Tuesday, November 30, 2010

Nanedi Valles

A branch of Nanedi Valles entered a crater and deposited a delta that fills the majority of the crater floor.

Photo credit: NASA/JPL/Arizona State University

Scoured Bedrock on the Floor of Eos Chasma

The scoured and scabby floor of Eos Chasma, located east of Valles Marineris, is covered with dunes or ripples and eroded craters. The reddish-brown color likely represents older, eroded basalt. Much of this erosion may have been accomplished by water.

An eroded crater exposes compositional differences below the surface: the bluish tones are probably fresher, boulder-rich exposures of basalt and the lighter-toned material near the base of the crater wall may have a different composition. The bottom of the crater is filled with material that is similarly-toned to the surface of Eos Chasma, and was likely eroded and transported there by the wind.

Photo credit: NASA/JPL/University of Arizona

Monday, November 29, 2010

Shalbatana Vallis

Streamlined islands indicate the direction of flow in this VIS image of Shalbatana Vallis.

Photo credit: NASA/JPL/Arizona State University

Landforms on the South Polar Residual Cap

This HiRISE image is located on the carbon-dioxide rich residual south polar ice cap near 86 degrees South, 353 degrees East. These rounded landforms evolve relatively quickly and erode into the surface of the ice cap (approximately 4-5 meters or 15 feet per year).

Their interesting shapes make for a striking appearance on the surface.

Photo credit: NASA/JPL/University of Arizona

Sunday, November 28, 2010

Ganges Chasma

This VIS image shows part of the floor of Ganges Chasma. Sand dunes and windstreaks indicate long term wind action in the area.

Photo credit: NASA/JPL/Arizona State University

Spider Features in the South Polar Region

This image is part of an ongoing seasonal monitoring effort in this location in the southern polar region of Mars.

Mars' south polar region changes significantly during the Martian year. During the southern hemisphere's winter, the polar cap increases dramatically as the lowered temperatures make a large portion of the atmosphere freeze out into ice. As spring approaches and the polar region begins to warm once again, the cap recedes revealing terrains like those visible in this image.

The polygonal features in this image are termed "spiders" and their origin is still unknown (although there are several hypotheses). One possible hypothesis for the black fan-shaped features is that they may be formed by a geyser-like process. As the Sun heats the ground layer below the carbon dioxide ice, the ice on the bottom begins to sublimate, or turn directly from a solid to a gas. This gas then builds up in pressure as more of it sublimates, until a critical pressure is achieved and it erupts through the ice layer much as a geyser would, spewing the debris that is thought to make up the dark fan shaped features.

Photo credit: NASA/JPL/University of Arizona

Note: The location of this photo is in Planum Australe, to the south of Australe Scopuli.

Saturday, November 27, 2010

Nili Patera Dunes

Individual sand dunes are visible in this image of Nili Patera.

Photo credit: NASA/JPL/Arizona State University

Sorted Boulders on the Northern Plains

This image covers a large crater on the northern plains of Mars. The crater is old and has been heavily modified by ground ice processes.

The most prominent of these is the network of polygonal fractures visible throughout the image. These form when temperature changes over the course of a year cause ice in the ground to expand, contract, and break. The ground moves fractionally every time this occurs.

At the center of this image, this repetitive process has shifted boulders on the surface, causing them to line up with the fractures and form striking geometric patterns.

Photo credit: NASA/JPL/University of Arizona

Note: This crater is located in the Panchaia Rupes region of Vastitas Borealis, to the north of Utopia Planitia.

Friday, November 26, 2010

Gullies in Tempe Terra

The southern rim of this unnamed crater in Tempe Terra is dissected by numerous gullies.

Photo credit: NASA/JPL/Arizona State University

Glacier in Protonilus Mensae

Ice can be a powerful force of erosion, particularly when it accumulates into thick deposits. Glaciers on Mars were once proposed to be likely because of the planet's cold temperatures. The global average temperature of Mars is about -68 Celsius (-90 Fahrenheit).

Glacial-looking landforms are now seen to be commonplace, and even abundant in mountainous regions at higher latitudes such as here in Protonilus Mensae. These landforms are quite similar in appearance to glaciers on Earth.

