Fossa is a term used in
planetary geologyPlanetary geology, alternatively known as astrogeology or exogeology, is a planetary science discipline concerned with the geology of the celestial bodies such as the planets and their moons, asteroids, comets, and meteorites....
to describe a long, narrow, shallow depression on the body of an extraterrestrial body, such as a planet or moon. The term, which means "ditch" or "trench" in
LatinLatin is an Italic language originally spoken in Latium and Ancient Rome. Through the Roman conquest, Latin spread throughout the Mediterranean and a large part of Europe...
, is not a geological term as such but is used in the naming of particular features, such as the Cerberus Fossae on
MarsMars is the fourth planet from the Sun in the Solar System. The planet is named after Mars, the Roman god of war. It is also referred to as the "Red Planet" because of its reddish appearance, due to iron oxide prevalent on its surface....
.
Fossae are believed to be the result of a number of geological processes, such as faulting,
subsidenceSubsidence is the motion of a surface as it shifts downward relative to a datum such as sea-level. The opposite of subsidence is uplift, which results in an increase in elevation...
or floods of water or some other viscous liquid.
The
Tharsis quadrangleThe Tharsis quadrangle covers the area from 90° to 135° west longitude and 0° to 30° north latitude on Mars. The Tharsis quadrangle contains most of a high plateau called Tharsis or the Tharsis Rise. The plateau is about as high as Earth's Mount Everest and about as big in area as all of Europe. ...
is home to large troughs (long narrow depressions) called fossae in the geographical language used for Mars.
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Fossa is a term used in
planetary geologyPlanetary geology, alternatively known as astrogeology or exogeology, is a planetary science discipline concerned with the geology of the celestial bodies such as the planets and their moons, asteroids, comets, and meteorites....
to describe a long, narrow, shallow depression on the body of an extraterrestrial body, such as a planet or moon. The term, which means "ditch" or "trench" in
LatinLatin is an Italic language originally spoken in Latium and Ancient Rome. Through the Roman conquest, Latin spread throughout the Mediterranean and a large part of Europe...
, is not a geological term as such but is used in the naming of particular features, such as the Cerberus Fossae on
MarsMars is the fourth planet from the Sun in the Solar System. The planet is named after Mars, the Roman god of war. It is also referred to as the "Red Planet" because of its reddish appearance, due to iron oxide prevalent on its surface....
.
Fossae are believed to be the result of a number of geological processes, such as faulting,
subsidenceSubsidence is the motion of a surface as it shifts downward relative to a datum such as sea-level. The opposite of subsidence is uplift, which results in an increase in elevation...
or floods of water or some other viscous liquid.
Fossa on Mars
The
Tharsis quadrangleThe Tharsis quadrangle covers the area from 90° to 135° west longitude and 0° to 30° north latitude on Mars. The Tharsis quadrangle contains most of a high plateau called Tharsis or the Tharsis Rise. The plateau is about as high as Earth's Mount Everest and about as big in area as all of Europe. ...
is home to large troughs (long narrow depressions) called fossae in the geographical language used for Mars. This term is derived from Latin; therefore fossa is singular and fossae is plural. Troughs form when the crust is stretched until it breaks. The stretching can be due to the large weight of a nearby volcano. Fossae/pit craters are common near volcanoes in the Tharsis and Elysium system of volcanoes. A trough often has two breaks with a middle section moving down, leaving steep cliffs along the sides; such a trough is called a graben.
Lake GeorgeLake George, nicknamed the Queen of American Lakes,
[Bolton Landing Chamber of Commerce, , Retrieved May 12, 2008; Albany International Airport, , 2004. Retrieved May 12, 2008; The Hyde Collection, , September, 2005...]
, in northern New York State, is a lake that sits in a graben. Sometimes, a line of pits form as material collapse into a void that results from the stretching. Pit craters do not have rims or ejecta around them, like impact craters do. Studies have found that on Mars a fault may be as deep as 5 km, that is the break in the rock goes down to 5 km. Moreover, the crack or fault sometimes widens or dialates. This widening causes a void to form with a relatively high volume. When material slides into the void, a pit crater or a pit crater chain forms. On Mars, individual pit craters can join to form chains or even to form troughs that are sometimes scalloped.. Other ideas have been suggested for the formation of fossae and pit craters. There is evidence that they are associated with dikes of magma. Magma might move along, under the surface, breaking the rock and more importantly melting ice. The resulting action would cause a crack to form at the surface. Dikes caused both by tectonic stretching (extension) and by dikes are found in
IcelandThe Republic of Iceland is a European island country located in the North Atlantic Ocean. It has a population of about 320,000 and a total area of 103,000 km². Its capital and largest city is Reykjavík, whose surrounding area is home to approximately two thirds of the national population...
. Pit craters are not common on Earth. Sinkholes, where the ground falls into a hole (sometimes in the middle of a town) resemble pit craters on Mars. However, on the Earth these holes are caused by limestone being dissolved thereby causing a void.
Knowledge of the locations and formation mechanisms of pit craters and fossae is important for the future colonization of Mars because they may be reservoirs of water.
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