting together or in sequence, which cause rock breakdown.  These processes cut across the conventional categorisation into weathering and erosion and illustrate the synergistic associations of chemical, biological and physical weathering and aeolian abrasion.  Whilst there is no exact correlation between the processes at work and the features formed, because of geomorphological equifinality and complexity, nevertheless the appearance of breakdown features is a visual signature of the processes at work.


Image 1: Boulders, cobbles and gravel strewn on the desert surface. a) Mars. b) Namib Desert

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Ancient sedimentary rocks in the Mawrth Vallis region, Mars

Post by Joe Michalski, Planetary Science Institute, Tucson, Arizona, USA

On Earth, the most ancient sedimentary rock record has been largely obliterated by plate tectonics and erosion. Those that remain are from the early history of the Earth and are severely deformed and mineralogically altered. Evidence for the earliest life on Earth found within these strata is often controversial because the rocks are so severely changed from their original state.


Image 1: Rugged, eroded terrain in the northwest portion of the image (north is up), and an eroded butte in the southeast contain rocks layered at the scale of decimeters to meters. Reddish-brown colors correspond to surfaces that are rich in nontronite – an Fe-rich smectite clay mineral. The bluish areas surrounding the butte in the central part of the image correspond to surfaces that are rich in hydrated silica and aluminous clay minerals (such as montmorillonite and kaolinite). In the south-central and eastern parts of the image, relatively flat terrain bears massive fractures at multiple scales. One set of fractures is found at the scale of 100s of meters and one at the scale of several meters. This type of geomorphology if found in association with many layered deposits on Mars, but it is particularly well developed here. Most likely, the fractures form in response to volume decrease associated with dehydration of expandable (smectite) clay minerals. [HiRISE image ESP_011383_2030]

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Pseudocraters on Earth and Mars

Post by Dr. Jim Zimbelman , Center for Earth and Planetary Studies, Smithsonian Institution, Washington DC, USA.  


Image 1. View of pseudocrater at Lake Myvatn, Iceland (JRZ, 8/25/10).

Pseudocraters are distinctive landforms generated when a lava flow moves across ground containing either water or ice; the heat from the lava causes the water or ice to flash to steam, generating localized explosions through the lava.  In the Eifel area of Germany, such explosion craters are often (but not always) later filled with water, and they are called maars.  Important aspects of their formation, which distinguishes them from cinder cones and other monogenetic volcanic vents, is the lack of a source for erupting lava beneath the lava flow or resulting crater; the explosive action is strictly the result of the sudden generation of steam resulting from the heat of the overlying lava flow.  Pseudocraters are typically much broader and shallower than cinder cones, and they may excavate through the entire thickness of the overlying lava flow, ejecting some materials from the rock beneath the flow.  A classic locality for pseudocraters is the Lake Myvatn area of northern Iceland, where a 2000-year-old lava flow moved across wet or icy ground, generating numerous rootless explosion craters that were subsequently surrounded by the shallow waters of Lake Myvatn (Images 1 and 2). Read the full post »

Hematite-rich regions on Mars

Post by Cathy Weitz and Melissa Lane Planetary Science Institute, Tucson, Arizona, USA.

Fine-grained red hematite is a common mineral on the surface of Mars and explains much of the reddish color for martian soils and rocks. However, hematite can also be gray in color if it is coarser grained. Gray, crystalline hematite has been identified by the Thermal Emission Spectrometer (TES) at several sites on Mars , including: Meridiani Planum, Aram Chaos, Valles Marineris, Aureum Chaos, and Iani Chaos (Image 1) [Christensen et al., 2000; 2001; Glotch and Christensen, 2005; Glotch and Rogers, 2007; Noe Dobrea et al., 2007; Weitz et al., 2007]. At Meridiani, Aram Chaos, Iani Chaos, and Aureum Chaos the hematite units are confined to a specific layer or fairly continuous unit [e.g., Christensen et al., 2001, Glotch and Christensen, 2005]. Whereas,  in Valles Marineris the gray hematite is more patchy in distribution and scattered in separate troughs [Weitz et al., 2007; Le Deit et al., 2008].

August 2010

Image 1: Three locations where TES has detected gray hematite. The colors represent non-absolute estimated abundances, with red indicating highest abundances and blues lower amounts. (a) Central Valles Marineris. (b) Aram Chaos. (c) Meridiani Planum, where the location of the Mars Exploration Rover Opportunity landing site is shown by a black cross.

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Rectilinear Fluvial Networks on Titan

Post by Devon Burr1, Sarah Drummond1 and Robert Jacobsen2.

