Wednesday, March 31, 2010

Layers and Dark Debris in Melas Chasma

This subimage shows layering in a light-toned deposit in Melas Chasma.

The layers are sedimentary in origin, but there are many processes that could have deposited them, such as volcanic airfall from explosive eruptions, or dust-size particles settling out of the atmosphere due to cyclic changes, and deposition in standing bodies of water.

By looking at the slopes in the layers and how the layers intersect each other, scientists can rule out various origins. A darker material can be seen covering much of the layered deposit. Some of this dark material is loose and can be seen accumulating as debris aprons at the base of steep slopes. Other dark material appears indurated and has been eroded by the wind to form etched edges with topographic expressions.

The lack of impact craters on the layered deposit indicates that it is a relatively young deposit, or the craters have been removed by the wind, or the deposit was quickly buried and is now being exhumed.

Photo credit: NASA/JPL/University of Arizona

Tuesday, March 30, 2010

Opportunity at the Edge of Concepción Crater

This image shows the Mars Exploration Rover Opportunity perched on the [southwestern] edge of Concepción Crater in Meridiani Planum, Mars.

Concepción Crater is a fresh, 10 meter-diameter crater with dark rays that clearly overprint the north trending aeolian ripples. The dark rays are produced by shadows cast by blocky ejecta and the presence of the rays and similar relationships with other fresh craters in Meridiani Planum indicate that this is likely the youngest crater visited by either rover on Mars (estimated to have impacted thousands to tens of thousands of years ago).

This image was acquired by HiRISE on 13 February 2010, on sol 2153 of Opportunity’s mission on Mars. Note the rover tracks in the ripples to the north and northwest of the rover. Scientists use these high-resolution images (about 25 cm/pixel) to help navigate the rover. In addition, rover exploration of areas covered by such high-resolution images provides “ground truth” for the orbital data.

Photo credit: NASA/JPL/University of Arizona

Monday, March 29, 2010

Rotational Landslides or Slumps Along Walls of Bahram Vallis

Bahram Vallis is a narrow-winding valley (20-22 North, 301-304 East) that terminates at the circum-Chyrse Basin on Mars.

The valley has numerous circular to sub-circular alcoves along its slopes, some with large deposits directly below on the valley floor. These features are evident from earlier image datasets of Mars including THEMIS, MOC, and HRSC, and are indicative of mass-wasting processes that have occurred along the valley walls.

A portion of the valley was imaged by the HiRISE camera at approximately 30 centimeters/pixel resolution in a location with both alcoves and valley floor deposits. Several features are apparent: a well-defined circular crown and main scarp, tensional cracks along the crown margins, and a well-defined accumulation zone with slump deposits.

The general appearance of these landslides is similar to terrestrial rock and/or loose earth rotational landslides. The Bahram landslides are also different from other well-documented landslides on Mars, such as those in the Valles Marineris canyon system that have lobate forms and longitudinal and/or transverse ridges on their surfaces. Future study of these landslide deposits will incorporate elevation data from the digital topographic model to assess the stability of valley walls using standard earth geotechnical models.

Credit: NASA/JPL/University of Arizona/USGS

Note: While doing research for the various links in this post, I came across this short flyby animation of the Bahram Vallis that uses HiRISE data. Enjoy!

Sunday, March 28, 2010

Deformed Layered Sediments in Western Hellas Planitia

The western margin of Alpheus Colles (the large plateau in Hellas Planitia) is bound by a large depression that is the deepest point in the Hellas basin and also the lowest terrain on Mars.

This region is characterized by highly deformed layered sediment nicknamed "honeycomb" or "taffy pull" terrain. The origin of this unusual layered sediment is unknown, but it may be related to an ancient lake or ocean in Hellas.

Photo credit: NASA/JPL/University of Arizona

Saturday, March 27, 2010

Dune Symmetry

Dunes of sand-sized materials have been trapped on the floors of many Martian craters. This is one example, from a crater in Noachis Terra, west of the giant Hellas impact basin.

