Dunes and Ripples in Valles Marineris

Two types of wind-blown sedimentary deposits are pictured in this scene of the floor of Ius Chasma in the Valles Marineris.

Smaller light toned ridge-like ripples draped over the bright bedrock are visible in this subimage. Long dark sand dunes superpose the small ridges, indicating that the sand dunes formed more recently than the ridges. Earlier observations have shown that the small ridges, known as "transverse aeolian ridges" or TARs, appear to be fixed in place. They are typically found near the equator of Mars, in places where the winds alternate in direction over daily or seasonal cycles.

Detailed investigations by the MER rovers revealed that the TARs were armored by a surface layer of coarse granules left behind after the smaller particles were winnowed away by the wind. These granules are too large to be lifted by the wind and preserve the TARs from further erosion. In contrast, recent HiRISE observations show that many of the dark sand dunes on Mars are actively on the move.

From these facts, we can hypothesize the recent history of the aeolian deposits here in Ius Chasma. Unconsolidated sediments were formed in the canyon by impact fragmentation and erosion of the steep canyon walls. These sediments were eroded and shaped into dunes by the winds that blow up and down the canyon, alternating direction between day and night. Eventually the tireless winds won the battle over sediment supply, and the remaining sediments were sifted into the TARs visible in the image, oriented perpendicular to the length of the canyon (transverse to the winds).

More recently, a fresh supply of sand was introduced into the canyon that the winds have not yet had time to tame. Instead of forming simple crescent dunes, the bidirectional winds have shaped the sand into long linear dunes punctuated by short slip faces. At high resolution, we see that the linear sand dunes are ruffled along their lengths by ripples transverse to the wind directions. Ultimately, most of this sand will be swept away, leaving the TARs trapped behind.

Photo credit: NASA/JPL/University of Arizona

The Phoenix Lander After Two Mars Years

This is one of a series of images to monitor frost patterns at the Phoenix landing site.

The lander and backshell are visible, but not the parachute or the dark halo around the lander which is covered by dust. (Although the lander may appear strange, we have to remember that its solar arrays have collapsed.)

This is the same appearance to the hardware as 1 Mars years ago, in 2010. For views of the lander during the active mission in 2008, see our special releases page.

Photo credit: NASA/JPL/University of Arizona

Looking for an Impact Crater on a Dune

This dune field image was requested since a prior lower-resolution (THEMIS VIS) image of this area had suggested the possible presence of an impact crater on the dunes. Finding an impact crater on a dune field would be quite important: as of 2011, no craters have been found on Martian dunes, which strongly supports the hypothesis that the dune fields are very young features and either formed or have actively evolved during the last tens of thousands of years.

No crater is visible in this dune field image, which is consistent with the "active" and "fresh" appearance of these dunes: (1) they have sharp crestlines and (2) slipfaces (the downwind slope; generally pointing towards the south-southwest in this field, although there are some signs of a reversing slipface, implying that some past winds have pushed sand towards the northeast-north northeast) are generally very smooth in appearance, except for some small avalanche features (which form as sand accumulating at the upper-portion of the slipface).

The search for a dune-field crater will need to continue...

Photo credit: NASA/JPL/University of Arizona

Note: This image is located in an unnamed crater in Bosporus Planum northwest of Argyre Planitia.

Spirit Lander and Bonneville Crater in Color

HiRISE has never before imaged the actual lander for the Spirit rover in color, on the west side of Bonneville Crater. The lander is still bright, but with a reddish color, probably due to a dust cover (lower left in the subimage).

A bright spot from a remnant of the heat shield is still visible on the north rim of Bonneville Crater. The backshell and parachute are still bright, but were not captured in the narrow color swath.

The rover itself can still be seen near "home plate" in the Columbia Hills, but there is no obvious sign of rover tracks--erased by the wind.

Photo credit: NASA/JPL/University of Arizona

MARSIS' Map of Mars' Northern Hemisphere

A pole-to-equator map of the Martian northern hemisphere, displayed in polar stereographic projections. The map is color-coded to indicate the MARSIS mean dielectric constant of a number of geological units.