This image shows an example of such a landform. The mountain valley to the north (toward the bottom of the unprojected image) would be the zone of accumulation of snow and ice, which then flowed downhill (toward the top of the image) and out onto a neighboring plain. The evidence of this flow comes from the myriad of stream lines and flow fronts visible in the surface topography. Some of these topographic features may also be "moraines," ridges of rock and soil debris common on the surface of glaciers and at the boundaries.

Boulders up to 3 meters (9 feet) in size are visible on the surface of this feature. If you trace the streamlines from these boulders back uphill into the accumulation zone then you'll see where boulders have tumbled off the valley walls before being rafted downhill to their current location. This process continues today even though the feature itself may not be flowing significantly anymore.

Once onto the more level plain, the ice flow stalled and spread out into a bulb shaped pile where it would have gradually evaporated, called the ablation zone." Melting of the ice might have also occurred, though geologic evidence of melting has not yet been found.

Today, Mars is very dry place, and surface ice is unstable everywhere except on the polar caps. Any ice left on the surface would evaporate without ever melting, a process called "sublimation." However, past climate changes may have periodically allowed snow and ice to be stable on the Martian surface and even to build into glacial masses, hundreds of meters (yards) or more in thickness.

In this image, the surface is made up of regolith (rock and soil debris) and no ice is visible. Interestingly, subsurface ice may still be present as relatively soil-free ice, which would then be called a "debris covered glacier." Ice may also occur as a cement between rocky material throughout the glacial deposit and would also be capable of flowing like a glacier, which is called a "rock glacier." Alternatively, the ice may have all sublimated and what we see now is a residue of the "glacier till," remnant ice-free rock and soil debris.

Future stereo images of this landform will help scientists to understand the surface tilt and the forces driving ice flow under Martian gravity. In addition, stereo topography may help in estimating the thickness of the feature we see here and if any subsurface ice may still be present.

Photo credit: NASA/JPL/University of Arizona

Thursday, November 25, 2010

Melas Chasma Landslides

This VIS image shows a small portion of two landslide deposits within Melas Chasma.

Photo credit: NASA/JPL/Arizona State University

Polygonal Patterned Ground

Ice-rich frozen ground on Earth often develops a remarkably regular set of patterns of mounds and interconnected troughs, loosely resembling to a slice of a honeycomb, referred to as “polygonal ground.” These patterns develop when icy permafrost cracks each winter when the ground cools and contracts.

Over hundreds to thousands of years the surface patterns develop into clearly visible connecting troughs. Typically, these polygons are several meters (yards) or more across. Mud cracks are analogous features that form when wet soil dries and contracts, but are typically form patterns only inches in scale.

Mars experiences seasons and winter cooling fractures the permanently frozen ground in much the same way. As a result, polygonal patterns are wide spread throughout the middle and high latitudes. This image shows an example of such polygonal terrain. Larger impact craters, such as the 400 meter (yard) crater visible in the full image, are often muted or reduced to a remnant ring or scattered boulders, partly by infilling and mantling with wind-blown soil and dust. Small craters that are tens of meters (yards) across are mostly absent from this terrain. This image has three maybe four such craters. These large and small crater characteristics suggests to us that this surface is young and has experienced substantial changes over geologically recent times.

The polygons themselves may be partly responsible for keeping the surface "fresh." As new polygons form over top over existing polygonal patterns they continually churn the surface by developing new troughs and mounds. Indeed, close inspection of seemingly young small craters reveals that polygons rapidly form in the crater interiors and begin to erode the crater walls.

Photo credit: NASA/JPL/University of Arizona

Wednesday, November 24, 2010

Ganges Chasma

This VIS image of the floor of Ganges Chasma shows eroded fill material and extensive sand deposits.

Photo credit: NASA/JPL/Arizona State University

Small Winding Channel in Tartarus Colles

Small Winding Channel in Tartarus Colles

This observation shows a thin channel between knobs in the northern hemisphere. These knobs are part of a local group of knobs called Tartarus Colles.

Both knobs visible in this image have dark slope streaks. It was originally thought that slope streaks might be locations of surface water wetting and darkening soil, but it is now commonly believed that slope streaks are mini-avalanches of dust. Slope streaks fade over time as wind erosion blends them in with their surroundings.

