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92-614: Tshwa'i 'Dam is the Wylie romanization of the Tibetan name ཚྭ འི ་ འདམ ་ , meaning " Salt Marsh "; the Tibetan Pinyin romanization of the same name is Caidam . Qaidam is the GNC romanization of its transcription into Mongolian ; Tsaidam is a variant romanization of the same name. Chaidamu is the pinyin romanization of its transcription into Chinese characters ;

184-559: A Latin keyboard. Since the Wylie system is not intuitive for use by linguists unfamiliar with Tibetan, a new transliteration system based on the International Phonetic Alphabet has been proposed to replace Wylie in articles on Tibetan historical phonology . (Some of the following links require installation of Tibetan fonts to display properly) Mars (planet) Mars is the fourth planet from

276-522: A Martian solar day ( sol ) is equal to 24.6 hours, and a Martian solar year is equal to 1.88 Earth years (687 Earth days). Mars has two natural satellites that are small and irregular in shape: Phobos and Deimos . The relatively flat plains in northern parts of Mars strongly contrast with the cratered terrain in southern highlands – this terrain observation is known as the Martian dichotomy . Mars hosts many enormous extinct volcanoes (the tallest

368-489: A classical albedo feature it contains. In April 2023, The New York Times reported an updated global map of Mars based on images from the Hope spacecraft . A related, but much more detailed, global Mars map was released by NASA on 16 April 2023. The vast upland region Tharsis contains several massive volcanoes, which include the shield volcano Olympus Mons . The edifice is over 600 km (370 mi) wide. Because

460-456: A few other saline lakes occupy over one-fourth of the basin, with the sediments deposited since the Jurassic as deep as 10 to 14 km (6–9   mi) in places despite tectonic activity having repeatedly shifted the center of the region's sedimentation. The seasonal nature and commercial exploitation of some of the lakes makes an exact count problematic: one count reckoned there were 27 lakes in

552-422: A global magnetic field, the types and distribution of auroras there differ from those on Earth; rather than being mostly restricted to polar regions as is the case on Earth, a Martian aurora can encompass the planet. In September 2017, NASA reported radiation levels on the surface of the planet Mars were temporarily doubled , and were associated with an aurora 25 times brighter than any observed earlier, due to

644-488: A high ratio of deuterium in Gale Crater , though not significantly high enough to suggest the former presence of an ocean. Other scientists caution that these results have not been confirmed, and point out that Martian climate models have not yet shown that the planet was warm enough in the past to support bodies of liquid water. Near the northern polar cap is the 81.4 kilometres (50.6 mi) wide Korolev Crater , which

736-490: A low of 30  Pa (0.0044  psi ) on Olympus Mons to over 1,155 Pa (0.1675 psi) in Hellas Planitia , with a mean pressure at the surface level of 600 Pa (0.087 psi). The highest atmospheric density on Mars is equal to that found 35 kilometres (22 mi) above Earth's surface. The resulting mean surface pressure is only 0.6% of Earth's 101.3 kPa (14.69 psi). The scale height of

828-442: A massive, and unexpected, solar storm in the middle of the month. Mars has seasons, alternating between its northern and southern hemispheres, similar to on Earth. Additionally the orbit of Mars has, compared to Earth's, a large eccentricity and approaches perihelion when it is summer in its southern hemisphere and winter in its northern, and aphelion when it is winter in its southern hemisphere and summer in its northern. As

920-542: A minimum thickness of 6 kilometres (3.7 mi) in Isidis Planitia , and a maximum thickness of 117 kilometres (73 mi) in the southern Tharsis plateau. For comparison, Earth's crust averages 27.3 ± 4.8 km in thickness. The most abundant elements in the Martian crust are silicon , oxygen , iron , magnesium , aluminium , calcium , and potassium . Mars is confirmed to be seismically active; in 2019 it

1012-473: A record of erosion caused by the catastrophic release of water from subsurface aquifers, though some of these structures have been hypothesized to result from the action of glaciers or lava. One of the larger examples, Ma'adim Vallis , is 700 kilometres (430 mi) long, much greater than the Grand Canyon, with a width of 20 kilometres (12 mi) and a depth of 2 kilometres (1.2 mi) in places. It

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1104-588: A remnant of that ring. The geological history of Mars can be split into many periods, but the following are the three primary periods: Geological activity is still taking place on Mars. The Athabasca Valles is home to sheet-like lava flows created about 200 million years ago. Water flows in the grabens called the Cerberus Fossae occurred less than 20 million years ago, indicating equally recent volcanic intrusions. The Mars Reconnaissance Orbiter has captured images of avalanches. Mars