Map credit: Figure courtesy of J. Mouginot et al.

Notes: For further details see Mouginot, J., et al., "Dielectric map of the Martian northern hemisphere and the nature of plain filling materials", 2012, Geophysical Research Letters, 39, L02202. DOI:10.1029/2011GL050286 For more information, see Mars Radar Finds Possible Ocean Sediments.

Late Afternoon on Mars

NASA's Mars Exploration Rover Opportunity used its panoramic camera to capture this low-light raw image during the late afternoon of the rover's 2,847th Martian day, or sol, of work on Mars (January 27, 2012).

The rover is positioned for the Mars winter at "Greeley Haven," an outcrop located on the north end of Cape York on the rim of Endeavour Crater. This site provides an approximate 15-degree northerly tilt for favorable solar energy production.

Plans for research continuing through the winter months at Greeley Haven include a radio-science investigation of the interior of Mars, inspections of mineral compositions and textures on the outcrop, and assembly of a full-circle, color panorama of the surroundings.

Photo credit: NASA/JPL-Caltech/Cornell/Arizona State University

Crater with Gullies on a Central Structure

The 40-kilometer diameter unnamed crater (49 degrees North, 21 degrees East) in this image is located west of Lyot Crater and north of Deuteronilus Mensae in the Northern Plains of Mars.

As seen in the subimage, gully systems in the central structure have eroded underlying layers (undercutting) that are less resistant to erosion than the surface rock of the central structure. Previous channelized water flows likely transported the eroded sediments toward the southeast and deposited them forming the expansive debris aprons.

The formation of channels on the debris aprons supports the hypothesis that these sediments were transported down the gullies and then deposited onto the aprons by flowing water. In the larger, northernmost system, sediments have partially filled in the channel segments and winds have remobilized these sediments forming the dunes that line the gullies.

This is a stereo pair with PSP_009298_2295.

Photo credit: NASA/JPL/University of Arizona

The Floor of Toro Crater

Toro Crater may have experienced hydrothermal alteration, producing diverse minerals. The mineral diversity leads to diverse color in HiRISE, especially when enhanced as in this subimage.

In general the blue and green colors indicate unaltered minerals like pyroxene and olivine, whereas the warmer colors indicate alteration into clays and other minerals. The linear north-south trending features are windblown dunes that are much younger than the bedrock.

This is a stereo pair with ESP_025344_1970.

Photo credit: NASA/JPL/University of Arizona

Active Erosion in Pasteur Crater

This image shows knobs and bluffs that are being actively eroded by the Martian wind. Fine, light-toned sedimentary layering is exposed in the bedrock at the base of the cliffs.

Also in this scene are two types of unconsolidated aeolian sediments. The reddish ridges are relatively immobile, and are probably similar to granule ripples on Earth that are protected from the winds by a surface layer of coarse grains. The dark gray dunes are probably made up of fine (approximately 0.1 mm) basaltic sand. Previous HiRISE images (PSP_001756_1995, PSP_010643_1995) showed that the sand in Pasteur Crater is currently mobile.

This sand is thought to be locally derived, from dark deposits within a small crater called Euphrates that is located within Pasteur, upwind of the sand dunes. The movement of this sand contributes to the erosion of the ancient bedrock, sandblasting the formation into the knobs seen today and exposing layers that were deposited in ages past.

Photo credit: NASA/JPL/University of Arizona

Well-Preserved Crater in Terra Sabaea

Shown here is a stereo pair (see the anaglyph) of a well-preserved impact crater about 6 or 7 kilometers wide from rim to rim. By well-preserved we mean that the crater has a sharp rim, deep cavity, impact morphologies preserved down to scales of tens of meters, and little sign of infilling or degradation by a range of processes (other impacts, volcanism, tectonism, icy flow, aeolian erosion and infill, etc.).

