Linear Ridge Networks

Linear ridge networks are found in various places on Mars in and around craters. These features have also been called "polygonal ridge networks," "boxwork ridges", and "reticulate ridges." 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.
It is reasonable to think that on Mars impacts broke the ground with cracks since faults are often formed in impact craters on Earth. One could guess that these ridge networks were dikes, but dikes would go more or less in the same direction, as compared to these ridges that have a large variety of orientations. 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 in these locations. Clay may also preserve fossils or other traces of past life.

These ridges could be formed by large impacts that produced fractures, faults, or dikes made up of melted rock and/or crushed rock (breccia). One formation mechanism proposed by Quinn and Ehlmann in 2017 was that sediment was deposited and eventually the sediment underwent diagenesis which caused a loss of volume and fractures. After erosion exposed the fractures, they were filled with minerals possibly by acid-sulfate fluids. More erosion removed softer materials and left the more resistant ridges behind. If the impact-caused dike is made of purely melted rock from the heat of the impact, it is called a pseudotachylite .
Also, hydrothermalism may have been involved due to the heat generated during impacts. Strong evidence for hydrothermalism was reported by a team of researchers studying Auki Crater. This crater contains ridges that may have been produced after fractures formed with an impact. Using instruments on the Mars Reconnaissance Orbiter they found the minerals smectite, silica, zeolite, serpentine, carbonate, and chlorite that are common in impact-induced hydrothermal systems on Earth. Other evidence of post-impact hydrothermal systems on Mars from other scientists who studied other Martian craters.

Because ridges seem to be found in older crust only, it is believed that they occurred early in the history of Mars when there were more and larger asteroids striking the planet.
These early impacts may have caused the early crust to be full of interconnected channels.
These networks have been found many regions of Mars including in Arabia Terra ( Arabia quadrangle), northern Meridiani Planum, Solis Planum, Noachis Terra (Noachis quadrangle), Atlantis Chaos, and Nepenthes Mensa ( Mare Tyrrhenum quadrangle).

A somewhat different ridge formation has been discovered in the Eastern Medusae Fossae Formation; these dark ridges can be 50 meters in height and erode into dark boulders. It has been suggested that there are from lava filling fractures in the Medusae Fossae Formation which is surrounded by lava flows. Kerber, L., et al. 2017. Polygonal ridge networks on Mars: Diversity of morphologies and the special case of the Eastern Medusae Fossae Formation. Icarus: 281, 200-219.

Linear ridge networks in Mare Tyrrhenum quadrangle

Some of these may be from hydrothermal systems produced after an impact.

ESP 036893 1765ridgesnepenthestop.jpg, Linear ridge network, as seen by HiRISE under HiWish program

ESP 045992 1780ridges.jpg, Wide view of several groups of linear ridges, as seen by HiRISE under HiWish program
45992 1780curvedridges.jpg, Close view of curved ridges, as seen by HiRISE under HiWish program Note: this is an enlargement of previous image.
45992 1780ridgeswide.jpg, Close view of ridges, from a previous image, as seen by HiRISE under HiWish program
45992 1780blocks.jpg, Close view of ridges, from a previous image, as seen by HiRISE under HiWish program Arrows indicate fractures in ridge
45992 1780roughblocks.jpg, Blocks probably formed after fracturing in ridges Image, as seen by HiRISE under HiWish program

Linear ridge networks in Casius quadrangle

ESP 043845 2130ridges.jpg, Network of ridges, as seen by HiRISE under HiWish program Ridges may be formed in various ways.
ESP 043845 2130ridgesclose.jpg, Color, close-up of ridges seen in previous image, as seen by HiRISE under HiWish program
ESP 043845 2130ridgeswide.jpg, More ridges from the same place as the previous two images, as seen by HiRISE under HiWish program

ESP 036869 2105ridgeswide.jpg, Linear ridge network, as seen by HiRISE under HiWish program
ESP 036869 2105ridgesclose.jpg, Close-up and color image of previous image of linear ridge network, as seen by HiRISe under HiWish program
ESP 036869 2105ridgesbottom.jpg, More linear ridge networks from same location as previous two images, as seen by HiRISE under HiWish program


ESP 048236 2105ridgeswide.jpg, Wide view of network of ridges, as seen by HiRISE under HiWish program Portions of this image are enlarged in following images.