1Earth and Planetary Sciences Department and Planetary Geosciences Institute, University of Tennessee Knoxville, USA
2Geology Department, Colorado College, USA

Titan, like Earth, has a solid surface enveloped by a substantial atmosphere. Both atmospheres contain a few mass percent of volatiles – hydrocarbons on Titan, water on Earth – that are close to their triple points. These conditions are conducive to precipitation and runoff, resulting in fluvial processes. At Titan, data from the Cassini-Huygens mission indicate the occurrence of methane rainfall and precipitation runoff [Lunine et al., 2008]. In addition, the Descent Imager and Spectral Radiometer (DISR) on the Huygens probe observed branched lineations interpreted as fluvial valley networks with inset streams formed by flowing methane [Tomasko et al., 2005; Perron et al., 2006].

Image 1: Network patterns (Howard, 1967). The implications of some of these patterns are provided in Table 1.

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Morphology+Mineralogy : what high-resolution morphology combined with infrared color and spectra can tell us about Mars environments

Posted by DR Bethany Ehlmann, Brown University.

The past decade of high resolution orbital imaging of Mars has revealed gullies, dune forms, fresh impact craters, polar layered deposits, and sedimentary stratigraphic sections through the use of the Mars Orbiter Camera (MOC; 1.5 m/pixel), the High Resolution Stereo Camera (HRSC; 2.3 m/pixel), the Context Imager (CTX, 5m/pixel), and the High-Resolution Imaging Science Experiment (HiRISE; 25cm/pixel). These have permitted detailed studies of aeolian, glacial/periglacial, and past fluvial processes that have shaped the development of Mars’ landscapes. Equally, the past five years of Mars exploration with orbital visible/near-infrared spectroscopy have led to the discovery of numerous classes of alteration minerals including clays, sulfates, and carbonates that provide information on the duration and chemical conditions of aqueous alteration, using the Observatoire pour la Minéralogie l’Eau les Glaces et l’Activité (OMEGA; 300m/pixel) and the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM; 18m/pixel).

Image 1: A mineral map derived from CRISM infrared spectra merged with a CTX image (a) shows that most of the thick sedimentary units filling the 40km crater are Fe/Mg smectite-bearing (magenta) but that these are overlain by a distinct, bright-toned kaolinite bearing material (green). Both have been exposed from beneath a capping unit (purple) by fluvial erosion of the deposits.

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Catastrophic flood bedforms on Earth and Mars

Posted by Goro Komatsu, International Research School of Planetary Sciences, Pescara, Italy.

Subaqueous bedforms produced by catastrophic floods are often represented by gravel dunes (also known as “giant current ripples”). While they may resemble aeolian dunes in remote sensing data, field observation reveals that they are composed of coarse-grained sediment including up to meter-scale boulders. Such examples are widely known in the Channeled Scabland (Baker, 1982) in North America, in Altai (Carling et al., 2002) and Sayan (Komatsu et al., 2009) mountain provinces of Siberia (e.g., Images 1 and 2).

Image 1: Gravel dune fields near Kyzyl, capital city of Tuva, along the Yenisei River, Sayan Mountains, Siberia. Gravel dune fields are commonly positioned at the lower end of alluvial fans emanating from nearby massifs, implying that at least some sediments were locally derived from the fans. They are also located downstream of topographic constrictions, indicating that floodwater conditions had to change along its route for their formation. Image is approximately 5 km wide. From Komatsu et al. (2009).

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Lakes on Titan

Posted by Dr. Mary Bourke .

Surface conditions on Titan are near the triple point of methane, suggesting a methane-based hydrologic cycle which may incorporate solid, liquid, and gaseous phases. Albedo patterns on Titan’s surface evident in early Earth-based observations were interpreted as dark hydrocarbon liquids in topographic lows between exposures of bright water-ice bedrock (Lorenz and Lunine, 2005; Smith et al., 1996).

Initial data from the Cassini-Huygens mission detected more than 75 radar dark patches in the northern portion of a 6,000 km long swath of the surface (Image 1). These features measured from 3 km to in excess of 70km across. The backscatter of some of the dark patches had much lower reflectivity than previously imaged areas on Titan, including the radar-dark sand dunes observed near Titan’s equator (Sept. 2007 PGWG featured image).

mage 1: Radar imaging data from a Cassini flyby. The intensity in this false-coloured image is proportional to how much radar brightness is returned. The lakes, darker than the surrounding terrain, are emphasized by tinting regions of low backscatter in blue. Radar-brighter regions are shown in tan. The strip of radar imagery is foreshortened to simulate an oblique view of the highest latitude region, seen from a point to its west. This radar image was acquired by the Cassini radar instrument in synthetic aperture mode on July 22, 2006. The image is centered near 80° north, 35° west and is about 140 kilometers (84 miles) across. Smallest details in this image are about 500 meters (1,640 feet) across. Credit: NASA/JPL

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Wind abraded ventifacts on Mars and Earth

Post by Dr. Julie Laity .

