Amazonis quadrangle

MC-08

Amazonis

0–30° N

135–180° W

Quadrangles

Atlas

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  Amazonis quadrangle elevations

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This area is considered to be among the youngest parts of Mars because it has a very low density of craters. The Amazonia period is named after this area. This quadrangle contains special, unusual features called Sulci and the Medusae Fossae Formation. As per the rest of Mars, this region contains some very beautiful landscapes. The Amazonis quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) . The Amazonis quadrangle is also referred to as MC-8 (Mars Chart-8). The quadrangle covers the area from 0° to 30° north latitude and 135° to 180° west longitude (225-180 E ). The Amazonis quadrangle contains the classic region called Amazonis Planitia.

In this article, some of the best pictures from a number of spacecraft will show what the landscape looks like in this region. The origins and significance of all features will be explained as they are currently understood.

Name

Its name derives from the mythical land of the Amazons. In Greek mythology, the Amazons were a tribe of warrior women believed to live in Asia Minor. In this myth, Amazons were the daughters of Ares and Harmonia (mythology) (a nymph of the Akmonian Wood). They were brutal and aggressive--their main concern in life was war.

Medusae Fossae Formation

The Amazonis quadrangle is of great interest to scientists because it contains a major part of a formation, called the Medusae Fossae Formation. This unit 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, and was most likely formed by the deposition of wind-blown dust or volcanic ash. Using a global climate model, a group of researchers concluded that the Medusae Fossae Formation could have easily been formed from ash from the volcanoes Apollinaris Mons, Arsia Mons, and possibly from Pavonis Mons. Another 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. 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. Researchers found that nearly all the dust that falls out of the atmosphere and that coats everything on Mars has its origin in the Medusae Fossae formation. 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. 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.

An analysis of data from the 2001 Mars Odyssey Neutron Spectrometer revealed that portions of the Medusae Fossae Formation contain water.

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  Medusae Fossae Formation and its location relative to Olympus Mons, as seen by THEMIS.

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  Plateau made up of Medusae Fossae materials and rootless cones, as seen by HiRISE

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  Yardangs in the Medusae Fossae formation

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  Yardangs, as seen by HiRISE under HiWish program Location is near Gordii Dorsum in the Amazonis quadrangle. These yardangs are in the upper member of the Medusae Fossae Formation.

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  Yardangs Location is near Gordii Dorsum in the Amazonis quadrangle. Note: this is an enlargement of previous image.

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  Yardangs Location is near Gordii Dorsum in the Amazonis quadrangle. Note: this is an enlargement of previous image.

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  Yardangs near a crater Location is in the Amazonis quadrangle.

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  Close, color view of yardangs Box shows size of a football field.

Sulci

A very rugged terrain extends from the base of Olympus Mons, the largest volcano on Mars. This terrain 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. 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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  Layered features in Lycus Sulci, as seen by HiRISE under HiWish program

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  Dark slope streaks on mound in Lycus Sulci

Columnar Jointing

                       Columnar jointing in a crater in Marte Vallis

Lava flows sometimes cool to form large groups of more-or-less equally sized columns. Since Mars is largely covered by lava flow, it was expected that these joints were on Mars. With the superior resolution of the HiRISE images, scientists finally found columnar jointing in various locations in 2009. Pictures below show examples of columnar jointing both on Mars and on the Earth. Many tourists travel to see these formations in our National Parks, like Yellowstone.

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  Columnar jointing on the Earth.

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  Columnar jointing on the Earth.

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  Columnar Jointing in Yellowstone National Park.

Craters

Craters give us insight into what lies under the ground. Since the collision that produces an impact crater is like a powerful explosion, rocks from deep underground are tossed onto the surface. Hence, by examining the material or ejecta thrown out by the impact, we can see what lies deep under the surface. Some craters, especially the more recent ones, will display layers on their walls. These layers can help us tell the kinds of rocks that were formed in the past. For example, layers that contain dark, blocky boulders likely originated as lava flows. As craters get larger (greater than 10 km in diameter) they usually have a central peak. The peak is caused by a rebound of the crater floor following the impact. Scientists are eager to examine those central peaks because they contain samples of rocks from deep underground. Instruments, called spectroscopes, can tell us the mineral composition of these rocks. We believe that pits in Tooting Crater 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.

Based on study of years of HiRISE images, researchers believe over 200 new craters are formed each year on Mars, based on study of years of HiRISE images.

