Medusae Fossae Formation
Encyclopedia
The Medusae Fossae Formation is a broad geological unit of uncertain origin on the planet Mars
. It is named for the Medusa of Greek mythology. "Fossae" is Latin for "trenches". Located roughly at 5°S 213°E, it straddles the highland - lowland boundary near the Tharsis
and Elysium volcanic areas.
The Medusae Fossae Formation is a soft, easily eroded deposit that extends for nearly 1,000 km along the equator
of Mars
. Sometimes, the formation appears as a smooth and gently undulating surface, however in places it is wind-sculpted into ridges and grooves.
Radar imaging has suggested that the region may contain either extremely porous rock (for example volcanic ash) or deep layers of glacier-like ice deposits amounting to about the same quantity as is stored in Mars' south polar cap. Another evidence for a fine-grained composition is that the area gives almost no radar return. For this reason it has been called a "stealth" region. The formation is divided into three subunits (members) that are all considered to be Amazonian age, the youngest era in martian geological history.
Inverted Relief
The lower portion (member) of Medusae Fossae Formation contins many patterns and shapes that are thought to be the remains of streams. It is believed that streams formed valleys that were filled and became resistant to erosion by cementation of minerals or by the gathering of a coarse covering layer. These inverted stream beds are sometimes called sinuous ridges or raised curvilinear features. They have been divided into six classes: flat-crested, narrow-crested, round-crested, branching, non-branching, and multilevel. They may be a kilometer or so in length. Their height ranges from a meter to greater than 10 meters, while the width of the narrow ones is less than 10 meters.
Yardang
The surface of the formation has been eroded by the wind into a series of linear ridges called yardangs. These ridges generally point in direction of the prevailing winds
that carved them, and demonstrate the erosive power of martian winds. The easily eroded nature of the Medusae Fossae Formation suggests that it is composed of weakly cemented particles, and was most likely formed by the deposition of wind-blown dust or volcanic ash
. Layers are seen in parts of the formation. A resistant caprock on the top of yardangs has been observed in Viking, Mars Global Surveyor
, and HiRISE
photos. Images from spacecraft show that they have different degrees of hardness probably because of significant variations in the physical properties, composition, particle size, and/or cementation
. Very few impact craters are visible throughout the area so the surface is relatively young.
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
. It is named for the Medusa of Greek mythology. "Fossae" is Latin for "trenches". Located roughly at 5°S 213°E, it straddles the highland - lowland boundary near the Tharsis
Tharsis
The Tharsis region on Mars is a vast volcanic plateau centered near the equator in Mars’ western hemisphere. The region is home to the largest volcanoes in the Solar System, including the three enormous shield volcanoes Arsia Mons, Pavonis Mons, and Ascraeus Mons, which are collectively known as...
and Elysium volcanic areas.
The Medusae Fossae Formation is a soft, easily eroded deposit that extends for nearly 1,000 km along the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
of Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
. Sometimes, the formation appears as a smooth and gently undulating surface, however in places it is wind-sculpted into ridges and grooves.
Radar imaging has suggested that the region may contain either extremely porous rock (for example volcanic ash) or deep layers of glacier-like ice deposits amounting to about the same quantity as is stored in Mars' south polar cap. Another evidence for a fine-grained composition is that the area gives almost no radar return. For this reason it has been called a "stealth" region. The formation is divided into three subunits (members) that are all considered to be Amazonian age, the youngest era in martian geological history.
Inverted ReliefInverted ReliefInverted relief is a landscape that is part of a planet's surface, e.g. Mars, that contains positive landforms, i.e. hills and ridges, that were once depressions in its surface...
The lower portion (member) of Medusae Fossae Formation contins many patterns and shapes that are thought to be the remains of streams. It is believed that streams formed valleys that were filled and became resistant to erosion by cementation of minerals or by the gathering of a coarse covering layer. These inverted stream beds are sometimes called sinuous ridges or raised curvilinear features. They have been divided into six classes: flat-crested, narrow-crested, round-crested, branching, non-branching, and multilevel. They may be a kilometer or so in length. Their height ranges from a meter to greater than 10 meters, while the width of the narrow ones is less than 10 meters.YardangYardangA yardang is a streamlined hill carved from bedrock or any consolidated or semiconsolidated material by the dual action of wind abrasion, dust and sand, and deflation. Yardangs become elongated features typically three or more times longer than wide, and when viewed from above, resemble the hull of...
s
The surface of the formation has been eroded by the wind into a series of linear ridges called yardangs. These ridges generally point in direction of the prevailing windsPrevailing winds
Prevailing winds are winds that blow predominantly from a single general direction over a particular point on Earth's surface. The dominant winds are the trends in direction of wind with the highest speed over a particular point on the Earth's surface. A region's prevailing and dominant winds...
that carved them, and demonstrate the erosive power of martian winds. The easily eroded nature of the Medusae Fossae Formation suggests that it is composed of weakly cemented particles, and was most likely formed by the deposition of wind-blown dust or volcanic ash
Volcanic ash
Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact...
. Layers are seen in parts of the formation. A resistant caprock on the top of yardangs has been observed in Viking, Mars Global Surveyor
Mars Global Surveyor
The Mars Global Surveyor was a US spacecraft developed by NASA's Jet Propulsion Laboratory and launched November 1996. It began the United States's return to Mars after a 10-year absence. It completed its primary mission in January 2001 and was in its third extended mission phase when, on 2...
, and HiRISE
HiRISE
High Resolution Imaging Science Experiment is a camera on board the Mars Reconnaissance Orbiter. The 65 kg , $40 million instrument was built under the direction of the University of Arizona's Lunar and Planetary Laboratory by Ball Aerospace & Technologies Corp....
photos. Images from spacecraft show that they have different degrees of hardness probably because of significant variations in the physical properties, composition, particle size, and/or cementation
Cementation
Cementation may refer to:*Cementation , the process of deposition of dissolved mineral components in the interstices of sediments*Cementation , a small deposit of calcium, similar to a cyst...
. Very few impact craters are visible throughout the area so the surface is relatively young.
See also
- Amazonis PlanitiaAmazonis PlanitiaAmazonis Planitia is one of the smoothest plains on Mars. It is located between the Tharsis and Elysium volcanic provinces to the west of Olympus Mons in the Valles Marineris region of the Memnonia quadrangle, centered at...
- Inverted reliefInverted ReliefInverted relief is a landscape that is part of a planet's surface, e.g. Mars, that contains positive landforms, i.e. hills and ridges, that were once depressions in its surface...
- Geology of MarsGeology of MarsThe 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 fully analogous to the field of terrestrial geology. In planetary science, the term geology is...
- Impact craterImpact craterIn the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...
- YardangYardangA yardang is a streamlined hill carved from bedrock or any consolidated or semiconsolidated material by the dual action of wind abrasion, dust and sand, and deflation. Yardangs become elongated features typically three or more times longer than wide, and when viewed from above, resemble the hull of...
External links
- The Medusa Fossae formation on Mars (Mars ExpressMars ExpressMars Express is a space exploration mission being conducted by the European Space Agency . The Mars Express mission is exploring the planet Mars, and is the first planetary mission attempted by the agency. "Express" originally referred to the speed and efficiency with which the spacecraft was...
)