Ventifacts are rocks abraded and shaped by windblown particles, characterized by their distinctive morphology and texture (Laity, 1994). Many show one or more facets, separated by sharp keels that form through progressive planation by impacting sand grains (Laity and Bridges, 2008).

Image 1: Martian ventifacts showing windward-facing beveled surfaces (facets) and striations that parallel the wind direction. Wind tails often form behind the ventifacts. Spirit Sol 584, 11:41:36 Local Solar – PanCam, Left 2

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Yardangs in Australia and on Mars

Post by Dr. Jonathan Clarke.

Yardangs are elongate wind erosion features that occur at all scales from micro-yardangs (centimetres in height, up to a metre in length) to meso-yardangs (metres in height, ten or so metres in length) and ultimately mega-yardangs (tens of metres in height, hundreds of metres of kilometres in length).

Image 1: Pseudo-true colour, oblique projected HRSC image of mega-yardangs south of Olympus Mons being eroded into the Medusae Fossae Formation. HRSC Image Archive

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Retrogressive Thaw Slumps on Mars and Earth

Post by Dr. Colman Gallagher.

Mars’s Athabasca Vallis is a 10 km wide, 300 km long channel carved by floods originating in the Cerberus Fossae. Recent images acquired by the HiRISE instrument aboard the Mars Reconnaissance Orbiter provides strong evidence that the head reaches of Athabasca Vallis experienced repeated cycles of freezing, with the development of ground ice and polygonised terrain, and warming, marked by ground ice thaw.

Image 1: Retrogressive thaw slumps (RTSs) on the inclined margins (examples marked A) of thermokarst depressions (examples marked B). RTSs have steep, shallow headwalls fronted by inclined flow slumps. Thaw consolidation and ground lowering precedes retrogressive backwearing of the headwall (Czudek and Demek, 1970). RTS headwalls are often facetted due to retrogression exploiting exposed, thawing ice wedges spatially arranged in polygons. Thaw fluids transported through gullies and channels on the slump, from melting ground ice exposed in the headwall, are stored in the depressions fronting the RTSs. However, depressions frequently merge by the retrogressive erosion of inter-depressions. When this occurs, fluid in the higher depression may be tapped into the lower through breaches (examples arrowed), exposing the floor of the drained depression. So, as the depressions fronting these RTSs filled and later drained by tapping, residual taliks froze, epigenetic polygons formed on the exposed floor due to ice segregation and heave and pingos formed by the intrusion of pressurised liquid water into the frozen surface and/or by the freezing of enclosed taliks (e.g. at point of arrow marked C). The resulting “alas” form is a basin with an undulating floor pierced by conical pingo mounds and enclosed by gentle polygonised slopes. White boxes are approximate footprints of Images 2 and 3. All Mars images are sub-scenes from HiRISE image PSP_007843_1905. Image credit NASA/JPL/UofA.

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Evidence of glacial processes in Mamers Valles, Mars

Post by Daniela Tirsch.

Glacial and fluvial landforms that date to ancient Noachian and Hesperian times indicate an abundance of liquid water on Mars at that time. Of interest is evidence of younger (i.e., Amazonian) glacial activities. These processes have recently been suggested for some locations in the Marmers Valles region of Mars [Kress et al., 2006; Di Achille and Ori, 2008; Tirsch, 2009a] (Image 1).

Mamers Vallis, Mars

Image 1: Crater near Mamers Valles (HRSC orbit 3304, perspective view, north is to the left).

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Low-Latitude Landscape of Fire and Ice on Mars

Post by Mark Bishop.

Cone fields of the Tartarus Colles of Mars (~190° W, 26° N) comprise part of the volcanic province of the Elysium Rise. They lie amongst the mesas, ridges, small knobs and hills from which the region derives its name. Considerable interest exists in regard to cone location and origin, as their occurrence may be associated with recent volcanism, as well as the occurrence of near surface ground ice; the presence of which has consequences for past and present climate, astrobiological activity, and future exploration.