The channel between the knobs has a variable depth as seen by the varying shadow lengths. The origin of the channel is unknown, but it is probably not a fluvial channel because there are no obvious source or deposit regions. The channel is probably a collapse feature.

One portion of it, (see subimage) contains a bridge, and is probably a remnant of the original surface. A depression that extends from the channel northwards — but which is not as deep as the majority of the channel — might be in the process of collapsing and enlarging the channel.

Photo credit: NASA/JPL/University of Arizona

Note: If this channel is indeed a collapse feature as opposed to a stream channel, then the channel is probably a collapsed lava tube. See here and here for further discussion on this topic.

Tuesday, November 23, 2010

Zephyria Planum

Eroded by countless years of wind action, the material in this region of Zephyria Planum is being sculpted into yardangs - long, thin hills separated by narrow valleys.

Photo credit: NASA/JPL/Arizona State University

Light Material in Ganges Chasma Wall

The troughs and chasms of the Valles Marineris system contain light toned deposits of enigmatic origin. The light materials, often layered, have variously been proposed to be volcanic ash or sediments laid down by rivers, lakes or sand dunes.

One aspect of the light toned material that has remained unclear is the timing of its deposition relative to canyon formation--was the material deposited in the troughs, or does it crop out in the walls, indicating that it existed before the Valles Marineris system formed?

This HiRISE image shows a part of the wall of Ganges Chasma. (This image, taken during the major dust storms which have raged through the summer of 2007, is grainy and low-contrast because of dust in the atmosphere.) The plateau above the chasm is at the bottom of the image, with the wall of the trough descending to the north. A few fine layers, likely basalt flows, form the cap layers.

In the spur at the center of the image, light material appears to crop out, contrasting with the relatively dark material elsewhere in the wall of the trough. At least some of this material is inherently lighter than other wall rock; changes in tone occur at several sites where there are no breaks in slope. The light material appears be forming spurs and ridges similar to the surrounding rock, suggesting that it comprises at least some part of the walls. However, darker, bouldery material occurs at the same level just to the west (left) of the light patch, indicating that the light outcrop may not extend very far.

Images like this provide clues to help unravel the history of deposition and deformation in Valles Marineris, and may eventually tell a complex story. In order to fully understand what this image means, several questions must be addressed: is this light material the same as intensively layered deposits observed elsewhere? How extensive are light wall materials? Are these materials conformable (part of a continuous sequence) with the rest of the wall? More HiRISE imaging will help address these questions.

Photo credit: NASA/JPL/University of Arizona

Monday, November 22, 2010

Naktong Vallis

Today's VIS image shows a small section of Naktong Vallis.

Photo credit: NASA/JPL/Arizona State University

Scallop and Polygonal Features in Utopia Planitia

This observation, in Utopia Planitia, is marked by depressions in the mantle, several of which have coalesced together, and possess scalloped edges and layers.

Scalloped pits, such as these, are typical features of the mid-latitude mantle and are most commonly found at approximately 55 degrees North and South latitude; in Utopia Planitia, scalloped terrain is found between 45-50 degrees North latitude where the mantle is highly discontinuous. The presence of scalloped pits has led to hypotheses of the removal of subsurface material, possibly interstitial ice, by sublimation (evaporation). Scalloped depressions in Utopia Planitia have also been interpreted to be thermokarst lakes created by melting of a permafrost (frozen ground) and collapse of the dry surface layer.

Scalloped pits typically have a steep pole-facing scarp and a gentler equator-facing slope. This is most likely due to differences in solar heating.

On the surface surrounding the scalloped depressions are several large boulders (see subimage). Sources for these rocks may include ejecta from nearby craters, volcanic floods, or boulders emplaced by glaciers or periglacial processes. Also on the surrounding surface is a polygonal pattern of fractures. This is commonly associated with scalloped terrain, and indicates that the surface has undergone stress, potentially caused by subsidence, desiccation, or thermal contraction.

Variations in the sizes of the polygons seems to be partly dependent on their location with small polygons appearing within the scallops and larger polygons appearing outside the scallops on the surface of the mantle. Several cracks cut through the side of the scallops indicating that they must be at least as deep as the scallops. The polygons may have been present previous to the erosion of the mantle.

