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Lineated valley fill (LVF), also called lineated floor deposit, is a feature of the floors of some channels on
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
, exhibiting ridges and grooves that seem to flow around obstacles. Shadow measurements show that at least some of the ridges are several metres high. LVF is believed to be ice-rich. Hundreds of metres of ice probably lie protected in LVF under a thin layer of debris. The debris consists of wind-borne dust, material from alcove walls, and lag material remaining after ice sublimated (changed from a solid directly to a gas) from a rock-ice mixture. Some
glacier A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such a ...
s on Earth show similar ridges. High-resolution pictures taken with
HiRISE High Resolution Imaging Science Experiment is a camera on board the '' Mars Reconnaissance Orbiter'' which has been orbiting and studying Mars since 2006. The 65 kg (143 lb), US$40 million instrument was built under the direction ...
reveal that some of the surfaces of lineated valley fill are covered with strange patterns called closed-cell and open-cell brain terrain. The terrain resembles a human brain. It is believed to be caused by cracks in the surface accumulating dust and other debris, together with ice sublimating from some of the surfaces. The cracks are the result stress from gravity and seasonal heating and cooling. This same type of surface is present on
Lobate debris aprons Lobate debris aprons (LDAs) are geological features on Mars, first seen by the Viking Orbiters, consisting of piles of rock debris below cliffs. These features have a convex topography and a gentle slope from cliffs or escarpments, which suggest fl ...
and
Concentric crater fill A concentric crater fill (CCF) is a landform where the floor of a crater is mostly covered with many parallel ridges. It is common in the mid-latitudes of Mars, and is widely believed to be caused by glacial movement. Areas on Mars called Deutero ...
so all three are believed to be related. Wikifrettedctxpo5.jpg, Wide CTX view of mesa showing lineated valley fill and lobate debris apron (LDA). Both are believed to be debris-covered glaciers. Location is Ismenius Lacus quadrangle. Wikifretesp 027639 2210lda.jpg, Close-up of lobate debris apron from the previous CTX image of a mesa. Image shows open-cell brain terrain and closed-cell brain terrain, which is more common. Open-cell brain terrain is thought to hold a core of ice. Image is from HiRISE under HiWish program. File:25246brainseroding.jpg, Closed-cell brain terrain, as seen by HiRISE under the HiWish program. This type of surface is common on lobate debris aprons, concentric crater fill, and lineated valley fill. File:Htalk23815 2215lvfclose.jpg, Open- and closed-cell brain terrain, as seen by HiRISE, under HiWish program. Wikifrettedctxp22.jpg, Wide CTX view showing mesa and buttes with lobate debris aprons and lineated valley fill around them. Location is Ismenius Lacus quadrangle. WikiESP 020769 2225fretted.jpg, Close-up of lineated valley fill (LVF), as seen by HiRISE under HiWish program. Note: this is an enlargement of the previous CTX image. ESP 046061 2190lvf.jpg, Lineated valley fill, as seen by HiRISE under HiWish program. 46061 2190closelvf..jpg, Close view of Lineated valley fill, as seen by HiRISE under HiWish program ESP 046061 2190closebrains.jpg, Close, color view of Lineated valley fill, as seen by HiRISE under HiWish program ESP 048658 2150flow.jpg, Valley showing Lineated valley fill, as seen by HiRISE under HiWish program Linear valley flow is caused by ice movements. Location is Casius quadrangle. ESP 050137 2185lvf.jpg, Lineated valley fill in valley, as seen by HiRISE under HiWish program Linear valley flow is ice covered by debris. Location is Ismenius Lacus quadrangle. ESP 050137 2185lvfclosecolor.jpg, Close, color view of lineated valley fill, as seen by HiRISE under HiWish program ESP 052138 1435lvf.jpg, Lineated valley fill, as seen by HiRISE under HiWish program Image located in Hellas quadrangle. Lineated floor deposits began as
lobate debris apron Lobate debris aprons (LDAs) are geological features on Mars, first seen by the Viking Orbiters, consisting of piles of rock debris below cliffs. These features have a convex topography and a gentle slope from cliffs or escarpments, which suggest fl ...
s (LDAs), which form as material leaves narrow mountain valleys and spreads out as an apron. By tracing the paths of the ridges on LDAs, researchers have come to believe that the curved ridges characteristic of lobate debris aprons straighten out to form the more or less straight ridges of LVF. In the regions where LVF and LDAs occur, many craters have
concentric crater fill A concentric crater fill (CCF) is a landform where the floor of a crater is mostly covered with many parallel ridges. It is common in the mid-latitudes of Mars, and is widely believed to be caused by glacial movement. Areas on Mars called Deutero ...
: large ridges and other surfaces nicknamed brain terrain, after the surface corrugations of the human brain. The study of lineated valley fill and other features related to debris-covered ice has been greatly aided by the abundance of data received from Mars orbiting instruments. Excellent images have been obtained from
THEMIS In Greek mythology and religion, Themis (; grc, Θέμις, Themis, justice, law, custom) is one of the twelve Titan children of Gaia and Uranus, and the second wife of Zeus. She is the goddess and personification of justice, divine order, fai ...
, MOC, CTX, and
HiRISE High Resolution Imaging Science Experiment is a camera on board the '' Mars Reconnaissance Orbiter'' which has been orbiting and studying Mars since 2006. The 65 kg (143 lb), US$40 million instrument was built under the direction ...
. Detailed altimetry was collected by MOLA. The
Mars Reconnaissance Orbiter ''Mars Reconnaissance Orbiter'' (MRO) is a spacecraft designed to study the geology and climate of Mars, provide reconnaissance of future landing sites, and relay data from surface missions back to Earth. It was launched on August 12, 2005, an ...
's Shallow Radar gave a strong reflection from the top and base of LDAs, meaning that pure water ice made up the bulk of the formation (between the two reflections), strong evidence that the LDAs in Hellas Planitia are glaciers covered with a thin layer of rocks. Since lineated valley terrain is derived from lobate debris aprons, it probably contains buried ice—at least in places.


