Hellas quadrangle

The Hellas quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Hellas quadrangle is also referred to as MC-28 (Mars Chart-28).
The Hellas quadrangle covers the area from 240° to 300° west longitude and 30° to 65° south latitude on the planet Mars. Within the Hellas quadrangle lies the classic features Hellas Planitia and Promethei Terra. Many interesting and mysterious features have been discovered in the Hellas quadrangle, including the giant river valleys Dao Vallis, Niger Vallis, Harmakhis, and Reull Vallis—all of which may have contributed water to a lake in the Hellas basin in the distant past. Many places in the Hellas quadrangle show signs of ice in the ground, especially places with glacier-like flow features.

Hellas Basin

The Hellas quadrangle contains part of the Hellas Basin, the largest known impact crater on the surface of Mars and the second largest in the solar system. The depth of the crater is 7152 mMartian Weather Observation
MGS radio science measured 11.50 mbar at 34.4° S 59.6° E -7152 meters. (23,000 ft) below the standard topographic datum of Mars. The basin is located in the southern highlands of Mars and is thought to have been formed about 3.9 billion years ago, during the Late Heavy Bombardment. Studies suggest that when an impact created the Hellas Basin, the entire surface of Mars was heated hundreds of degrees, 70 meters of molted rock fell on the planet, and an atmosphere of gaseous rock was formed. This rock atmosphere was 10 times as thick as the Earth's atmosphere. In a few days, the rock would have condensed out and covered the whole planet with an additional 10 m of molten rock. In the Northwest portion of Hellas Planitia is a strange type of surface called complex banded terrain or taffy-pull terrain. Its process of formation is still largely unknown, although it appears to be due to erosion of hard and soft sediment along with ductile deformation. Ductile deformation results from layers undergoing strain.

Early in the planet's history, it is believed that a giant lake existed in the Hellas Basin. Possible shorelines have been discovered. These are evident in alternating benches and scarps visible in Mars orbiting camera narrow-angle images. In addition, Mars orbiting laser altimeter (MOLA) data show that the contacts of these sedimentary units mark contours of constant elevation for thousands of km, and in one case all around the basin. Channels, believed to be formed by water, enter into the basin. The Hellas drainage basin may be almost one-fifth that of the entire northern plains. A lake in Hellas in today's Martian climate would form a thick ice at the top that would eventually sublimate away. That is the ice would turn directly from a solid to a gas. This is similar to how dry ice (solid carbon dioxide) behaves on Earth. Glacial features (terminal moraines, drumlins, and eskers) have been found that may have been formed when the water froze.

Image:Hellas basin topo.jpg, Hellas Basin Area topography. Crater depth is 7152 m (23,000 ft) below the standard topographic datum of Mars.
Image:False color of Hellas Planitia.jpeg, Hellas Basin with graph showing the great depth of the crater. It is the deepest crater on Mars and has the highest surface pressure: 1155 Pa (11.55 mbar, 0.17 psi, or 0.01 atm).
Image:Twisted Ground in Hellas.jpg, Twisted Ground in Hellas, as seen by HiRISE This is one more example of how difficult it would be to walk on Mars.

Lobate debris aprons

One very important feature common in east Hellas are piles of material surrounding cliffs. The formation is called a lobate debris apron (LDA). Recently, research with the Shallow Radar on the Mars Reconnaissance Orbiter has provided strong evidence that the LDAs are glaciers that are covered with a thin layer of rocks. Large amounts of water ice are believed to be in the LDAs. Available evidence strongly suggests that the eastern part of Hellas accumulated snow in the past. When the tilt (obliquity) of Mars increases the southern ice cap releases large amounts of water vapor. Climate models predict that when this occurs, water vapor condenses and falls where LDAs are located. The tilt of the earth changes little because our relatively large moon keeps it stable. The two tiny Martian moons do not stabilize their planet, so the rotational axis of Mars undergoes large variations. Lobate debris aprons may be a major source of water for future Mars colonists. Their major advantage over other sources of Martian water are that they can easily mapped from orbit and they are closer to the equator, where manned missions are more likely to land.

