Amazonis quadrangle

Amazonis quadrangle

Map of Amazonis quadrangle from Mars Orbiter Laser Altimeter (MOLA) data. The highest elevations are red and the lowest are blue.
Coordinates	15°00′N157°30′W / 15°N 157.5°W / 15; -157.5

The Amazonis quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Amazonis quadrangle is also referred to as MC-8 (Mars Chart-8). ^[1]

Contents

• Medusae Fossae Formation
• Sulci
• Columnar Jointing
• Craters
• Linear ridge networks
• Dark Slope Streaks
• Streamlined shapes
• Layers
• Dust devils
• More images
• Other Mars quadrangles
• Interactive Mars map
• See also
• References
• External links

The quadrangle covers the area from 135° to 180° west longitude and 0° to 30° north latitude on Mars. The Amazonis quadrangle contains the region called Amazonis Planitia. This area is thought to be among the youngest parts of Mars because it has a very low density of craters. The Amazonian Epoch is named after this area. This quadrangle contains special, unusual features called the Medusae Fossae Formation and Sulci.

Medusae Fossae Formation

The Amazonis quadrangle is of great interest to scientists because it contains a big part of a formation, called the Medusae Fossae Formation. It is a soft, easily eroded deposit that extends for nearly 1,000 km along the equator of Mars. The surface of the formation has been eroded by the wind into a series of linear ridges called yardangs. These ridges generally point in direction of the prevailing winds that carved them and demonstrate the erosive power of Martian winds. The easily eroded nature of the Medusae Fossae Formation suggests that it is composed of weakly cemented particles, ^[2] and was most likely formed by the deposition of wind-blown dust or volcanic ash. Using a global climate model, a group of researchers headed by Laura Kerber found that the Medusae Fossae Formation could have easily been formed from ash from the volcanoes Apollinaris Mons, Arsia Mons, and possibly Pavonis Mons. ^[3] Another piece of evidence for a fine-grained composition is that the area gives almost no radar return. For this reason it has been called a "stealth" region. ^[4] Layers are seen in parts of the formation. Images from spacecraft show that they have different degrees of hardness probably because of significant variations in the physical properties, composition, particle size, and/or cementation. Very few impact craters are visible throughout the area so the surface is relatively young. ^[5] Researchers found that nearly all the dust in that coats everything and is in the atmosphere has its origin in the Medusae Fossae formation. ^[6] It turns out that the chemical elements (sulfur and chlorine) in this formation, in the atmosphere, and covering the surface are the same. The amount of dust on Mars is sufficient to form a 2 to 12 meters thick layer over the entire planet. ^{[7] [8]} Since there are relatively few depositional features in the Medusae Fossae Formation, most of the materials being eroded are probably small enough to be suspended in the atmosphere and transported long distances. ^[9]

An analysis of data from the 2001 Mars Odyssey Neutron Spectrometer revealed that parts of the Medusae Fossae Formation contain water. ^[10]

Sulci

A very rugged terrain extends from the base of Olympus Mons. It is called Lycus Sulci. Sulci is a Latin term for the furrows on the surface of a brain, so Lycus Sulci has many furrows or grooves. The furrows are huge—up to a full kilometer deep. ^[11] It would be extremely difficult to walk across it or to land a space ship there. A picture of this area is shown below.

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  Sulci in Amazonis, as seen by THEMIS. "Sulci" in Mars geography language means a furrow, like a furrow on a brain's surface. This Sulci came from the basal scarp of Olympus Mons.
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  Lycus Sulci, as seen by HiRISE. Click on image for a better view of dark slope streaks.
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  Layered features in Lycus Sulci, as seen by HiRISE under HiWish program
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  Dark slope streaks on mound in Lycus Sulci, as seen by HiRISE under HiWish program

Columnar Jointing

Lava flows sometimes cool to form large groups of more-or-less equally sized columns. ^[12] The resolution of the HiRISE images is such that the columns were found in various locations in 2009.