1196-460: A result, the seasons in its southern hemisphere are more extreme and the seasons in its northern are milder than would otherwise be the case. The summer temperatures in the south can be warmer than the equivalent summer temperatures in the north by up to 30 °C (54 °F). Martian surface temperatures vary from lows of about −110 °C (−166 °F) to highs of up to 35 °C (95 °F) in equatorial summer. The wide range in temperatures

1288-471: A small crater (later called Airy-0 ), located in the Sinus Meridiani ("Middle Bay" or "Meridian Bay"), was chosen by Merton E. Davies , Harold Masursky , and Gérard de Vaucouleurs for the definition of 0.0° longitude to coincide with the original selection. Because Mars has no oceans, and hence no " sea level ", a zero-elevation surface had to be selected as a reference level; this is called

1380-481: A storm over a small area, to gigantic storms that cover the entire planet. They tend to occur when Mars is closest to the Sun, and have been shown to increase global temperature. Seasons also produce dry ice covering polar ice caps . Large areas of the polar regions of Mars While Mars contains water in larger amounts , most of it is dust covered water ice at the Martian polar ice caps . The volume of water ice in

1472-576: A surface 50–60 m (160–200 ft) above the present levels of its successors. At the same time, a river from the "Kunlun" paleolake to its south was enriching the Sanhu region with enormous reserves of lithium derived from hot springs near Mount Buka Daban which now feed into the Narin Gol River that flows into East Taijinar Lake . Around 30 kya , the lake in the Kunluns dried up and

1564-609: A typical English-language typewriter . The system is named for the American scholar Turrell V. Wylie , who created the system and published it in a 1959 Harvard Journal of Asiatic Studies article. It has subsequently become a standard transliteration scheme in Tibetan studies, especially in the United States. Any Tibetan language romanization scheme faces the dilemma of whether it should seek to accurately reproduce

1656-491: A very thick lithosphere compared to Earth. Below this the mantle gradually becomes more ductile, and the seismic wave velocity starts to grow again. The Martian mantle does not appear to have a thermally insulating layer analogous to Earth's lower mantle ; instead, below 1050 km in depth, it becomes mineralogically similar to Earth's transition zone . At the bottom of the mantle lies a basal liquid silicate layer approximately 150–180 km thick. Mars's iron and nickel core

1748-471: A year, there are large surface temperature swings on the surface between −78.5 °C (−109.3 °F) to 5.7 °C (42.3 °F) similar to Earth's seasons , as both planets have significant axial tilt . Mars was formed approximately 4.5 billion years ago. During the Noachian period (4.5 to 3.5 billion years ago), Mars's surface was marked by meteor impacts , valley formation, erosion, and

1840-537: Is Olympus Mons , 21.9 km or 13.6 mi tall) and one of the largest canyons in the Solar System ( Valles Marineris , 4,000 km or 2,500 mi long). Geologically , the planet is fairly active with marsquakes trembling underneath the ground, dust devils sweeping across the landscape, and cirrus clouds . Carbon dioxide is substantially present in Mars's polar ice caps and thin atmosphere . During

1932-452: Is Syrtis Major Planum . The permanent northern polar ice cap is named Planum Boreum . The southern cap is called Planum Australe . Mars's equator is defined by its rotation, but the location of its Prime Meridian was specified, as was Earth's (at Greenwich ), by choice of an arbitrary point; Mädler and Beer selected a line for their first maps of Mars in 1830. After the spacecraft Mariner 9 provided extensive imagery of Mars in 1972,

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2024-413: Is g.yang . The four vowel marks (here applied to the base letter ཨ ) are transliterated: When a syllable has no explicit vowel marking, the letter a is used to represent the default vowel "a" (e.g. ཨ་ = a). Many previous systems of Tibetan transliteration included internal capitalisation schemes—essentially, capitalising the root letter rather than the first letter of a word, when the first letter

2116-406: Is a light albedo feature clearly visible from Earth. There are other notable impact features, such as Argyre , which is around 1,800 kilometres (1,100 mi) in diameter, and Isidis , which is around 1,500 kilometres (930 mi) in diameter. Due to the smaller mass and size of Mars, the probability of an object colliding with the planet is about half that of Earth. Mars is located closer to

2208-408: Is a prefix consonant. Tibetan dictionaries are organized by root letter, and prefixes are often silent, so knowing the root letter gives a better idea of pronunciation. However, these schemes were often applied inconsistently, and usually only when the word would normally be capitalised according to the norms of Latin text (i.e. at the beginning of a sentence). On the grounds that internal capitalisation