Image:Lobate Debris Apron closeup.jpg, Close-up of surface of a lobate debris apron. Note the lines that are common in rock glaciers on the Earth. Image located in Hellas quadrangle.
Image:CTX Context image for debris apron in Terra Cimmeria.JPG, CTX Context image for next two images of debris apron around mound.
Image:Red Rocks Park feature.JPG, Surface of Debris Apron. There is also a feature similar to features in Red Rocks Park Colorado. Feature seems to be composed of slanted rock layers. Image taken with HiRISE, under the HiWish program.
Image:Frost in Debris Apron in Terra Cimmeria.jpg, Surface of debris apron in Terra Cimmeria, as seen by HiRISE, under the HiWish program. Colored parts may be frost deposits.

Lineated Floor Deposits

On the floors of some channels are features called lineated floor deposits or lineated valley fill. They are ridged and grooved materials that seem to deflect around obstacles. They are believed to be ice-rich. Some glaciers on the Earth show such features. Lineated floor deposits may be related to lobate debris aprons, which have been proven to contain large amounts of ice. Reull Vallis, as pictured below, displays these deposits.

Image:Reull Vallis.JPG, Drainage features in Reull Vallis, as seen by THEMIS. Click on image to see relationship of Reull Vallis to other features.
File:Reull Vallis lineated deposits.jpg, Reull Vallis with lineated floor deposits, as seen by THEMIS. Click on image to see relationship to other features.
ESP 052138 1435lvf.jpg, Lineated valley fill, as seen by HiRISE under HiWish program
File:ESP 055421 1395reullvallis.jpg, Reull Vallis floor showing lineated valley fill at the top and hollows near bottom, as seen by HiRISE under HiWish program

File:55421 1395lvfclose.jpg, Close, color view of lineated valley fill, as seen by HiRISE under HiWish program

Image:Reull Vallisl layers.JPG, Layers in Reull Vallis, as seen by THEMIS.
Image:Fretted terrain near ReullVallis.jpg, Fretted terrain near Reull Vallis, as seen by HiRISE.
Image:Close-up of Fretted Terrain near Reull Vallis.JPG, Close-up of Fretted Terrain near Reull Vallis, as seen by HiRISE. This area would be a challenge to walk across.
Image:Layers in Monument Valley.jpg, Layers in Monument Valley. These are accepted as being formed, at least in part, by water deposition. Since Mars contains similar layers, water remains as a major cause of layering on Mars.

Ice-rich mantle

Much of the surface of Mars is covered by a thick smooth mantle that is thought to be a mixture of ice and dust. This ice-rich mantle, a few yards thick, smoothes the land, but in places it displays a bumpy texture, resembling the surface of a basketball. Because there are few craters on this mantle, the mantle is relatively young. The image at the right shows a good view of this smooth mantle around Niger Vallis, as observed with HiRISE.
Changes in Mars's orbit and tilt cause significant changes in the distribution of water ice from polar regions down to latitudes equivalent to Texas. During certain climate periods water vapor leaves polar ice and enters the atmosphere. The water returns to the ground at lower latitudes as deposits of frost or snow mixed generously with dust. The atmosphere of Mars contains a great deal of fine dust particles. Water vapor condenses on the particles, then they fall down to the ground due to the additional weight of the water coating. When ice at the top of the mantling layer goes back into the atmosphere, it leaves behind dust, which insulates the remaining ice.

45070 1440mantlelayers.jpg, Smooth mantle with layers, as seen by HiRISE under HiWish program
46270 1445mantle.jpg, Close view of mantle, as seen by HiRISE under HiWish program
ESP 048063 1395crater.jpg, Crater showing how thick mantle is in place, as seen by HiRISE under the HiWish program

48063 1395mantle.jpg, Close view of the edge of mantle, as seen by HiRISE under the HiWish program

Upper Plains Unit

Remnants of a 50-100 meter thick mantling, called the upper plains unit, has been discovered in the mid-latitudes of Mars. First investigated in the Deuteronilus Mensae region, but it occurs in other places as well. The remnants consist of sets of dipping layers in craters and along mesas. Sets of dipping layers may be of various sizes and shapes—some look like Aztec pyramids from Central America.