The formation of some scalloped depressions is believed to be an ongoing process today.

Photo credit: NASA/JPL/University of Arizona

Sunday, November 21, 2010

Two Views of Yankee Clipper Crater

"Yankee Clipper" crater on Mars carries the name of the command and service module of NASA's 1969 Apollo 12 mission to the Moon. NASA's Mars Exploration Rover Opportunity recorded this view of the crater during a pause in a 102-meter (365-foot) drive during the 2,410th Martian day, or sol, of the rover's work on Mars (November 4, 2010).

This view is a mosaic of three frames taken by the left eye of Opportunity's navigation camera. Yankee Clipper crater is about 10 meters (33 feet) in diameter.

The rover science team uses a convention of assigning the names of historic ships of exploration as the informal names for craters seen by Opportunity. Apollo 12's Yankee Clipper orbited Earth's Moon while the mission's lunar module carried two astronauts to the lunar surface on November 19, 1969, and later brought all three of the mission's astronauts back to Earth, arriving November 24, 1969. A dramatic view of Earth rising over a lunar horizon, taken from Apollo 12's Yankee Clipper, is online at http://spaceflight.nasa.gov/gallery/images/apollo/apollo12/html/as12-47-6891.html.

Photo credit: NASA/JPL-Caltech

Note: The bottom photo is an anaglyph image, requiring red-green glasses.

Three Views of Intrepid Crater

"Intrepid" crater on Mars carries the name of the lunar module of NASA's Apollo 12 mission, which landed on Earth's Moon November 19, 1969. NASA's Mars Exploration Rover Opportunity recorded this view of the crater during the 2,417th Martian day, or sol, of the rover's work on Mars (November 11, 2010).

This view is presented in approximately true color, combining exposures taken by Opportunity's panoramic camera (Pancam) through three filters admitting wavelengths of 752 nanometers, 535 nanometers and 432 nanometers. Intrepid crater is about 20 meters (66 feet) in diameter. That is about the same size as the crater where Opportunity spent its first two months on Mars: Eagle crater. The rover's look-back image into Eagle crater after driving out of it in 2004 is at PIA05755.

The rover science team uses a convention of assigning the names of historic ships of exploration as the informal names for craters seen by Opportunity. Apollo 12's lunar module Intrepid carried astronauts Alan Bean and Pete Conrad to the surface of Earth's Moon while crewmate Dick Gordon orbited overhead in the mission's command and service module, Yankee Clipper. A view of Bean next to Intrepid on the moon is online at http://spaceflight.nasa.gov/gallery/images/apollo/apollo12/html/as12-46-6749.html. An image of Conrad inspecting robotic lander Surveyor 3, with Intrepid on the lunar horizon nearby, is online at http://spaceflight.nasa.gov/gallery/images/apollo/apollo12/html/as12-48-7133.html.

Photo credit: NASA/JPL-Caltech/Cornell University

Note: The middle photo is a false color image of the crater, designed to make differences in surface materials more visible. The bottom photo is an anaglyph image of the crater.

Saturday, November 20, 2010

Kasei Valles

The Kasei Valles region is very complex. This VIS image illustrates that, with features created by fluvial action (channels) and tectonic processes (fractures).

Photo credit: NASA/JPL/Arizona State University

Unusual Gully Channels

This observation shows gullies in a southern hemisphere crater, whose floor has large mounds of material that are likely slump blocks that fell off the crater walls during a late stage of formation. There are also a large number of dunes of different sizes and facing different directions on the crater floor.

The gullies visible in this image formed over a period of time. The majority of them have experienced modification since they formed. This can be seen in the form of polygonal fractures on their walls, dunes or ripples on their channel floors, and rocks and material fallen from their walls (see subimage). Some of the gullies facing east were active more recently. They do not have polygonal fractures or they have fractures that are less well-developed. A narrow, primarily unmodified channel is also visible.

It is unknown over what period of time gullies formed in individual settings and globally. It is possible that gully formation continues today.

Photo credit: NASA/JPL/University of Arizona

Note: This crater is located west of Newton Crater in Terra Sirenum.