Cone fields, Mars

Image 1: MOC NA image M08-01962 (4.52 m/pixel) showing the cone fields and enlarged insets of geomorphic features. Geomorphic details are highlighted and numbered (1-3). Illumination is from the left.

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Slope Streaks on Mars

Post by Frank Chuang.

The High Resolution Imaging Science Experiment (HiRISE) onboard Mars Reconnaissance Orbiter (MRO) has imaged the Martian surface for two full Earth years at spatial scales up to 25 centimeters/pixel. These images allow very detailed studies of small surface features, such as slope streaks, commonly seen in the high albedo, low thermal inertia, and dust-rich equatorial regions of Mars. Slope streaks have been observed in all spacecraft images from the early Mariner missions to the most recent Mars Reconnaissance Orbiter (MRO) mission to Mars [1-8]. Recently formed slope streaks are typically darker than their surroundings and appear to fade (i.e., brighten) over time (Image 1). Typical characteristics of slope streaks are initiation at a point source, one streak splitting into two, deflection around or over obstacles such as small boulders or crater rims, widening below the source area up to a few hundred meters, and lengths of up to a few kilometers. Numerous models have been proposed for their formation, both dry- and wet-based, and these are described briefly in [6].

Slope Streaks near Naktong Vallis, Mars

Image 1: Portion of HiRISE image PSP_003259_1850 (5.0 N, 32.7 E) near Naktong Vallis with dark slope streaks along the interior slope of an impact crater. Arrows point to the margin of slope streaks that have topographic relief where the streaked surface is lower than the surrounding un-streaked surface. Several of the streaks are triggered by impact craters that have dark ejecta. Image credit: HiRISE (NASA/JPL/Univ. of Arizona)

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Ventifacts on Earth and Mars

Post by Nathan Bridges.

Definition and Significance of Ventifacts

Ventifacts are rocks abraded by windblown particles, generally or exclusively sand (Laity and Bridges, 2009). On Earth, they are found mostly in arid regions with little vegetation, a fairly abundant supply of sand (or an ancient supply for relict ventifacts), and winds capable of exceeding the threshold speed necessary for sand movement. Their form depends on original rock texture, shape, and composition, with common forms including facets sloping into the wind and wind-aligned elongated pits, flutes, and grooves. The direction of facet dip slopes and the long axes of textures serve as proxies for the predominant highest speed winds that carried the sand and thereby serve as paleowind indicators. It is common for ventifact textures to result from mineralogical or petrological hardness variations in the rock or from primary textures such as vesicles.

Dunes West of Hellas Planitia, Mars

Image 1:a) Elongated pits and flutes in limestone/marble within the Little Cowhole Mountains, Mojave Desert, CA. b) Pits, some maybe primary vesicles, and flutes in basalt from the Cady Mountains, Mojave Desert, c) Flutes in Diorite from hills east of Silver Lake, Mojave Desert.

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Alluvial Fans on Mars

Post by Ross Irwin.

Alluvial fans are sedimentary deposits that accumulate where streams emerge from steep mountain watersheds onto low-gradient plains. Flooding in the upland area transports a wide range of sediment sizes, and when the stream emerges onto the plain, it no longer has the power to transport the same quantity and size of sediment. Only part of an alluvial fan’s width is active at any one time, but as sediment accumulates in that area, flows will move to steeper routes elsewhere on the fan surface. Sediment may be delivered through normal stream flows or debris flows, which are concentrated slurries of sediment and water. Alluvial fans that were formed mostly by debris flows are usually steeper than their stream-dominated counterparts.

Holden Crater, Mars

Holden Crater, Mars
Image 1: Holden crater (26°S, 34°W) in a Thermal Emission Imaging System (THEMIS) daytime infrared mosaic (230 m/pixel) colored with Mars Orbiter Laser Altimeter topography. Warm colors are high elevations, cool colors are low, and contour lines mark each 50 m interval of elevation. The green-shaded deposits along the western wall of the crater are the Holden bajada.

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LayeLayered sediments in Martian craters: Crommelin Crater, Mars

Post by Angelo Pio Rossi

Although rocks of volcanic origin are the most common type on Mars, complex sedimentary sequences do occur, often with enormous thickness and lateral extent. Arabia Terra, in particular, hosts several large craters with extensive outcrops of sedimentary or sedimentary-like rocks (Malin and Edgett, 2000). The sedimentary rocks in this area are thought to be very old and some date back to the Noachian Era (from about 4.6 to about 3.7 billion years ago).