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  Columnar jointing in a crater in Marte Vallis
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  Columnar jointing on Earth
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  Columnar jointing on Earth
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  Columnar Jointing in Yellowstone National Park

Craters

Impact craters generally have a rim with ejecta around them, in contrast volcanic craters usually do not have a rim or ejecta deposits. As craters get larger (greater than 10 km in diameter) they usually have a central peak. ^[13] The peak is caused by a rebound of the crater floor following the impact. ^[14] Sometimes craters will display layers. Since the collision that produces a crater is like a powerful explosion, rocks from deep underground are tossed onto the surface. Hence, craters can show us what lies deep under the surface.

A pedestal crater is a crater with its ejecta sitting above the surrounding terrain and thereby forming a raised platform. They form when an impact crater ejects material which forms an erosion resistant layer, thus protecting the immediate area from erosion. As a result of this hard covering, the crater and its ejecta become elevated, as erosion removes the softer material beyond the ejecta. Some pedestals have been accurately measured to be hundreds of meters above the surrounding area. This means that hundreds of meters of material were eroded away. Pedestal craters were first observed during the Mariner missions. ^{[16] [17] [18]}

Research published in the journal Icarus has found pits in Tooting Crater that are caused by hot ejecta falling on ground containing ice. The pits are formed by heat forming steam that rushes out from groups of pits simultaneously, thereby blowing away from the pit ejecta. ^{[19] [20]}

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  Pedestal crater in Amazonis with Dark Slope Streaks, as seen by HiRISE
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  Pedestal crater with layers, as seen by HiRISE under HiWish program
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  Pedestal crater, as seen by HiRISE under HiWish program
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  Pedestal craters form when the ejecta from impacts protect the underlying material from erosion. As a result of this process, craters appear perched above their surroundings.
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  Drawing shows a later idea of how some pedestal craters form. In this way of thinking, an impacting projectile goes into an ice-rich layer—but no further. Heat and wind from the impact hardens the surface against erosion. This hardening can be accomplished by the melting of ice which produces a salt/mineral solution thereby cementing the surface.
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  Wall of Tooting Crater, as seen by HiRISE
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  Pettit Crater rim, as seen by HiRISE
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  Nicholson mound with dark streaks, as seen by HiRISE

Linear ridge networks

Linear ridge networks are found in various places on Mars in and around craters. ^[21] Ridges often appear as mostly straight segments that intersect in a lattice-like manner. They are hundreds of meters long, tens of meters high, and several meters wide. It is thought that impacts created fractures in the surface, these fractures later acted as channels for fluids. Fluids cemented the structures. With the passage of time, surrounding material was eroded away, thereby leaving hard ridges behind. ^[22] Since the ridges occur in locations with clay, these formations could serve as a marker for clay which requires water for its formation. ^{[23] [24] [25]} Water here could have supported past life in these locations. Clay may also preserve fossils or other traces of past life.

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  Narrow ridges, as seen by HiRISE under HiWish program. The ridges may be the result of impacts fracturing the surface.
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  Linear ridge networks, as seen by HiRISE under HiWish program
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  Close-up of ridge network, as seen by HiRISE under HiWish program. This is an enlargement of a previous image.
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  Close-up of ridge network, as seen by HiRISE under HiWish program. This is an enlargement of a previous image.
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  Linear ridge networks, as seen by HiRISE under HiWish program
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  Close-up of layers and ridges, as seen by HiRISE under HiWish program

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  Wide view of polygon ridges, as seen by HiRISE under HiWish program
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  Polygonal ridges, as seen by HiRISE under HiWish program
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  Polygonal ridges, as seen by HiRISE under HiWish program
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  Close, color view of polygonal ridges, as seen by HiRISE under HiWish program

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  Wide view of large ridge network, as seen by HiRISE under HiWish program
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  Close view of ridge network, as seen by HiRISE under HiWish program Box shows size of football field.
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  Close view of contact between ridge network and overlying layer, as seen by HiRISE under HiWish program
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  Close, color view of ridges, as seen by HiRISE under HiWish program
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  Wide view of curved ridges, as seen by HiRISE under HiWish program
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  Close view of curved ridges, as seen by HiRISE under HiWish program. These formed underground and then were uncovered by erosion.

