Monday, February 27, 2012

Well-Speckled Polar Dunes

These barchan (crescent-shaped) sand dunes are found within the North Polar erg of Mars. This type of dune provides a great record of the wind environment when they formed and moved: barchan dunes' horns point downwind. Although the question of present-day sand motion is still open, it appears possible that these dunes are active (when not covered in frost) as their crestlines are very sharp and their slipfaces (the inner curved region between the horns/downwind surface) appears very smooth and steep.

In this image, taken during the northern spring season, the dunes and ground are still covered in seasonal frost. The speckled appearance is due to the warming of the area -- as the carbon dioxide frost and ice on the dunes warms, small areas warm and sublimate (turn from solid to gas) faster, creating small jets that expose/deposit dark sand and dust onto the surface. Notice that there are no spots on the ground between the dunes -- that is because the ground stays more uniformly cold, unlike the darker dune sand.

As spring continues, more spots will appear on the dunes until, suddenly, all of the frost on the dunes and ground will be gone and the dark dune sand will be exposed until next winter.

Photo credit: NASA/JPL/University of Arizona

Note: This image is located in Olympia Mensae.

Sunday, February 26, 2012

Utopia Planitia Scallops, Polygons, and Boulders

This terrain is covered by pits and scallops (pits open on one side), perhaps due to collapse after sublimation of subsurface ice.

This full-resolution anaglyph sample shows that the surface is cut into many polygons about 10 meters wide, that form as ice expands and contracts with temperature changes. There are also many meter-scale boulders on the surface, which must be rocks rather than blocks of ice, or they would not be stable on the surface.

More than 10 meters thickness of ice must have sublimated from some areas. (Sublimation is the process of going from a solid directly to a gas). How did the ice get deposited? One idea is that it's from snowfall (in a different climate), but then it is difficult to explain the presence of the boulders. The other possibility is transport through the shallow subsurface in very thin films of water over many years.

This is a stereo pair with ESP_025277_2275.

Photo credit: NASA/JPL/University of Arizona

Note: This image is located in northwestern Utopia Planitia; the closest named feature is Nier Crater, which is some distance off to the southeast.

Saturday, February 25, 2012

Dunes in Late Fall: Frost in the Ripples

These dunes in Aonia Terra are being monitored for changes such as gullies, which form over the winter from the action of carbon dioxide frost.

The season in which this image was acquired was late fall in the Southern hemisphere. Frost is just starting to accumulate here, and is concentrated on pole-facing slopes and in the troughs between the meter-scale ripples.

The colors have been enhanced in the subimage.

Photo credit: NASA/JPL/University of Arizona

Friday, February 24, 2012

Imaging in Deep Shadows

This image of an impact crater in Terra Cimmeria was acquired when the Sun was just 11 degrees above the horizon, so a long shadow extends over most of the crater interior.

However, there is still diffuse illumination from the sky and HiRISE has the ability to acquire sufficient signal over faint targets to make useful images. The subimage shows an area entirely in shadow, but with pixel values "stretched" to show the detail.

The crater interior shows a pattern of ridges and mounds suggestive of icy flow, which is common at this latitude on Mars.

Photo credit: NASA/JPL/University of Arizona

Tuesday, February 21, 2012

Search for the Mars 6 Lander

The Soviet Mars 6 lander arrived at Mars on 12 March 1974. The descent module entered the atmosphere and the parachute opened at 09:08:32 UT--the craft was collecting and returning data.

Contact with the descent module was lost at 09:11:05 UT, about when expected to encounter the surface.

Because we know that the parachute opened and have some idea where it was headed, we have a chance of locating the hardware on the surface with HiRISE. In fact, an anomalous small bright patch was seen by MRO's Context Camera (CTX) team, which a CTX team member then suggested as a target for HiRISE.

The bright parachutes were the easiest thing to spot on the ground at 5 of the 6 past successful landing sites. In this subimage we see the bright spot at full HiRISE resolution, and it appears to be a patch of relatively bright bedrock, with a pattern of thin lines (fractures) typical of such outcrops.

We'll keep trying to find this and other failed landers, but there is a lot of surface area to cover on Mars and the hardware may be covered by dust and look much like natural features on Mars.