When seen at full HiRISE resolution, almost all craters on Mars do show some modification such as subsequent smaller impacts, wind-blown deposition and/or erosion, and downslope movement of material on steep slopes.

We have imaged hundreds of well-preserved impact craters on Mars ranging from 1 meter to more than 100 kilometers wide. These targets are of great interest for multiple reasons: first, we want to better understand impact cratering, a fundamental surface process. Second, such craters often contain good exposures of bedrock in the steep walls and, if the crater is large enough, in the central uplift. Just like terrestrial geologists are attracted to good bedrock outcrops like road cuts, planetary geologists are attracted to well-preserved craters.

Third, the steep slopes often reveal active processes, such as formation of gullies, boulder falls, and slope streaks that could form in a variety of ways. Some of these active processes could be related to water, since the crater may expose lenses of ice or salty water, or create deep shadows that trap volatiles, or expose salts that can extract water from the air.

This is a stereo pair with ESP_024738_1595.

Photo credit: NASA/JPL/University of Arizona

Note: This crater is located on the border of Terra Sabaea, being to the northwest of Hellas Planitia. The closest named feature is Harris Crater.

Very Fresh Impact Crater Superposing a Wrinkle Ridge in Hesperia Planum

The ridge captured in this HiRISE image is called a wrinkle ridge. This wrinkle ridge is located in Hesperia Planum, a region of over two million square kilometers (over 770,000 square miles) in the southern highlands of Mars. It is located northwest of the Hellas basin and adjacent to Tyrrhena Patera and contains abundant orthogonal and intersecting wrinkle ridges.

Wrinkle ridges are long, winding topographic highs and are often characterized by a broad arch with superposed narrow asymmetric ridges. These features have also been identified on the Moon, Mercury, and Venus. Their origin is attributed to horizontal compression or shortening of the crust due to faulting and folding. They commonly have asymmetrical cross sectional profiles and an offset in elevation on either side of the ridge.

Superposing or located on top of the wrinkle ridge, is a very fresh impact crater. We can tell that this crater is fresh because of its relatively sharp or crisp rim and unmodified shape. If you look closely, you can see faint rays of relatively fine material, boulders, and smaller secondary craters radiating from the crater and superposing the wrinkle ridge and older surrounding craters.

Photo credit: NASA/JPL/University of Arizona

Note: For an mp4 video clip of this area, including additional photographs, click here.

Opportunity's Three-Year Trek Across Mars

During the three-year trek of NASA's Mars Rover Opportunity from Victoria crater to Endeavour crater, rover planners captured a horizon photograph at the end of each drive. 309 images taken during the 13-mile journey appear in this video.

Video credit: NASA/JPL-Caltech/Cornell/Arizona State University

Dunes in Noachis Terra

This enhanced-color image shows sand dunes trapped in an impact crater in Noachis Terra, Mars. Dunes and sand ripples of various shapes and sizes display the natural beauty created by physical processes. The area covered in the image is about six-tenths of a mile (1 kilometer) across.

Sand dunes are among the most widespread wind-formed features on Mars. Their distribution and shapes are affected by changes in wind direction and wind strength. Patterns of dune erosion and deposition provide insight into the sedimentary history of the surrounding terrain.

The image is one product from an observation by the High Resolution Imaging Science Experiment (HiRISE) camera taken on November 29, 2011, at 42 degrees south latitude, 42 degrees east longitude. Other image products from the same observation are at http://www.uahirise.org/ESP_025042_1375.

Photo credit: NASA/JPL-Caltech/University of Arizona

Note: This caption is very similar to that of the recent post, Sand Dunes in Noachis Terra. Although the pictures are different, I wouldn't be surprised if both images come from the same crater.

Double Layer Ejecta in an Arabia Region Crater

When impact craters form, they are generally surrounded by "ejecta": material that is thrown out from the crater by the impact and that settles onto the surrounding terrain. Sometimes there are multiple phases of material that fall to the ground (although both result from the same impact), creating the appearance of layered-ejecta.