2300-636: Is about 2 million metric tons of petroleum and 8.5 billion cubic meters of natural gas. A pipeline connects the Huatugou field with a major refinery at Golmud , and the Sebei gas fields are connected to Xining , Lanzhou , and Yinchuan . Qaidam has reserves of asbestos , borax , gypsum , and several metals , with the greatest reserves of lithium , magnesium , potassium , and sodium found anywhere in China. The Xining-Golmud rail line (the first stage of

2392-432: Is approximately half the diameter of Earth, with a surface area only slightly less than the total area of Earth's dry land. Mars is less dense than Earth, having about 15% of Earth's volume and 11% of Earth's mass , resulting in about 38% of Earth's surface gravity . Mars is the only presently known example of a desert planet , a rocky planet with a surface akin to that of Earth's hot deserts . The red-orange appearance of

2484-752: Is broadly divided into three blocks: the Mangya Depression, a northern fault zone, and the Sanhu Depression . Qaidam is an intermontane basin, surrounded on all sides by mountain ranges. In the south, the Kunlun Mountains separate it from the higher central section of the Tibetan Plateau . In the north, a number of smaller ridges like the Shulenanshan separate it from another higher plateau, which usually referenced by

2576-766: Is completely molten, with no solid inner core. It is around half of Mars's radius, approximately 1650–1675 km, and is enriched in light elements such as sulfur , oxygen, carbon , and hydrogen . Mars is a terrestrial planet with a surface that consists of minerals containing silicon and oxygen, metals , and other elements that typically make up rock . The Martian surface is primarily composed of tholeiitic basalt , although parts are more silica -rich than typical basalt and may be similar to andesitic rocks on Earth, or silica glass. Regions of low albedo suggest concentrations of plagioclase feldspar , with northern low albedo regions displaying higher than normal concentrations of sheet silicates and high-silicon glass. Parts of

2668-429: Is divided into two kinds of areas, with differing albedo. The paler plains covered with dust and sand rich in reddish iron oxides were once thought of as Martian "continents" and given names like Arabia Terra ( land of Arabia ) or Amazonis Planitia ( Amazonian plain ). The dark features were thought to be seas, hence their names Mare Erythraeum , Mare Sirenum and Aurorae Sinus . The largest dark feature seen from Earth

2760-426: Is due to the thin atmosphere which cannot store much solar heat, the low atmospheric pressure (about 1% that of the atmosphere of Earth ), and the low thermal inertia of Martian soil. The planet is 1.52 times as far from the Sun as Earth, resulting in just 43% of the amount of sunlight. Mars has the largest dust storms in the Solar System, reaching speeds of over 160 km/h (100 mph). These can vary from

2852-409: Is not capable of transliterating all Tibetan-script texts. In particular, it has no correspondences for most Tibetan punctuation symbols, and lacks the ability to represent non-Tibetan words written in Tibetan script (Sanskrit and phonetic Chinese are the most common cases). Accordingly, various scholars have adopted ad hoc and incomplete conventions as needed. The Tibetan and Himalayan Library at

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2944-519: Is striking: northern plains flattened by lava flows contrast with the southern highlands, pitted and cratered by ancient impacts. It is possible that, four billion years ago, the Northern Hemisphere of Mars was struck by an object one-tenth to two-thirds the size of Earth's Moon . If this is the case, the Northern Hemisphere of Mars would be the site of an impact crater 10,600 by 8,500 kilometres (6,600 by 5,300 mi) in size, or roughly

3036-606: Is thought to have been carved by flowing water early in Mars's history. The youngest of these channels is thought to have formed only a few million years ago. Elsewhere, particularly on the oldest areas of the Martian surface, finer-scale, dendritic networks of valleys are spread across significant proportions of the landscape. Features of these valleys and their distribution strongly imply that they were carved by runoff resulting from precipitation in early Mars history. Subsurface water flow and groundwater sapping may play important subsidiary roles in some networks, but precipitation

3128-550: The areoid of Mars, analogous to the terrestrial geoid . Zero altitude was defined by the height at which there is 610.5  Pa (6.105  mbar ) of atmospheric pressure. This pressure corresponds to the triple point of water, and it is about 0.6% of the sea level surface pressure on Earth (0.006 atm). For mapping purposes, the United States Geological Survey divides the surface of Mars into thirty cartographic quadrangles , each named for