Dark Slope Streaks

Dark slope streaks are narrow, avalanche-like features common on dust-covered slopes in the equatorial regions of Mars. ^[26] They form in relatively steep terrain, such as along escarpments and crater walls. ^[27] Although first recognized in Viking Orbiter images from the late 1970s, ^{[28] [29]} dark slope streaks were not studied in detail until higher-resolution images from the Mars Global Surveyor (MGS) and Mars Reconnaissance Orbiter (MRO) spacecraft became available in the late 1990s and 2000s. ^{[30] [31]}

The physical process that produces dark slope streaks is still uncertain. They are most likely caused by the mass movement of loose, fine-grained material on oversteepened slopes (i.e., dust avalanches). ^{[32] [33]} The avalanching disturbs and removes a bright surface layer of dust to expose a darker substrate. ^[34]

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  Dark slope streaks on layered mesa, as seen by HiRISE under HiWish program
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  Dark slope streaks on mesa, as seen by HiRISE under HiWish program. Location is Amazonis quadrangle.
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  Layers in Gordii Dorsum Region, as seen by HiRISE under HiWish program. Dark lines are dark slope streaks.
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  Animation showing changes in streaks on slopes of ridges within the Olympus Mons Aureole. The changes happened in six years.

Research, published in January 2012 in Icarus, found that dark streaks were initiated by airblasts from meteorites traveling at supersonic speeds. The team of scientists was led by Kaylan Burleigh, an undergraduate at the University of Arizona. After counting some 65,000 dark streaks around the impact site of a group of five new craters, patterns emerged. The number of streaks was greatest closer to the impact site. So, the impact somehow probably caused the streaks. Also, the distribution of the streaks formed a pattern with two wings extending from the impact site. The curved wings resembled scimitars, curved knives. This pattern suggests that an interaction of airblasts from the group of meteorites shook dust loose enough to start dust avalanches that formed the many dark streaks. At first it was thought that the shaking of the ground from the impact caused the dust avalanches, but if that was the case the dark streaks would have been arranged symmetrically around the impacts, rather than being concentrated into curved shapes.

The crater cluster lies near the equator 510 miles) south of Olympus Mons, on a type of terrain called the Medusae Fossae formation. The formation is coated with dust and contains wind-carved ridges called yardangs. These yardangs have steep slopes thickly covered with dust, so when the sonic boom of the airblast arrived from the impacts dust started to move down the slope. Using photos from Mars Global Surveyor and HiRISE camera on NASA's Mars Reconnaissance Orbiter, scientists have found about 20 new impacts each year on Mars. Because the spacecraft have been imaging Mars almost continuously for a span of 14 years, newer images with suspected recent craters can be compared to older images to determine when the craters were formed. Since the craters were spotted in a HiRISE image from February 2006, but were not present in a Mars Global Surveyor image taken in May 2004, the impact occurred in that time frame.

The largest crater in the cluster is about 22 meters (72 feet) in diameter with close to the area of a basketball court. As the meteorite traveled through the Martian atmosphere it probably broke up; hence a tight group of impact craters resulted. Dark slope streaks have been seen for some time, and many ideas have been advanced to explain them. This research may have finally solved this mystery. ^{[35] [36] [37]}

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  Image indicates crater cluster and curved lines formed by airblast from meteorites. Meteorites caused airblast which caused dust avalanches on steep slopes. Image is from HiRISE.
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  Mesa with dark slope streaks, as seen by HiRISE under HiWish program
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  Close up of previous image along light/dark boundary. Dark line in middle of image shows border between light and dark area of curved lines. Green arrows show high areas of ridges. Loose dust moved down steep slopes when it felt the airblast from meteorite strikes. Image is from HiRISE.

Streamlined shapes

When a fluid moves by a feature like a mound, it will become streamlined. Often flowing water makes the shape and later lava flows spread over the region. In the pictures below this has occurred.