This DLE [double layer ejecta] crater formed at the edge of an older/pre-existing crater, the rim of which deflected some of its ejecta. As it deflected the two phases of falling ejecta differently, we can use it to study how ejecta is transported and deposited. With HiRISE resolution, it may be possible for us to determine topography of the rim and then to see how high the barrier was that deflected some of the ejecta flow.

This is also an unusual crater because it is outside the Northern Plains and is relatively young.

This is a stereo pair with ESP_017356_2175.

Photo credit: NASA/JPL/University of Arizona

Notes: This crater is located along the "shore" between Arabia Terra and Chryse Planitia. The closest named feature is Cydonia Mensae to the west. Also, Note: For an mp4 video clip on this impact crater, including additional photographs, click here.

Fluvial Fan on a Crater Floor

This observation shows a terrific fan-shaped deposit, beginning where the channel enters a crater. This is suggestive of a delta: a deposit that forms when water in a channel flows into a larger area (such as an ocean or a lake). As the water spreads out, it moves slower and drops the sediment that it is carrying, forming the delta. (E.g., a famous Earth example is the Nile River delta.)

The THEMIS instrument also photographed this area (I03235002), as well as the Context Camera (CTX) aboard the Mars Reconnaissance Orbiter. The resolution of HiRISE helps scientists determine the topography of the region which is needed for establishing the stratigraphic relations and flow direction of the area.

Here is a view of the terrain to the south of the craters in the full image.

Photo credit: NASA/JPL/University of Arizona

Notes: This crater is located in Tempe Terra to the west of Chryse Planitia and to the north of Kasei Valles. The closest named crater is Sytinskaya. Also, for an mp4 video clip about this crater, including additional photographs, click here.

Greeley Haven in False Color on Opportunity's Eighth Anniversary

This mosaic of images taken in mid-January 2012 shows the windswept vista northward (left) to northeastward (right) from the location where NASA's Mars Exploration Rover Opportunity is spending its fifth Martian winter, an outcrop informally named "Greeley Haven."

Opportunity's Panoramic Camera (Pancam) took the component images as part of full-circle view being assembled from Greeley Haven.

The view includes sand ripples and other wind-sculpted features in the foreground and mid-field. The northern edge of the the "Cape York" segment of the rim of Endeavour Crater forms an arc across the upper half of the scene.

Opportunity landed on Mars on January 25, 2004, Universal Time and EST (January 24, PST). It has driven 21.4 miles (34.4 kilometers) as of its eighth anniversary on the planet. In late 2011, the rover team drove Opportunity up onto Greeley Haven to take advantage of the outcrop's Sun-facing slope to boost output from the rover's dusty solar panels during the Martian winter.

Research activities while at Greeley Haven include a radio-science investigation of the interior of Mars, inspections of mineral compositions and textures on the outcrop, and monitoring of wind-caused changes on scales from dunes to individual soil particles.

The image combines exposures taken through Pancam filters centered on wavelengths of 753 nanometers (near infrared), 535 nanometers (green) and 432 nanometers (violet). The view is presented in false color to make some differences between materials easier to see.

Photo credit: NASA/JPL-Caltech/Cornell/Arizona State University

Note: For a true-color image of the same view, see PIA15281: Opportunity's Eighth Anniversary View From 'Greeley Haven'.

Sand Dunes in Noachis Terra

Sand dunes are among the most widespread aeolian (wind-formed) features present on Mars. Their spatial distribution and morphology are affected by changes in wind direction and wind strength. Patterns of dune erosion and deposition provide insight into the sedimentary history of the surrounding terrain.

This image shows sand dunes trapped in an impact crater in Noachis Terra. Dunes and sand ripples of various shapes and sizes, such as in this enhanced-color subimage, show the natural beauty created by physical processes.

This is a stereo pair with ESP_024976_1375.

