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95-410: Mars is a terrestrial planet , which has undergone the process of planetary differentiation . The InSight lander mission is designed to study the deep interior of Mars. The mission landed on 26 November 2018. and deployed a sensitive seismometer to enable 3D structure mapping of the deep interior. On 25 October 2023, scientists, helped by information from InSight, reported that the planet Mars has

190-409: A radioactive magma ocean under its crust. Mars has a number of distinct, large-scale surface features that indicate the types of geological processes that have operated on the planet over time. This section introduces several of the larger physiographic regions of Mars. Together, these regions illustrate how geologic processes involving volcanism , tectonism , water, ice, and impacts have shaped

285-428: A diverse range of crater populations of widely differing ages. Over 42,000 impact craters greater than 5 km in diameter have been catalogued on Mars, and the number of smaller craters is probably innumerable. The density of craters on Mars is highest in the southern hemisphere, south of the dichotomy boundary. This is where most of the large craters and basins are located. Crater morphology provides information about

380-404: A higher radar echo strength than other volcanic structures on the planet. This could indicate that the lava flows on the flanks of Ascraeus Mons consist of rough ʻAʻā -type flows, a conclusion supported by photogeologic analysis of lava flow morphologies. The flanks of Ascraeus Mons have a rumpled appearance caused by numerous low, rounded terrace -like structures arranged concentrically around

475-498: A lake, and dune fields have all been observed in the preserved strata by rovers at Meridiani Planum and Gale crater. One group of researchers proposed that some of the layers on Mars were caused by groundwater rising to the surface in many places, especially inside of craters. According to the theory, groundwater with dissolved minerals came to the surface, in and later around craters, and helped to form layers by adding minerals (especially sulfate) and cementing sediments. This hypothesis

570-446: A maximum thickness of about 58 km (36 mi), whereas the crust in the northern lowlands "peaks" at around 32 km (20 mi) in thickness. The location of the dichotomy boundary varies in latitude across Mars and depends on which of the three physical expressions of the dichotomy is being considered. The origin and age of the hemispheric dichotomy are still debated. Hypotheses of origin generally fall into two categories: one,

665-557: A mixture of the material from the bright and dark areas. Impact craters were first identified on Mars by the Mariner 4 spacecraft in 1965. Early observations showed that Martian craters were generally shallower and smoother than lunar craters, indicating that Mars has a more active history of erosion and deposition than the Moon. In other aspects, Martian craters resemble lunar craters. Both are products of hypervelocity impacts and show

760-458: A model of the planet's structure. Where there have been landers or multiple orbiting spacecraft, these models are constrained by seismological data and also moment of inertia data derived from the spacecraft's orbits. Where such data is not available, uncertainties are inevitably higher. The uncompressed densities of the rounded terrestrial bodies directly orbiting the Sun trend towards lower values as

855-430: A progression of morphology types with increasing size. Martian craters below about 7 km in diameter are called simple craters; they are bowl-shaped with sharp raised rims and have depth/diameter ratios of about 1/5. Martian craters change from simple to more complex types at diameters of roughly 5 to 8 km. Complex craters have central peaks (or peak complexes), relatively flat floors, and terracing or slumping along

950-573: A quarter of the planet's circumference. If placed on Earth, Valles Marineris would span the width of North America. In places, the canyons are up to 300 km wide and 10 km deep. Often compared to Earth's Grand Canyon , the Valles Marineris has a very different origin than its tinier, so-called counterpart on Earth. The Grand Canyon is largely a product of water erosion. The Martian equatorial canyons were of tectonic origin, i.e. they were formed mostly by faulting. They could be similar to

1045-478: A similar density but has a significant ice layer on the surface: for this reason, it is sometimes considered an icy planet instead. Terrestrial planets can have surface structures such as canyons , craters , mountains , volcanoes , and others, depending on the presence at any time of an erosive liquid or tectonic activity or both. Terrestrial planets have secondary atmospheres , generated by volcanic out-gassing or from comet impact debris. This contrasts with

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1140-400: A similar structure; possibly so does the smaller one 21 Lutetia . Another rocky asteroid 2 Pallas is about the same size as Vesta, but is significantly less dense; it appears to have never differentiated a core and a mantle. The Earth's Moon and Jupiter's moon Io have similar structures to terrestrial planets, but Earth's Moon has a much smaller iron core. Another Jovian moon Europa has

1235-485: A solid planetary surface , making them substantially different from larger gaseous planets , which are composed mostly of some combination of hydrogen , helium , and water existing in various physical states . All terrestrial planets in the Solar System have the same basic structure, such as a central metallic core (mostly iron ) with a surrounding silicate mantle . The large rocky asteroid 4 Vesta has