Connection to past climate

Studies of LDAs and LVF give evidence that there have been multiple episodes of glaciation on Mars, including ones that produced glaciers nearing a kilometre in thickness. These
ice ages An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages and gree ...
are related to major climate shifts caused by major variations in
axial tilt In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, which is the line perpendicular to its orbital plane; equivalently, it is the angle between its equatorial plane and orb ...
. Earth's rather large moon prevents large changes in its tilt. The two moons of Mars are tiny. So Mars undergoes large periods when its ice cap receives more direct sunlight. During this time ice in the cap sublimates, and thick snow falls in mid-latitudes — the zones where concentric crater fill, lineated valley fill and lobate debris aprons are common. The distribution of craters on LVF indicates a late Amazonian age for at least some areas.


Where located

Lineated valley fill is common in the middle latitudes, especially near the northern
dichotomy A dichotomy is a partition of a whole (or a set) into two parts (subsets). In other words, this couple of parts must be * jointly exhaustive: everything must belong to one part or the other, and * mutually exclusive: nothing can belong simul ...
boundary. The Nilosyrtis Mensae,
Protonilus Mensae Protonilus Mensae is an area of Mars in the Ismenius Lacus quadrangle. It is centered on the coordinates of 43.86° N and 49.4° E. Its western and eastern longitudes are 37° E and 59.7° E. North and south latitudes are 47.06° N and 39.87° ...
and
Deuteronilus Mensae Deuteronilus Mensae is a region on Mars 937 km across and centered at . It covers 344°–325° West and 40°–48° North. Deuteronilus region lies just to the north of Arabia Terra and is included in the Ismenius Lacus quadrangle. It is ...
bear many examples of LVF. Ismenius Lacus quadrangle and Hellas quadrangle contain many valleys displaying lineated valley fill. LVF and other ice-related forms are collectively known as fretted terrain, which includes winding and straight valleys with isolating plateaus and mesas.


Importance of lineated valley fill

Studies of lineated valley fill have added evidence that the
climate of Mars The climate of Mars has been a topic of scientific curiosity for centuries, in part because it is the only terrestrial planet whose surface can be directly observed in detail from the Earth with help from a telescope. Although Mars is smaller t ...
has undergone many large changes in the past. At times there is snow, and at times the snow may melt. The resulting small areas of liquid water cause weathering of the rocks and may provide a favourable environment for life. Understanding lineated valley fill and other manifestations of buried ice will allow future colonists to find sources of
water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...
. Reull Vallis, as pictured below, displays such deposits. Sometimes the lineated floor deposits show a chevron pattern which is further evidence of movement. The picture below taken with HiRISE of Reull Vallis shows these patterns. Image:Coloe Fossae Lineated Valley Fill.JPG, Lineated valley fill in Coloe Fossae, seen by HiRISE. Scale bar is 500 meters long. Image located in Ismenius Lacus quadrangle. File:Reull Vallis lineated deposits.jpg, Lineated floor deposits in Reull Vallis, seen by THEMIS. Click on image to see relationship to other features. Image located in Hellas quadrangle. ESP 053630 2195lvf.jpg, Wide view of Lineated Valley Fill, as seen by HiRISE under HiWish program Location is Ismenius Lacus quadrangle. 53630 2195brainslvfclose.jpg, Close view of surface of Lineated Valley fill, as seen by HiRISE under HiWish program Location is Ismenius Lacus quadrangle. Image shows open and closed brain terrain. 53630 2195brainslvf.jpg, Enlarged view of brain terrain on the surface of Lineated Valley Fill, as seen by HiRISE under HiWish program Location is Ismenius Lacus quadrangle. ESP 053630 2195closecolorviewlvf.jpg, Close, color view of Lineated Valley Fill, as seen by HiRISE under HiWish program Location is Ismenius Lacus quadrangle.


See also

*
Geology of Mars The geology of Mars is the scientific study of the surface, crust, and interior of the planet Mars. It emphasizes the composition, structure, history, and physical processes that shape the planet. It is analogous to the field of terrestrial g ...
*
Lobate debris apron Lobate debris aprons (LDAs) are geological features on Mars, first seen by the Viking Orbiters, consisting of piles of rock debris below cliffs. These features have a convex topography and a gentle slope from cliffs or escarpments, which suggest fl ...
*
Concentric crater fill A concentric crater fill (CCF) is a landform where the floor of a crater is mostly covered with many parallel ridges. It is common in the mid-latitudes of Mars, and is widely believed to be caused by glacial movement. Areas on Mars called Deutero ...
*
Glacier A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such a ...
* Glaciers on Mars *
Protonilus Mensae Protonilus Mensae is an area of Mars in the Ismenius Lacus quadrangle. It is centered on the coordinates of 43.86° N and 49.4° E. Its western and eastern longitudes are 37° E and 59.7° E. North and south latitudes are 47.06° N and 39.87° ...
*
Deuteronilus Mensae Deuteronilus Mensae is a region on Mars 937 km across and centered at . It covers 344°–325° West and 40°–48° North. Deuteronilus region lies just to the north of Arabia Terra and is included in the Ismenius Lacus quadrangle. It is ...
* Nilosyrtis Mensae


References


External links


Martian Ice - Jim Secosky - 16th Annual International Mars Society Convention
{{Geography of Mars Surface features of Mars Geology of Mars