Friday, November 19, 2010

Wind Streaks at Alba Mons

This VIS image shows lava flows of Alba Mons and windstreaks behind craters in the area. Windstreak tail directions indicate winds from the east and east-northeast.

Photo credit: NASA/JPL/Arizona State University

Gorgonum Chaos Mesas

This observation shows mesas that are part of Gorgonum Chaos, a region of chaotic terrain, which is a jumble of mounds and mesas grouped together. Chaotic terrain is most commonly found in Mars near the sources of the gigantic outflow channels. Gorgonum Chaos is one of the few exceptions.

Some of the troughs between the mesas appear to have V-shaped bottoms; there is no obvious flat floor in between. Others have dunes running down their centers probably indicating flat floors. It is possible that the mesas were once connected and that something caused fractures in the original mesa's surface that were then preferentially eroded.

The subimage is of the far left side of the second trough from the bottom. The top left and bottom right are bordering mesa tops. Prominently displayed on the south (bottom) facing trough wall is a group of gullies that have a set of dark materials running across them. The materials are probably dunes, and they are on top of the gully channels indicating that they formed more recently.

Photo credit: NASA/JPL/University of Arizona

Thursday, November 18, 2010

Maja Valles

The streamlined islands in this VIS image are located in Maja Valles.

Photo credit: NASA/JPL/Arizona State University

Sinuous Ridges in Peta Crater

This image shows a series of long meandering ridges on the floor of a large ancient crater. Ridges such as these can be indicative of a number of geologic processes and tells us a story of the history of this region of Mars.

In some cases magma (molten rock) below the surface may fill an existing and somewhat vertical tectonic fracture, even pushing the fracture open in the process. As the magma cools, it solidifies into a tabular rock mass. This resulting cooled volcanic rock is called a "dike." The new rock is often harder and more resistant to erosion than the surrounding country rock (the fractured rock of the original landscape). Later the entire region might have experience erosion from wind or water, removing weaker rocks and soils and leaving stronger rock outcrops standing. As the landscape is stripped away the harder volcanic rock remains standing as a long wall or ridge.

Alternatively glaciers often contain internal rivers from melting ice that flow along their base where the ice meets the ground. These subglacial rivers can carry enormous amounts of rocks and soil sediments, depositing them along their length. When the glacier retreats it leave behind a narrow ridge of river-bed sediments that stands above the surrounding surface. In this case the ridge is called an "esker."

A river flowing along the surface in the absence of a glacier can produce erosion and deposition along the river bed. It can also chemically alter the river bottom, through deposition of minerals and salts that cement the soils and rocks. Later, after the river has dried up, erosion of the landscape can leave the altered river bed standing above the surrounding terrain, called an "inverted channel."

So what happened in Peta Crater? Analysis of this image might reveal characteristics, such as layers along the ridge walls that would indicate the ridge was deposited by flowing water. Rocks and boulders might be found eroding from the ridge, their size and shape offering clues to the strength of the ridge material; fractured and angular solid rock from a dike or loosely bound rounded boulders tumbled along a river bed.

Photo credit: NASA/JPL/University of Arizona

Wednesday, November 17, 2010

Kasei Valles

This VIS image shows a portion of the northern branch of Kasei Valles.

Photo credit: NASA/JPL/Arizona State University

Blocks and Valleys in Southwestern Melas Chasma

This HiRISE image covers a portion of the wallrock and canyon floor in southwestern Melas Chasma.

Along the floor of Melas Chasma is an unusual blocky deposit composed of light-toned blocks in a darker matrix. The high resolution of the HiRISE image reveals layers only a few meters thick in some of the light-toned blocks. The blocks vary in size but most fall between 100-500 meters in diameter.

Although most blocks appear rounded, others have angular edges and can be very elongated. The morphologies of the blocks suggest ductile deformation, such as from a flow or by tectonic disruption after emplacement. Aeolian ripples are interspersed between the blocks in the darker matrix.

Small valleys can be seen along the wallrock to the south. The wallrock is a mixture of two geologic units that differ mainly in their reflectance. The light-toned unit appears to be thinner and only exposed in localized spots. Several of the light-toned deposits are seen only in the valleys, suggesting they were either deposited or are exposed by erosion.