3220-658: The Golmud-Korla Railway in September 2013, which would stretch across the western portion of the Qaidam Basin. Construction began in November 2014 and concluded in 2020. 37°16′N 94°27′E  /  37.267°N 94.450°E  / 37.267; 94.450 Wylie romanization Wylie transliteration is a method for transliterating Tibetan script using only the letters available on

3312-628: The Pliocene (5–2.5   Ma), the focus of most sedimentation was at what is now Kunteyi but, during the Pleistocene (after 2.5   Ma), tectonic activity shifted the basin's tributaries and floor, moving the focus of sedimentation from the Dalangtan to Qarhan area. During this time, the record's glacial intervals suggest a low-temperature climate and its sandstone yardangs attest to strong winds. From 770,000 and 30,000 years ago,

3404-631: The Qinghai–Tibet Railway ), which crossed the eastern part of the Qaidam Basin in the early 1980s, is an essential transportation link for accessing the region's mineral resources. Additional railroads spanning the basin include the Golmud–Dunhuang Railway completed in December 2019 and a 25 km private railway constructed by Zangge Mining Co., Ltd. The National Development and Reform Commission began conducting preliminary planning for

3496-688: The Sun . The surface of Mars is orange-red because it is covered in iron(III) oxide dust, giving it the nickname " the Red Planet ". Mars is among the brightest objects in Earth's sky , and its high-contrast albedo features have made it a common subject for telescope viewing. It is classified as a terrestrial planet and is the second smallest of the Solar System 's planets with a diameter of 6,779 km (4,212 mi). In terms of orbital motion,

3588-546: The University of Virginia developed a standard, EWTS —the Extended Wylie Transliteration Scheme—that addresses these deficiencies systematically. It uses capital letters and Latin punctuation to represent the missing characters. Several software systems, including Tise , now use this standard to allow one to type unrestricted Tibetan script (including the full Unicode Tibetan character set) on

3680-656: The Yellowknife Bay area in the Glenelg terrain. In September 2015, NASA announced that they had found strong evidence of hydrated brine flows in recurring slope lineae , based on spectrometer readings of the darkened areas of slopes. These streaks flow downhill in Martian summer, when the temperature is above −23 °C, and freeze at lower temperatures. These observations supported earlier hypotheses, based on timing of formation and their rate of growth, that these dark streaks resulted from water flowing just below

3772-415: The asteroid belt , so it has an increased chance of being struck by materials from that source. Mars is more likely to be struck by short-period comets , i.e. , those that lie within the orbit of Jupiter . Martian craters can have a morphology that suggests the ground became wet after the meteor impact. The large canyon, Valles Marineris (Latin for " Mariner Valleys", also known as Agathodaemon in

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3864-469: The possible presence of water oceans . The Hesperian period (3.5 to 3.3–2.9 billion years ago) was dominated by widespread volcanic activity and flooding that carved immense outflow channels . The Amazonian period, which continues to the present, has been marked by the wind as a dominant influence on geological processes . Due to Mars's geological history, the possibility of past or present life on Mars remains of great scientific interest. Since

3956-524: The 2020s no such mission is planned. Scientists have theorized that during the Solar System's formation , Mars was created as the result of a random process of run-away accretion of material from the protoplanetary disk that orbited the Sun. Mars has many distinctive chemical features caused by its position in the Solar System. Elements with comparatively low boiling points, such as chlorine , phosphorus , and sulfur , are much more common on Mars than on Earth; these elements were probably pushed outward by

4048-591: The Late Heavy Bombardment. There is evidence of an enormous impact basin in the Northern Hemisphere of Mars, spanning 10,600 by 8,500 kilometres (6,600 by 5,300 mi), or roughly four times the size of the Moon's South Pole–Aitken basin , which would be the largest impact basin yet discovered if confirmed. It has been hypothesized that the basin was formed when Mars was struck by a Pluto -sized body about four billion years ago. The event, thought to be

4140-478: The Martian ionosphere , lowering the atmospheric density by stripping away atoms from the outer layer. Both Mars Global Surveyor and Mars Express have detected ionized atmospheric particles trailing off into space behind Mars, and this atmospheric loss is being studied by the MAVEN orbiter. Compared to Earth, the atmosphere of Mars is quite rarefied. Atmospheric pressure on the surface today ranges from

4232-538: The Martian sky a tawny color when seen from the surface. It may take on a pink hue due to iron oxide particles suspended in it. The concentration of methane in the Martian atmosphere fluctuates from about 0.24 ppb during the northern winter to about 0.65 ppb during the summer. Estimates of its lifetime range from 0.6 to 4 years, so its presence indicates that an active source of the gas must be present. Methane could be produced by non-biological process such as serpentinization involving water, carbon dioxide, and

