Arabia Terra is a large upland region in the north of Mars that lies mostly in the Arabia quadrangle, but a small part is in the Mare Acidalium quadrangle. It is densely cratered and heavily eroded. This battered topography indicates great age, and Arabia Terra is presumed to be one of the oldest terrains on the planet. It covers as much as 4,500 km (2,800 mi) at its longest extent, centered roughly at 21°N6°E / 21°N 6°E [1] with its eastern and southern regions rising 4 km (13,000 ft) above the north-west. Alongside its many craters, canyons wind through the Arabia Terra, many emptying into the large northern lowlands of the planet, which borders Arabia Terra to the north.
Arabia contains many interesting features. There are some good examples of pedestal craters in the area. A pedestal crater has its ejecta above the surrounding terrain, often forming a steep cliff. The ejecta forms a resistant layer that protects the underlying material from erosion. [3] Mounds and buttes on the floor of some craters display many layers. The layers may have formed by volcanic processes, by wind, or by underwater deposition. [4] [5] Dark slope streaks have been observed in Tikhonravov Basin, a large eroded crater. The streaks appear on steep slopes and change over time. At first they are dark, then turn a lighter color, probably by the deposition of fine, light colored dust from the atmosphere. [6] These streaks are thought by some to form by dust moving downslope in a way similar to snow avalanches on Earth. [7]
Arabia Terra was named in 1879 after a corresponding albedo feature on a map by Giovanni Schiaparelli, who named it in turn after the Arabian Peninsula.
Research on the region was undertaken in 1997 and the individuality of the province better defined. [8] An equatorial belt was noted with a crater age distinctly younger than the northern part of the province and of Noachis Terra to the south. This was interpreted as an "incipient back-arc system" provoked by the subduction of Mars lowlands under Arabia Terra during Noachian times. Regional fracture patterns were also explained in this manner, and the rotational instability of the planet as a cause was not supported. It contains extension tectonic features [9]
A 2013 study proposed that a number of craters within Arabia Terra, including Eden Patera, [10] Euphrates Patera, [11] Siloe Patera, [12] and possibly Semeykin crater, [13] Ismenia Patera, [14] Oxus Patera [15] and Oxus Cavus, [16] represent calderas formed by massive explosive volcanic eruptions [17] (supervolcanoes) [18] of Late Noachian to Early Hesperian age. [19] Termed "plains-style caldera complexes", these very low relief volcanic features appear to be older than the large Hesperian-age shield volcanoes of Tharsis or Elysium. Eden Patera, for example, is an irregular, 55 by 85 km depression up to 1.8 km deep, surrounded by ridged basaltic plains. It contains three linked interior depressions, demarcated by arcuate scarps, that have terraces suggestive of lava lake drainage and faults suggestive of collapse. The features indicative of impact origin that would be expected in an impact crater of comparable diameter and depth are absent. [19] The authors regard crustal thinning due to regional extension to be a more likely explanation for the origin of the volcanic activity than putative subduction. [19] Rapid ascent of magma through the thin crust and a consequent relative absence of degassing may explain the more explosive eruption style associated with these paterae relative to that of the shield volcanoes. The eruptions would have contributed to the layered deposits of Arabia Terra, which are among the fine-grained deposits widespread in the equatorial regions of Mars. Total eruptive volumes of at least 4,600–7,200 km3 per caldera complex (over its history) were inferred. [19]
A meteorite impacted in Arabia Terra some time between 30 June 2002 and 5 October 2003. A single small crater of about 22.6 meters (about 74 feet) in diameter is surrounded by light and dark-toned ejecta – indicating that this impact excavated to a depth where light colored strata exists. The crater occurs near 20.6 degrees north latitude, 356.8 degrees west longitude, in Arabia Terra. Images of the area show how the impact site appeared to the Mars Odyssey Thermal Emission Imaging System infrared instrument before and after the impact. [20]
In the 2011 novel The Martian by Andy Weir, the protagonist encounters a dust storm in Arabia Terra while traveling from Acidalia Planitia to Schiaparelli crater. [21]
Many places on Mars show rocks arranged in layers. Rock can form layers in a variety of ways. Volcanoes, wind, or water can produce layers. [22] Layers may be formed by groundwater rising up depositing minerals and cementing sediments. The hardened layers are consequently more protected from erosion. This process may occur instead of layers forming under lakes.