1330-607: A solid surface, but are composed of ice and rock rather than of rock and metal. These include the dwarf planets, such as Ceres , Pluto and Eris , which are found today only in the regions beyond the formation snow line where water ice was stable under direct sunlight in the early Solar System. It also includes the other round moons, which are ice-rock (e.g. Ganymede , Callisto , Titan , and Triton ) or even almost pure (at least 99%) ice ( Tethys and Iapetus ). Some of these bodies are known to have subsurface hydrospheres (Ganymede, Callisto, Enceladus , and Titan), like Europa, and it

1425-541: A stream bed or materials being cemented by minerals dissolved in water. On Earth, materials cemented by silica are highly resistant to all kinds of erosional forces. Examples of inverted channels on Earth are found in the Cedar Mountain Formation near Green River, Utah . Inverted relief in the shape of streams are further evidence of water flowing on the Martian surface in past times. Inverted relief in

1520-497: A terrestrial planet is the average density its materials would have at zero pressure . A greater uncompressed density indicates a greater metal content. Uncompressed density differs from the true average density (also often called "bulk" density) because compression within planet cores increases their density; the average density depends on planet size, temperature distribution, and material stiffness as well as composition. Calculations to estimate uncompressed density inherently require

1615-504: A thinner crust in the north, similar to what is occurring at spreading plate boundaries on Earth. Whatever its origin, the Martian dichotomy appears to be extremely old. A new theory based on the Southern Polar Giant Impact and validated by the discovery of twelve hemispherical alignments shows that exogenic theories appear to be stronger than endogenic theories and that Mars never had plate tectonics that could modify

1710-435: A wide variety of wet environments, including in alluvial fans , meandering channels, deltas , lakes , and perhaps even oceans. The processes of deposition and transportation are associated with gravity. Due to gravity, related differences in water fluxes and flow speeds, inferred from grain size distributions, Martian landscapes were created by different environmental conditions. Nevertheless, there are other ways of estimating

1805-928: Is a planet that is composed primarily of silicate , rocks or metals . Within the Solar System , the terrestrial planets accepted by the IAU are the inner planets closest to the Sun : Mercury , Venus , Earth and Mars . Among astronomers who use the geophysical definition of a planet , two or three planetary-mass satellites – Earth's Moon , Io , and sometimes Europa – may also be considered terrestrial planets. The large rocky asteroids Pallas and Vesta are sometimes included as well, albeit rarely. The terms "terrestrial planet" and "telluric planet" are derived from Latin words for Earth ( Terra and Tellus ), as these planets are, in terms of structure, Earth-like . Terrestrial planets are generally studied by geologists , astronomers , and geophysicists . Terrestrial planets have

1900-441: Is a first-order relief feature on par with the elevation difference between Earth's continents and ocean basins. The dichotomy is also expressed in two other ways: as a difference in impact crater density and crustal thickness between the two hemispheres. The hemisphere south of the dichotomy boundary (often called the southern highlands or uplands) is very heavily cratered and ancient, characterized by rugged surfaces that date back to

1995-519: Is a large shield volcano located in the Tharsis region of the planet Mars . It is the northernmost and tallest of three shield volcanoes collectively known as the Tharsis Montes . The volcano's location corresponds to the classical albedo feature Ascraeus Lacus. Ascraeus Mons was discovered by the Mariner 9 spacecraft in 1971. The volcano was originally called North Spot because it

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2090-534: Is also possible for some others (e.g. Ceres, Mimas , Dione , Miranda , Ariel , Triton, and Pluto). Titan even has surface bodies of liquid, albeit liquid methane rather than water. Jupiter's Ganymede, though icy, does have a metallic core like the Moon, Io, Europa, and the terrestrial planets. The name Terran world has been suggested to define all solid worlds (bodies assuming a rounded shape), without regard to their composition. It would thus include both terrestrial and icy planets. The uncompressed density of

2185-603: Is located in the southeast-central portion of the Tharsis quadrangle at 11.8°N, 255.5°E in Mars' western hemisphere. A group of three smaller volcanoes (the Ceraunius-Uranius group ) lies about 700 km to the northeast, and Pavonis Mons (the middle volcano of the Tharsis Montes) lies 500 km to the southwest. The 70-km diameter crater Poynting is located 300 km to the west-southwest. Ascraeus Mons

2280-645: Is readily visible is the Hellas basin located in the southern hemisphere. It is the second largest confirmed impact structure on the planet, centered at about 64°E longitude and 40°S latitude. The central part of the basin (Hellas Planitia) is 1,800 km in diameter and surrounded by a broad, heavily eroded annular rim structure characterized by closely spaced rugged irregular mountains ( massifs ), which probably represent uplifted, jostled blocks of old pre-basin crust. (See Anseris Mons , for example.) Ancient, low-relief volcanic constructs (highland paterae) are located on

