Syrtis Major
Encyclopedia
Syrtis Major Planum is a "dark spot" (an albedo feature
) located in the boundary between the northern lowlands and southern highlands of Mars
. It was discovered, on the basis of data from Mars Global Surveyor
, to be a low-relief shield volcano
, but was formerly believed to be a plain
, and was then known as Syrtis Major Planitia. The dark color comes from the basalt
ic volcanic rock of the region and the relative lack of dust.
. It encompasses a large slope from its western edge at Aeria dropping 4 km (2.5 mi) to its eastern edge at Isidis Planitia
. It includes a high-altitude bulge that rises 6 km (3.7 mi) at 310° W. Most of Syrtis Major has slopes of less than 1°, a much lower inclination than the slopes of the Tharsis
shield volcanoes. It has a 350x150 km north-south elongated central depression containing the caldera
s Nili Patera and Meroe Patera, which are about 2 km deep. The floors of the calderas are not elevated relative to the terrain surrounding Syrtis Major. The floor of Nili Patera is the less cratered, and therefore the younger, of the two. While most of the rock is basaltic, dacite
has also been detected in Nili Patera. Satellite gravity field measurements show a positive gravity anomaly centered on the caldera complex, suggesting the presence of a 600x300 km north-south elongated extinct magma chamber
below, containing dense minerals (probably mainly pyroxene
, with olivine
also possible) that precipitated out of magma
before eruptions. Crater counts date Syrtis Major to the early Hesperian epoch; it postdates formation of the adjacent Isidis impact basin.
name Syrtis maior for the Gulf of Sidra
on the coast of Libya
(classical Cyrenaica
).
Syrtis Major was the first documented surface feature of another planet
. It was discovered by Christiaan Huygens, who included it in a drawing of Mars in 1659. The feature was originally known as the Hourglass Sea but has been given different names by different cartographers. In 1840, Johann Heinrich von Mädler
compiled a map of Mars from his observations and called the feature Atlantic Canale. In Richard Proctor's 1867 map it is called then Kaiser Sea (after Frederik Kaiser
of the Leiden Observatory
). Camille Flammarion
called it the Mer du Sablier (French for "Hourglass Sea") when he revised Proctor's nomenclature in 1876. The name "Syrtis Major" was chosen by Giovanni Schiaparelli
when he created a map based on observations made during Mars' close approach to Earth in 1877.
and Viking
planetary probes led scientists to conclude that the variations were caused by wind blowing dust and sand across the area. It has many windblown deposits that include light-colored halos or plumose streaks that form downwind of crater
s. These streaks are accumulations of dust resulting from disruption of the wind by the elevated rims
of the craters ('wind shadows').
Albedo feature
An albedo feature is a large area on the surface of a planet which shows a contrast in brightness or darkness with adjacent areas....
) located in the boundary between the northern lowlands and southern highlands 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...
. It was discovered, on the basis of data from 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...
, to be a low-relief shield volcano
Shield volcano
A shield volcano is a type of volcano usually built almost entirely of fluid lava flows. They are named for their large size and low profile, resembling a warrior's shield. This is caused by the highly fluid lava they erupt, which travels farther than lava erupted from more explosive volcanoes...
, but was formerly believed to be a plain
Plain
In geography, a plain is land with relatively low relief, that is flat or gently rolling. Prairies and steppes are types of plains, and the archetype for a plain is often thought of as a grassland, but plains in their natural state may also be covered in shrublands, woodland and forest, or...
, and was then known as Syrtis Major Planitia. The dark color comes from the basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
ic volcanic rock of the region and the relative lack of dust.
Geography and geology
Syrtis Major is centered near at 8.4°N 69.5°W, extends some 1500 km (932.1 mi) north from the planet's equator, and spans 1000 km (621.4 mi) from west to east. It is in the Syrtis Major quadrangleSyrtis Major quadrangle
The Syrtis Major quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey Astrogeology Research Program...
. It encompasses a large slope from its western edge at Aeria dropping 4 km (2.5 mi) to its eastern edge at Isidis Planitia
Isidis Planitia
Isidis Planitia is a plain located inside a giant impact basin on Mars, centered at . It is the third biggest impact structure on the planet after the Hellas and Argyre basins – it is about 1500 km in diameter...
. It includes a high-altitude bulge that rises 6 km (3.7 mi) at 310° W. Most of Syrtis Major has slopes of less than 1°, a much lower inclination than the slopes of 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...
shield volcanoes. It has a 350x150 km north-south elongated central depression containing the caldera
Caldera
A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...
s Nili Patera and Meroe Patera, which are about 2 km deep. The floors of the calderas are not elevated relative to the terrain surrounding Syrtis Major. The floor of Nili Patera is the less cratered, and therefore the younger, of the two. While most of the rock is basaltic, dacite
Dacite
Dacite is an igneous, volcanic rock. It has an aphanitic to porphyritic texture and is intermediate in composition between andesite and rhyolite. The relative proportions of feldspars and quartz in dacite, and in many other volcanic rocks, are illustrated in the QAPF diagram...
has also been detected in Nili Patera. Satellite gravity field measurements show a positive gravity anomaly centered on the caldera complex, suggesting the presence of a 600x300 km north-south elongated extinct magma chamber
Magma chamber
A magma chamber is a large underground pool of molten rock found beneath the surface of the Earth. The molten rock in such a chamber is under great pressure, and given enough time, that pressure can gradually fracture the rock around it creating outlets for the magma...
below, containing dense minerals (probably mainly pyroxene
Pyroxene
The pyroxenes are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. They share a common structure consisting of single chains of silica tetrahedra and they crystallize in the monoclinic and orthorhombic systems...