The dunes here are linear, thought to be due to shifting wind directions. In places, each dune is remarkably similar to adjacent dunes, including a reddish (or dust colored) band on northeast-facing slopes. Large angular boulders litter the floor between dunes.

The most extensive linear dune fields know in the Solar System are on Saturn's large moon Titan. Titan has a very different environment and composition, so at meter-scale resolution they probably are very different from Martian dunes.

Photo credit: NASA/JPL/University of Arizona

Friday, March 26, 2010

Frost-Covered Dunes in Crater

Dunes are often found on crater floors. In the winter time at high northern latitudes the terrain is covered by carbon dioxide ice (dry ice). In the spring as this seasonal ice evaporates many unusual features unique to Mars are visible.

On the floor of this crater where there are no dunes, the ice forms an uninterrupted layer. On the dunes however, dark streaks form as surface material from below the ice is mobilized and deposited on top of the ice. In some cases this mobile material probably slides down the steep face of the dune, while in other cases it may be literally blown out in a process of gas release similar to removing a cork from a champagne bottle.

Photo credit: NASA/JPL/University of Arizona

Note: This image was taken in a crater located high up in the Vastitas Borealis, just south of the Planum Boreum, the Martian northern polar ice cap.

Thursday, March 25, 2010

Colorful Streaks

This is an image of the central pit of an impact crater in the ancient highlands.

The central uplifts of large impact craters often collapse to form pits on Mars, but they are still structural uplifts and often expose deep bedrock with diverse rock types which have a variety of colors.

In this enhanced color subimage, we see colorful streaks, where the bedrock is eroding, moving downhill a bit, then getting swept by the wind.

Photo credit:  NASA/JPL/University of Arizona

Note: This crater is located in the Memnonia Quadrangle; the closest significant crater to this location is Magelhaens Crater, which is named after the Portuguese explorer, Fernão de Magalhães (1480-1521), better known in the English language as Ferdinand Magellan. Magelhaens Crater is to the southeast of this image.

Wednesday, March 24, 2010

Phoenix Lander in Springtime

With early spring at the Phoenix landing site comes the progressive sublimation of the carbon dioxide frost that has blanketed the lander and surrounding terrain throughout the winter.

During the long polar-winter night atmospheric carbon dioxide freezes onto the surface building up a layer of frost roughly 30 centimeters (about one foot) thick. In the spring this frost returns to atmosphere gas (sublimates) over the course of several months. This image, part of a seasonal frost monitoring sequence, shows some areas of bare ground are beginning to be exposed. However, extensive frost patches remain in the topographic lows, such as the troughs of the local polygonally patterned surface.

The solar arrays on the lander were clearly discernible from their distinctive bluish color in HiRISE images acquired last Martian northern summer. The enhanced color subimage [the image above] has green boxes around the backshell (top), heat shield, and lander (bottom). They are not discernible in this new image, probably because the patchy frost effectively camouflages them. (For a comparison, see PSP_008855_2485, particularly the subimage there.)

Even when the frost has completely sublimated, dust deposited during the winter may obscure them. The parachute attached to the backshell is also not apparent in this image, and we'll see if it reappears in later images. Also gone are the dark halos around the lander, backshell, and heat shield, again due to seasonal frost and/or dust. This and future images will help calibrate expectations for finding the Mars Polar Lander hardware which encountered Mars in 1999.

Photo credit: NASA/JPL/University of Arizona

Tuesday, March 23, 2010

Record-Breaking Dust Devil Caught in the Act

Sometimes HiRISE finds something unexpected.

This image was targeted to study knobs in Mars' northern plains, just north of Scandia Crater. The knobs are clearly imaged, but what surprised scientists was a dust devil visible in the south-central part of the image.

As on Earth, dust devils form when ground heated by sunlight warms the air above it. The hot air rises, forming an updraft accompanied by vortical motions. Because warm ground is a requirement, dust devils on Mars generally form in late spring to summer, especially at high latitudes.