2375-408: Is roughly 480 km in diameter and is the second highest mountain on Mars, with a summit elevation of 18.1 km. The volcano has a very low profile with an average flank slope of 7°. Slopes are steepest in the middle portion of the flanks, flattening out toward the base and near the top where a broad summit plateau and caldera (collapse crater) complex are located. Volcanic vents, located on

2470-406: Is still a topic of debate, though extensive study of analogous environments (e.g. Hawaii, the Moon, elsewhere on Mars) and morphologic features by multiple researchers has led to the conclusion that a volcanic origin is most probable. The caldera complex consists of a central caldera surrounded by four coalesced calderas. The central caldera measures about 24 km across and 3.4 km deep and

2565-512: Is supported by a groundwater model and by sulfates discovered in a wide area. At first, by examining surface materials with Opportunity Rover , scientists discovered that groundwater had repeatedly risen and deposited sulfates. Later studies with instruments on board the Mars Reconnaissance Orbiter showed that the same kinds of materials existed in a large area that included Arabia. On February 19, 2008, images obtained by

2660-484: Is the youngest of the collapse structures. Crater counting indicates that the central caldera is about 100 million years (Myr) old. The surrounding calderas have ages of about 200, 400, and 800 Myr old, or earlier. A small, partly preserved depression southeast of the main caldera may be as old as 3.8 billion years (Gyr). If the dates are valid, then Ascraeus Mons may have been active through most of Mars' history. An area of peculiar, fan-shaped deposits (FSD) lies on

2755-782: Is thought to arise when the impacting object melts ice in the subsurface. Liquid water in the ejected material forms a muddy slurry that flows along the surface, producing the characteristic lobe shapes. The crater Yuty is a good example of a rampart crater , which is so called because of the rampart-like edge to its ejecta blanket. Martian craters are commonly classified by their ejecta. Craters with one ejecta layer are called single-layer ejecta (SLE) craters. Craters with two superposed ejecta blankets are called double-layer ejecta (DLE) craters, and craters with more than two ejecta layers are called multiple-layered ejecta (MLE) craters. These morphological differences are thought to reflect compositional differences (i.e. interlayered ice, rock, or water) in

2850-469: Is thousands of kilometers in diameter and covers up to 25% of the planet's surface. Averaging 7–10 km above datum (Martian "sea" level), Tharsis contains the highest elevations on the planet and the largest known volcanoes in the Solar System. Three enormous volcanoes, Ascraeus Mons , Pavonis Mons , and Arsia Mons (collectively known as the Tharsis Montes ), sit aligned NE-SW along the crest of

2945-733: Is unknown whether extrasolar terrestrial planets in general will follow such a trend. The data in the tables below are mostly taken from a list of gravitationally rounded objects of the Solar System and planetary-mass moon . All distances from the Sun are averages. Most of the planets discovered outside the Solar System are giant planets, because they are more easily detectable. But since 2005, hundreds of potentially terrestrial extrasolar planets have also been found, with several being confirmed as terrestrial. Most of these are super-Earths , i.e. planets with masses between Earth's and Neptune's; super-Earths may be gas planets or terrestrial, depending on their mass and other parameters. During

Geology of Mars - Misplaced Pages Continue

3040-459: The Curiosity rover on the planet Mars at " Rocknest " performed the first X-ray diffraction analysis of Martian soil . The results from the rover's CheMin analyzer revealed the presence of several minerals, including feldspar , pyroxenes and olivine , and suggested that the Martian soil in the sample was similar to the "weathered basaltic soils " of Hawaiian volcanoes . In July 2015,

3135-539: The Odyssey spacecraft have spotted what might be seven caves on the flanks of the Arsia Mons volcano on Mars . The pit entrances measure from 100 to 252 metres (328 to 827 ft) wide and they are thought to be at least 73 to 96 metres (240 to 315 ft) deep. See image below: the pits have been informally named (A) Dena, (B) Chloe, (C) Wendy, (D) Annie, (E) Abby (left) and Nikki, and (F) Jeanne. Dena's floor

3230-507: The Argyre and Isidis basins. Like Hellas, Argyre (800 km in diameter) is located in the southern highlands and is surrounded by a broad ring of mountains. The mountains in the southern portion of the rim, Charitum Montes , may have been eroded by valley glaciers and ice sheets at some point in Mars's history. The Isidis basin (roughly 1,000 km in diameter) lies on the dichotomy boundary at about 87°E longitude. The northeastern part of

3325-549: The East African Rift valleys. The canyons represent the surface expression of a powerful extensional strain in the Martian crust, probably due to loading from the Tharsis bulge. The terrain at the eastern end of the Valles Marineris grades into dense jumbles of low rounded hills that seem to have formed by the collapse of upland surfaces to form broad, rubble-filled hollows. Called chaotic terrain , these areas mark

