Coprates quadrangle

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Mars topography (MOLA dataset) HiRes (1).jpg
MC-18 Coprates 0–30° S 45–90° W Quadrangles Atlas


The Coprates Quadrangle contains perhaps the most outstanding feature on Mars—the Valles Marineris chasma system, a set of canyons that would stretch across the United States.

Location and name

The Coprates quadrangle goes from 0° to 30° south latitude and 45° to 90° west longitude (315-270 E). Coprates quadrangle is famous for depicting the "Grand Canyon of Mars", the Valles Marineris Canyon System. Impressive signs of water exist in this quadrangle, with ancient river valleys and networks of stream channels showing up as inverted terrain and lakes inside of Valles Marineris.[1]

The Coprates quadrangle contains parts of many of the old classical regions of Mars: Sinai Planum, Solis Planum, Thaumasia Planum, Lunae Planum, Noachis Terra, and Xanthe Terra. Because Mars has a very thin, clear atmosphere astronomers have been able to see surface markings for hundreds of years. Early observers gave names to them—many from old names from the Bible or old writings. The name Coprates refers to an old name for a river in Persia.[2] The river is the Dez River, a tributary of the Karun in modern Iran. Water from the Dez eventually empties into the Shatt al-Arab near its Persian Gulf estuary. The name was approved by the International Astronomical Union (IAU) in 1958.[3] [4]

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.

Valles Marineris canyon system

Wide view of Mars centered on Valles Marineris, taken with Viking images Note, this picture will greatly enlarge by clicking on it several times.

Valles Marineris is the largest canyon system in the solar system; this great canyon would go almost all the way across the United States. This section describes the system with words; pictures in this article also show all these features/names.The name for the whole system of canyons is Valles Marineris. Starting at the west with Noctis Labyrinthus in the Phoenicis Lacus quadrangle, the canyon system ends in the Margaritifer Sinus quadrangle with Capri Chasma and Eos Chasma (in the south). The word Chasma has been designated by the International Astronomical Union to refer to an elongate, steep-sided depression. Valles Marineris was discovered by and named for the Mariner 9 mission. Moving east from Noctis Labyrinthus, the canyon splits into two troughs, named Tithonium Chasma and Ius Chasma (in the south). In the middle of the system are the very wide valleys of Ophir Chasma (north), Candor Chasma, and Melas Chasma (south). Going farther to the east, one comes to Coprates Chasma. At the end of Coprates Chasma, the valley gets wider to form Capri Chasma in the north and Eos Chasma in the south.

The walls of the canyons often contain many layers. The floors of some of the canyons contain large deposits of layered materials. The layers may have formed when water once filled the canyons.[5] [6][7] [8] The canyons are deep as well as long; in places they are 8-10 kilometers deep, much deeper than the Earth's Grand Canyon, which is only 1.6 kilometers deep.[9]

Melas Chasma, as seen by THEMIS.
Cliff in Candor Chasma Plateau, as seen by THEMIS.
Cliff in northern wall of Ganges Chasma, as seen by THEMIS.

Interior layered deposits and sulfate

This quadrangle, as indeed many other quadrangles of Mars, show much evidence of vast amounts of water in the past. Some features like old stream beds clearly point toward a water-rich past for Mars. However, layered features and their chemistry, although not as striking, provide additional support for large amounts of water in the past. Parts of the floors of Candor Chasma and Juventae Chasma contain layered deposits that have been given the name interior layered deposits (ILD's) and Equatorial Layered Deposits (ELD's). These layers may have formed when the whole area was a giant lake.

However, many other ideas have been advanced to explain them.[10] High-resolution structural and geologic mapping in west Candor Chasma, presented in 2015, showed that the deposits on the floor of the Candor Chasma are basin filling sediments that were deposited in a wet playa like setting; hence water was involved in their formation.[11] Some places on Mars contain hydrated sulfate deposits, including ILD's. Sulfate formation involves the presence of water. The European Space Agency's Mars Express found possible evidence of the sulfates epsomite and kieserite. Sulfates that contain water are found in many places on the planet. Usually, they show up in pictures as light-toned materials. These are in striking contrast to the widespread dark volcanic surfaces. Scientists want to visit these areas with robotic rovers.[12] These deposits have been found to contain ferric oxides in the form of crystalline grey hematite.[13] [14] [15] Grey hematite is another sign of water as it usually forms with the aid of water.