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  Wide view of streamlined shape and rafts of lava, as seen by HiRISE under HiWish program
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  Closer view of previous image, showing layers, as seen by HiRISE under HiWish program
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  Close view of lava rafts from previous images, as seen by HiRISE under HiWish program
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  Streamlined Island in Marte Vallis, as seen by HiRISE. Click on image for good view of dark slope streaks. Island is just to the west of Pettit Crater. Scale bar is 500 meters long.
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  Streamlined shape showing layers, as seen by HiRISE under HiWish program
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  Streamlined shapes and layers, as seen by HiRISE under HiWish program
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  Streamlined feature, as seen by HiRISE under HiWish program

Layers

,

Many places on Mars show rocks arranged in layers. Rock can form layers in a variety of ways. Volcanoes, wind, or water can produce layers. ^[38] A detailed discussion of layering with many Martian examples can be found in Sedimentary Geology of Mars. ^[39] Sometimes the layers are of different colors. Light-toned rocks on Mars have been associated with hydrated minerals like sulfates. The Mars rover Opportunity examined such layers close-up with several instruments. Some layers are probably made up of fine particles because they seem to break up into find dust. Other layers break up into large boulders so they are probably much harder. Basalt, a volcanic rock, is thought to in the layers that form boulders. Basalt has been identified on Mars in many places. Instruments on orbiting spacecraft have detected clay (also called phyllosilicate) in some layers.

A detailed discussion of layering with many Martian examples can be found in Sedimentary Geology of Mars. ^[39]

Layers can be hardened by the action of groundwater. Martian ground water probably moved hundreds of kilometers, and in the process it dissolved many minerals from the rock it passed through. When ground water surfaces in low areas containing sediments, water evaporates in the thin atmosphere and leaves behind minerals as deposits and/or cementing agents. Consequently, layers of dust could not later easily erode away since they were cemented together.

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  Wide view of layers, as seen by HiRISE under HiWish program
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  Close view of layers, as seen by HiRISE under HiWish program
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  Wide view of scarp showing layers, as seen by HiRISE under HiWish program
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  Close view of layers from previous image, as seen by HiRISE under HiWish program
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  Layers in trough and dark slope streaks, as seen by HiRISE under HiWish program
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  Wide view of layers, as seen by HiRISE under HiWish program
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  Layers and dark slope streaks, as seen by HiRISE under HiWish program
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  Layered mesas, as seen by HiRISE under HiWish program

Dust devils

Dust devil tracks can be very pretty. They are caused by giant dust devils removing bright colored dust from the Martian surface; thereby exposing a dark layer. Dust devils on Mars have been photographed both from the ground and high overhead from orbit. They have even blown dust off the solar panels of two Rovers on Mars, thereby greatly extending their useful lifetime. ^[40] The pattern of the tracks has been shown to change every few months. ^[41] A study that combined data from the High Resolution Stereo Camera (HRSC) and the Mars Orbiter Camera (MOC) found that some large dust devils on Mars have a diameter of 700 metres (2,300 ft) and last at least 26 minutes. ^[42]

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  Martian Dust Devil - in Amazonis Planitia (April 10, 2001) (also) (video (02:19)).
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  A dust devil on hilly terrain in the Amazonis region

More images

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  Map of Amazonis quadrangle
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  Yardangs in the Medusae Fossae formation, as seen by HiRISE under HiWish program
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  Tartarus Colles channel, as seen by HiRISE. Scale bar is 500 meters. Click on image to see bridge across channel.
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  Olympus Mons scarp, as seen by HiRISE. Scale bar is 500 meters long.
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  Channels From Fissure, as seen by HiRISE. The fissure probably started the water flowing to make the channel. The channels look somewhat better in the enlarged view of the original image.
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  Possible inverted stream channels in Phlegra Dorsa region, as seen by HiRISE under HiWish program. The ridges were probably once stream valleys that have become full of sediment and cemented, so they became hardened against erosion which removed surrounding material.

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  Tilted blocks It is as if something pushed up from under the ground.
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  Lava flows affected by obstacles, as seen by HiRISE under HiWish program. Arrows show two obstacles that are changing the flow.
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  View of a lava lobe, as seen by HiRISE under HiWish program. The box shows the size of a football field.
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  Close view of a lava lobe, as seen by HiRISE under HiWish program. The box shows the size of a football field.