4324-415: The Martian surface is caused by ferric oxide , or rust . It can look like butterscotch ; other common surface colors include golden, brown, tan, and greenish, depending on the minerals present. Like Earth, Mars is differentiated into a dense metallic core overlaid by less dense rocky layers. The outermost layer is the crust, which is on average about 42–56 kilometres (26–35 mi) thick, with

4416-542: The Moon, Johann Heinrich von Mädler and Wilhelm Beer were the first areographers. They began by establishing that most of Mars's surface features were permanent and by more precisely determining the planet's rotation period. In 1840, Mädler combined ten years of observations and drew the first map of Mars. Features on Mars are named from a variety of sources. Albedo features are named for classical mythology. Craters larger than roughly 50 km are named for deceased scientists and writers and others who have contributed to

4508-464: The Qaidam Basin proper from that of Qinghai Lake to the east. Despite this lower elevation, Qaidam is still high enough that its mean annual temperature is 2–4 °C (36–39 °F) despite lying on the same latitude as Algeria , Greece , and Virginia in the United States . The crescent-shaped basin covers an area of approximately 120,000 km (46,000 sq mi). Its substrate

4600-523: The Qarhan was cut off from sufficient inflows of fresh water. It became saline again, beginning to precipitate salts about 25,000 years ago. The basin's continuing formation and evolution is controlled by the Altyn Tagh fault constituting the northern basin boundary. The basin's large mineral deposits caused a great deal of investment interest from 2005. Qarhan Playa , a salt flat including about ten of

4692-462: The area of Europe, Asia, and Australia combined, surpassing Utopia Planitia and the Moon's South Pole–Aitken basin as the largest impact crater in the Solar System. Mars is scarred by a number of impact craters: a total of 43,000 observed craters with a diameter of 5 kilometres (3.1 mi) or greater have been found. The largest exposed crater is Hellas , which is 2,300 kilometres (1,400 mi) wide and 7,000 metres (23,000 ft) deep, and

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4784-419: The atmosphere is about 10.8 kilometres (6.7 mi), which is higher than Earth's 6 kilometres (3.7 mi), because the surface gravity of Mars is only about 38% of Earth's. The atmosphere of Mars consists of about 96% carbon dioxide , 1.93% argon and 1.89% nitrogen along with traces of oxygen and water. The atmosphere is quite dusty, containing particulates about 1.5 μm in diameter which give

4876-406: The atmosphere is small, but enough to produce larger clouds of water ice and different cases of snow and frost , often mixed with snow of carbon dioxide dry ice . Landforms visible on Mars strongly suggest that liquid water has existed on the planet's surface. Huge linear swathes of scoured ground, known as outflow channels , cut across the surface in about 25 places. These are thought to be

4968-661: The basin, another reckoned 43 with a total area of 16,509 km (6,374 sq mi). The aridity, salinity, wide diurnal and seasonal temperature swings, and relatively high ultraviolet radiation has led to Qaidam being studied by the China Geological Survey as a Mars analogue for use in testing spectroscopy and equipment for China's 2020 Mars rover program . Qaidam was part of the North China Craton from at least 1 billion years ago, before breaking off c.  560 million years ago at

5060-467: The broken fragments of "Tintina" rock and "Sutton Inlier" rock as well as in veins and nodules in other rocks like "Knorr" rock and "Wernicke" rock . Analysis using the rover's DAN instrument provided evidence of subsurface water, amounting to as much as 4% water content, down to a depth of 60 centimetres (24 in), during the rover's traverse from the Bradbury Landing site to

5152-466: The cause of the Martian hemispheric dichotomy , created the smooth Borealis basin that covers 40% of the planet. A 2023 study shows evidence, based on the orbital inclination of Deimos (a small moon of Mars), that Mars may once have had a ring system 3.5 billion years to 4 billion years ago. This ring system may have been formed from a moon, 20 times more massive than Phobos , orbiting Mars billions of years ago; and Phobos would be

5244-458: The edges of boulders and other obstacles in their path. The commonly accepted hypotheses include that they are dark underlying layers of soil revealed after avalanches of bright dust or dust devils . Several other explanations have been put forward, including those that involve water or even the growth of organisms. Environmental radiation levels on the surface are on average 0.64 millisieverts of radiation per day, and significantly less than

5336-617: The end of the Neoproterozoic . It was an island in a shallow sea until uplift beginning around 400   Ma finally rejoined it to the mainland by 200   Ma. Three-dimensional modeling shows that the present basin has been squeezed to an irregular diamond shape since the beginning of the Cenozoic , with the Indian Plate beginning to impact the ancient Tibetan shoreline somewhere between 55–35   Ma. At first, Qaidam