Photo credit: NASA/JPL/University of Arizona

Tuesday, November 16, 2010

Channel in Terra Cimmeria

This VIS image shows part of an unnamed channel in Terra Cimmeria.

Photo credit: NASA/JPL/Arizona State University

Firsoff Crater

From the USGS Astrogeology Science Center:

The name Firsoff has been approved for the Martian crater located at 2.6N, 9.4W. For more information, see the database information and the map of MC-11 in the Gazetteer of Planetary Nomenclature.

Note: Firsoff Crater is located in Meridiani Planum, and is slightly southeast of Crommelin Crater. Firsoff Crater is named after Valdemar Axel Firsoff; an English amateur astronomer of Swedish descent (1910-1981) who is known for his many books on the Moon, Mars, and the other terrestrial planets.

Monday, November 15, 2010

Ascraeus Mons

This VIS image of the southern flank of Ascraeus Mons shows a small sample of collapse features that are common in the area.

Photo credit: NASA/JPL/Arizona State University

Note: While collapse features may include pit craters, what we see in this photo are primarily collapsed lava tubes; see this post for a more detailed explanation of similar features on Pavonis Mons. What I find interesting is that some of the older lava tubes have been so eroded away (by the wind) that there are only faint traces of what must have been deeper depressions like those seen on the right hand side of the picture.

Inverted Channels and Layers Near Juventae Chasma

This image shows plains north of the southwestern Juventae Chasma, a canyon part of the gigantic Valles Marineris system.

There are three distinct terrains in this image, plains with possible inverted channels, plains with exposed layers, and layers on a wall of Juventae Chasma.

The top half of the image contains plains with craters and sinuous ridge features that are possibly inverted stream channels. Inverted relief occurs when a formerly low-lying area becomes high-standing. There are several possible reasons why channels might stand out in inverted relief. The streambed material may become cemented by precipating minerals, contain larger rocks, or become filled with lava, all which are more resistant to erosion. Finer-grained, more erodable material surrounding the channel is blown away by the wind or carried away by water, leaving the resistant channel bed high and dry around its environs.

Another example of erosion can be seen in the next terrain which covers about 2/3 of the bottom half of the image. Erosion has exposed a beautiful series of light and dark tone layers (approximately 1 kilometer across). In the subimage, the smallest of the rings is the deepest exposed layer.

Layers are common in the Martian canyons, but it is unknown what process formed them. It is likely that the layers in the plains here are made of the same material as the layer in the canyons.

Photo credit: NASA/JPL/University of Arizona

Sunday, November 14, 2010

Intrepid Crater

This view of "Intrepid" crater, about 20 meters (66 feet) in diameter, is a mosaic of images taken by the navigation camera on NASA's Mars Exploration Rover Opportunity. The view spans 180 degrees and is centered toward the east.

Opportunity approached the crater with a 36.4-meter (119-foot) drive during the 2,415th Martian day, or sol, of the rover's mission on Mars (November 9, 2010), and then took the component images of this scene on the same sol. The view is presented as a cylindrical projection.

Photo credit: NASA/JPL-Caltech

Crater Central Peak

This observation shows a central peak of a large, degraded impact crater in the Terra Sirenum region of the southern hemisphere. Central peaks form during crater formation when a particularly large impactor hits the surface.

The central peak visible here (about 2/3 of the way down the full image) is interesting because it has some fluvial-like features on its south side. At lower resolution, these features appear to be channels with some connecting pits. At higher resolution (see subimage), the features appear to be troughs that are filled with dunes.

What is most interesting is the chain of pits that extends down the center of some of the troughs as seen in the subimage. It is possible that these pits are evidence of subsurface piping or hydrothermal activity. Piping occurs when subsurface water flows through soil, takes some soil with it, and causes the overlying ground to collapse. These fluvial-like features and the connected pits may have formed during a late stage of crater formation when temperatures were suitable for liquid water.

Photo credit: NASA/JPL/University of Arizona

Saturday, November 13, 2010

Ceraunius Tholus Caldera

This VIS image shows part of the summit caldera of Ceraunius Tholus, one of the smaller volcanoes of the Tharsis region.