A detailed discussion of layering with many Martian examples can be found in Sedimentary Geology of Mars. [23]
Many places on Mars show channels of different sizes. Many of these channels probably carried water, at least for a time. One study that used HiRISE pictures found over 17,000 km of ancient river valleys in Arabia Terra. [24] [25] Many ancient river valleys have been determined to be relatively recent, according to research published in 2016 in the Journal of Geophysical Research: Planets. These valleys carried water into lake basins. One lake, nicknamed "Heart Lake," had a volume similar to Lake Ontario. [26] [27] The climate of Mars may have been such in the past that water ran on its surface. It has been known for some time that Mars undergoes many large changes in its tilt or obliquity because its two small moons lack the gravity to stabilize it, as the Moon stabilizes Earth; at times the tilt has even been greater than 80 degrees [28] [29]
Parts of northern Arabia Terra contains the upper plains unit. The Upper Plains Unit is the remnants of a 50–100 meter thick mantling in the mid-latitudes. It was first investigated in the Deuteronilus Mensae (Ismenius Lacus quadrangle) region, but it occurs in other places as well. The remnants consist of sets of dipping layers in craters and along mesas. [30]
Some regions of the upper plains unit display large fractures and troughs with raised rims; such regions are called ribbed upper plains. Fractures are believed to have started with small cracks from stresses. Stress is suggested to initiate the fracture process since ribbed upper plains are common when debris aprons come together or near the edge of debris aprons—such sites would generate compressional stresses. Cracks exposed more surfaces, and consequently more ice in the material sublimates into the planet's thin atmosphere. Eventually, small cracks become large canyons or troughs.
This unit also degrades into brain terrain. Brain terrain is a region of maze-like ridges 3–5 meters high. Some ridges may consist of an ice core, so they may be sources of water for future colonists.
Linear ridge networks are found in various places on Mars in and around craters. [31] Ridges often appear as mostly straight segments that intersect in a lattice-like manner. They are hundreds of meters long, tens of meters high, and several meters wide. It is thought that impacts created fractures in the surface, these fractures later acted as channels for fluids. Fluids cemented the structures. With the passage of time, surrounding material was eroded away, thereby leaving hard ridges behind. Since the ridges occur in locations with clay, these formations could serve as a marker for clay which requires water for its formation. [32] [33] [34] Water here could have supported past life in these locations. Clay may also preserve fossils or other traces of past life.
Pingos are believed to be present on Mars. They are mounds that contain cracks. They contain pure water ice, so they would be a great source of water for future colonists on Mars
In places large fractures break up surfaces. Sometimes straight edges are formed and large cubes are created by the fractures.
For mapping purposes, the United States Geological Survey divides the surface of Mars into thirty "quadrangles", each named for a prominent physiographic feature within that quadrangle. [35] [36] The quadrangles can be seen and explored via the interactive image map below.
Tempe Terra is a heavily cratered highland region in the northern hemisphere of the planet Mars. Located at the northeastern edge of the Tharsis volcanic province, Tempe Terra is notable for its high degree of crustal fracturing and deformation. The region also contains many small shield volcanoes, lava flows, and other volcanic structures.
Tyrrhena Terra is a large area on Mars, centered south of the Martian equator and immediately northeast of the Hellas basin. Its coordinates are 14.8°S 90°E, and it covers 2300 km at its broadest extent. It was named for a classic albedo feature of the planet and is in the Mare Tyrrhenum quadrangle of Mars. Tyrrhena Terra is typical of the southern Martian terrae, with heavily cratered highlands and other rugged terrain. It contains the large volcano Tyrrhena Patera, one of the oldest volcanoes on Mars. Its largest crater is Herschel. Licus Vallis and the Ausonia Montes are other major features in the region. Some channels and dunes are visible in Tyrrhena Terra, as shown in the images below.