3420-483: The HiRISE camera on the Mars Reconnaissance Orbiter showed a spectacular avalanche, in which debris thought to be fine-grained ice, dust, and large blocks fell from a 700-metre (2,300 ft) high cliff. Evidence of the avalanche included dust clouds rising from the cliff afterwards. Such geological events are theorized to be the cause of geologic patterns known as slope streaks. NASA scientists studying pictures from

3515-466: The Martian Surface .) The dust forms a mantle over the surface that obscures or mutes much of the fine-scale topography and geology of the region. Tharsis is probably dusty because of its high elevations. The atmospheric density is too low to mobilize and remove dust once it is deposited. The atmospheric pressure at the summit of Ascraeus Mons averages 100 pascal (1.0 mbar); this is only 17% of

3610-680: The Milky Way galaxy . The following exoplanets have a density of at least 5 g/cm and a mass below Neptune's and are thus very likely terrestrial: Kepler-10b , Kepler-20b , Kepler-36b , Kepler-48d , Kepler 68c , Kepler-78b , Kepler-89b , Kepler-93b , Kepler-97b , Kepler-99b , Kepler-100b , Kepler-101c , Kepler-102b , Kepler-102d , Kepler-113b , Kepler-131b , Kepler-131c , Kepler-138c , Kepler-406b , Kepler-406c , Kepler-409b . In 2013, astronomers reported, based on Kepler space mission data, that there could be as many as 40 billion Earth- and super-Earth-sized planets orbiting in

3705-607: The habitable zones of Sun-like stars and red dwarfs within the Milky Way . Eleven billion of these estimated planets may be orbiting Sun-like stars. The nearest such planet may be 12 light-years away, according to the scientists. However, this does not give estimates for the number of extrasolar terrestrial planets, because there are planets as small as Earth that have been shown to be gas planets (see Kepler-138d ). Estimates show that about 80% of potentially habitable worlds are covered by land, and about 20% are ocean planets. Planets with rations more like those of Earth, which

3800-484: The outer , giant planets , whose atmospheres are primary; primary atmospheres were captured directly from the original solar nebula . The Solar System has four terrestrial planets under the dynamical definition: Mercury , Venus , Earth and Mars . The Earth's Moon as well as Jupiter's moons Io and Europa would also count geophysically, as well as perhaps the large protoplanet-asteroids Pallas and Vesta (though those are borderline cases). Among these bodies, only

3895-597: The transit method. In the same year, the Kepler space telescope mission team released a list of 1235 extrasolar planet candidates , including six that are "Earth-size" or "super-Earth-size" (i.e. they have a radius less than twice that of the Earth) and in the habitable zone of their star. Since then, Kepler has discovered hundreds of planets ranging from Moon-sized to super-Earths, with many more candidates in this size range (see image). In 2016, statistical modeling of

Geology of Mars - Misplaced Pages Continue

3990-458: The 1960s, we have known that the seasonal caps (those seen in the telescope to grow and wane seasonally) are composed of carbon dioxide (CO 2 ) ice that condenses out of the atmosphere as temperatures fall to 148 K, the frost point of CO 2 , during the polar wintertime. In the north, the CO 2 ice completely dissipates ( sublimes ) in summer, leaving behind a residual cap of water (H 2 O) ice. At

4085-455: The Earth has an active surface hydrosphere . Europa is believed to have an active hydrosphere under its ice layer. During the formation of the Solar System, there were many terrestrial planetesimals and proto-planets , but most merged with or were ejected by the four terrestrial planets, leaving only Pallas and Vesta to survive more or less intact. These two were likely both dwarf planets in

4180-515: The MG C database across the entire surface of Mars. It has been suggested that human explorers on Mars could use lava tubes as shelters. The caves may be the only natural structures offering protection from the micrometeoroids , UV radiation , solar flares , and high energy particles that bombard the planet's surface. These features may enhance preservation of biosignatures over long periods of time and make caves an attractive astrobiology target in

4275-492: The abundance of pit craters probably indicate the presence of near-surface ice at the time of impact. Polewards of 30 degrees of latitude, the form of older impact craters is rounded out (" softened ") by acceleration of soil creep by ground ice. The most notable difference between Martian craters and other craters in the Solar System is the presence of lobate (fluidized) ejecta blankets. Many craters at equatorial and mid-latitudes on Mars have this form of ejecta morphology, which

4370-400: The amount of water on ancient Mars (see: Water on Mars ). Groundwater has been implicated in the cementation of aeolian sediments and the formation and transport of a wide variety of sedimentary minerals including clays, sulphates and hematite . When the surface has been dry, wind has been a major geomorphic agent. Wind driven sand bodies like megaripples and dunes are extremely common on