5428-502: The enormous lake which filled much of the southeastern basin alternated nine times between being a fresh- and saltwater lake. Pollen studies suggest the bed of Dabusun Lake in the Qarhan Playa—nearly the lowest point of the basin—was elevated about 700 m (2,300 ft) within the last 500,000 years. At around 30 kya , this great—at the time, freshwater—lake spread over at least 25,000 km (9,700 sq mi) with

5520-413: The entire basin, the mean annual rainfall is 26 mm (1 in) but the mean annual evaporation is 3,000–3,200 mm (120–130 in). Because of the low rainfall, these lakes have become saline or dried up completely. Presently, there are four main playas in the basin: Qarhan in the southeast and (from north to south) Kunteyi , Chahanshilatu , and Dalangtan in the northwest. These playas and

5612-429: The flanks of the volcano Arsia Mons . The caves, named after loved ones of their discoverers, are collectively known as the "seven sisters". Cave entrances measure from 100 to 252 metres (328 to 827 ft) wide and they are estimated to be at least 73 to 96 metres (240 to 315 ft) deep. Because light does not reach the floor of most of the caves, they may extend much deeper than these lower estimates and widen below

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5704-700: The lakes, contains over 50 billion metric tons (55 billion short tons) of salt . Beneath the salt, Qaidam is one of China's nine most important petroliferous basins and its largest center of onshore production. The Qinghai Oilfield, exploited since 1954, includes the Lenghu, Gasikule, Yuejin-2, and Huatugou oil fields and the Sebei-1, Sebei-2, and Tainan gas fields. All together, it has proven reserves of 347.65 million metric tons (more than 2 billion barrels ) of petroleum and 306.6 billion cubic meters (10.83 trillion cubic feet) of natural gas . Annual production capacity

5796-436: The lander showed that the Martian soil has a basic pH of 7.7, and contains 0.6% perchlorate by weight, concentrations that are toxic to humans . Streaks are common across Mars and new ones appear frequently on steep slopes of craters, troughs, and valleys. The streaks are dark at first and get lighter with age. The streaks can start in a tiny area, then spread out for hundreds of metres. They have been seen to follow

5888-567: The late 20th century, Mars has been explored by uncrewed spacecraft and rovers , with the first flyby by the Mariner 4 probe in 1965, the first orbit by the Mars 2 probe in 1971, and the first landing by the Viking 1 probe in 1976. As of 2023, there are at least 11 active probes orbiting Mars or on the Martian surface. Mars is an attractive target for future human exploration missions , though in

5980-418: The mineral jarosite . This forms only in the presence of acidic water, showing that water once existed on Mars. The Spirit rover found concentrated deposits of silica in 2007 that indicated wet conditions in the past, and in December 2011, the mineral gypsum , which also forms in the presence of water, was found on the surface by NASA's Mars rover Opportunity. It is estimated that the amount of water in

6072-613: The mineral olivine , which is known to be common on Mars, or by Martian life. Compared to Earth, its higher concentration of atmospheric CO 2 and lower surface pressure may be why sound is attenuated more on Mars, where natural sources are rare apart from the wind. Using acoustic recordings collected by the Perseverance rover, researchers concluded that the speed of sound there is approximately 240 m/s for frequencies below 240 Hz, and 250 m/s for those above. Auroras have been detected on Mars. Because Mars lacks

6164-427: The mountain is so large, with complex structure at its edges, giving a definite height to it is difficult. Its local relief, from the foot of the cliffs which form its northwest margin to its peak, is over 21 km (13 mi), a little over twice the height of Mauna Kea as measured from its base on the ocean floor. The total elevation change from the plains of Amazonis Planitia , over 1,000 km (620 mi) to

6256-431: The movement of dry dust. No partially degraded gullies have formed by weathering and no superimposed impact craters have been observed, indicating that these are young features, possibly still active. Other geological features, such as deltas and alluvial fans preserved in craters, are further evidence for warmer, wetter conditions at an interval or intervals in earlier Mars history. Such conditions necessarily require

6348-574: The name of its northern escarpment, the Qilian or Nanshan. In the northwest, the Altyn-Tagh separates it from the Kumtagh Desert of southeastern Xinjiang . Because of this position, Qaidam forms an endorheic basin accumulating lakes with no outlet to the sea. The area is among the most arid non-polar locations on Earth, with some places reporting an aridity index of 0.008–0.04. Across