48236 2105ridges3.jpg, Close view of network of ridges, as seen by HiRISE under HiWish program This is an enlargement of a previous image.

48236 2105ridges2.jpg, Close view of network of ridges, as seen by HiRISE under HiWish program This is an enlargement of a previous image. Box shows the size of a football field.

48236 2105ridges.jpg, Close view of network of ridges, as seen by HiRISE under HiWish program This is an enlargement of a previous image.

48236 2105ridgesmesa.jpg, Close view of ridges, as seen by HiRISE under HiWish program This is an enlargement of a previous image. A small mesa in the image displays layers.

ESP 048236 2105ridgesclosecolor.jpg, Close, color view of network of ridges, as seen by HiRISE under HiWish program This is an enlargement of a previous image.

Linear ridge networks in Syrtis Major quadrangle

Image:Huo Hsing Vallis in Syrtis Major.JPG, Huo Hsing Vallis in Syrtis Major, as seen by THEMIS. Straight ridges may be dikes in which liquid rock once flowed.
Image:Huo Hsing Vallis Ridges.JPG, Huo Hsing Vallis Ridges, as seen by HiRISE. Ridges may be caused by water moving along faults.
ESP 043410 1980ridges.jpg, Ridges, as seen by HiRISE under HiWish program These may be the result of dikes or faults.

Linear ridge networks in Phaethontis quadrangle

ESP 034887 1490ridgesphaethontis.jpg, Linear ridge networks, as seen by HiRISE under HiWish program
ESP 034887 1490ridgesphaethontisclose.jpg, Close-up of linear ridge networks from the previous image, as seen by HiRISE under HiWish program
ESP 036443 1495ridgesphaethontistop.jpg, Linear ridge networks, as seen by HiRISE under HiWish program
ESP 036443 1495ridgesphaethontisbottom.jpg, Linear ridge networks, as seen by HiRISE under HiWish program

Linear ridge networks in Amazonis quadrangle

Image:26552sharpridges.jpg, Narrow ridges, as seen by HiRISE under HiWish program. The ridges may be the result of impacts fracturing the surface.
ESP 036745 1905top.jpg, Linear ridge networks, as seen by HiRISE under HiWish program
36745 1905lridgesshort.jpg, Close-up of ridge network, as seen by HiRISE under HiWish program This is an enlargement of a previous image.
36745 1905ridgesx.jpg, Close-up of ridge network, as seen by HiRISE under HiWish program This is an enlargement of a previous image.
ESP 036745 1905ridges.jpg, Linear ridge networks, as seen by HiRISE under HiWish program

Linear ridge networks in Arabia quadrangle

ESP 036316 2015straightridges.jpg, Linear ridge network, as seen by HiRISE under HiWish program Dark line is not part of the picture.

Image:ESP_020230dikes.jpg, Dikes in Arabia, as seen by HiRISE, under the HiWish program. These straight features may indicate where valuable ore deposits may be found by future colonists. Scale bar is 500 meters. They may be part of linear ridges, hence related to impact craters.
Image:Ridgecomplex22919.jpg, Close-up of a complex group of ridges. The ridges may be the remains of old streams and/or linear ridge networks. Image taken by HiRISE under the HiWish program.

Linear ridge networks in Arcadia quadrangle

ESP 047054 2160ridges.jpg, Wide view of ridge network, as seen by HiRISE under HiWish program
47054 2160largeridges.jpg, Close view of ridge networks, as seen by HiRISE under HiWish program Arrow points to small, straight ridge.
47054 2160largeridgeschanging.jpg, Close view of small and large ridges, as seen by HiRISE under HiWish program
47054 2160smallridges.jpg, Close view of small and large ridges, as seen by HiRISE under HiWish program

See also

* Craters
* Dike (geology)
* Geology of Mars

References

{{Reflist, 30em

External links

Zooniverse - Project - Planet four ridges
: help scientists exploring Mars by discovering networks of polygonal ridges

Geology of Mars