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.


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.


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).


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


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


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


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.


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).


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.


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)


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.


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.


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.


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.


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.


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.


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.


Cryovolcanic features on Titan

Post by Dr Catherine Neish

Cryovolcanism (or ‘cold’ volcanism) describes the eruption of substances that are generally considered to be volatiles on the surface of Earth (eg. water, water-ammonia mixtures, etc.). Cryovolcanism is functionally similar to the volcanism we see on Earth, except that cryolavas (‘cold’ lavas, such as water) erupt at much lower temperatures than rock lavas. As with all forms of volcanism, two conditions must be met for cryovolcanic flows to be present on the surface of an icy moon: liquids must be present in the interior, and those liquids must then migrate to the surface. The latter requirement is more difficult to achieve for cryolavas than rock lavas, given that solid ice is less dense than water. The addition of some amount of ammonia can reduce the density difference – a liquid ammonia-water mixture of peritectic composition (33 wt. % ammonia, 946 kg m3) is near neutral buoyancy in ice (917 kg m3). Though these pockets would not easily become buoyant on their own (given the difference in density of ~20-30 kg m3), they are sufficiently close to the neutral buoyancy point that large-scale tectonic stress patterns (tides, non-synchronous rotation, satellite volume changes, solid state convection, or subsurface pressure gradients associated with topography) could enable the lavas to erupt effusively onto the surface.

Ganesa Macula, Titan

Image 1: A portion of the RADAR swath taken during the Cassini spacecraft’s TA (Titan-A) encounter on October 26, 2004 (Elachi et al. 2005). This image shows several possible cryovolcanic features, including overlapping flow features (right) and the large circular feature Ganesa Macula (left). Radar illumination is from the bottom.


Outflow Channels on Mars

Post by Dr. Mariam Sowe

The High Resolution Stereo Camera (HRSC) on board the Mars Express has a large swath and high resolution [Jaumann et al. 2007]. This enables the capture of large geomorphic features while retaining the ability to track small-scale features over long distances. The HRSC has observed all of the giant outflow channels on Mars. They are supposed to be eroded fluvially as a consequence of the catastrophic release of water [Baker et al., 1992]. Most of them emanate from chaotic terrain [Sharp, 1973], which is heavily collapsed terrain and assumed as their source region. Outflow channels give insight to a different Martian climate with respect to hydrological conditions that apparently were different in the Late Hesperian or Amazonian, when they were formed [Tanaka, 1986].

Mangala Vallis, Mars

Image 1: In this image we can see the Mangala Vallis outflow channel at 11.5S/151W.


Deltaic sediments on Mars

Post by Dr. Bethany Ehlmann

The Nili Fossae region of Mars has a diversity of minerals that include mafics and phyllosilicates. The mineral assemblage suggests widespread liquid water activity and a variety of alteration processes from surface weathering to hydrothermal processes (Mangold et al., 2007).

Nili Fossae, Mars

Image 1: CRISM infrared spectrometer data (wavelengths: 2.38 um (red), 1.80 um (green), 1.15 um (blue) acquired at 35 m/pixel have been used to colorize a Context Imager grayscale image, taken at 5 m/pixel resolution.


Yardangs on Earth and Mars

Post by Dr. Lori Fenton.

A yardang is a topographical feature that has been carved out of a surface by the wind. The word is derived from the Turkic word yar, which means ridge or steep bank. On Earth they are most commonly found in deserts where there is a sand supply, which abrades the surface when moved by the wind, and soft sedimentary rocks that the sand easily erodes. Over time, the sand wears down the surface into beautiful streamlined shapes that are aligned with the prevailing sand-moving winds.

Emmenides Dorsum, Mars

Image 1: Emmenides Dorsum on Mars. Image captured with the Thermal Emission Imaging System visual camera (THEMIS VIS V12350012), taken on Sept. 26, 2004. Yardangs reveal that this surface has been wind-sculpted and planed off by ~450 m.


Lava Flows on Mars, Io, and Earth

Post by Dr. Jim Zimbelman

Lava flows are one of the common landforms encountered on various objects throughout the inner solar system, as well as on Jupiter’s volcanically active moon Io. Cameras and other remote sensing instruments on various spacecraft have returned an incredible amount of data about lava flows on planetary surfaces. Here we will highlight a couple of examples, along with recent work on lava flows on Earth that is providing new insight into how we can study lava flows on other planets.