4465-528: The aprons and the Tharsis Montes chain. The presence of the lava aprons causes some disagreement in the actual dimensions of the volcano. If the aprons are included as part of the edifice then Ascraeus Mons has dimensions closer to 375 × 870 km. Like most of the Tharsis region, Ascraeus Mons has a high albedo (reflectivity) and low thermal inertia , indicating that the volcano and surrounding areas are covered with large amounts of fine dust. (See

4560-470: The average surface pressure of 600 pascal. Ascraeus Mons is surrounded by lava flow plains that are mid to late Amazonian in age. The elevation of the plains averages about 3 km above datum (Martian "sea" level), giving the volcano an average vertical relief of 15 km. However, the elevation of the plains varies considerably. The plains northwest of the volcano are less than 2 km in elevation. The plains are highest (>3 km) southeast of

4655-400: The basin rim has been eroded and is now buried by northern plains deposits, giving the basin a semicircular outline. The northwestern rim of the basin is characterized by arcuate grabens ( Nili Fossae ) that are circumferential to the basin. One additional large basin, Utopia , is completely buried by northern plains deposits. Its outline is clearly discernable only from altimetry data. All of

4750-425: The bulge. The vast Alba Mons (formerly Alba Patera) occupies the northern part of the region. The huge shield volcano Olympus Mons lies off the main bulge, at the western edge of the province. The extreme massiveness of Tharsis has placed tremendous stress on the planet's lithosphere . As a result, immense extensional fractures ( grabens and rift valleys ) radiate outward from Tharsis, extending halfway around

4845-502: The catalog of known exoplanets has increased significantly, and there have been several published refinements of the mass-radius model. As of 2024, the expected transition point between rocky and intermediate-mass planets sits at roughly 4.4 earth masses, and roughly 1.6 earth radii. In September 2020, astronomers using microlensing techniques reported the detection , for the first time, of an Earth-mass rogue planet (named OGLE-2016-BLG-1928 ) unbounded by any star, and free-floating in

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4940-509: The crater's ejecta forms a resistant layer so that the area nearest the crater erodes more slowly than the rest of the region. Some pedestals were hundreds of meters above the surrounding area, meaning that hundreds of meters of material were eroded. Pedestal craters were first observed during the Mariner 9 mission in 1972. Volcanic structures and landforms cover large parts of the Martian surface. The most conspicuous volcanoes on Mars are located in Tharsis and Elysium . Geologists think one of

5035-405: The dichotomy was produced by a mega-impact event or several large impacts early in the planet's history (exogenic theories) or two, the dichotomy was produced by crustal thinning in the northern hemisphere by mantle convection, overturning, or other chemical and thermal processes in the planet's interior (endogenic theories). One endogenic model proposes an early episode of plate tectonics producing

5130-407: The dichotomy. Laser altimeters and radar-sounding data from orbiting spacecraft have identified a large number of basin-sized structures previously hidden in visual images. Called quasi-circular depressions (QCDs), these features likely represent derelict impact craters from the period of heavy bombardment that are now covered by a veneer of younger deposits. Crater counting studies of QCDs suggest that

5225-475: The distance from the Sun increases, consistent with the temperature gradient that would have existed within the primordial solar nebula. The Galilean satellites show a similar trend going outwards from Jupiter; however, no such trend is observable for the icy satellites of Saturn or Uranus. The icy worlds typically have densities less than 2 g·cm . Eris is significantly denser ( 2.43 ± 0.05 g·cm ), and may be mostly rocky with some surface ice, like Europa. It

5320-453: The early 1990s, the first extrasolar planets were discovered orbiting the pulsar PSR B1257+12 , with masses of 0.02, 4.3, and 3.9 times that of Earth, by pulsar timing . When 51 Pegasi b , the first planet found around a star still undergoing fusion , was discovered, many astronomers assumed it to be a gigantic terrestrial, because it was assumed no gas giant could exist as close to its star (0.052 AU) as 51 Pegasi b did. It

5415-725: The flow solidify, leaving a central trough of molten, flowing lava. Partially collapsed lava tubes are visible as chains of pit craters. By examining the morphologies of lava flow structures on Ascraeus Mons, geologists are able to calculate the rheological properties of the lava and estimate the rate at which it poured out during eruption (effusion rate). Results show that the lava was highly fluid (low viscosity ) with low yield strength , resembling Hawaiian and Icelandic basaltic lavas. Average effusion rates are about 185 m /s. These rates are comparable to those seen in Hawaii and Iceland. Earth-based radar studies show that Ascraeus Mons has

5510-471: The flows that formed them correspondingly immense. For example, the peak discharge required to carve the 28-km-wide Ares Vallis is estimated to have been 14 million cubic metres (500 million cu ft) per second, over ten thousand times the average discharge of the Mississippi River. The polar ice caps are well-known telescopic features of Mars, first identified by Christiaan Huygens in 1672. Since