Photo credit: NASA/JPL/Arizona State University

Southern Hemisphere Crater with Gullies

This observation shows an approximately 6 kilometer diameter crater with gullies and interesting crater fill.

The crater fill may have formed from mass wasting (downward movement of material due to gravity) of ice-rich material. It is distinct from the walls of the crater, which is unusual. Often crater fill will take the form of concentric circles, suggesting that material has been transported down each wall similarly. This is not the case here.

There are two main sets of gullies, one deeply incised (left) next to one that is shallower (right). The gullies on the left are well developed and have likely experienced more flow than the gullies on the right. The well-developed gullies cross several wrinkles that wrap around much of the crater fill, indicating the gullies formed after the crater fill was in place. The gullies on the right (see subimage) are shallow and narrow. Several have linear depressions above their sources suggesting that subsurface water flowing to the gully heads removed some material creating the collapse depressions visible here.

Photo credit: NASA/JPL/University of Arizona

Note: This unnamed crater is located on the western edge of a larger unnamed crater, both of which are located in Terra Cimmeria. The craters lie to the west of Ariadnes Colles.

Friday, November 12, 2010

Avernus Colles

Avernus Colles is a region of 'hills' separated by arcuate fractures. These features are the margin between the southern highlands and Elysium Planitia to the north.

Photo credit: NASA/JPL/Arizona State University

Cerberus Fossae Fracture

This image shows part of a fracture that is approximately 800 meters (half a mile) wide. This fracture is part of a larger set of similar features that are collectively called Cerberus Fossae.

Some scientists suggest that lava, water, or both erupted from these fractures at some point in Mars' past. The presence of streamlined hills, such as those that are found in river channels on Earth, as well as lava flows, are some of the observations that lead scientists to this interpretation. Thus this fracture may be a large scale example of eruptive vents that form on volcanoes on Earth.

Photo credit: NASA/JPL/University of Arizona

Note: This photo looks very similar to Cerberus Fossae East of the Head of Athabasca Valles

Thursday, November 11, 2010

Lycus Sulci

Lycus Sulci is an extremely complex region surrounding the western and northern flanks of Olympus Mons. With a multitude of fault-formed cliff faces, dark slope streaks are a common occurrence.

Photo credit: NASA/JPL/Arizona State University

Lava Channel on the Flank of Ascraeus Mons

Ascraeus Mons is one of the giant shield volcanoes on Mars. Its flanks are built up of innumerable lava flows, but most are buried by too much dust to see features of interest.

This is one of the better preserved lava flows, showing a distinct channel running diagonally through the observation. As surges of hot lava spilled over the channels banks, levees were built up on either side of the flowing lava. Then, as the eruption slowed, the liquid lava drained out, leaving a long trough.

While a relatively young feature for Mars, this lava surface is still very ancient - as one can tell from the large number of impact craters scattered across the image. The other persistent geologic process has been the wind. Its effect can be seen in the form of bright streaks heading west from craters and other topographic obstacles. This is where bright dust is able to find shelter from the wind.

Photo credit: NASA/JPL/University of Arizona

Wednesday, November 10, 2010

Wind Effects Near Eumenides Dorsum

One of the most active agent of erosion on Mars today is the wind. This region, near Nicholson Crater, as been sculpted by untold years of blowing grit and wind.

Photo credit: NASA/JPL/Arizona State University

Note: This area is actually some distance away from Nicholson Crater, which lies well to the west. Rather, this picture was taken in the southern region of Eumenides Dorsum, which extends out of the Martian southern highlands toward Amazonis Planitia.

Cones Formed by Hot Lava Running over Water or Ice

These cones are similar in size and shape to cones found in Iceland where hot lava has run over wet ground.

The heat from the lava boils the water which bursts through the lava flow. These steam-driven exploding bubbles of lava throw chunks of molten and solid lava into the air.

A long series of such explosions is needed to build up one of the large cones. The cones appear in chains because the surface of the lava flow was moving while the series of explosions were taking place. This is sort of like a miniature version of how the Hawaiian Island chain forms. The hot spot under Hawaii is fixed but the Earth's crust slides past it.

This image forms a stereo pair with ESP_018457_2065.