Photo credit: NASA/JPL/University of Arizona

Notes: This crater is located a very short distance due west of Hellespontus Montes, which is to the west of Hellas Planitia. Also, for an mp4 video clip of these dunes, with additional photographs, click here.

Many Fantastically Colorful Gullies in a Fresh Impact Crater

This image covers a "fresh-looking" impact crater with a diameter of about 2 kilometers (1.2 miles).

There are gullies all around the steep inner slopes of this crater (you can even see them in the shadow by enhancing the brightness of this region), at 35 degrees South latitude. Many craters at this latitude in the southern hemisphere only have gullies on the south-facing slopes, which are shadowed in the wintertime. But this is an especially pristine crater so the slopes may be particularly steep and unstable.


The enhanced color sub image shows that gullies and their deposits have many different colors. This is due to diverse rock types exposed by the crater and the fact that the gullies have been recently active, so colors have not been homogenized by overlying regolith (soil) or windblown deposits. HiRISE will monitor this site in the future to see if the gullies are currently active.

How long ago did this crater form? It appears nearly pristine, preserving meter-scale morphologies in the ejecta, and there are almost no superimposed (younger) impact craters, so it is probably less than a million years old. That means the crater formed in the most recent 0.02 percent of Mars' existence. The ejecta includes a "herringbone" texture with V-shaped features pointing to the source crater.

Photo credit: NASA/JPL/University of Arizona

Note: This small crater is located in Bosporos Planum, just northeast of Aki Crater. Also, for an mp4 video clip of this impact crater, including additional information and photographs, click here.

Gullies in Bamberg Crater

This cluster of gullies is on the wall of Bamberg Crater.

The impact crater has an extremely eroded and terraced rim. However, the gullies do not have extensive aprons and overall there appears to be very little material accumulated on the crater floor -- unlike many other craters with gullies. This may indicate the gullies are young features.

However, gully formation on Mars is still not completely understood, and more information and observations are needed to improve our interpretation of these features.

Photo credit: NASA/JPL/University of Arizona

Note: For an mp4 video clip of the gullies of Bamberg Crater, including additional information and photographs, click here.

Tongue-Shaped Flow Below a Scarp in Phlegra Montes

This observation shows a tongue-shaped flow of material below a scarp in Phlegra Montes, a range of curving mountains and ridges on Mars.

This type of feature is sometimes formed by a debris flow, a landslide, or the flow of ice-rich material. However, the source of the material and how it was deposited here remains unclear.

Photo credit: NASA/JPL/University of Arizona

Note: For an mp4 video clip discussing the above-mentioned area, click here.

The Floor of Beer Crater

This crater was named after German astronomer Wilhelm Beer. It is an ancient crater more than 100 kilometers across, located south of Meridiani Planum.

A full-resolution color sample shows fractured bedrock with dark sand filling low areas. The circular rocky features are probably eroded impact craters and the thin linear features are windblown deposits.

The aeolian (wind) erosion and modification of this ancient surface make it difficult to deduce how the rocks were initially emplaced, but the channeled rims suggest that these could be alluvial fans: deposits carried by flowing water (probably not beer).

Photo credit: NASA/JPL/University of Arizona

Note: For an mp4 video clip discussing the floor of Beer Crater, click here.

Search for Beagle 2 Lander

This is the twelfth image from HiRISE in the part of Isidis basin where the British Beagle 2 spacecraft was supposed to land around Christmas time of 2003.

All contact was lost after its separation from the Mars Express spacecraft six days before atmospheric entry. The lack of telemetry on its way to the surface means there is little information about where the spacecraft may have landed on the surface--we can only search in the region where it was expected to land if the entry, descent, and landing (EDL) sequence had been nominal. EDL was probably not nominal, but perhaps the spacecraft did land correctly and failure occurred for some other reason.

Nothing resembling the Beagle lander has been seen in any of the HiRISE images, although we aren't sure that they've been thoroughly searched. For an idea of what the Beagle 2 hardware might look like, see this web page.