ESP 050793 1365pyramids.jpg, Tilted layers, as seen by HiRISE under HiWish program
50793 1365layers.jpg, Tilted layers, as seen by HiRISE under HiWish program
50793 1365layers2.jpg, Tilted layers, as seen by HiRISE under HiWish program

Image:ESP_024868pyramid.jpg, Layered feature probably formed by the erosion of the upper plains unit, as seen by HiRISE under HiWish program.
P1010377redrocksfall.jpg, Layered feature in Red Rocks Park, Colorado. This has a different origin than ones on Mars, but it has a similar shape. Features in Red Rocks region were caused by uplift of mountains.
Image:ESP 028692 1395pyramidcropped.jpg, Layered feature that is probably the remains of a once widespread unit that fell from the sky, as seen by HiRISE under the HiWish program
ESP 034509 1450pyramidshellas.jpg, Layered feature, as seen by HiRISE under the HiWish program
ESP 034072 1435pyramidhellas.jpg, Layered feature in crater, as seen by HiRISE under the HiWish program
ESP 045321 1415pyramid.jpg, Layered feature in crater, as seen by HiRISE under the HiWish program
ESP 046283 1435pyramid.jpg, Layers in crater, as seen by HiRISE under HiWish program
File:ESP 054485 1430craterpyramid.jpg, Layered feature in crater, as seen by HiRISE under HiWish program

File:ESP 054775 1400craterpyramid.jpg, Layered feature in crater, as seen by HiRISE under HiWish program
File:54775 1400pyramidcolor.jpg, Close, color view of layered feature in crater, as seen by HiRISE under HiWish program Different colors are due to different minerals.

ESP 019778 1385pyramid.jpg, Layered structure in crater that is probably what is left of a layered unit that once covered a much larger area. Material for this unit fell from the sky as ice-coated dust. The picture was taken by HiRISE, under the HiWish program.

This unit also degrades into brain terrain. Brain terrain is a region of maze-like ridges 3–5 meters high. Some ridges may consist of an ice core, so they may be sources of water for future colonists.

ESP 048011 1370upperunit.jpg, Wide view of upper plains unit breaking down into brain terrain, as seen by HiRISE under HiWish program

48011 1370upperunit.jpg, Close view of upper plains unit breaking down into brain terrain, as seen by HiRISE under HiWish program As ice leaves the ground, the ground collapses and winds blow the remaining dust away.

ESP 028336 1395pyramidhellas.jpg, Small, layered structure, as seen by HiRISE under the HiWish program Picture also shows brain terrain forming.

Some regions of the upper plains unit display large fractures and troughs with raised rims; such regions are called ribbed upper plains. Fractures are believed to have started with small cracks from stresses. Stress is suggested to initiate the fracture process since ribbed upper plains are common when debris aprons come together or near the edge of debris aprons—such sites would generate compressional stresses. Cracks exposed more surfaces, and consequently more ice in the material sublimates into the planet's thin atmosphere. Eventually, small cracks become large canyons or troughs. Small cracks often contain small pits and chains of pits; these are thought to be from sublimation of ice in the ground.Baker, D., J. Head. 2015. Extensive Middle Amazonian mantling of debris aprons and plains in Deuteronilus Mensae, Mars: Implication for the record of mid-latitude glaciation. Icarus: 260, 269-288.
Large areas of the Martian surface are loaded with ice that is protected by a meters thick layer of dust and other material. However, if cracks appear, a fresh surface will expose ice to the thin atmosphere. In a short time, the ice will disappear into the cold, thin atmosphere in a process called sublimation. Dry ice behaves in a similar fashion on the Earth. On Mars sublimation has been observed when the Phoenix lander uncovered chunks of ice that disappeared in a few days.Bright Chunks at ''Phoenix'' Lander's Mars Site Must Have Been Ice
– Official NASA press release (19.06.2008)
/ref> In addition, HiRISE has seen fresh craters with ice at the bottom. After a time, HiRISE saw the ice deposit disappear.

Image:Ice sublimating in the Dodo-Goldilocks trench.gif, Die-sized clumps of bright material in the enlarged "Dodo-Goldilocks" trench vanished over the course of four days, implying that they were composed of ice which sublimated following exposure.
Image:Evaporating ice on Mars Phoenix lander image.jpg, Color versions of the photos showing ice sublimation, with the lower left corner of the trench enlarged in the insets in the upper right of the images.

The upper plains unit is thought to have fallen from the sky. It drapes various surfaces, as if it fell evenly. As is the case for other mantle deposits, the upper plains unit has layers, is fine-grained, and is ice-rich. It is widespread; it does not seem to have a point source. The surface appearance of some regions of Mars is due to how this unit has degraded. It is a major cause of the surface appearance of lobate debris aprons.
The layering of the upper plains mantling unit and other mantling units are believed to be caused by major changes in the planet's climate. Models predict that the obliquity or tilt of the rotational axis has varied from its present 25 degrees to maybe over 80 degrees over geological time. Periods of high tilt will cause the ice in the polar caps to be redistributed and change the amount of dust in the atmosphere.