Lava Flow on Ascraeus Mons, Mars

Image 1: The image is a portion of frame S08-02516 taken by the Mars Orbiter Camera, which shows part of a heavily cratered lava flow on the flank of the Ascraeus Mons shield volcano in the Tharsis region. The abundance of impact craters on the flow indicates that it is not very recent.


Meridiani on the Murray

Post by Dr. Jonathan Clarke

Soon after landing at Meridiani Planum the Opportunity rover imaged some curious wind erosion features. These were the haematite concretions commonly known as “blueberries” standing out from the substrate on stalks up to a cm or so in length. Good examples were seen at Eagle Crater, others were imaged at Fram Crater (Image 1). In places, the concretion has protected the underlying substrate from erosion. Sediments hosting the hematitic concretions have been eroded, leaving some concretions perched on small stalks. Several rocks at the Spirit landing site also show pedestals or fingers projecting away from rock surfaces.

Dedos on Meridiani Planum, Mars

Image 1: Two approximate true colour Pancam images of a boulder in Fram Crater, Meridiani Planum showing haematite concretions with a residual tail or stalk. The circular depression in the lower panel is from drilling by the RAT instrument. It is 45 mm in diameter. Top panel Sol085B_P2532_1. Credit: NASA/JPL/Cornell. Bottom panel image Sol088B_P2542_1. Credit: NASA/JPL/Cornell.


Lobate Debris Aprons

Posted by Dr. Ernst Hauber

Lobate debris aprons (LDA) are distinctive geomorphic landforms showing evidence for the creep and deformation of ice-rich debris in Martian mid-latitudes [e.g., Carr and Schaber, 1977; Squyres, 1978, 1979; Lucchitta, 1984].

Lobate Debris Apron, Mars

Image 1: The image shows a textbook example of a typical Martian lobate debris apron, considered to be a mixture of ice and rocky particles (rock glaciers are a terrestrial analog). The lobate flow front and the convex-upward profile are characteristic for these phenomena. The data were acquired on May 29, 2004 with the Mars Express High Resolution Stereo Camera (HRSC). The 3D-perspective in this image was rendered to simulate an oblique view from the north. The mountain with the lobate debris apron is centered at 40.60 S and 103.01 E, in the Promethei Terra region, very close to Reull Vallis.


Inverted Paleochannels on Earth and Mars

Posted by Dr. Rebecca Williams

Inversion of relief is a common attribute of landscape evolution and can occur wherever materials in valley bottoms are, or become, more resistant to erosion than the adjacent valley slopes.

Sinuous ridge, Utah, Earth

Sinuous ridge, Utah, Earth
Image 1: An oblique aerial photograph of a carbonate-cemented, sinuous inverted paleochannel segment located approximately 11 kilometers southwest of Green River, Utah.


Layered Deposits, Candor Chasma, Mars

Post by Dr Mariam Sowe

Candor Chasma is situated in the central Valles Marineris (Image 1). It is characterised by Interior Layered Deposits (ILDs) that are exposed on its valley floor. ILDs are closely connected to sulphate minerals and iron oxide [Christensen et al., 2001; Gendrin et al., 2005; Mangold et al., 2007]. Using high resolution images and elevation data from the Mars Express HRSC experiment [Jaumann et al., 2007] their layer geometry can be measured.

Candor Chasma, Mars


Mars’s Moon Phobos

Post by Dr William Hartmann


The image is of Mars’s 27 x 19 km satellite, Phobos. It hints at many mysteries that await us there. The surface (contrary to the appearance of this well-exposed image) is dark black, probably similar to carbonaceous asteroids, but the exact composition and spectral properties are still uncertain (due partly to scattered reddish light from Mars). Spectra show the surface soil lacks any water, but that soil has been blasted off and recycled through dust belts circling Mars, and then re-accreted onto Phobos. This process likely removes any initial water from the dust, so we can’t be sure whether the surface represents the interior material.