This image was taken in early spring (2010), at a latitude of 61 degrees North. No dust devil has been seen this far from the equator at such an early season before.

Photo credit: NASA/JPL/University of Arizona

Note: The location of this dust devil and Scandia Crater are both in the Scandia Colles region of the Vastitas Borealis, and is located in the Diacria Quadrangle. Scandia Crater is located almost due north of Milankovic Crater, which is the most prominent crater in that region.

Monday, March 22, 2010

Candidate Landing Site over Potential Chloride Salt Deposits

There is an intriguing surface unit in parts of the ancient Martian highlands that may consist of chloride salts (like NaCl--table salt) which precipitated out of shallow lakes as in desert regions of Earth.

It has unusual thermal properties and distinctive morphologies, but lacks spectral absorption bands. All of these characteristics and the geologic settings are consistent with salt deposits. These deposits are often associated with clay minerals that do have distinctive absorption bands.

This particular location has been selected as a candidate landing site for the Mars Science Laboratory or another future rover. Hopefully the HiRISE images won't reveal too many boulders or steep slopes that would be hazardous. A stereo anaglyph is also available.

Photo credit: NASA/JPL/University of Arizona

Note: This candidate landing site is located in Meridiani Planum; the closest prominent crater to this location is Airy, which is to the east.

Sunday, March 21, 2010

Phobos Flyby Images by Mars Express

Images from the recent flyby of Phobos, on 7 March 2010, were released on March 15th. The images show Mars' rocky moon in exquisite detail, with a resolution of just 4.4 meters per pixel. They show the proposed landing sites for the forthcoming Phobos-Grunt mission.

ESA's Mars Express spacecraft orbits the Red Planet in a highly elliptical, polar orbit that brings it close to Phobos every five months. It is the only spacecraft currently in orbit around Mars whose orbit reaches far enough from the planet to provide a close-up view of Phobos.

Like our Moon, Phobos always shows the same side to the planet, so it is only by flying outside the orbit that it becomes possible to observe the far side. Mars Express did just this on 7, 10 and 13 March 2010. Mars Express also collected data with other instruments.

Phobos is an irregular body measuring some 27 × 22 × 19 km. Its origin is debated. It appears to share many surface characteristics with the class of 'carbonaceous C-type' asteroids, which suggests it might have been captured from this population. However, it is difficult to explain either the capture mechanism or the subsequent evolution of the orbit into the equatorial plane of Mars. An alternative hypothesis is that it formed around Mars, and is therefore a remnant from the planetary formation period.

In 2011 Russia will send a mission called Phobos–Grunt (meaning "Phobos-Soil") to land on the Martian moon, collect a soil sample and return it to Earth for analysis.

For operational and landing safety reasons, the proposed landing sites were selected on the far side of Phobos within the area 5°S-5°N, 230-235°E. This region was imaged by the HRSC high-resolution camera of Mars Express during the July-August 2008 flybys of Phobos. But new HRSC images showing the vicinity of the landing area under different conditions, such as better illumination from the Sun, remain highly valuable for mission planners.

It is expected that Earth-based ESA stations will take part in controlling Phobos-Grunt, receiving telemetry and making trajectory measurements, including implementation of very long-baseline interferometry (VLBI). This cooperation is realized on the basis of the agreement on collaboration of the Russian Federal Space Agency and ESA in the framework of the 'Phobos-Grunt' and 'ExoMars' projects.

Mars Express will continue to encounter Phobos until the end of March, when the moon will pass out of range. During the remaining flybys, HRSC and other instruments will continue to collect data.

Photo credit: ESA/DLR/FU Berlin (G. Neukum)

Nanedi Vallis: Tributaries and Albedo Changes

This HiRISE image shows a part of Nanedi Vallis, one of the Martian valley networks. The valley networks are thought to have formed by flowing water in the distant past when the climate on Mars was warmer and wetter than it is today.