5605-575: The form of stream channels suggests that the climate was different—much wetter—when the inverted channels were formed. In an article published in 2010, a large group of scientists endorsed the idea of searching for life in Miyamoto Crater because of inverted stream channels and minerals that indicated the past presence of water. Images of examples of inverted relief from various parts of Mars are shown below. Terrestrial planet A terrestrial planet , telluric planet , or rocky planet ,

5700-526: The greatest diversity of impact crater types of any planet in the Solar System. This is partly because the presence of both rocky and volatile-rich layers in the subsurface produces a range of morphologies even among craters within the same size classes. Mars also has an atmosphere that plays a role in ejecta emplacement and subsequent erosion. Moreover, Mars has a rate of volcanic and tectonic activity low enough that ancient, eroded craters are still preserved, yet high enough to have resurfaced large areas, producing

5795-475: The habitable zone of the star, so they could potentially be habitable, with Earth-like temperatures. Another possibly terrestrial planet, HD 85512 b , was discovered in 2011; it has at least 3.6 times the mass of Earth. The radius and composition of all these planets are unknown. The first confirmed terrestrial exoplanet , Kepler-10b , was found in 2011 by the Kepler space telescope , specifically designed to discover Earth-size planets around other stars using

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5890-556: The heads of huge outflow channels that emerge full size from the chaotic terrain and empty ( debouch ) northward into Chryse Planitia . The presence of streamlined islands and other geomorphic features indicate that the channels were most likely formed by catastrophic releases of water from aquifers or the melting of subsurface ice. However, these features could also be formed by abundant volcanic lava flows coming from Tharsis. The channels, which include Ares , Shalbatana , Simud, and Tiu Valles, are enormous by terrestrial standards, and

5985-404: The inner walls. Complex craters are shallower than simple craters in proportion to their widths, with depth/diameter ratios ranging from 1/5 at the simple-to-complex transition diameter (~7 km) to about 1/30 for a 100-km diameter crater. Another transition occurs at crater diameters of around 130 km as central peaks turn into concentric rings of hills to form multi-ring basins . Mars has

6080-544: The large basins on Mars are extremely old, dating to the late heavy bombardment. They are thought to be comparable in age to the Imbrium and Orientale basins on the Moon. Near the equator in the western hemisphere lies an immense system of deep, interconnected canyons and troughs collectively known as the Valles Marineris . The canyon system extends eastward from Tharsis for a length of over 4,000 km, nearly

6175-454: The lower layer of dark, rocky material. Dark markings are most distinct in a broad belt from 0° to 40° S latitude. However, the most prominent dark marking, Syrtis Major Planum , is in the northern hemisphere. The classical albedo feature, Mare Acidalium ( Acidalia Planitia ), is another prominent dark area in the northern hemisphere. A third type of area, intermediate in color and albedo, is also present and thought to represent regions containing

6270-496: The mass of Earth and orbits a star about 21,000 light-years away in the constellation Scorpius. From 2007 to 2010, three (possibly four) potential terrestrial planets were found orbiting within the Gliese 581 planetary system . The smallest, Gliese 581e , is only about 1.9 Earth masses, but orbits very close to the star. Two others, Gliese 581c and the disputed Gliese 581d , are more-massive super-Earths orbiting in or close to

6365-544: The modern Martian surface, and Opportunity has documented abundant aeolian sandstones on its traverse. Ventifacts , like Jake Matijevic (rock) , are another aeolian landform on the Martian Surface. A wide variety of other sedimentological facies are also present locally on Mars, including glacial deposits , hot springs , dry mass movement deposits (especially landslides ), and cryogenic and periglacial material, amongst many others. Evidence for ancient rivers,

6460-403: The northeastern and southwestern edges of the volcano, are sources for broad lava aprons, or fans, that bury nearby portions of the volcano and extend over 100 km out into the surrounding plains. The southwest–northeast orientation of the aprons matches the orientation of the Tharsis Montes, suggesting that a major fissure or rift in the Martian crust is responsible for the orientation of both

6555-462: The northeastern and southwestern parts of the rim. The basin floor contains thick, structurally complex sedimentary deposits that have a long geologic history of deposition, erosion, and internal deformation. The lowest elevations on the planet are located within the Hellas basin, with some areas of the basin floor lying over 8 km below datum. The two other large impact structures on the planet are

6650-464: The past, but have been battered out of equilibrium shapes by impacts. Some other protoplanets began to accrete and differentiate but suffered catastrophic collisions that left only a metallic or rocky core, like 16 Psyche or 8 Flora respectively. Many S-type and M-type asteroids may be such fragments. The other round bodies from the asteroid belt outward are geophysically icy planets . They are similar to terrestrial planets in that they have