Other Mars quadrangles

0°N180°W / 0°N 180°W / 0; -180

0°N0°W / 0°N -0°E / 0; -0

90°N0°W / 90°N -0°E / 90; -0

MC-01

Mare Boreum

MC-02

Diacria

MC-03

Arcadia

MC-04

Mare Acidalium

MC-05

Ismenius Lacus

MC-06

Casius

MC-07

Cebrenia

MC-08

Amazonis

MC-09

Tharsis

MC-10

Lunae Palus

MC-11

Oxia Palus

MC-12

Arabia

MC-13

Syrtis Major

MC-14

Amenthes

MC-15

Elysium

MC-16

Memnonia

MC-17

Phoenicis

MC-18

Coprates

MC-19

Margaritifer

MC-20

Sabaeus

MC-21

Iapygia

MC-22

Tyrrhenum

MC-23

Aeolis

MC-24

Phaethontis

MC-25

Thaumasia

MC-26

Argyre

MC-27

Noachis

MC-28

Hellas

MC-29

Eridania

MC-30

Mare Australe

Clickable image of the 30 cartographic quadrangles of Mars, defined by the USGS. ^{[43] [46]} Quadrangle numbers (beginning with MC for "Mars Chart") ^[47] and names link to the corresponding articles. North is at the top; 0°N180°W / 0°N 180°W / 0; -180 is at the far left on the equator. The map images were taken by the Mars Global Surveyor.

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See also

Related Research Articles

Amazonis Planitia is one of the smoothest plains on Mars. It is located between the Tharsis and Elysium volcanic provinces, to the west of Olympus Mons, in the Amazonis and Memnonia quadrangles, centered at 24.8°N 196.0°E. The plain's topography exhibits extremely smooth features at several different lengths of scale. A large part of the Medusae Fossae Formation lies in Amazonis Planitia.

The Memnonia quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Memnonia quadrangle is also referred to as MC-16.

The Medusae Fossae Formation is a large geological formation of probable volcanic origin on the planet Mars. It is named for the Medusa of Greek mythology. "Fossae" is Latin for "trenches". The formation is a collection of soft, easily eroded deposits that extends discontinuously for more than 5,000 km along the equator of Mars. Its roughly-shaped regions extend from just south of Olympus Mons to Apollinaris Patera, with a smaller additional region closer to Gale Crater.

The Casius quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The quadrangle is located in the north-central portion of Mars' eastern hemisphere and covers 60° to 120° east longitude and 30° to 65° north latitude. The quadrangle uses a Lambert conformal conic projection at a nominal scale of 1:5,000,000 (1:5M). The Casius quadrangle is also referred to as MC-6. Casius quadrangle contains part of Utopia Planitia and a small part of Terra Sabaea. The southern and northern borders of the Casius quadrangle are approximately 3,065 km and 1,500 km wide, respectively. The north to south distance is about 2,050 km. The quadrangle covers an approximate area of 4.9 million square km, or a little over 3% of Mars' surface area.

The Diacria quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The quadrangle is located in the northwestern portion of Mars' western hemisphere and covers 180° to 240° east longitude and 30° to 65° north latitude. The quadrangle uses a Lambert conformal conic projection at a nominal scale of 1:5,000,000 (1:5M). The Diacria quadrangle is also referred to as MC-2. The Diacria quadrangle covers parts of Arcadia Planitia and Amazonis Planitia.

The Arcadia quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The quadrangle is located in the north-central portion of Mars’ western hemisphere and covers 240° to 300° east longitude and 30° to 65° north latitude. The quadrangle uses a Lambert conformal conic projection at a nominal scale of 1:5,000,000 (1:5M). The Arcadia quadrangle is also referred to as MC-3. The name comes from a mountainous region in southern Greece. It was adopted by IAU, in 1958.

The Arabia quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Arabia quadrangle is also referred to as MC-12.

The Syrtis Major quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Syrtis Major quadrangle is also referred to as MC-13.

