Ismenius Lacus quadrangle

MC-05

Ismenius Lacus

30–65° N

0–60° E

Quadrangles

Atlas

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  Elevations

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This quadrangle has some of the most mysterious-looking landscapes on the planet. It truly looks like another world here. The Ismenius Lacus quadrangle contains regions called Deuteronilus Mensae and Protonilus Mensae, two places that are of special interest to scientists. They contain abundant evidence of present and past glacial activity. They also have a landscape unique to Mars, called Fretted terrain. The largest crater in the area is Lyot Crater, which contains channels probably carved by liquid water. The Ismenius Lacus quadrangle is located in the northern hemisphere and covers 30° to 65° north latitude and 300° to 360° west longitude (60° to 0° east longitude). The southern and northern borders of the Ismenius Lacus quadrangle are approximately 3065 km (1,905 mi) and 1500 km wide (930 mi) respectively. The north-to-south distance is about 2050 km (1,270 mi) (a bit less than the length of Greenland). The Ismenius Lacus quadrangle contains parts of regions named Acidalia Planitia, Arabia Terra, Vastitas Borealis, and Terra Sabaea.

Origin of names

Ismenius Lacus is the name of a classical albedo feature located at 40° N and 30° E on Mars. The term is Latin for Ismenian Lake, and refers to the Ismenian Spring near Thebes in Greece where Cadmus slew the guardian dragon. Cadmus was the legendary founder of Thebes, and had come to the spring to fetch water. The name was approved by the International Astronomical Union (IAU) in 1958. All names suggested for astronomical features have to eventually approved by the International Astronomical Union (IAU). Some important areas in this quadrangle derive from the names of canals that some early astronomers saw in this broad area. One such large canal they called Nilus. Since 1881–1882 it was split into other canals, some were called Nilosyrtis, Protonilus (first Nile),and Deuteronilus (second Nile).

Channels (Rivers)

Many features were probably rivers with water flowing in them billions of years ago. Pictures below show many channels and parts of channels.

The channel shown below goes quite a long distance and has branches. It ends in a depression that may have been a lake at one time. The first picture is a wide angle, taken with CTX; while the second is a close up taken with HiRISE.

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  Channels in Arabia, as seen by CTX This channel winds along for a good distance and has branches. It ends in a depression that may have been a lake at one time.

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  Channel in Arabia, as seen by HiRISE under HiWish program. This is an enlargement of the previous image that was taken with CTX to give a wide view.

Some places (like below) display a smaller channel within a larger, wider channel or valley. When this occurs it means water went through the region at least two times in the past. This implies that water was not here once for just a short period of time.

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  Channel within larger channel The existence of the smaller channel suggests water went through the region at least two times in the past.

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  Close-up of channel within larger channel The existence of the smaller channel suggests water went through the region at least two times in the past. The black box represents the size of a football field. Some parts of the surface would be difficult to walk on with the many small hills and depressions.

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  Channel system that travels through part of a crater

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  Channel that cut through a crater rim

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  Channel system that travels through part of a crater Note: this is an enlargement of a previous image.

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  Channel that travels through part of a crater The arrow shows a crater that was eroded by the channel. Note: this is an enlargement of a previous image.

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  Channels

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  Meander in a channel Meanders are commonly formed in old river systems when the water is moving slowly.

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  Wide view of channels

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  Close view of channel

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  Channel that has cut through a crater rim

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  Wide view of channels, as seen by HiRISE under HiWish program

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  Wide view of channels

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  Channel

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  Wide view of channels

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  Channel with hanging valley

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  Wide view of channels

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  Wide view of channels, as seen by HiRISE under HiWish program

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  Channel

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  Channels

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  Channels, as seen by HiRISE under HiWish program

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  Channels, Some parts of the image show mantle and others show no mantle covering the surface.

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  Possible inverted channel Here after a stream bed got filled with erosion resistant materials, the surrounding, softer landscape eroded away.

Lyot Crater

The vast northern plains of Mars are generally flat and smooth with few craters. However, a few large craters do stand out. The giant impact crater, Lyot, is easy to see in the northern part of Ismenius Lacus. There are only a very few craters along the far northern latitudes. Lyot Crater is the deepest point in Mars's northern hemisphere. One image below of Lyot Crater Dunes shows a variety of interesting forms: dark dunes, light-toned deposits, and Dust Devil Tracks. Dust devils, which resemble miniature tornados, create tracks by removing a thin, but bright deposit of dust to reveal the darker underlying surface. 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 do the trick. Note on units: a micron is an older name for micrometre or micrometer. The width of a single human hair ranges from approximately 20 to 200 microns (μm); hence, the dust that can cover dust devil tracks may only be the thickness of a human hair. Light-toned materials are an important find because they are widely believed to contain minerals formed in water. Research, published in June 2010, described evidence for liquid water in Lyot crater in the past.