Crommelin Crater, Mars

Image 1: Perspective view of Crommelin central bulge. The image is centered at about 350° E, 5° N. The image consists of a mosaic of Mars Reconnaissance Orbiter (MRO) Context (CTX) images (P01_001401_1846_XI_04N010W, P02_002021_1848_XI_04N010W, P02_001876_1852_XI_05N010W, P06_003432_1852_XI_05N009W) draped over High Resolution Stereo Camera (HRSC) Stereo-derived Digital Elevation Model obtained from Mars Express (MEX) orbits: 2108, 3253, 3264, 5091. The width of the scene is about 50 km. The perspective view is north-pointing (see image 3). Vertical exaggeration is 2x.

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Linear-Lee Dunes on Mars and Earth

Post by Haim Tsoar.

The discovery of dunes on Mars:

Mariner 9, launched on May 30, 1971 conducted an intensive orbital reconnaissance of the red planet between November 14, 1971 and October 22, 1972. One of the astonishing discoveries of Mariner 9 was vast dune fields all over the Red Planet. Viking discovered many more dune fields in the late 1970s. However, the resolution of the images taken by Mariner 9 and Viking 1 and 2 was very poor and one dominant dune type of barchan and transverse dunes was chiefly discerned by this low resolution (Tsoar et al, 1979). The Mars Global Surveyor (MGS) was the next successful mission to Mars, launched 20 years after Viking, in November 1996, and operated for 10 years. The Mars Orbiter Camera (MOC) on board MGS acquired high resolution images of the sand dunes on Mars and revealed some other dune types that were not known before. The latest mission to Mars, the Mars Reconnaissance Orbiter not only reveals the variety of dunes but its high resolution camera (HiRISE) allows us to see the smaller ripples on the dunes.

Dunes West of Hellas Planitia, Mars

Image 1: Barchan and linear dunes west of Hellas Planitia near 41.8°S, 315.5°W, formed on the floor of a crater and extending from a mesa. Note the breakdown of the rectilinear dune into barchans with distance from the flow obstruction. HiRISE Image PSP_007676_1385.

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Impact Craters on Earth and Mars: Monturaqui and Bonneville

Post by Nathalie Cabrol and the High Lakes Science Expedition.

Impact processes are fundamental in the creation of planets, the modification of their landscape, and for Earth, in the evolution of life. However, unlike the other planets of our solar system, Earth has not kept a large record of its impact history. Plate tectonic and erosional processes have erased most of them with time. Small impact craters, in particular, are difficult to preserve but there are still a few left, including the Monturaqui impact crater (23°56’S/68°17’W) located in the Atacama Desert in Chile.

Maturaqui Crater, Chile, Earth

Image 1: Monturaqui impact crater in the Atacama Desert of Chile. Credit: Planetary Spherules Project, Nathalie A. Cabrol, NASA Ames/SETI CSC.

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Caves on Mars

Post by Dr. Bradley J. Thompson.

On Earth, caves are naturally formed subterranean chambers that form unique geologic and biologic environments. Although terrestrial caves are commonly formed in limestone where slightly acidic water has partially dissolved the host rock, caves can also form in ice or even in solidified lava (flowing lava will often form a roofed-over channel or tube that remains hollow once the lava cools and solidifies). Caves provided early humans with their first form of shelter, and the walls of some caves still record evidence of their presence in the form of cave paintings. From an environmental standpoint, caves provide near constant temperature and relative humidity year-round, and thus can serve as a refuge when conditions at the surface are too extreme.

Collapse pit, Arsia Mons, Mars

Subset of HIRISE image PSP_004847_1745 showing the illuminated wall of a collapse pit on the north east flank of a giant volcano on Mars, Arsia Mons.

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Stratigraphy of the Martian North Polar Ice Cap

Post by Kathryn Fishbaugh.

At the north pole of Mars lies Planum Boreum, a dome of layered, icy materials similar in some ways to the large ice caps in Greenland and Antarctica and comparable in size to the former. The dome itself consists of the polar layered deposits, consisting of over 90% ice with a little bit of dust, and the basal unit, consisting of ice, dust, and sand.

Mars Polar Deposits

An enhanced color image from the Mars Reconnaissance Orbiter (MRO) High Resolution Imaging Science Experiment (HiRISE) shows a portion of the martian north polar layered deposits, the basal unit, and the Olympia Undae dune field. The image is 1.2 km (0.75 mi) across. This image is best understood if you imagine yourself flying over a cliff in a plane. Note that the colors in an enhanced color image do not re-create what it would look like to the naked, human eye, but rather bring out the compositional differences between the materials.

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