The Amenthes quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Amenthes quadrangle is also referred to as MC-14. The quadrangle covers the area from 225° to 270° west longitude and from 0° to 30° north latitude on Mars. Amenthes quadrangle contains parts of Utopia Planitia, Isidis Planitia, Terra Cimmeria, and Tyrrhena Terra.

The Elysium quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Elysium quadrangle is also referred to as MC-15.

The Tharsis quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Tharsis quadrangle is also referred to as MC-9 . The name Tharsis refers to a land mentioned in the Bible. It may be at the location of the old town of Tartessus at the mouth of Guadalquivir.

The Lunae Palus quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The quadrangle is also referred to as MC-10. Lunae Planum and parts of Xanthe Terra and Chryse Planitia are found in the Lunae Palus quadrangle. The Lunae Palus quadrangle contains many ancient river valleys.

The Aeolis quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Aeolis quadrangle is also referred to as MC-23 . The Aeolis quadrangle covers 180° to 225° W and 0° to 30° south on Mars, and contains parts of the regions Elysium Planitia and Terra Cimmeria. A small part of the Medusae Fossae Formation lies in this quadrangle.

The Phoenicis Lacus quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Phoenicis Lacus quadrangle is also referred to as MC-17. Parts of Daedalia Planum, Sinai Planum, and Solis Planum are found in this quadrangle. Phoenicis Lacus is named after the phoenix which according to myth burns itself up every 500 years and then is reborn.

The Phaethontis quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Phaethontis quadrangle is also referred to as MC-24.

Dark slope streaks are narrow, avalanche-like features common on dust-covered slopes in the equatorial regions of Mars. They form in relatively steep terrain, such as along escarpments and crater walls. Although first recognized in Viking Orbiter images from the late 1970s, dark slope streaks were not studied in detail until higher-resolution images from the Mars Global Surveyor (MGS) and Mars Reconnaissance Orbiter (MRO) spacecraft became available in the late 1990s and 2000s.

HiWish is a program created by NASA so that anyone can suggest a place for the HiRISE camera on the Mars Reconnaissance Orbiter to photograph. It was started in January 2010. In the first few months of the program 3000 people signed up to use HiRISE. The first images were released in April 2010. Over 12,000 suggestions were made by the public; suggestions were made for targets in each of the 30 quadrangles of Mars. Selected images released were used for three talks at the 16th Annual International Mars Society Convention. Below are some of the over 4,224 images that have been released from the HiWish program as of March 2016.

The common surface features of Mars include dark slope streaks, dust devil tracks, sand dunes, Medusae Fossae Formation, fretted terrain, layers, gullies, glaciers, scalloped topography, chaos terrain, possible ancient rivers, pedestal craters, brain terrain, and ring mold craters.

The Amazonian is a geologic system and time period on the planet Mars characterized by low rates of meteorite and asteroid impacts and by cold, hyperarid conditions broadly similar to those on Mars today. The transition from the preceding Hesperian period is somewhat poorly defined. The Amazonian is thought to have begun around 3 billion years ago, although error bars on this date are extremely large. The period is sometimes subdivided into the Early, Middle, and Late Amazonian. The Amazonian continues to the present day.

Yardangs are common in some regions on Mars, especially in the Medusae Fossae Formation. This formation is found in the Amazonis quadrangle and near the equator. They are formed by the action of wind on sand sized particles; hence they often point in the prevailing direction that the winds were blowing when they were formed. Yardangs exhibit very few impact craters, indicating that the surface exposed is relatively young and the process of erosion may be active. The easily eroded nature of the Medusae Fossae Formation suggests that it is composed of weakly cemented particles, and was most likely formed by the deposition of wind-blown dust or volcanic ash. Yardangs are parts of rock that have been sand blasted into long, skinny ridges by bouncing sand particles blowing in the wind. Layers are seen in parts of the formation. A resistant caprock on the top of yardangs has been observed in Viking, Mars Global Surveyor, and HiRISE photos. Images from spacecraft show that they have different degrees of hardness probably because of significant variations in the physical properties, composition, particle size, and/or cementation.

References

External links

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