Climate change caused ice-rich features

Many features on Mars, including ones in Hellas quadrangle, are believed to contain large amounts of ice. The most popular model for the origin of the ice is climate change from large changes in the tilt of the planet's rotational axis. At times the tilt has even been greater than 80 degrees Large changes in the tilt explains many ice-rich features on Mars.

Studies have shown that when the tilt of Mars reaches 45 degrees from its current 25 degrees, ice is no longer stable at the poles. Furthermore, at this high tilt, stores of solid carbon dioxide (dry ice) sublimate, thereby increasing the atmospheric pressure. This increased pressure allows more dust to be held in the atmosphere. Moisture in the atmosphere will fall as snow or as ice frozen onto dust grains. Calculations suggest this material will concentrate in the mid-latitudes. General circulation models of the Martian atmosphere predict accumulations of ice-rich dust in the same areas where ice-rich features are found.
When the tilt begins to return to lower values, the ice sublimates (turns directly to a gas) and leaves behind a lag of dust. The lag deposit caps the underlying material so with each cycle of high tilt levels, some ice-rich mantle remains behind. Note, that the smooth surface mantle layer probably represents only relative recent material.

Origin of Dao Vallis

Dao Vallis begins near a large volcano, called Hadriaca Patera, so it is thought to have received water when hot magma melted huge amounts of ice in the frozen ground. The partially circular depressions on the left side of the channel in the adjacent image suggests that groundwater sapping also contributed water.

Dust devil tracks

Many areas on Mars, including the Hellas quadrangle, experience the passage of giant dust devils. 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. Dust devils have been seen from the ground and from orbiting spacecraft. They have even blown the dust off of the solar panels of the two Rovers on Mars, thereby greatly extending their lives.NASA.gov
/ref> The twin Rovers were designed to last for 3 months, instead they have lasted more than five years. The pattern of the tracks have 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 meters and last at least 26 minutes.

Wikiwallacedevils.jpg, Dust devil tracks on floor of Wallace Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter)
ESP 049304 1215streaks.jpg, Dust devil tracks, as seen by HiRISE under HIWish program

File:57044 1325colordevilsboulders.jpg, Dust devil tracks and boulders, as seen by HiRISE under HIWish program

File:ESP 057533 1445devilswide.jpg, Wide view of dust devil tracks, as seen by HiRISE under HIWish program

File:ESP 057533 1445devilscolor.jpg, Close color view of dust devil tracks, as seen by HiRISE under HIWish program

File:57533 1445widedevil.jpg, Close color view of dust devil tracks, as seen by HiRISE under HIWish program

File:57876 1285streakspatterned.jpg, Close color view of dust devil tracks, as seen by HiRISE under HIWish program patterned ground is visible in the background.

Evidence for possible recent liquid water

The Mars Reconnaissance Orbiter discovered changes on the wall of Penticton Crater between 1999 and 2004. One interpretation of the changes was that they were caused by water flowing on the surface. A further analysis, published about a year later, revealed that the deposit could have been caused by gravity moving material down slope (a landslide). The slope where the deposit was sighted was close to the stability limits of dry, unconsolidated materials.

Other 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. The peak is caused by a rebound of the crater floor following the impact. Sometimes craters will display layers. Craters can show us what lies deep under the surface.

ESP 047615 1275pedestal.jpg, Pedestal crater, as seen by HiRISE under HiWish program

Image:Pedestal crater3.jpg, 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.

Image:Pedestaldrawingcolor2.jpg, 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.

File:ESP 055449 1175pedestals.jpg, Pedestal craters, as seen by HiRISE under HiWish program

Image:Spallanzani.JPG, Stair-stepping mesas in interior deposit of Spallanzani Crater, as seen by THEMIS

ESP 048854 1455crater.jpg, Side view of crater that was cut by a wall, as seen by HiRISE under HiWish program Other craters are also in this view.