Some scientists have suggested that the valley networks could have been produced in a climate like the dry, cold one of Mars today if the liquid water was protected by an overlying ice layer. Others think that glacial activity may be responsible for them, but the majority believe that the valley networks are evidence of ancient flowing water.

Valley networks are characterized by their blunt, theater-shaped heads and their approximately constant width along their reaches. They often have tributaries, as seen in this image, that connect with the main trunk of the valley.

Photo credit: NASA/JPL/University of Arizona

Saturday, March 20, 2010

Mantled Surface of Ascraeus Mons

This image shows a part of the western flank of Ascraeus Mons. Ascraeus Mons is one of the giant volcanoes of the Tharsis volcanic region of Mars.

It is a shield volcano, so named because of the gently-sloped round shape. Terrestrial examples, like Mauna Loa and Kilauea on Hawaii, are formed mostly by repeated eruptions of fluid (basaltic) lava. Martian volcanoes can attain much larger sizes partially because Mars lacks plate tectonics, allowing eruptions to persist at the same site for a long time.

In this HiRISE image, the surface is covered by a mantle of dusty material which obscured the underlying surface. This has been sculpted into regular textures, probably by aeolian (wind) erosion. It appears that there are multiple layers, as the southeast portion of the image shows textured knobs standing above a similarly patterned surface. The origin of the dusty mantle is unclear. It could be wind-blown dust, but it is also possible that some of it is volcanic ash erupted from Ascraeus Mons.

Photo credit: NASA/JPL/University of Arizona

Friday, March 19, 2010

Tongue-Shaped Flow Feature in Hellas Planitia

This image captures a tongue-shaped lobate flow feature along a interior crater wall located in eastern Hellas Planitia.

The flow feature is approximately 5 kilometers long and 1 kilometer wide with a partial double inner ridge and raised outer margin. The flow feature's surface is generally devoid of impact craters and parts of its outer margin have deflected around obstacles.

Similar flow features, though not as distinctively tongue-shaped as this one, are found in many other craters throughout the southern mid-latitudes of Mars.

Recent studies of these flow features have determined a latitudinal dependence to which side of the crater interior these features are formed upon. For this particular flow feature, it has formed on the pole-facing slope. This polar or equatorial-facing preference has implications for the amount of solar insolation these slopes are receiving, which may be a result of recent climate change due to shifts from low to high obliquity.

Although these Martian flow features may have Earth analogs such as rock glaciers, uncertainty remains as to what types of fluvial, glacial and mass-wasting processes are involved in their formation. This particular flow feature was imaged previously by the Mars Orbiter Camera (MOC) onboard NASA's Mars Global Surveyor spacecraft.

Photo credit: NASA/JPL/University of Arizona

Thursday, March 18, 2010

Shield Volcano with a Summit Caldera

Although there are a few truly giant shield volcanoes on Mars, there are also many smaller shield volcanoes. We are interested in imaging the vent regions of volcanoes to understand volcanic processes, and also to search for any signs of especially recent activity.

It has been suggested that active volcanism is one possible explanation for the methane gas that has been detected in the atmosphere of Mars. This HiRISE image shows that the summit caldera is mantled by dust and covered by small impact craters, so there is essentially zero chance that this volcano was active recently enough to affect current atmospheric trace gases.

Photo credit: NASA/JPL/University of Arizona

Note: This volcano is located in the Tharsis Quadrangle of Mars (at 20.1 North, 250.3 East), between Ascraeus Mons to the southeast and Olympica Fossae to the northwest.

Wednesday, March 17, 2010

Contortions on the Floor of Hellas Basin

The floor of Hellas Basin is often obscured by atmospheric haze and dust, but it tends to be quite clear this time of year (northern spring and southern fall).

HiRISE images are revealing some very strange landforms on the floor of Hellas. Materials appear to have flowed in a viscous manner, like ice. Viscous flow features are common over the middle latitudes of Mars, but those in Hellas are often distinctive for unknown reasons.