The easiest thing to spot would be the bright parachute, if it actually deployed. The parachutes are still easy to spot at the MER and Pathfinder landing sites, so dust deposition over the past eight years probably would not disguise the bright feature over equatorial regions of Mars. At high latitudes the brightness patterns are reset each winter by the seasonal deposits of carbon-dioxide and dust, as seen at the Phoenix landing site. However, beware of bright cosmic-ray hits.

EDL on Mars is difficult! Only the United States has succeeded, with Viking 1, Viking 2, Mars Pathfinder, Spirit, Opportunity, and Phoenix. The 1999 Mars Polar Lander was a failure, as was Beagle 2 and six landing attempts by the former Soviet Union. One of the Soviet landers, Mars 3, made it to the surface and transmitted some data or noise for 20 seconds before failure. We haven't been able to locate any of the Soviet lander hardware from HiRISE images.

Searching for this hardware is like looking for a needle in a really big haystack, and we don't know what the needle looks like. In August 2012 NASA will attempt to land the biggest rover ever sent to Mars, MSL or Curiosity. HiRISE will attempt to image MSL during descent, as it did for Phoenix, and after what is hopefully a successful landing.

Photo credit: NASA/JPL/University of Arizona

Banded Wall Outcrop in Ius Chasma

This area was covered in a well-known MOC image of October 1997 (AB1-01303) that shows what appears to be layered rock, deep below the Martian surface.

At the time, this was considered to be revolutionary and seemed to contradict the general view of the upper crust of Mars as being a lunar-like "megaregolith." Later coverage of this outcrop area by MOC is not particularly good and the CTX (Context Camera) coverage doesn't improve on spatial resolution much.

However, experience with other HiRISE images suggests the "layering" will be less obvious at sub-meter-per-pixel scales, but nonetheless we'll see some interesting things. This was thought to be an important area for the development of some post-Viking views of Mars. This underscores how much technology has changed since the 1970s.

Photo credit: NASA/JPL/University of Arizona

Aram Chaos

The southern cap rock in Aram Chaos is situated in the Martian equatorial region, to the east of the Tharsis region.

In Ancient Greek, "chaos" meant an emptiness or void, the gap that existed between the heavens and the earth; here, we use the word to describe terrain that is jumbled and "confused." As the image shows us, Aram Chaos is actually a heavily eroded impact crater, with material on the floor that is blocky in contrast to some of the surrounding terrain.

This would be an interesting area to explore and to send a rover, because we think that water might have existed in the underground as ice.

Photo credit: NASA/JPL/University of Arizona

Defrosting Barchan Dunes

This HiRISE image shows sand dunes near the eastern part of North Polar erg.

The dunes imaged here are similar to barchan dunes, commonly found in desert regions on Earth. Barchan dunes are generally crescent-shaped with a steep slip face bordered by horns oriented in the downwind direction. Barchan dunes form by winds blowing mainly in one direction and thus are good indicators of the dominant wind direction when the dunes formed.

The dunes and surrounding surface appear bright because they are covered with seasonal frost left over from the northern hemisphere winter. Sunlight is now falling on the North Polar region, and carbon dioxide frost that accumulated during winter is sublimating (going directly from solid to gas) and the surface beneath the frost is being revealed.

Composed primarily of basaltic sand, the dunes will appear dark during the northern hemisphere summer. The dark spots are areas where some of this frost has begun to sublime away, and/or where wind has exposed the underlying dark sand.

Photo credit: NASA/JPL/University of Arizona

Note: This image is located west of Olympia Mensae, and north of Louth Crater. I am not quite sure what "north polar erg" the author is referring to in the first sentence. The eastern end of the primary north polar erg, Olympia Undae, is actually on the other side of the planet. This location is much closer to the western end of Olympia Undae, although that is still some distance away. Personally, I would say that the image location is in Vastitas Borealis.

Floral-Shaped Volcano on Cerberus Fossae

This is a small volcano superposed on the flanks of a larger one of the Cerberus Tholi.