6440-514: The northwest, to the summit approaches 26 km (16 mi), roughly three times the height of Mount Everest , which in comparison stands at just over 8.8 kilometres (5.5 mi). Consequently, Olympus Mons is either the tallest or second-tallest mountain in the Solar System ; the only known mountain which might be taller is the Rheasilvia peak on the asteroid Vesta , at 20–25 km (12–16 mi). The dichotomy of Martian topography

6532-468: The old canal maps ), has a length of 4,000 kilometres (2,500 mi) and a depth of up to 7 kilometres (4.3 mi). The length of Valles Marineris is equivalent to the length of Europe and extends across one-fifth the circumference of Mars. By comparison, the Grand Canyon on Earth is only 446 kilometres (277 mi) long and nearly 2 kilometres (1.2 mi) deep. Valles Marineris was formed due to

6624-842: The past. This paleomagnetism of magnetically susceptible minerals is similar to the alternating bands found on Earth's ocean floors . One hypothesis, published in 1999 and re-examined in October ;2005 (with the help of the Mars Global Surveyor ), is that these bands suggest plate tectonic activity on Mars four billion years ago, before the planetary dynamo ceased to function and the planet's magnetic field faded. The Phoenix lander returned data showing Martian soil to be slightly alkaline and containing elements such as magnesium , sodium , potassium and chlorine . These nutrients are found in soils on Earth. They are necessary for growth of plants. Experiments performed by

6716-566: The radiation of 1.84 millisieverts per day or 22 millirads per day during the flight to and from Mars. For comparison the radiation levels in low Earth orbit , where Earth's space stations orbit, are around 0.5 millisieverts of radiation per day. Hellas Planitia has the lowest surface radiation at about 0.342 millisieverts per day, featuring lava tubes southwest of Hadriacus Mons with potentially levels as low as 0.064 millisieverts per day, comparable to radiation levels during flights on Earth. Although better remembered for mapping

6808-424: The root letter (forming a "stack"). The Wylie system does not normally distinguish these as in practice no ambiguity is possible under the rules of Tibetan spelling. The exception is the sequence gy- , which may be written either with a prefix g or a subfix y . In the Wylie system, these are distinguished by inserting a period between a prefix g and initial y . E.g. གྱང "wall" is gyang , while གཡང་ "chasm"

6900-651: The same name was formerly romanized as the Zaidam Swamp for the Chinese Postal Map . Orographically , the Qaidam Basin is a comparatively low area in the northeastern part of the Qinghai–Tibet Plateau . With an elevation of around 3,000 m (10,000 ft), Qaidam forms a kind of shelf between Tibet to the south (around 4,300 m or 14,000 ft) and Gansu to the north (around 1,100 m or 3,500 ft). A low water divide separates

6992-467: The size of Earth's Arctic Ocean . This finding was derived from the ratio of protium to deuterium in the modern Martian atmosphere compared to that ratio on Earth. The amount of Martian deuterium (D/H = 9.3 ± 1.7 10 ) is five to seven times the amount on Earth (D/H = 1.56 10 ), suggesting that ancient Mars had significantly higher levels of water. Results from the Curiosity rover had previously found

7084-497: The sounds of spoken Tibetan or the spelling of written Tibetan. These differ widely, as Tibetan orthography became fixed in the 11th century, while pronunciation continued to evolve , comparable to the English orthography and French orthography , which reflect late medieval pronunciation. Previous transcription schemes sought to split the difference with the result that they achieved neither goal perfectly. Wylie transliteration

7176-422: The south polar ice cap, if melted, would be enough to cover most of the surface of the planet with a depth of 11 metres (36 ft). Water in its liquid form cannot prevail on the surface of Mars due to the low atmospheric pressure on Mars, which is less than 1% that of Earth, only at the lowest of elevations pressure and temperature is high enough for water being able to be liquid for short periods. Water in

7268-461: The southern highlands include detectable amounts of high-calcium pyroxenes . Localized concentrations of hematite and olivine have been found. Much of the surface is deeply covered by finely grained iron(III) oxide dust. Although Mars has no evidence of a structured global magnetic field , observations show that parts of the planet's crust have been magnetized, suggesting that alternating polarity reversals of its dipole field have occurred in

7360-505: The study of Mars. Smaller craters are named for towns and villages of the world with populations of less than 100,000. Large valleys are named for the word "Mars" or "star" in various languages; smaller valleys are named for rivers. Large albedo features retain many of the older names but are often updated to reflect new knowledge of the nature of the features. For example, Nix Olympica (the snows of Olympus) has become Olympus Mons (Mount Olympus). The surface of Mars as seen from Earth