Layers

Layers in the canyon wall in Coprates, as seen by Mars Global Surveyor, under the MOC Public Targeting Program.


Perhaps, the best location to view layers on Mars is in the Coprates quadrangle. This is because of so many huge, deep canyons that display layer after layer in their walls. Images of canyon walls almost always show layers.[16] Layered rocks have different characteristics. Some layers appear tougher than others. In the image below of Ganges Chasma Layers, as seen by HiRISE, one can see that the upper, light-toned deposits are eroding much faster than the lower darker layers. Some cliffs on Mars show a few darker layers standing out and often breaking into large pieces; these are thought to be hard volcanic rock instead of soft ash deposits. An example of hard layers is shown abovr in the picture of layers in the canyon wall in Coprates, as seen by Mars Global Surveyor. Because of its closeness to the Tharsis volcanic region, rock layers may be made of layer after layer of lava flows, probably mixed with deposits of volcanic ash that fell out of the air following big eruptions. Rock strata visible in the walls preserve a long geological history of Mars.[17] The Earth does not possess long records of geological history since plate tectonics erases rock materials at more or less regular intervals. Dark layers in canyon walls may be due to dark lava flows. The dark volcanic rock basalt dominates the Martian surface. However, light-toned deposits appear in many spots, and those deposits may have resulted from rivers, lakes, volcanic ash, or windblown deposits of sand or dust.[18] The Mars Rovers found light-toned rocks to contain sulfates. Having been formed in water, sulfate deposits are of great interest to scientists because they may contain traces of ancient life.[19]

Wide view of layers in wall of Valles Marineris, as seen by HiRISE under HiWish program
Close-up of layers in wall of Valles Marineris
Layers in Monument Valley. These are accepted as being formed, at least in part, under bodies of water. Since Mars contains similar layers, water is thought to be a major cause of layering on Mars.
Two views of Melas Chasma Layered Deposits, as seen by HiRISE. Left picture lies north of other picture on the right. Pictures are not the same scale.
Close view of layers south of Ius Chasma Note: this is an enlargement of the previous wide view. (ESP_047187_1725
Wide view of layers south of Ius Chasma, as seen by HiRISE under HiWish program


Wide view of layers in Louros Valles, as seen by HiRISE under HiWish program Louros Valles is part of the Ius Chasma.
Close view of layers in Louros Valles, as seen by HiRISE under HiWish program Note this is an enlargement of a previous image. (ESP_048980_1725)
Close view of layers in Louros Valles Note this is an enlargement of a previous image. (ESP_048980_1725)

Hebes Chasma and hydrated deposits

Hebes Chasma, a large enclosed valley, may have once held water. Hydrated minerals have been found there. It is thought that large-scale underground springs of groundwater at different times burst to the surface to form deposits called Light Toned Deposits (LTD's). Some suggest present or fossilized life forms may be found there because the deposits are relatively young.[20]

Layers in Hebes Chasma
Layers in Hebes Chasma

Nirgal Vallis and sapping

Nirgal Vallis, as seen by Mariner 9 This is one of the first images to show evidence of past water on Mars.

Nirgal Vallis is one of the longest valley networks on Mars. It is so large that it is found on more than one quadrangle. Scientists do not know how all the ancient river valleys were formed. There is evidence that instead of rain or snow, the water that formed the valleys originated underground. One mechanism that has been advanced is groundwater sapping.[21] In the process of sapping, the ground just gives away as water comes out. Sapping is common in some desert areas in America's Southwest. Sapping forms alcoves and stubby tributaries. These features are visible in the picture below of Nigal Vallis taken with Mars Odyssey's THEMIS.

Nirgal Vallis that runs in two quadrangles has features looking like those caused by sapping. Picture taken with THEMIS.