Photo credit: NASA/JPL/University of Arizona

Note: This location is on the border between southern Margaritifer Terra and northern Noachis Terra, to the northeast of Argyre Planitia.

Monday, February 20, 2012

Opportunity's Self-Portrait

This self portrait from NASA's Mars Exploration Rover Opportunity shows dust accumulation on the rover's solar panels as the mission approached its fifth Martian winter. The dust reduces the rover's power supply, and the rover's mobility is limited until the winter is over or wind cleans the panels.

This is a mosaic of images taken by Opportunity's panoramic camera (Pancam) during the 2,111th to 2,814th Martian days, or sols, of the rover's mission (December 21 to December 24, 2011). The downward-looking view omits the mast on which the camera is mounted.

The portrait combines exposures taken through Pancam filters centered on wavelengths of 601 nanometers, 535 nanometers and 482 nanometers. It is presented in approximate true color, the camera team's best estimate of what the scene would look like if humans were there and able to see it with their own eyes.

Earlier panoramas of Opportunity's deck provide comparison for the dust deposition: sols 322-323 PIA07372, sols 652-663 PIA03271 and sols 1282-1284 PIA15114.

Opportunity has worked through four Martian southern hemisphere winters since it landed in in January 2004 about 14 miles (23 kilometers) northwest of its current location. Closer to the equator than its twin rover, Spirit, Opportunity has not needed to stay on a Sun-facing slope during the previous winters. Now, however, Opportunity's solar panels carry a thicker coating of dust, and the team is using a strategy employed for three winters with Spirit: staying on a Sun-facing slope. The Sun will pass relatively low in the northern sky from the rover's perspective for several months of shortened daylight before and after the southern Mars winter solstice on March 30, 2012. Opportunity is conducting research while located on the north-facing slope of a site called "Greeley Haven."

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

Sunday, February 19, 2012

Uplifted Jumble of Ancient Bedrock

Impact craters larger than a certain size have complex forms, including central peaks or other structures that result from structural uplift of the target material. This provides a mechanism for exposing deep, ancient bedrock.

The enhanced-color subimage shows a great variety of colors and textures in the bedrock, where it is exposed from beneath a dark fine-grained mantle. The mantle is sometimes modified by the wind into dunes.

The bedrock here includes massive, layered, and broken-up (brecciated) areas. This crater is located in the volcanic plains between Argyre Planitia and Valles Marineris.

Photo credit: NASA/JPL/University of Arizona

Note: This crater is located in northwestern Noachis Terra, to the east of Nectaris Fossae. It is also located northwest of Ritchey Crater.

Saturday, February 18, 2012

Bedrock Exposures in an Acidalia Planitia Crater Wall

This mid-latitude (53 degrees North) crater appears well-preserved, with a clear ejecta blanket and well-defined rim. Bedrock exposures are visible near the top of the rim. Studying this site can yield information about the underlying terrain within this region.

Additionally, HiRISE images show small-scale features formed through modification and degradation processes; for example, few-meter-wide cracks that run perpendicular to the slope are likely formed through slumping and periglacial processes.

Gullies and flow features are also likely to be found along the crater wall -- possible shallow channels starting at the bedrock exposures are visible in along the rim in the upper/left portion of the image.

Photo credit: NASA/JPL/University of Arizona

Note: This crater is located in Acidalia Planitia, to the northwest of Lyot Crater.

Friday, February 17, 2012

Polar Layers in Gemini Scopuli

This is an especially pretty image due to the color variations and lighting geometry.

The color variations are due to mixtures of reddish dust with white frost and ice. The image was acquired as a "rider" with either a Context Camera or CRISM target.

One of these other MRO experiments chose this location to point at with the spacecraft, then the HiRISE science lead for this 2-week planning cycle decided to add a HiRISE image here for a high-resolution sample.

Photo credit: NASA/JPL/University of Arizona

Note: This image is located along one of the canyons in the Gemini Scopuli region of Planum Boreum.

Monday, February 13, 2012

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

Sunday, February 12, 2012

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

Saturday, February 11, 2012

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.

Friday, February 10, 2012

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

Tuesday, February 7, 2012

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

Monday, February 6, 2012

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

Sunday, February 5, 2012

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

Saturday, February 4, 2012

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

Friday, February 3, 2012

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.

Wednesday, February 1, 2012

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.