The subimage shows an interesting area in color (reddish areas are dustier).

This image completes a stereo pair with PSP_007715_1420, so be sure to check out the stereo anaglyph.

Photo credit: NASA/JPL/University of Arizona

Tuesday, March 16, 2010

A Very Recent Crater in Syria Planum

This image shows a very fresh-looking impact crater with extensive radial ejecta.

The crater was first seen in an image acquired with MRO's Context Camera (CTX). The best image of this region prior to CTX was from one of the Viking Orbiters, and the crater isn't apparent in that image. This could mean that the crater formed sometime between 1976 and 1999, or there may have been more dust on the surface in 1976 or the air may have been hazy, obscuring the crater.

Based on the HiRISE image, we suspect that the crater is more than several decades old, because at full resolution we see a textured surface that is common in dust-mantled regions of Mars, but absent in the youngest craters.

Photo credit: NASA/JPL/University of Arizona

Note: This crater is located in Syria Planum, which is south of Noctis Labyrinthus.

Monday, March 15, 2010

A Burst of Spring

In the winter a layer of carbon dioxide ice (dry ice) covers the north polar sand dunes. In the spring the sublimation of the ice (going directly from ice to gas) causes a host of uniquely Martian phenomena.

In this subimage streaks of dark basaltic sand have been carried from below the ice layer to form fan-shaped deposits on top of the seasonal ice. The similarity in the directions of the fans suggests that they formed at the same time, when the wind direction and speed was the same. They often form along the boundary between the dune and the surface below the dunes.

Photo credit: NASA/JPL/University of Arizona

Note: This image is from the Olympia Undae region of the Vastitas Borealis.

Sunday, March 14, 2010

Cerberus Fossae East of the Head of Athabasca Valles

This image shows part of Cerberus Fossae, a long system of extensional (normal) faults arranged in trough-bounding (graben-bounding) pairs. Cerberus Fossae served as the source of a large volcanic eruption that draped Athabasca Valles in lava.

Large boulders that have been dislodged from the graben walls are visible on the floor of Cerberus Fossae. The first subimage shows an example of an approximately 6 meter (20 feet) boulder that left a distinct track as it moved downhill. Although this track is quite clear, ripples inside the track are discernible, indicating that enough time has passed for wind activity to rework loose material into the form of ripples. With close examination of this observation, one can see many boulder tracks, some with ripples and some without ripples.

Wind streaks emanating from impact craters are visible on the plains surrounding Cerberus Fossae. The second subimage shows a false color image of an approximately 33 meters (108 feet) impact crater. Material on the crater floor (blue in the color image) is being moved by the wind out of the crater and across the plains. The wind streaks in this observation indicate that the predominant wind direction in this region is from East to West.

Photo credit: NASA/JPL/University of Arizona

Saturday, March 13, 2010

Candidate Landing Site in Possible Salt Playa

This image covers part of a candidate landing site that appears to be a shallow depression with a deposit perhaps consisting of chlorides, like table salt.

The relatively bright material broken up into polygons or other patterns is possibly chloride. Such deposits occur in playas on Earth, and imply the past presence of water and a habitable (but not necessarily inhabited) environment. The HiRISE images will help to interpret the geology and to determine if this spot is a sufficiently safe landing site—not too many boulders or steep slopes. If it is safe enough, this site will be considered further as a landing site for the 2011 Mars Science Laboratory or for a European or NASA rover to be launched in 2018 according to current plans.

Be sure also to look at the stereo anaglyph for more detail.

Photo credit: NASA/JPL/University of Arizona

Note: This image is located in the Meridiani Planum, east of the Margaritifer Chaos.

Friday, March 12, 2010

Northern Hemisphere Gullies with Layers

This observation shows northern hemisphere gullies on a layered crater wall.