Great flood in Holden Crater

Topographic map of Holden Crater

Water from Nirgal Vallis contributed to a great flood that went through the rim of Holden Crater and helped form a lake in the crater. It's estimated that Nirgal Vallis had a discharge of 4800 cubic meters/second.[22] Water from Nirgal Vallis was inbounded in Uzboi Vallis because the rim of Holden Crater blocked the flow. At a certain point the stored water broke through the rim of Holden and created a lake 200–250 m deep.[23] Water with a depth of at least 50 m entered Holden at a rate that 5-10 times the discharge of the Mississippi River.[24] [25] [26] [27] Terraces and the presence of large rocks (tens of meters across) support these high discharge rates.[28] [29] [30] [31]

Inverted relief

Some areas of Mars show inverted relief, where features that were once depressions, like streams, are now instead above the surface. These may have been formed when materials, like large rocks, were deposited in low-lying areas, and then left behind after erosion (perhaps wind, which cannot move large rocks) removed much of the surface layers. Other ways of making inverted relief might be lava flowing down a stream bed or cementation of rock material by minerals dissolved in water. Some cementing materials are very hard and resistant to erosion. On Earth, materials cemented by silica are highly resistant to all kinds of erosional forces. Inverted relief in the shape of streams is further evidence of water flowing on the Martian surface in past times. There are many examples of inverted channels near Juventae Chasma; some are shown in the image of Juventae Chasma below.[32] [33] [34]


Inverted Channels near Juventae Chasma, as seen by HiRISE. Channels were once regular stream channels. Scale bar is 500 meters long.

Vallis

Vallis (plural valles) is the Latin word for valley. It is used in planetary geology for the naming of landform features on other planets. The term “Vallis” was used for old river valleys that were discovered on Mars, when probes were first sent to Mars. The Viking Orbiters caused a revolution in our ideas about water on Mars; huge river valleys were found in many areas. Spacecraft cameras showed that floods of water broke through dams, carved deep valleys, eroded grooves into bedrock, and traveled thousands of kilometers.[35] [36] [37]

Recurrent slope lineae

Wide view of part of Valles Marineris, as seen by HiRISE under HiWish program Box shows location of recurrent slope lineae that are enlarged in next image.

Recurrent slope lineae (RSL) are small dark streaks on slopes that elongate in warm seasons. They may be evidence of liquid water.[38][39][40]

Close, color view of recurrent slope lineae, as seen by HiRISE under HiWish program Arrows point to some of the recurrent slope lineae


Recurrent slope lineae elongate when the slopes are at their warmest. Near the equator, RSL elongate on northern slopes in the northern summer and on the southern slopes in the southern summer.

Channels from Rainfall?

Latitude dependent mantle, as seen by HiRISE under HiWish program This smooth appearing material is rich in ice and falls from the sky at times.
Branching channels on floor of Melas Chasma. Image taken with THEMIS.
Channels near the rim of Ius Chasma, as seen by HiRISE. The pattern and high density of these channels support precipitation as the source of the water.
Channels West of Echus Chasma. The fine pattern of branching stream beds were probably formed from water moving across the surface. Image taken with THEMIS.
Dendritic channels on mesa of Echus Chasma. Image is 20 mile wide

Scientists have wondered if Mars ever had rainfall. They do know that moisture has been transported around the planet as snow and ice-covered dust. Moisture from the poles migrates to mid latitudes and ends up in latitude dependent mantle. This mantle appears smooth; hence it covers all the irregularities on the Martian surface. Sometimes it occurs in layers. However, there is much observational evidence for rainfall--with much of it in the Coprates quadrangle. Large surface units are covered with small branching channels which would be expected from rainfall. Pictures below saw some of these small branching channels.

Other features in the Coprates quadrangle

False color image of Candor Chasma showing locations of hydrated sulfate deposits, as seen by THEMIS. Red colors show rocky places. Greens and blues show sandy, dusty areas.
Trough cutting a wrinkle ridge, as seen by HiRISE under HiWish program
Band, as seen by HiRISE under HiWish program

The Coprates quadrangle has so many interesting sights. It was probably the most popular site for suggestions for HiRISE pictures from both the professional and the amateur communities. The layers in the canyons date back billions of years. Those canyons probably once held great lakes. The evidence for this is in the presence of layers on the floor from lakes. In addition, the layers contain minerals that form in water. The main water containing minerals are various types of sulfates.

See Also

References:

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  2. Blunck, J. 1982. Mars and its Satellites. Exposition Press. Smithtown, N.Y.
  3. "Coprates quadrangle". Gazetteer of Planetary Nomenclature. USGS Astrogeology Research Program.
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