Terra Sabaea is a large area on Mars. Its coordinates are 2°N42°E and it covers 4,700 kilometres (2,900 mi) at its broadest extent. It was named in 1979 after a classic albedo feature on the planet. Terra Sabaea is fairly large and parts of it are found in five quadrangles: Arabia quadrangle, Syrtis Major quadrangle, Iapygia quadrangle, Ismenius Lacus quadrangle, and Sinus Sabaeus quadrangle.
The Noachis quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Noachis quadrangle is also referred to as MC-27.
The Ismenius Lacus quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The quadrangle is located in the northwestern portion of Mars' eastern hemisphere and covers 0° to 60° east longitude and 30° to 65° north latitude. The quadrangle uses a Lambert conformal conic projection at a nominal scale of 1:5,000,000 (1:5M). The Ismenius Lacus quadrangle is also referred to as MC-5. The southern and northern borders of the Ismenius Lacus quadrangle are approximately 3,065 km (1,905 mi) and 1,500 km (930 mi) wide, respectively. The north-to-south distance is about 2,050 km (1,270 mi). The quadrangle covers an approximate area of 4.9 million square km, or a little over 3% of Mars' surface area. The Ismenius Lacus quadrangle contains parts of Acidalia Planitia, Arabia Terra, Vastitas Borealis, and Terra Sabaea.
The Casius quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The quadrangle is located in the north-central portion of Mars' eastern hemisphere and covers 60° to 120° east longitude and 30° to 65° north latitude. The quadrangle uses a Lambert conformal conic projection at a nominal scale of 1:5,000,000 (1:5M). The Casius quadrangle is also referred to as MC-6. Casius quadrangle contains part of Utopia Planitia and a small part of Terra Sabaea. The southern and northern borders of the Casius quadrangle are approximately 3,065 km and 1,500 km wide, respectively. The north to south distance is about 2,050 km. The quadrangle covers an approximate area of 4.9 million square km, or a little over 3% of Mars' surface area.
The Arcadia quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The quadrangle is located in the north-central portion of Mars’ western hemisphere and covers 240° to 300° east longitude and 30° to 65° north latitude. The quadrangle uses a Lambert conformal conic projection at a nominal scale of 1:5,000,000 (1:5M). The Arcadia quadrangle is also referred to as MC-3. The name comes from a mountainous region in southern Greece. It was adopted by IAU, in 1958.
The Mare Acidalium quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The quadrangle is located in the northeastern portion of Mars' western hemisphere and covers 300° to 360° east longitude and 30° to 65° north latitude. The quadrangle uses a Lambert conformal conic projection at a nominal scale of 1:5,000,000 (1:5M). The Mare Acidalium quadrangle is also referred to as MC-4.
The Arabia quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Arabia quadrangle is also referred to as MC-12.
The Sinus Sabaeus quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. It is also referred to as MC-20 . The Sinus Sabaeus quadrangle covers the area from 315° to 360° west longitude and 0° to 30° degrees south latitude on Mars. It contains Schiaparelli, a large, easily visible crater that sits close to the equator. The Sinus Sabaeus quadrangle contains parts of Noachis Terra and Terra Sabaea.
The Mare Tyrrhenum quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. This quadrangle is also referred to as MC-22. It contains parts of the regions Tyrrhena Terra, Hesperia Planum, and Terra Cimmeria.
Tikhonravov is a large, eroded crater in the Arabia quadrangle of Mars. It is 344 kilometres (214 mi) in diameter and was named after Mikhail Tikhonravov, a Russian rocket scientist. Tikhonravov is believed to have once held a giant lake that drained into the 4,500-kilometre-long (2,800 mi) Naktong-Scamander-Mamers lake-chain system. An inflow and outflow channel has been identified. Many craters once contained lakes.