Photo credit: NASA/JPL/University of Arizona

Note: This area is located in the northeastern reaches of Elysium Planitia, south of Arcadia Planitia and southeast of Adams and Lockyer craters.

Tuesday, November 9, 2010

Acheron Fossae

Channels dissect the complex region of Acheron Fossae, located north of Olympus Mons.

Photo credit: NASA/JPL/Arizona State University

Channel and Fan in Lyot Crater

Extensive flow of liquid water across the surface of Mars is generally constrained to the first billion years of the planet's evolution. There are some specific places, however, where liquid water may have been stable later in the planet's history, when Mars is considered to have been cold and dry. Lyot Crater is one of those places.

Lyot Crater is a "peak-ring basin" that formed in the lowlands of the northern hemisphere of Mars, making it the lowest topographic point in the northern hemisphere. Additionally, we know that the Lyot impact event occurred after the most significant era of fluvial activity on Mars, so any features observed in Lyot were formed after that era as well.

This observation shows what appears to be a very unusual fan of material that is sourced by a valley that extends upslope for almost 50 kilometers along the floor of Lyot Crater (top-right of the full image [see also here]). The fan is not fresh, so this activity pre-dates the Martian gullies (a few of which can be seen at the top of this image). The fan has been mantled by smooth material which has been removed in some areas and fractured in others. This makes it difficult to tell what the fan looked like when it was originally emplaced.

Lyot Crater is found in a region of Mars that is thought to host many debris-covered glaciers (some of which are found within Lyot itself) and ice-rich mantling units. These could provide potential sources of water that, under conditions slightly more favorable than those of today, could melt and create features like we see here.

Photo credit: NASA/JPL/University of Arizona

Sunday, November 7, 2010

Nirgal Vallis

This VIS image shows a small section of Nirgal Vallis.

Photo credit: NASA/JPL/Arizona State University

Fading Impact Crater

This young impact site was discovered by the MRO CTX Science Team.

A new dark spot appeared in a CTX image from July 2008 that was not seen when the region was previously imaged by the Mars Odyssey THEMIS VIS instrument in November 2004. High resolution imaging by HiRISE in November 2008 (left panel of the subimage) confirmed that the dark spot was ejecta from a cluster of craters.

Three large craters ranging from 3 to 5 meters diameter and at least 5 smaller craters make up the cluster pictured. A smaller outlier (approximately 2 meters in diameter, not pictured in the subimage) landed 300 meters away to the northwest (bottom right in the non-map projected subimages [see also here]). These craters were likely produced by a single impactor that broke into pieces as it fell through the Martian atmosphere.

The impactor probably approached from the northwest, judging from the shape of the ejecta pattern and the location of the small outlier. The impacts sprayed the site with dark ejecta excavated from beneath the bright surface. The conspicuous, newly formed feature provides an ideal location to monitor the effects of wind on the modern Martian surface.

HiRISE imaged the site again in September 2010 (right panel of the subimage), after the passage of a full Martian year when the illumination was similar to the previous HiRISE image. By luck, the incidence angle (the zenith angle of the Sun) of the later image was only 0.2 degrees different from that of the earlier image. However, the phase angle (the angle between the Sun, the target, and the camera) was smaller by about 14 degrees as the spacecraft rolled in the opposite direction.

The new picture shows the ejecta pattern apparently faded in comparison to the previous image. The contrast of other features in the scene (such as the hills and boulders at the bottom of the cutout) is similar, but the ejecta from the crater cluster is noticeably brighter in the HiRISE image from 2010. One possibility is that the dark ejecta reflects sunlight differently than the bright surrounding terrain, becoming darker more rapidly as phase angle increases. Another possibility is that the ejecta pattern was mantled by a thin layer of bright dust that settled out of the atmosphere during the 20 month interval between the two images. Further monitoring of this site by HiRISE will help choose between these hypotheses.

This target illustrates how the various instruments on MRO work together. The spatial coverage of HiRISE is too limited to search for new impact craters across the Martian globe. Yet the spatial resolution of HiRISE can be used to verify and study details in sites identified as suspicious by CTX. The complimentary capabilities of the MRO instruments provide a fuller understanding of Mars together than their insights taken separately.

Photo credit: NASA/JPL/University of Arizona