Image:Penticton Crater Gullies.JPG, Penticton Crater gullies, as seen by HiRISE
Image:Lipik Crater Channels.jpg, Lipik Crater Channels, as seen by THEMIS
Wikitikhov.jpg, Tikhov Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter)
Wikiwallacefloor.jpg, Floor of Wallace Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter)
Wikiwallacedevils.jpg, Dust devil tracks on floor of Wallace Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter). Note this is an enlargement of the previous image of the floor of Wallace Crater.
Wikihuxley.jpg, Huxley Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter)
Wikigledhill.jpg, Gledhill Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter)
Wikiredi.jpg, Redi Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter)
Wikiredidevils.jpg, Redi Crater, showing dust devil tracks and mantle, as seen by CTX camera (on Mars Reconnaissance Orbiter). Note: this is an enlargement of the previous image of Redi Crater.

Glacial Features

Glaciers, loosely defined as patches of currently or recently flowing ice, are thought to be present across large but restricted areas of the modern Martian surface, and are inferred to have been more widely distributed at times in the past."The Surface of Mars" Series: Cambridge Planetary Science (No. 6) Michael H. Carr, United States Geological Survey, Menlo Park Lobate convex features on the surface known as viscous flow features and lobate debris aprons, which show the characteristics of non-Newtonian flow, are now almost unanimously regarded as true glaciers.

A climate model, reported in the journal Science in 2006, found that large amounts of ice should accumulate in the Hellas region, in the same places where glaciers are observed. Water is transported from the south polar area to northern Hellas and falls as precipitation.

ESP 051151 1445flow.jpg, Flows, as seen by HiRISE under HiWish program
ESP 051151 1445closecolor.jpg, Close, color view of flow, as seen by HiRISE under HIWish program

ESP 051162 1460flows.jpg, Flows, as seen by HiRISE under HiWish program

File:ESP 054973 1405tongue.jpg, Flow, as seen by HiRISE under HiWish program

ESP 051162 1460flowclosecolor.jpg, Close, color view of flow, as seen by HiRISE under HiWish program Patterned ground is visible in the photo.

ESP 051175 1430flow.jpg, Flow, as seen by HiRISE under HiWish program Flows, as seen by HiRISE under HiWish program
File:ESP 055065 1405flow.jpg, Flow, as seen by HiRISE under HiWish program
File:ESP 055091 1405flow.jpg, Flow, as seen by HiRISE under HiWish program

ESP 049527 1420tongue.jpg, Flow, as seen by HiRISE under HiWish program
49527 1420tongueclose.jpg, Close view of snout of flow, as seen by HiRISE under HiWish program Polygonal patterned ground is visible.

ESP 049949 1420tongues.jpg, Wide view of tongue-shaped glaciers, as seen by HiRISE under HiWish program
49949 1420polygons.jpg, Close view of tongue-shaped glaciers, as seen by HiRISE under HiWish program Polygons are visible.

Image:Gully Flow Features.JPG, Surface features that show down hill movement, as seen by HiRISE.
Image:CTX image of Cirque near Hellas.JPG, CTX context image of Hellas Planitia showing location of next two images.
Image:Glacial features in Hellas.JPG, Surface in Hellas quadrangle, as seen by HiRISE, under the HiWish program.
Image:Glacial Cirque in Hellas.JPG, Possible Glacial Cirque in Hellas Planitia, as seen by HiRISE, under the HiWish program. Lines are probably due to downhill movement.
Wikielephantglacier.jpg, Romer Lake's Elephant Foot Glacier in the Earth's Arctic, as seen by Landsat 8. This picture shows several glaciers that have the same shape as many features on Mars that are believed to also be glaciers.
ESP 045505 1400flow.jpg, Flow feature that was probably a glacier, as seen by HiRISE under HiWish program
ESP 046270 1445flowridges.jpg, Flow ridges, as seen by HiRISE under the HiWish program Ridges probably formed at the end of old glacier.
Image:ESP_020319flowcontext.jpg, Context for the next image of the end of a flow feature or glacier. Location is Hellas quadrangle.
Image:ESP_020319flowsclose-up.jpg, Close-up of the area in the box in the previous image. This may be called by some the terminal moraine of a glacier. For scale, the box shows the approximate size of a football field. Image taken with HiRISE under the HiWish program. Location is Hellas quadrangle.
Image:20543 gap in crater rim.jpg, Material Flowing through a crater rim, as seen by HiRISE, under the HiWish program. Lateral moraines are labeled.
Image:ESP020886 with tongue shaped glacier.jpg, Glaciers, as seen by HiRISE, under HiWish program. Glacier on left is thin because it has lost much of its ice. Glacier on the right, on the other hand, is thick; it still contains a lot of ice that is under a thin layer of dirt and rock.
Image:Tongue23141.jpg, Tongue-shaped glacier, as seen by HiRISE under the HiWish program. Ice may exist in the glacier, even today, beneath an insulating layer of dirt.
Image:Tongue23141close.jpg, Close-up of tongue-shaped glacier, as seen by HiRISE under the HiWish program Resolution is about 1 meter, so one can see objects a few meters across in this image. Ice may exist in the glacier, even today, beneath an insulating layer of dirt.
ESP 045070 1440tongues.jpg, Tongue-shaped glaciers indicated with arrows, as seen by HiRISE under the HiWish program
45070 1440glacialsnout.jpg, Close view of snout of glacier, as seen by HiRISE under the HiWish program High center polygons are visible. Box shows size of football field.
45070 1440polygons.jpg, Close view of high center polygons near glacier, as seen by HiRISE under the HiWish program
45070 1440polygonsclose.jpg, Close view of high center polygons near glacier, as seen by HiRISE under the HiWish program
45070 1440polygonscloseshadows.jpg, Close view of high center polygons near glacier, as seen by HiRISE under the HiWish program Box shows size of football field.
45070 1440polygonshadows.jpg, Close view of high center polygons near glacier, as seen by HiRISE under the HiWish program