Fretted terrain is a type of surface feature common to certain areas of Mars and was discovered in Mariner 9 images. It lies between two different types of terrain. The surface of Mars can be divided into two parts: low, young, uncratered plains that cover most of the northern hemisphere, and high-standing, old, heavily cratered areas that cover the southern and a small part of the northern hemisphere. Between these two zones is a region called the Martian dichotomy and parts of it contain fretted terrain. This terrain contains a complicated mix of cliffs, mesas, buttes, and straight-walled and sinuous canyons. It 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. Fretted terrain shows up in northern Arabia, between latitudes 30°N and 50°N and longitudes 270°W and 360°W, and in Aeolis Mensae, between 10 N and 10 S latitude and 240 W and 210 W longitude. Two good examples of fretted terrain are Deuteronilus Mensae and Protonilus Mensae.
A Ring mold crater is a kind of crater on the planet Mars that looks like the ring molds used in baking. They are believed to be caused by an impact into ice. The ice is covered by a layer of debris. They are found in parts of Mars that have buried ice. Laboratory experiments confirm that impacts into ice result in a "ring mold shape." They are also bigger than other craters in which an asteroid impacted solid rock. Impacts into ice warm the ice and cause it to flow into the ring mold shape. These craters are common in lobate debris aprons and lineated valley fill. Many have been found in Mamers Valles, a channel found along the dichotomy boundary in Deuteronilus Mensae. They may be an easy way for future colonists of Mars to find water ice.
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° N. Protonilus Mensae is between Deuteronilus Mensae and Nilosyrtis Mensae; all lie along the Martian dichotomy boundary. Its name was adapted by the IAU in 1973.
HiWish is a program created by NASA so that anyone can suggest a place for the HiRISE camera on the Mars Reconnaissance Orbiter to photograph. It was started in January 2010. In the first few months of the program 3000 people signed up to use HiRISE. The first images were released in April 2010. Over 12,000 suggestions were made by the public; suggestions were made for targets in each of the 30 quadrangles of Mars. Selected images released were used for three talks at the 16th Annual International Mars Society Convention. Below are some of the over 4,224 images that have been released from the HiWish program as of March 2016.
The common surface features of Mars include dark slope streaks, dust devil tracks, sand dunes, Medusae Fossae Formation, fretted terrain, layers, gullies, glaciers, scalloped topography, chaos terrain, possible ancient rivers, pedestal craters, brain terrain, and ring mold craters.
Brain terrain, also called knobs-brain coral and brain coral terrain, is a feature of the Martian surface, consisting of complex ridges found on lobate debris aprons, lineated valley fill and concentric crater fill. It is so named because it suggests the ridges on the surface of the human brain. Wide ridges are called closed-cell brain terrain, and the less common narrow ridges are called open-cell brain terrain. It is thought that the wide closed-cell terrain contains a core of ice, and when the ice disappears the center of the wide ridge collapses to produce the narrow ridges of the open-cell brain terrain. Shadow measurements from HiRISE indicate the ridges are 4-5 meters high. Brain terrain has been observed to form from what has been called an "Upper Plains Unit." The process begins with the formation of stress cracks. The upper plains unit fell from the sky as snow and as ice coated dust.
Firsoff is an impact crater in the region called Meridiani Planum in the Oxia Palus quadrangle of Mars, located at 2.66°N latitude and 9.42°W longitude. It is 90 km in diameter. It was named after British astronomer Axel Firsoff, and the name was approved in 2010.
The upper plains unit is the remnants of a 50-100 meter thick mantling that has been discovered in the mid-latitudes of the planet Mars. It was first investigated in the Deuteronilus Mensae region, but it occurs in other places as well. The remnants consist of sets of dipping layers in impact craters, in depressions, and along mesas. Sets of dipping layers may be of various sizes and shapes—some look like Aztec pyramids from Central America.