, with olivine
Olivine
The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....
also possible) that precipitated out of magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
before eruptions. Crater counts date Syrtis Major to the early Hesperian epoch; it postdates formation of the adjacent Isidis impact basin.
Discovery and name
The name Syrtis Major is derived from the classical RomanAncient Rome
Ancient Rome was a thriving civilization that grew on the Italian Peninsula as early as the 8th century BC. Located along the Mediterranean Sea and centered on the city of Rome, it expanded to one of the largest empires in the ancient world....
name Syrtis maior for the Gulf of Sidra
Gulf of Sidra
Gulf of Sidra is a body of water in the Mediterranean Sea on the northern coast of Libya; it is also known as Gulf of Sirte or the Great Sirte or Greater Syrtis .- Geography :The Gulf of Sidra has been a major centre for tuna fishing in the Mediterranean for centuries...
on the coast of Libya
Libya
Libya is an African country in the Maghreb region of North Africa bordered by the Mediterranean Sea to the north, Egypt to the east, Sudan to the southeast, Chad and Niger to the south, and Algeria and Tunisia to the west....
(classical Cyrenaica
Cyrenaica
Cyrenaica is the eastern coastal region of Libya.Also known as Pentapolis in antiquity, it was part of the Creta et Cyrenaica province during the Roman period, later divided in Libia Pentapolis and Libia Sicca...
).
Syrtis Major was the first documented surface feature of another planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
. It was discovered by Christiaan Huygens, who included it in a drawing of Mars in 1659. The feature was originally known as the Hourglass Sea but has been given different names by different cartographers. In 1840, Johann Heinrich von Mädler
Johann Heinrich von Mädler
Johann Heinrich von Mädler was a German astronomer.He was orphaned at age 19 by an outbreak of typhus, and found himself responsible for raising three younger sisters...
compiled a map of Mars from his observations and called the feature Atlantic Canale. In Richard Proctor's 1867 map it is called then Kaiser Sea (after Frederik Kaiser
Frederik Kaiser
Frederik Kaiser was a Dutch astronomer.He was director of the Leiden Observatory from 1838 until his death....
of the Leiden Observatory
Leiden Observatory
Leiden Observatory is an astronomical observatory in the city of Leiden, Netherlands. It was established by Leiden University in 1633, to house the quadrant of Snellius, and is the oldest operating University observatory in the world Leiden Observatory (Sterrewacht Leiden in Dutch) is an...
). Camille Flammarion
Camille Flammarion
Nicolas Camille Flammarion was a French astronomer and author. He was a prolific author of more than fifty titles, including popular science works about astronomy, several notable early science fiction novels, and several works about Spiritism and related topics. He also published the magazine...
called it the Mer du Sablier (French for "Hourglass Sea") when he revised Proctor's nomenclature in 1876. The name "Syrtis Major" was chosen by Giovanni Schiaparelli
Giovanni Schiaparelli
Giovanni Virginio Schiaparelli was an Italian astronomer and science historian. He studied at the University of Turin and Berlin Observatory. In 1859-1860 he worked in Pulkovo Observatory and then worked for over forty years at Brera Observatory...
when he created a map based on observations made during Mars' close approach to Earth in 1877.
Seasonal variations
Syrtis Major was the object of much observation due to its seasonal and long-term variations. This led to theories that it was a shallow sea and later that its variability was due to seasonal vegetation. However, in the 1960s and 1970s, the MarinerMariner program
The Mariner program was a program conducted by the American space agency NASA that launched a series of robotic interplanetary probes designed to investigate Mars, Venus and Mercury from 1963 to 1973...
and Viking
Viking program
The Viking program consisted of a pair of American space probes sent to Mars, Viking 1 and Viking 2. Each spacecraft was composed of two main parts, an orbiter designed to photograph the surface of Mars from orbit, and a lander designed to study the planet from the surface...
planetary probes led scientists to conclude that the variations were caused by wind blowing dust and sand across the area. It has many windblown deposits that include light-colored halos or plumose streaks that form downwind of crater
Impact crater
In 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...
s. These streaks are accumulations of dust resulting from disruption of the wind by the elevated rims
Rim (craters)
The rim of a crater is the part that extends above the height of the local surface, usually in a circular or elliptical pattern. In a more specific sense, the rim may refer to the circular or elliptical edge that represents the uppermost tip of this raised portion...
of the craters ('wind shadows').