Many channels are visible emanating from beneath layers suggesting that the layers are permeable and carried water to the slope face via the subsurface. It is also possible that the source of water came from the surface. The gullies that do not originate at a layer likely did at one time and have subsequently experienced headward erosion, eroding the layers upslope of their original location.

A mantled unit (smooth terrain) is visible the sources of and within many of the gullies in this image. The mantled unit has been proposed to be remnant snowpack that melts at its bottom to carve gullies. The mantled unit is less abundant in locations where the gullies are most deeply incised, which supports the melting snowpack theory.

Deeper incision typically involves more water and/or more flow events. If the mantled unit is the source of the liquid for the gullies, then it is expected that locations with evidence of larger or more frequent flows would be associated with regions of less mantled unit. It is unknown whether the mantled unit can insulate the surface sufficiently to allow temperatures and pressures appropriate for liquid water formation. An answer to this awaits future modeling of snowpack under Martian conditions.

Within the subimage, channels can clearly be seen to originate at a variety of layers. Also noticeable is the smooth, mantled material located between layers above these gullies.

Photo credit: NASA/JPL/University of Arizona

Note: The crater of which this photo was taken is located near the center of Isidis Planitia.

Thursday, March 11, 2010

At the Summit of Arsia Mons

Like the other major shield volcanoes on Mars, Arsia Mons has a caldera (large volcanic crater) at its summit.

Calderas form when magma (molten rock) is removed from the magma chamber in the volcano, and the roof of the magma chamber collapses into the resulting void. In the case of Arsia Mons, there are relatively young lava flows that overtop the northeast rim of the caldera.

This HiRISE image samples some of these lava flows. The long elliptical depression is the summit crater of a small shield volcano that fed some of these lava flows. At HiRISE resolution, we see that even these younger lavas are covered by a thick layer of dust. The small dark-rayed crater in the southwest edge of the image shows that the rock under the dust is dark, as expected of lava.

Photo credit: NASA/JPL/University of Arizona

Wednesday, March 10, 2010

Monitoring of Polar Avalanche Region

This HiRISE image shows the scarp that demarcates the boundary between layered deposits covering the north polar region and the lower surrounding terrain, which includes sand dunes.

This image was taken in the northern hemisphere Martian spring, where it is still cold enough that white carbon dioxide frost covers most of the area. At about the same time in the previous Martian spring (February 2008), HiRISE caught four avalanches at this location.

This image does not show any active avalanches, but shows many avalanche deposits. Comparison of this new image with the one taken in 2008 will give an indication of activity over the last Martian year.

Photo Credit: NASA/JPL/University of Arizona

Tuesday, March 9, 2010

Dunes and Inverted Craters in Arabia Terra

This image shows dark sand dunes and inverted craters in the Arabia Terra region of Mars.

The sand is dark because it was probably derived from basalt, a black volcanic rock that is common on Mars. Unlike traditional craters that are depressions, those here stick up above the surrounding plains. Such "inverted topography" is found on Mars and Earth where erosion has stripped away surrounding topography.

In this case, the craters were filled with sediment. Subsequent erosion stripped away the terrain around the filled craters, leaving the inverted topography visible here. The enlarged color view shows one of the inverted craters surrounded by the dark dunes.

Photo credit: NASA/JPL/University of Arizona

Monday, March 8, 2010

Gullies and... Gullies? in Terra Sirenum

This observation shows part of an unnamed crater, itself located inside the much larger Newton Crater, in Terra Sirenum. This unnamed crater is approximately 7 kilometers in diameter (over 4 miles) and some 700 meters (760 yards) deep.

Numerous gully systems are visible on the east- and south-facing walls of the crater; their characteristics are astonishingly diverse.

The subimage [the light-colored photo above] covers an area of nearly 610 x 740 meters (670 x 800 yards). Downhill is toward the bottom of the image, north is up; illumination is from the northwest. This subimage depicts several gullies or troughs carved in the southwest-facing wall of the crater.