This smaller feature has a single vent, aligned along a Cerberus Fossae trough, and it has flows radiating away from this vent in all directions, somewhat looking like a flower.

These flows appear somewhat darker than their surroundings, though this might be owing to roughness as much as to relative youth. Note that even at Context Camera (CTX) scale, we can see that there are some small impact craters superimposed on this feature, indicating that it is not entirely young.

This is a stereo pair with ESP_023811_1880.

Photo credit: NASA/JPL/University of Arizona

Note: Cerberus Tholi is a group of seven volcanic hills located in Elysium Planitia. Cerberus Tholi is located south of the eastern end of Cerberus Fossae, and roughly encircle Tombaugh Crater.

Transverse Aeolian Ridges in Proctor Crater

Transverse Aeolian Ridges (or TARs) are small aeolian bedforms that are distinct from typical dunes or ripples. TARs are found all over Mars, and are typically located near layered terrains, or near fields of large dark dunes as they are here in Proctor Crater in the southern hemisphere.

TARS form transverse (perpendicular) to the wind direction and are thought to be composed of coarse-grained material. They also appear to be indurated (hardened) and may be much less mobile than the larger dunes.

This is a stereo pair with ESP_024515_1320.

Photo credit: NASA/JPL/University of Arizona

Lava Flow Oozing into a Crater

This image captures a fairly rare situation. In general, as lava flows along, it fills in low points and holes it encounters in its path and flows around high points such as hills and ridges. In this image there are two lava flows interacting with an impact crater.

Although an impact crater approximately 3 kilometers (1.8 miles) wide such as this is a deep hole in the ground (likely a couple hundred meters or several hundred feet deep), it is surrounded by a rim crest that is actually higher than the surrounding terrain, lifted up during the powerful impact that formed the crater originally. On the south side of the crater, a smooth-surfaced lava flow (with some knobs in the southwest) has come in contact with the exterior of the crater rim, burying any sign of ejecta from the crater and covering most of the rim, almost up to the rim crest.

However, because the height of the crater rim was slightly greater than the thickness of the lava flow, the crater rim acted like a wall and prevented the deep crater from being overrun and filled with the lava. Later, however, a different, younger, heavily ridged lava flow approached the crater from the north - the thickness of this ridged lava flow is visible along its flow front in the eastern part of the image. Unlike the earlier flow, the ridged flow overtopped the crater's northeast rim, and a single lobe of lava is descending to the floor of the crater. If the rim had been any lower, or if the lava had advanced any further, the crater would have been filled and buried and we would not be lucky enough to see this snapshot of the dramatic interaction of lava with this crater.

By studying how lava reacts to obstacles and to variation in slope, like this lobe falling down the crater's inside wall, scientists may be able to learn about the thickness, viscosity (or stickiness), and strength of the lava flow, which in turn could help constrain the composition and temperature of the lava.

This is a stereo pair with ESP_024877_1465.

Photo credit: NASA/JPL/University of Arizona

Note: The location of this image is in far northeastern Terra Sirenum, northwest of Pickering Crater.

What is This Stuff?

This image covers plains near Aureum Chaos. A puzzling ridged texture was first seen in an image from the Context Camera on MRO, leading to this suggestion for a HiRISE image.

In this image we can see much detail, but the origin of the surface texture is still puzzling. The enhanced color subimage helps to correlate rock units, but is also puzzling.

Here's a hypothetical geologic history that might explain this scene: layered sediments were deposited by water or airfall (including volcanic pyroclastics). A crudely polygonal patterned ground was created by stresses in the sediments, and groundwater followed the fractures and deposited minerals that cemented the sediments. This was followed by perhaps billions of years of erosion by the wind, leaving the cemented fractures as high-standing ridges.

Of course, this story is almost certainly incomplete if not totally wrong.