6745-424: The period of heavy bombardment . In contrast, the lowlands north of the dichotomy boundary have few large craters, are very smooth and flat, and have other features indicating that extensive resurfacing has occurred since the southern highlands formed. The third distinction between the two hemispheres is in crustal thickness. Topographic and geophysical gravity data indicate that the crust in the southern highlands has

6840-446: The physical structure and composition of the surface and subsurface at the time of impact. For example, the size of central peaks in Martian craters is larger than comparable craters on Mercury or the Moon. In addition, the central peaks of many large craters on Mars have pit craters at their summits. Central pit craters are rare on the Moon but are very common on Mars and the icy satellites of the outer Solar System. Large central peaks and

6935-546: The pits consist of steep, overhanging ledges. The bottoms of both pits contain sediments and large boulders. These rimless pit craters are believed to form by collapse of surface material into a subsurface void created either by a dike or lava tube. They are analogous to volcanic pit craters on Earth, such as the Devil's Throat crater on the upper east rift zone of Kilauea Volcano, Hawaii. In some cases, they may mark skylights/entrances to subsurface lava caves . Ascraeus Mons

7030-421: The planet on a global scale. The northern and southern hemispheres of Mars are strikingly different from each other in topography and physiography. This dichotomy is a fundamental global geologic feature of the planet. The northern part is an enormous topographic depression. About one-third of the surface (mostly in the northern hemisphere) lies 3–6 km lower in elevation than the southern two-thirds. This

7125-568: The planet. A smaller volcanic center lies several thousand kilometers west of Tharsis in Elysium . The Elysium volcanic complex is about 2,000 kilometers in diameter and consists of three main volcanoes, Elysium Mons , Hecates Tholus , and Albor Tholus . The Elysium group of volcanoes is thought to be somewhat different from the Tharsis Montes, in that development of the former involved both lavas and pyroclastics . Several enormous, circular impact basins are present on Mars. The largest one that

7220-413: The polar ice caps, but the permanent ice (seen as the high albedo, white surfaces in images) forms only a relatively thin mantle on top of the layered deposits. The layered deposits probably represent alternating cycles of dust and ice deposition caused by climate changes related to variations in the planet's orbital parameters over time (see also Milankovitch cycles ). The polar layered deposits are some of

7315-480: The reasons volcanoes on Mars were able to grow so large is that Mars has fewer tectonic boundaries in comparison to Earth. Lava from a stationary hot spot was able to accumulate at one location on the surface for many hundreds of millions of years. Scientists have never recorded an active volcano eruption on the surface of Mars. Searches for thermal signatures and surface changes within the last decade have not yielded evidence for active volcanism. On October 17, 2012,

7410-450: The relationship between a planet's mass and radius using a broken power law appeared to suggest that the transition point between rocky, terrestrial worlds and mini-Neptunes without a defined surface was in fact very close to Earth and Venus's, suggesting that rocky worlds much larger than our own are in fact quite rare. This resulted in some advocating for the retirement of the term "super-earth" as being scientifically misleading. Since 2016

7505-490: The same rover identified tridymite in a rock sample from Gale Crater, leading scientists to conclude that silicic volcanism might have played a much more prevalent role in the planet's volcanic history than previously thought. Flowing water appears to have been common on the surface of Mars at various points in its history, and especially on ancient Mars. Many of these flows carved the surface, forming valley networks and producing sediment. This sediment has been redeposited in

7600-419: The search for evidence of life beyond Earth. Some areas of Mars show inverted relief, where features that were once depressions, like streams, are now above the surface. It is believed that materials like large rocks were deposited in low-lying areas. Later, wind erosion removed much of the surface layers, but left behind the more resistant deposits. Other ways of making inverted relief might be lava flowing down

7695-475: The south pole, a small residual cap of CO 2 ice remains in summer. Both residual ice caps overlie thick layered deposits of interbedded ice and dust. In the north, the layered deposits form a 3 km-high, 1,000 km-diameter plateau called Planum Boreum . A similar kilometers-thick plateau, Planum Australe , lies in the south. Both plana (the Latin plural of planum) are sometimes treated as synonymous with

7790-409: The southwestern and northeastern edges of the volcano are the sources of the lava aprons that spread out across the surrounding plains. The fissures seem to have formed by the merger of numerous, narrow rille -like depressions. In places, the depressions form sinuous channels with islands and other features suggestive of erosion by a fluid. Whether the channels were formed predominately by water or lava

7885-401: The subsurface at the time of impact. Martian craters show a large diversity of preservational states, from extremely fresh to old and eroded. Degraded and infilled impact craters record variations in volcanic , fluvial , and eolian activity over geologic time. Pedestal craters are craters with their ejecta sitting above the surrounding terrain to form raised platforms. They occur because