These troughs are extremely rectilinear, lack tributaries, and do not seem to have terminal fan deposits: they terminate rather abruptly, some of them in a spatula-like shape. Their characteristics contrast sharply with those of gully systems elsewhere in this same crater, which are sinuous, have numerous tributaries, and show distinct fan deposits.

HiRISE is unveiling the large diversity exhibited by Martian gully systems, thanks to its high-resolution, stereo, and color capabilities. The diverse types of gullies observed may have been produced by different mechanisms. Current leading hypotheses explaining the origin of gullies include erosion from seepage or eruption of water from a subsurface aquifer, melting of ground ice, or surface snow; and dry landslides.
Photo credits: NASA/JPL/University of Arizona

Sunday, March 7, 2010

Northern Meridiani Etched Terrain and Hematite Plains Contact

This observation shows the contact between the hematite bearing plains and etched terrain in northern Meridiani Planum.

The hematite bearing plains (exposed at the bottom left of the full image) are dark, smooth and full of dune fields. This unit is laterally extensive and the same unit that the Mars Exploration Rover Opportunity was sitting on about 400 kilometers to the southwest (in 2007). Based on observations by Opportunity, this unit is interpreted to be a thin aeolian (wind-blown) mantle of basaltic sand and hematite concretions sitting on the etched terrain.

The etched terrain in this image is split into two units. The darker unit at the top of the image is filling in an approximately 120 kilometer NW-SE trending valley, while the brighter etched terrain in the middle of the image is stratigraphically and topographically higher than the lower etched terrain in the valley. This upper etched terrain is a plateau-forming unit with a geomorphic pattern that ranges from relatively flat plains to dissected plateaus and mesas. The lower etched terrain is flat with low albedo, and covered in dunes.

It is in these etched terrains that CRISM, and previously OMEGA, have detected hydrated sulfates, which makes a sedimentary origin seems most likely for these layered deposits of etched terrain found in Meridiani.

Credit: NASA/JPL/University of Arizona

Saturday, March 6, 2010

Craters on an Ice-Rich Débris Apron

This observation shows a swath of a debris apron east of Hellas Basin. Features like this are often found surrounding isolated mountains in this area. Material flowed down off of the top of the mountain and settled in an area around its base. The bottom of the image (to the south) shows the base of the mountain, where material is sliding off and piling up into ridges. The top of the image (to the north) shows the lobate edge of the apron, where it stopped flowing.

Recently, the SHARAD (Shallow Ground-Penetrating Radar) instrument (also on board the Mars Reconnaissance Orbiter with HiRISE) measured large amounts of water ice mixed into this and other debris aprons. The water ice is what gives the apron its unique texture, which is especially clear at HiRISE's high resolution. Parallel ridges and grooves indicate material has moved slowly while remaining solid - a process called "creep." Pits and buttes may have formed when the dust- and debris-covered ice cracked and sublimated (went directly from a solid to a gas phase).

We can also use this HiRISE image to study the small impact craters found in these areas. Débris aprons like this one have fewer craters than their surroundings. Because impacts generally occur indiscriminately over all of Mars, this means that either the débris apron is younger than its surroundings, or some process is erasing craters on the apron - a process which is not occurring as rapidly on the surrounding plains.

The fact that this apron is rich in water ice is a clue to what is happening. Another clue is the craters on the apron themselves: they have a different appearance than most craters. Some of these degraded craters are "inverted" (higher in the middle than at the edges, which is the opposite of normal craters).

Craters like this have been modified, so we can tell the surface has been active at some time since the impact that formed the crater. For this reason we can't estimate the age of the flow by counting craters, like we are be able to do on some surfaces. However, we can use these craters to study the processes that are actively modifying the apron material.

Photo Credit: NASA/JPL/University of Arizona

Wednesday, March 3, 2010

Candidate Landing Site in Northeast Syrtis Major

These images lie on the eastern edge of a candidate landing site in the northeastern part of Syrtis Major, a huge shield volcano, and near the northwestern rim of Isidis Planitia, a giant impact basin.