Photo credit: NASA/JPL/University of Arizona

Greeley Haven in False Color

This mosaic was acquired by the Mars Exploration Rover Opportunity's Panoramic Camera (Pancam) on Sol 2793 (December 2, 2011). It shows a north-facing outcrop, informally named "Greeley Haven," where Opportunity will work during the rover's fifth Martian winter. The rover team chose this designation as a tribute to the influential planetary geologist Ronald Greeley (1939-2011), who was a member of the science team for the Mars rovers and many other interplanetary missions.

The site is of interest not only for its geologic features but because it has favorable northerly slopes to optimize Opportunity's solar energy as winter approaches in the southern hemisphere of Mars. After this mosaic was acquired, Opportunity backed up the slope to park at approximately 16 degrees northerly tilt and used tools on its robotic arm (Instrument Deployment Device, or IDD) to examine rock and soil targets. After deciding that the site could serve the mission well for the next several months, the team designated it as a memorial for Greeley, who taught generations of planetary scientists at Arizona State University, Tempe, until his death on October 27, 2011.

The site is near the northern tip of the "Cape York" segment of the western rim of Endeavour Crater.

The image combines exposures taken through Pancam filters centered on wavelengths of 753 nanometers (near infrared), 535 nanometers (green) and 432 nanometers (violet). The view is presented in false color to make some differences between materials easier to see.

Plans for research continuing through the months at Greeley Haven include a radio-science investigation of the interior of Mars, inspections of mineral compositions and textures on the outcrop, and assembly of a full-circle, color panorama of the surroundings. The planned full-circle image will be called the Greeley Panorama.

Photo credit: NASA/JPL-Caltech/Cornell/Arizona State University

Note: For other pictures in this series, see PIA15118: Approaching 'Greeley Haven' on Endeavour Rim, PIA15119: 'Greeley Haven' Site for Opportunity's Fifth Martian Winter and PIA15276: Locator Map for 'Greeley Haven' on Endeavour Rim.

Valley in Ismenius Lacus Region

A valley extends across the center of the image, and a tributary joins it from the north, while another branch connects from the south. This branch--which resembles half of a crater--is really just a bend in the channel, much more incised than the muted valley going across the scene.

There is evidence of mass wasting (gravity moving dry materials off high-standing regions onto low-lying regions), visible where a series of ridges appear to be piling up near the floor of the bend.

The terrain surrounding the valley has craters of a range of ages, judging by their different states of degradation. One small fresh crater near the right side of the image has dark, high-standing rays extending from it. A larger more degraded crater is located in the bottom third of the image. A great deal of material has flowed off the crater walls into its center. It is likely that ground ice aided the movement of this material.

Photo credit: NASA/JPL/University of Arizona

Note: The location of this image, Ismenius Lacus, lies in the larger region of Arabia Terra and is located northeast of Cerulli Crater.

Radargram of Mars' North Polar Plateau

The upper panel is a radargram profile from the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS), showing data from the subsurface of Mars in the ice-rich north polar plateau of Mars. It shows layers detected to a depth of about 1.5 miles (2.7 kilometers) beneath the surface in a transect about 930 miles (1,500 kilometers) long. A basal unit of a sand- and dust-rich icy material comprises more than half of the bulk of the polar plateau in this radargram profile. Its base can be traced from beneath the Olympia Undae sand sea at left, across the entire polar stack, to the margin of the Rupes Tenuis plateau at right, where there are no overlying north polar layered deposits (NPLD). The vertical dimension is time delay of radio-signal echo. The apparent deepening of the basal unit's lower boundary at the center is an artifact of the slowing of the radar wave in the icy material. In fact, the lower boundary is nearly flat.

The lower panel shows the path of the spacecraft ground track while these radar observations were being made, on a topographical map derived from Mars Orbiter Laser Altimeter data. Total relief in the topography from highest (red) to lowest (purple) is 1.7 miles (2.7 kilometers).

Image credit: ESA/NASA/JPL-Caltech/Univ. of Rome/ASI/GSFC

Note: For more information, see MARSIS Completes Measurement Campaign Over Martian North Pole.