ESP 051017 1420glacier.jpg, Tongue-shaped glacier, as seen by HiRISE under the HiWish program

ESP 047193 1440tongues.jpg, Wide view of tongue-shaped flows, as seen by HiRISE under the HiWish program
47193 1440tonguesclose.jpg, Close view of tongue-shaped flows, as seen by HiRISE under the HiWish program
47193 1440polygons.jpg, Close view of tongue-shaped flows and polygonal terrain (which is labeled), as seen by HiRISE under the HiWish program
47193 1440polygonsclose2.jpg, Close view of polygonal terrain near tongue-shaped flows, as seen by HiRISE under the HiWish program

48854 1455grooves.jpg, Grooves caused by movement of glacier, as seen by HiRISE under HiWish program

ESP 048854 1455polygonsclosecolor.jpg, Close, color view of polygons, as seen by HiRISE under HiWish program Polygons are common in ice-rich ground.

Channels

There is enormous evidence that water once flowed in river valleys on Mars. Images of curved channels have been seen in images from Mars spacecraft dating back to the early seventies with the Mariner 9 orbiter. Indeed, a study published in June 2017, calculated that the volume of water needed to carve all the channels on Mars was even larger than the proposed ocean that the planet may have had. Water was probably recycled many times from the ocean to rainfall around Mars.

Image:Mad Vallis.JPG, Mad Vallis, as seen by HiRISE. Picture on right is an enlargement of part of the other picture.
ESP 039902 1455channel.jpg, Channels, as seen by HiRISE under HiWish program.
ESP 041972 1490channel.jpg, Streamlined shape in old river valley, as seen by HiRISE under HiWish program. The streamlined shape is evidence of running water.
ESP 045492 1430channel.jpg, Channel, as seen by HiRISE under HiWish program
ESP 045492 1430channeltop.jpg, Channel, as seen by HiRISE under HiWish program
ESP 047997 1415channels.jpg, Channels, as seen by HiRISE under HiWish program

ESP 048196 1460meteorite.jpg, Wide view of small channels, as seen by HiRISE under HiWish program
48196 1460channels.jpg, Close view of channels, as seen by HiRISE under HiWish program

ESP 048855 1450channels.jpg, Channel network, as seen by HiRISE under HiWish program

ESP 050886 1475valley.jpg, Valley, as seen by HiRISE under HiWish program

ESP 052494 1395meanders.jpg, Channel, as seen by HiRISE under HiWish program Arrows indicate evidence of a meander.

File:55091 1405mantlechannels.jpg, Close view of small channels that seem to originate in a mantle layer, as seen by HiRISE under HiWish program

ESP 050964 1410channel.jpg, Channels, as seen by HiRISE under the 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.
A detailed discussion of layering with many Martian examples can be found in Sedimentary Geology of Mars.

ESP 051110 1465layers.jpg, Layers, as seen by HiRISE under HiWish program
51110 1465layerswide.jpg, Layers, as seen by HiRISE under HiWish program
51110 1465layersblocks.jpg, Close view of layers, as seen by HiRISE under HiWish program Boulders are also visible in the image.