This region exposes Early Noachian bedrock, more than 4 billion years old, and contains a diversity of hydrated minerals. This would be an excellent place to explore early Mars, when the environment may have been conducive to life.

HiRISE images will aid geologic interpretations and help determine if this spot is sufficiently safe for landing--not too many boulders or steep slopes. If it is sufficiently safe, it may be considered for the 2011 Mars Science Laboratory or the 2018 rovers from Europe and the USA [ESA-NASA ExoMars Program].
Photo Credit: NASA/JPL/University of Arizona

Tuesday, March 2, 2010

Well-Preserved Layering in Oudemans Crater's Central Uplift

This HiRISE image covers a portion of the central uplift of the 120 kilometer diameter Oudemans Crater.

Oudemans is located at the western end of Valles Marineris and just south of the great canyon system by the Noctis Labyrinthus. Images from the Mars Orbital Camera (MOC) were the first to reveal that this large impact crater exposed layered rock in its central uplift feature.

Such beautifully preserved layered rocks, although rare, are no surprise to planetary scientists. First, layered rocks exposed in the central uplifts are common in terrestrial impact structures. Secondly, there is abundant layering exposed in the nearby Valles Marineris canyon system — a gash that exposes layering down to 7 kilometers beneath the mean surface. This suggests that layered materials exist to great depths in the subsurface, which is supported by the Oudemans central uplift observation.

Based on estimates of the depth of excavation for a crater the size of Oudemans, these layers originated from just as deep as those exposed in Valles Marineris and possibly deeper. A comparison of the layers in Valles Marineris and in the Oudemans central uplift may prove that they are similar rock types that share the same mode of origin. The fact that these layers are so well intact gives planetary scientists specific clues regarding the subsurface and history of the general area.

Additionally, three other craters, Martin (21.2 degrees South, 290.7 degree East), Mazamba (27.3 degrees South, 290.2 degrees East) and a yet unnamed crater (28.4 degrees South, 305 degrees Eeast) also possess finely layered materials in their central uplift features and lie within the circum-Tharsis region. The preservation of the layering and geographical occurrence of these four craters suggests that they could be ash layers deposited from numerous episodes from the Tharsis volcanoes. Voluminous volcanic episodes could have produced large volumes of layered rock that could have been rapidly buried and protected from cratering.
Photo Credit: NASA/JPL/University of Arizona

Monday, March 1, 2010

Slope Streaks in Acheron Fossae

This observation shows a portion of the wall (light-toned material) and floor of a trough in the Acheron Fossae region of Mars.

Many dark and light-toned slope streaks are visible on the wall of the trough surrounded by dunes. Slope streak formation is among the few known processes currently active on Mars. While the mechanism of formation and triggering is debated, they are most commonly believed to form by downslope movement of extremely dry sand or very fine-grained dust in an almost fluidlike manner (analogous to a terrestrial snow avalanche) exposing darker underlying material.

Some of the slope streaks show evidence that downslope movement is being diverted around obstacles, such as large boulders, and a few appear to originate at boulders or clumps of rocky material. These slope streaks, as well as others on the planet, do not have deposits of displaced material at their downslope ends. The darkest slope streaks are youngest and can be seen to cross cut and lie on top of the older and lighter-toned streaks. The lighter-toned streaks are believed to be dark streaks that are lightening with time as new dust is deposited on their surface.
Photo Credit: NASA/JPL/University of Arizona

Note: See also Slope Streaks in Terra Sabaea for a similar phenomenon.

Update: Astronomy Picture of the Day has highlighted the above photo, and included two interesting links with respect to this photo that I've included below. The first is a wide-angle, black-and-white photo by HiRise that is directly overhead of the slope streaks in Acheron Fossae:

The second link goes to a very short Youtube video, embedded below, in which someone playing with a pile of sand demonstrates the way in which the sands on Mars have created these slope streaks.