Many channels have been found near Lyot Crater. Research, published in 2017, concluded that the channels were made from water released when the hot ejecta landed on a layer of ice that was 20 to 300 meters thick. Calculations suggest that the ejecta would have had a temperature of at least 250 degrees Fahrenheit. The valleys seem to start from beneath the ejecta near the outer edge of the ejecta. The existence of these channels is unusual because although Mars used to have water in rivers, lakes, and an ocean, these features have been dated to times after we had thought that many of these features had disappeared.

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  Wide view of channels in Lyot Crater, as seen by HiRISE unser HiWish program

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  Close view of channels in Lyot Crater

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  Close view of channels in Lyot Crater, as seen by HiRISE under HiWish program

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  Lyot Crater Dunes, as seen by HiRISE. Click on image to see light-toned deposits and dust devil tracks.

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  Channel

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 in their walls. Since the collision that produces a crater is like a powerful explosion, rocks from deep underground are tossed unto the surface. Hence, craters are useful for showing us what lies deep under the surface.

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  Fresh crater, as seen by HiRISE under HiWish program This is a young crater because one can easily see the rim and ejecta. They have not yet been eroded.

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  West side of Sinton Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter) A central peak is visible--it occurs in larger craters and is caused by a rebound from the force of the impact.

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  Crater with a bench A crater with a bench may be formed from settling of the crater wall or it may be due to impact into something with vastly different types of layers.

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  Possible expanded secondary craters, as seen by HiRISE under HiWish program These craters may have become much wider, as ice left the ground around the rims.

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  Impact crater that may have formed in ice-rich ground, as seen by HiRISE under HiWish program

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  Impact crater that may have formed in ice-rich ground Note that the ejecta seems lower than the surroundings. The hot ejecta may have caused some of the ice to go away; thus lowering the level of the ejecta.

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  Pedestal crater The crater's ejecta protected the underlying ground from eroding.

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  Pedestal crater Mesa on the crater floor formed after the crater.

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  Valleys on the Ejecta Blanket from Cerulli Crater, as seen by HiRISE.

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  Cerulli Crater, as seen by HiRISE It looks like a delta was formed as channels bought in debris and dumped then in a lake that was in the crater.

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  Northeast rim of Quenisset Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter). Note: this is an enlargement of the previous image of Quenisset Crater. Arrows indicate old glaciers.

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  Group of layers in crater

Fretted terrain

The Ismenius Lacus quadrangle contains several interesting features such as fretted terrain, parts of which are found in Deuteronilus Mensae and Protonilus Mensae. Fretted terrain contains smooth, flat lowlands along with steep cliffs. The scarps or cliffs are usually 1 to 2 km high. Channels in the area have wide, flat floors and steep walls. Many buttes and mesas are present. In fretted terrain the land seems to transition from narrow straight valleys to isolated mesas. Most of the mesas are surrounded by forms that have been called a variety of names: circum-mesa aprons, debris aprons, rock glaciers, and lobate debris apron (LDA)s. The flat floors here often display many lines or lineations that scientists call lineated valley fill (LVF). These are cause by glacier-like flow. At first they appeared to resemble rock glaciers on Earth. But scientists could not be sure. Even after the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) took a variety of pictures of fretted terrain, experts could not tell for sure if material was moving or flowing as it would in an ice-rich deposit (glacier). Eventually, proof of their true nature was discovered by radar studies with the Mars Reconnaissance Orbiter showed that they contain pure water ice covered with a thin layer of rocks that insulated the ice.

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  Fretted terrain of Ismenius Lacus showing flat floored valleys and cliffs. Photo taken with Mars Orbiter Camera (MOC)on the Mars Global Surveyor, under the MOC Public Targeting Program. The white rectangle indicates the position of a high resolution image.

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  Enlargement of the photo on the left showing cliff. Photo taken with high-resolution camera of Mars Global Surveyor (MGS), under the MOC Public Targeting Program.

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  Wide view of mesa with CTX showing cliff face and location of lobate debris apron (LDA). Location is Ismenius Lacus quadrangle.

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  Enlargement of previous CTX image of mesa. This image shows the cliff face and detail in the LDA. Image taken with HiRISE under HiWish program. Location is Ismenius Lacus quadrangle.

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  Wide CTX view showing mesa and buttes with lobate debris aprons and lineated valley fill around them. Location is Ismenius Lacus quadrangle.

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  Close-up of lineated valley fill (LVF), as seen by HiRISE under HiWish program. Note: this is an enlargement of the previous CTX image.

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  Example of frettered terrain, as seen by HiRISE under HiWish program Fretted terrain contains many wide, flat-floored valleys.

See also

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

References

• Mars Global Surveyor