ESP 045507 1470layers.jpg, Wide view of layers, as seen by HiRISE under HiWish program
ESP 045507 1470layeredcrater.jpg, Close view of layered deposit in crater, as seen by HiRISE under HiWish program
45507 1470layers.jpg, Close view of layers, as seen by HiRISE under HiWish program
45507 1470layerswhite.jpg, Layered formation, as seen by HiRISE under HiWish program
45507 1470layerswhiteclose.jpg, Close view of layers from previous image, as seen by HiRISE under HiWish program
46139 1375layers.jpg, Layers, as seen by HiRISE under HiWish program
ESP 047154 1410layers.jpg, Wide view of layers, as seen by HiRISE under HiWish program
47154 1410gullyclose.jpg, Channel of a gully indicated with arrows Picture enlarged from previous image
47154 1410layersclose.jpg, Close view of layers, as seen by HiRISE under HiWish program


ESP 048144 1475layers.jpg, Wide view of layers, as seen by HiRISE under HiWish program
48144 1475layers.jpg, Close view of layers, as seen by HiRISE under HiWish program
48144 1475layerscubes.jpg, Close view of layers, as seen by HiRISE under HiWish program Some of the layers are breaking up into large blocks
48144 1475cubes.jpg, Close view of layers, as seen by HiRISE under HiWish program Some of the layers are breaking up into large blocks
48605 1485layers.jpg, Layers, as seen by HiRISE under HiWish program

ESP 048882 1490lighttoned.jpg, Layers, as seen by HiRISE under HiWish program Some layers are light-toned which means that they may have been associated with water.

48882 1490layers.jpg, Close view of layers, as seen by HiRISE under HiWish program Some layers are light-toned which means that they may have been associated with water.

ESP 048882 1490layersclosecolor.jpg, Close view of light-toned materials, as seen by HiRISE under HiWish program Light-toned materials have been associated with water.

File:ESP 054763 1500layers.jpg, Wide view of light and dark toned layers, as seen by HiRISE under HiWish program
File:54763 1500layers.jpg, Close view of light and dark toned layers, as seen by HiRISE under HiWish program
File:54763 1500layers2.jpg, Close view of light and dark toned layers, as seen by HiRISE under HiWish program
File:54763 1500layerscolor.jpg, Close, color view of layers, as seen by HiRISE under HiWish program The different colors represent different minerals.

File:ESP 055053 1485layers.jpg, Wide view of light and dark toned layers, as seen by HiRISE under HiWish program

File:55053 1485layersclosecolor.jpg, Close, color view of layers, as seen by HiRISE under HiWish program The different colors represent different minerals.
File:55053 1485layersclosecolor2.jpg, Close, color view of layers, as seen by HiRISE under HiWish program

File:ESP 055581 1470layers.jpg, Wide view of layers in mounds, as seen by HiRISE under HiWish program

File:55581 1470layered mounds.jpg, Close view of layers in mound, as seen by HiRISE under HiWish program

Honeycomb terrain

These relatively flat-lying “cells” appear to have concentric layers or bands, similar to a honeycomb. This "honeycomb" terrain was first discovered in the northwestern part of Hellas. The geologic process responsible for creating these features remains unresolved. Some calculations indicate that this formation may have been caused by ice moving up through the ground in this region. The ice layer would have been between 100 m and 1 km thick. When one substance moves up through another denser substance, it is called a diapir. So, it seems that large masses of ice have pushed up layers of rock into domes that were eroded. After erosion removed the top of the layered domes, circular features remained.

Diapirs are thought to be responsible for features on Neptune's moon Triton, Jupiter's moon Europa, Saturn's moon Enceladus, and Uranus's moon Miranda.

ESP 048130 1380honeycomb.jpg, Concentric bands and layers that has been called "honeycomb terrain" Picture was taken by HiRISE under the HiWish program.
ESP 045348 1415rings.jpg, Circular layers, as seen by HiRISE under HiWish program
ESP 046139 1375ridgeslayers.jpg, layers and ridges that form strange patterns, as seen by HiRISE under HiWish program
46139 1375ridges.jpg, Close view of ridges forming strange patterns, as seen by HiRISE under HiWish program

ESP 049330 1425honeycomb.jpg, Honeycomb terrain, as seen by HiRISE under HiWish program

ESP 049330 1425honeycombcolor.jpg, Close, color view of honeycomb terrain, as seen by HiRISE under HiWish program

49330 1425honeycombcubes.jpg, Close view of honeycomb terrain, as seen by HiRISE under HiWish program

49330 1425honeycombcubesclose.jpg, Close view of honeycomb terrain, as seen by HiRISE under HiWish program This enlargement shows material breaking up into blocks. Arrow indicates a cube-shaped block.