Medusae Fossae Formation on Mars


Valley Networks on Venus

Posted by Dr. Goro Komatsu, IRSPS, Univ. G.d’Annunzio, Italy.  

(Re-posted from IAG Image of the Month, December, 2007)

“…excitement and pleasure in science derive not so much from achieving the final explanation as from discovering the fascinating range of new phenomena to be explained” (Baker and Komatsu, 1999).”

Networks on Venus

The Magellan spacecraft acquired SAR (Synthetic Aperture Radar) images of venusian surfaces at a spatial resolution range of about 100 m per pixel.


Unconsolidated Gravels on Asteroid Itokawa

Posted by Dr. Hirdy Miyamoto,    

(Re-posted from IAG Image of the Month, November 2007)

In November 2005, the Hayabusa spacecraft performed touchdown rehearsals, imaging navigation tests, and two touchdowns on Itokawa, which is by far the smallest asteroid ever studied at high resolution.

Asteroid Itokawa

Image courtesy ISAS/JAXA and University of Tokyo


Frozen Seas on Mars and Earth

Posted by
Dr. Matt Balme, Open University, UK. 

(Re-posted from IAG Image of the Month, October, 2007)

Elysium Planitia

Images of the ‘frozen sea’ on Mars (a,b) from the High Resolution Stereo Camera of the ESA Mars Express Mission, and pack-ice (c) in the terrestrial Antarctic.


Longitudinal dunes on Saturn’s moon Titan

Posted by  Dr. Jani Radebaugh, Department of Geological Sciences, Brigham Young University, Utah, USA

(Re-posted from IAG Image of the Month, September, 2007)

The Cassini spacecraft is in orbit around Saturn, and occasionally flies close to one of its many icy moons. Because of specially designed instruments on Cassini, the surface of Saturn’s largest moon, Titan, enshrouded in a thick, hydrocarbon haze-rich atmosphere, has been observed for the first time by this spacecraft.

Dunes on Titan

Cassini RADAR SAR image is north up, with resolution ~300 m. RADAR illumination direction and inclination angle is indicated by the open arrow. Image courtesy of the NASA Cassini Project.


A “Rubble-pile” Asteroid

Posted by Hirdy Miyamoto, University of Tokyo, Japan.

(Re-posted from IAG Image of the Month, August, 2007)

This image of asteroid 25143 Itokawa, photographed by the Japanese Hayabusa spacecraft during a two-month encounter, September-December, 2005, is suggestive of the “rubble-pile” conception of asteroid formation and structure.

Asteroid 25143 Itokawa

Asteroid 25143 Itokawa. Image courtesy ISAS/JAXA Japanese space agency.


Vir-Ava Chasma, Venus

Posted by Les Bleamaster, Planetary Science Institute, Tucson, Arizona, USA.

(Re-posted from IAG Image of the month, July 2007)

This false color, three-dimensional perspective view over the Turan Planum of Venus shows the interaction of tectonic structures and volcanic processes along chasmata or “rifts.”


Foreground is approximately 400 km, with a vertical exaggeration of 8x.


Mars Dunes

Posted by Mary Bourke, Geography, Trinity College, Dublin, Ireland.

(Re-posted from IAG Image of the Month, June, 2007)

Both Earth and Mars have atmospheres that can mobilize particles to form sand dunes. This image is from the caldera of an inactive Volcano (Nili Patera) on Mars. The steep avalanche face on the downwind side of the dunes indicates wind direction (see arrow). There are several types of sand dunes in this image, some of which have not been previously recognized on Mars. (more…)

Volcanic Regions on Venus

Posted by Les Bleamaster, Planetary Science Institute, Tucson, Arizona, USA.

(Re-posted from IAG Image of the Month, May, 2007)

Synthetic Aperture Radar (SAR) images from NASA’s Magellan mission to Venus (science mission complete in 1994) show two distinctly different volcanic regions within only a few hundred kilometers of each other. venusgeo (more…)

Landslide deposits on Mars

Posted by Bill Hartmann, Planetary Science Institute, Tucson, Arizona, USA.

(Re-posted from IAG Image of the month, March 2007)

This high-resolution MGS MOC image shows overlapping landslide deposits at the foot of the wall in the Ganges region of the Valles Marineris canyon complex on Mars. (more…)

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