7980-436: The summit of the volcano. The terraces are spaced 30 to 50 km apart, have lengths up to 100 km, radial widths of 30 km, and heights of about 3 km. Individual terraces are not continuous around the volcano, but instead consist of arcuate segments that overlap with each other, forming an imbricate pattern. They are interpreted to be the surface expression of thrust faults that formed due to compression along

8075-404: The underlying surface in the northern hemisphere is at least as old as the oldest exposed crust in the southern highlands. The ancient age of the dichotomy places a significant constraint on theories of its origin. Straddling the dichotomy boundary in Mars's western hemisphere is a massive volcano-tectonic province known as the Tharsis region or the Tharsis bulge. This immense, elevated structure

8170-404: The volcano's base for about 100 km. The origin of these deposits has been debated for decades. However, recent geologic evidence suggests that FSDs are deposits left by glaciers , which covered portions of the volcanoes during a recent period of high obliquity . During periods of high obliquity (axial tilt) the polar regions receive higher levels of sunlight. More water from the poles enters

8265-435: The volcano's flanks. Flank terraces are also common on Olympus Mons and the other Tharsis shield volcanoes. The source of the compressive stresses is still debated. The flank terraces may be due to compressional failure of the volcano, flexing of the underlying lithosphere due to the volcano's massive weight, cycles of magma chamber inflation and deflation, or shallow gravitational slumping . Fissures, or flank vents, at

8360-411: The volcano's western flank. The FSD consists of a zone of knobby terrain outlined by a semicircular zone of concentric ridges. Similar deposits are also found at the northwestern edges of the other two Tharsis Montes, Pavonis Mons and Arsia Mons, as well as on Olympus Mons. The FSD at Ascraeus Mons is the smallest of those on the Tharsis Montes, covering an area of 14,000 km and extending outward from

8455-557: The volcano. The lava plains northwest of Ascraeus Mons are notable for having two dark collapse pits photographed by the HiRISE camera on the Mars Reconnaissance Orbiter (MRO) in November 2010 (pictured in gallery below). The pits resemble those imaged around Arsia Mons by the Mars Odyssey spacecraft. The two pits measure about 180 and 310 m wide, and the larger pit is approximately 180 meters deep. The eastern walls of

8550-435: The youngest geologic units on Mars. No topography is visible on Mars from Earth. The bright areas and dark markings seen through a telescope are albedo features. The bright, red- ochre areas are locations where fine dust covers the surface. Bright areas (excluding the polar caps and clouds) include Hellas, Tharsis, and Arabia Terra . The dark gray markings represent areas that the wind has swept clean of dust, leaving behind

8645-634: Was 30% land and 70% ocean, only make up 1% of these worlds. Several possible classifications for solid planets have been proposed. Solar System   → Local Interstellar Cloud   → Local Bubble   → Gould Belt   → Orion Arm   → Milky Way   → Milky Way subgroup   → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster   → Local Hole   → Observable universe   → Universe Each arrow ( → ) may be read as "within" or "part of". Ascraeus Mons Ascraeus Mons / ə ˈ s k r iː ə s ˈ m ɒ n z /

8740-477: Was built by many thousands of fluid basaltic lava flows. Except for its great size, it resembles terrestrial shield volcanoes like those that form the Hawaiian Islands . The flanks of Ascraeus Mons are covered with narrow, lobate lava flows and lava channels. Many of the lava flows have levees along their margins. Levees are parallel ridges formed at the edges of lava flows. The cooler, outer margins of

8835-426: Was later found to be a gas giant. In 2005, the first planets orbiting a main-sequence star and which showed signs of being terrestrial planets were found: Gliese 876 d and OGLE-2005-BLG-390Lb . Gliese 876 d orbits the red dwarf Gliese 876 , 15 light years from Earth, and has a mass seven to nine times that of Earth and an orbital period of just two Earth days. OGLE-2005-BLG-390Lb has about 5.5 times

8930-515: Was observed and found to be 130 m deep. Further investigation suggested that these were not necessarily lava tube "skylights". Review of the images has resulted in yet more discoveries of deep pits. Recently, a global database (MG C ) of over 1,000 Martian cave candidates at Tharsis Montes has been developed by the USGS Astrogeology Science Center . In 2021, scientists are applying machine-learning algorithms to extend

9025-545: Was the northernmost of only four spots visible on the surface due to a global dust storm that was then enshrouding the planet. As the dust cleared, the spots were revealed to be extremely tall volcanoes whose summits had projected above the dust-laden, lower atmosphere. Ascraeus Lacus had been named after Ascra, the rustic birthplace of Hesiod ; in Greek, the word "ascraeus" is a poetic metonym for "rural." The volcano's name officially became Ascraeus Mons in 1973. The volcano

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