File:ESP 057110 1365ridges.jpg, Ridges, as seen by HiRISE under HiWish program

File:ESP 057110 1365ridgescircles.jpg, Close view of concentric and parallel ridges, as seen by HiRISE under HiWish program

File:ESP 057111 1455ridges.jpg, Wide view of ridge network, as seen by HiRISE under HiWish program

File:ESP 057111 1455ridges3.jpg, Close view of ridge network, as seen by HiRISE under HiWish program

File:57111 1455ridgenetwork.jpg, Close view of ridge network, as seen by HiRISE under HiWish program

Gullies

Gullies occur on steep slopes, especially on the walls of craters. Gullies are believed to be relatively young because they have few, if any craters. Moreover, they lie on top of sand dunes which themselves are considered to be quite young. Usually, each gully has an alcove, channel, and apron. Some studies have found that gullies occur on slopes that face all directions, others have found that the greater number of gullies are found on poleward facing slopes, especially from 30-44 S.

For years, many believed that gullies were formed by running water, but further observations demonstrate that they may be formed by dry ice. Recent studies describe using the High Resolution Imaging Science Experiment (HiRISE) camera on MRO to examine gullies at 356 sites, starting in 2006. Thirty-eight of the sites showed active gully formation. Before-and-after images demonstrated the timing of this activity coincided with seasonal carbon dioxide frost and temperatures that would not have allowed for liquid water. When dry ice frost changes to a gas, it may lubricate dry material to flow especially on steep slopes. In some years frost, perhaps as thick as 1 meter, triggers avalanches. This frost contains mostly dry ice, but also has tiny amounts of water ice.

ESP 048881 1415gullies.jpg, Gullies in crater, as seen by HiRISE under HiWish program

48881 1415polygons.jpg, Close view of gullies in crater, as seen by HiRISE under HiWish program Polygons are visible in this close view.

ESP 049185 1350gullieslayers.jpg, Wide view of layers and gullies, as seen by HiRISE under HiWish program Arrows point to small gullies.
49185 1350gully.jpg, Close view of small gully, as seen by HiRISE under HiWish program

File:ESP 057044 1325gullies.jpg, Wide view of gullies, as seen by HiRISE under HiWish program

File:57044 1325colorgullies.jpg, Close, color view of gullies, as seen by HiRISE under HiWish program

File:57044 1325curvedgullies.jpg, Close view of gullies, as seen by HiRISE under HiWish program Curves in channels are evidence that these gullies were not created by landslides.

Polygons

Some surfaces on Mars display polygons. These may be of different sizes. Polygons are an example of patterned ground. Polygonal, patterned ground is quite common in some regions of Mars.

49185 1350polygons.jpg, Group of polygons, as seen by HiRISE under HiWish program
File:040310 1475flagstones.jpg, Patterned ground in Hellas, as seen by HiRISE under HiWish program The rectangle shows the size of a football field.

ESP 049660 1200polygons.jpg, Wide view of polygons, as seen by HiRISE under HiWish program Parts of this image are enlarged in following images.
49660 1200polygonswide.jpg, Polygons, as seen by HiRISE under HiWish program

49660 1200polygonsrockscraters.jpg, Close view of polygons, as seen by HiRISE under HiWish program Arrow point to boulders that sit inside of small craters.

49660 1200polygonspits.jpg, Close view of polygons, as seen by HiRISE under HiWish program

49660 1200polygonsrockscratersclose.jpg, Close view of polygons, as seen by HiRISE under HiWish program

Exposed ice sheets

Thick deposits of ice were found by a team of researchers using instruments on board the Mars Reconnaissance Orbiter (MRO). The scientists found eight eroding slopes showing exposed water ice sheets as thick as 100 meters. Seven of the locations were in the southern hemisphere. Much evidence of buried ice under the ground on vast regions of Mars has already been found by past studies, but this study found that the ice was only covered by a layer of about 1 or 2 meters thick of soil.