7452-513: The surface. However, later work suggested that the lineae may be dry, granular flows instead, with at most a limited role for water in initiating the process. A definitive conclusion about the presence, extent, and role of liquid water on the Martian surface remains elusive. Researchers suspect much of the low northern plains of the planet were covered with an ocean hundreds of meters deep, though this theory remains controversial. In March 2015, scientists stated that such an ocean might have been

7544-430: The surface. "Dena" is the only exception; its floor is visible and was measured to be 130 metres (430 ft) deep. The interiors of these caverns may be protected from micrometeoroids, UV radiation, solar flares and high energy particles that bombard the planet's surface. Mars lost its magnetosphere 4 billion years ago, possibly because of numerous asteroid strikes, so the solar wind interacts directly with

7636-625: The swelling of the Tharsis area, which caused the crust in the area of Valles Marineris to collapse. In 2012, it was proposed that Valles Marineris is not just a graben , but a plate boundary where 150 kilometres (93 mi) of transverse motion has occurred, making Mars a planet with possibly a two- tectonic plate arrangement. Images from the Thermal Emission Imaging System (THEMIS) aboard NASA's Mars Odyssey orbiter have revealed seven possible cave entrances on

7728-507: The upper mantle of Mars, represented by hydroxyl ions contained within Martian minerals, is equal to or greater than that of Earth at 50–300 parts per million of water, which is enough to cover the entire planet to a depth of 200–1,000 metres (660–3,280 ft). On 18 March 2013, NASA reported evidence from instruments on the Curiosity rover of mineral hydration , likely hydrated calcium sulfate , in several rock samples including

7820-420: The widespread presence of crater lakes across a large proportion of the surface, for which there is independent mineralogical, sedimentological and geomorphological evidence. Further evidence that liquid water once existed on the surface of Mars comes from the detection of specific minerals such as hematite and goethite , both of which sometimes form in the presence of water. In 2004, Opportunity detected

7912-414: The young Sun's energetic solar wind . After the formation of the planets, the inner Solar System may have been subjected to the so-called Late Heavy Bombardment . About 60% of the surface of Mars shows a record of impacts from that era, whereas much of the remaining surface is probably underlain by immense impact basins caused by those events. However, more recent modeling has disputed the existence of

8004-456: Was among the largest lakes in the world . Nutrient-rich inflows contributed to plankton blooms, which supported an ecosystem that built up reserves of organic carbon. The Tibetan plateau's uplift, however, eventually cut it off from the warm and humid Indian monsoon . It went from a forest steppe to a desert . By 12   Ma, the climate had dried enough to break Qaidam's single lake into separate basins, which frequently became saline. During

8096-557: Was at a far lower elevation. Pollen found in core samples shows that the Oligocene (34–23   Ma) was relatively humid. A great lake slowly formed in the western basin, which two major tectonic movements raised and cut off from its original sources of sediment. At its greatest extent during the Miocene (23–5   Ma), this lake spread at the present 2,800 m (9,200 ft) elevation contour over 300 km (190 mi) and

8188-437: Was designed to precisely transcribe Tibetan script as written , which led to its acceptance in academic and historical studies. It is not intended to represent the pronunciation of Tibetan words. The Wylie scheme transliterates the Tibetan characters as follows: In Tibetan script, consonant clusters within a syllable may be represented through the use of prefixed or suffixed letters or by letters superscripted or subscripted to

8280-416: Was overly cumbersome, of limited usefulness in determining pronunciation, and probably superfluous to a reader able to use a Tibetan dictionary, Wylie specified that if a word was to be capitalised, the first letter should be capital, in conformity with Western capitalisation practices. Thus a particular Tibetan Buddhist sect ( Kagyu ) is capitalised Bka' brgyud and not bKa' brgyud . Wylie's original scheme

8372-629: Was probably the root cause of the incision in almost all cases. Along craters and canyon walls, there are thousands of features that appear similar to terrestrial gullies . The gullies tend to be in the highlands of the Southern Hemisphere and face the Equator; all are poleward of 30° latitude. A number of authors have suggested that their formation process involves liquid water, probably from melting ice, although others have argued for formation mechanisms involving carbon dioxide frost or

8464-437: Was reported that InSight had detected and recorded over 450 marsquakes and related events. Beneath the crust is a silicate mantle responsible for many of the tectonic and volcanic features on the planet's surface. The upper Martian mantle is a low-velocity zone , where the velocity of seismic waves is lower than surrounding depth intervals. The mantle appears to be rigid down to the depth of about 250 km, giving Mars

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