- before/March 27 & after/March 28, 2012

Pedestal Craters

A pedestal crater is an impact crater with its ejecta sitting on a raised platform above the surrounding terrain. They form when an impact crater ejects material which forms an erosion resistant layer, thus protecting the underlying materials from erosion. As a result of this hard covering, the crater and its ejecta become elevated, after 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.

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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

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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.

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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  Pettit Crater rim, as seen by HiRISE

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  Nicholson mound with dark streaks, as seen by HiRISE Nicholson Crater sits right on the equator.

Linear ridge networks

                                            Linear ridge networks

Linear ridge networks are found in various places on Mars in and around craters. 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. There origin is not completely understood. One idea for their origin is that impacts created fractures in the surface, these fractures later acted as channels for fluids. Fluids turned into hard ridges. With the passage of time, surrounding material was eroded away, thereby leaving hard ridges behind. Since the ridges occur in locations with clay, these formations could serve as a marker for clay which requires water for its formation. Water here could have supported past life. Clay may also preserve fossils or other traces of past life.

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  Narrow ridges The ridges may be the result of impacts fracturing the surface.

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  Close-up of ridge network 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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  Close, color view of polygonal ridges, as seen by HiRISE under HiWish program

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  Wide view of large ridge network

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  Close view of ridge network Box shows size of football field.

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  Close view of contact between ridge network and overlying layer

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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 These formed underground and then were uncovered by erosion.

Dark Slope Streaks

           Dark slope streaks on layered mesa, as seen by HiRISE under HiWish program

Dark slope streaks are narrow, avalanche-like features common on dust-covered slopes in the equatorial regions. They form in relatively steep sites, such as along escarpments and impact 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.

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). The avalanching disturbs and removes a bright surface layer of dust to expose a darker substrate.

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  Animation showing changes in streaks on slopes of ridges within the Olympus Mons Aureole. The changes happened in 6 years.

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  Dark slope streaks on mesa

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  Layers in Gordii Dorsum Region Dark lines are Dark Slope Streaks.

Research, published in January 2012 in Icarus, found that dark streaks were initiated by airblasts from meteorites traveling at supersonic speeds. The team, who did the study, 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 5 new craters, the team of scientists saw patterns. 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 curved knives, called scimitars. This pattern suggests that an interaction of airblasts from the group of meteorites shook dust loose enough to start dust avalanches that formed the 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. 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 slopes. 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--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.

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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.

Streamlined shapes

                 Streamlined shape showing layers, as seen by HiRISE under HiWish program

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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  Streamlined island showing layers

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  Close view of lava rafts from previous images

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  Streamlined Island in Marte Vallis, as seen by HiRISE. Island is just to the west of Pettit Crater. Scale bar is 500 meters long.

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  Streamlined feature

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. A detailed discussion of layering with many Martian examples can be found in Sedimentary Geology of Mars. 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 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. Finding clay is important because it has to have water to form. Evidence of past life may be found in clay deposits. A detailed discussion of layering with many Martian examples can be found in Sedimentary Geology of Mars. 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

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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

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  Layers in trough and dark slope streaks

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  Layered mesas

Dust devils

Dust devils can create very pretty tracks. Giant Martian dust devils remove bright colored dust from the Martian surface; thereby exposing a dark layer. A thin coating of fine bright dust covers most of the Martian surface. When a dust devil goes by it blows away the coating and exposes the underlying dark surface creating tracks. It does not take too much fine dust to cover those tracks--experiments in Earth laboratories demonstrate that only a few 10's of microns of dust will be enough. The width of a single human hair ranges from approximately 20 to 200 microns (μm); consequently, the dust that can cover dust devil tracks may only be the thickness of a human hair. 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. The pattern of tracks has been shown to change every few months. 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 m and last at least 26 minutes.

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  A dust devil on hilly terrain in the Amazonis region.

More images from Amazonis quadrangle

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  Map of Amazonis quadrangle. Green rectangles are places that were imaged by the high resolution camera on the mars Global Surveyor. Notice Nicholson crater at the bottom--it sits right at the equator.

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  Channels From Fissure, as seen by HiRISE. The fissure probably started the water flowing to make the channel.

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  Tilted blocks It is as if something pushed up from under the ground.

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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  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 The box shows the size of a football field.

                   Close view of a lava lobe The box shows the size of a football field.

See also

• Dark slope streaks
• High Resolution Imaging Science Experiment (HiRISE)
• HiWish program
• How are features on Mars Named?
• Layers on Mars
• Mars Global Surveyor
• Martian gullies
• Rivers on Mars

External links

• Changes in dust devil tracks
• Looking for Slope Streaks-old and new pictures of streaks