Mars

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This article is about the planet. Mars_sentence_0

For the deity, see Mars (mythology). Mars_sentence_1

For other uses, see Mars (disambiguation). Mars_sentence_2

Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, being larger than only Mercury. Mars_sentence_3

In English, Mars carries the name of the Roman god of war and is often referred to as the "Red Planet". Mars_sentence_4

The latter refers to the effect of the iron oxide prevalent on Mars's surface, which gives it a reddish appearance distinctive among the astronomical bodies visible to the naked eye. Mars_sentence_5

Mars is a terrestrial planet with a thin atmosphere, with surface features reminiscent of the impact craters of the Moon and the valleys, deserts and polar ice caps of Earth. Mars_sentence_6

The days and seasons are comparable to those of Earth, because the rotational period as well as the tilt of the rotational axis relative to the ecliptic plane are similar. Mars_sentence_7

Mars is the site of Olympus Mons, the largest volcano and highest known mountain on any planet in the Solar System, and of Valles Marineris, one of the largest canyons in the Solar System. Mars_sentence_8

The smooth Borealis basin in the northern hemisphere covers 40% of the planet and may be a giant impact feature. Mars_sentence_9

Mars has two moons, Phobos and Deimos, which are small and irregularly shaped. Mars_sentence_10

These may be captured asteroids, similar to 5261 Eureka, a Mars trojan. Mars_sentence_11

Mars has been explored by several uncrewed spacecraft. Mars_sentence_12

Mariner 4 was the first spacecraft to visit Mars; launched by NASA on 28 November 1964, it made its closest approach to the planet on 15 July 1965. Mars_sentence_13

Mariner 4 detected the weak Martian radiation belt, measured at about 0.1% that of Earth, and captured the first images of another planet from deep space. Mars_sentence_14

The Soviet Mars 3 mission included a lander, which achieved a soft landing in December 1971; however, contact was lost seconds after touchdown. Mars_sentence_15

On 20 July 1976, Viking 1 performed the first successful landing on the Martian surface. Mars_sentence_16

On 4 July 1997, the Mars Pathfinder spacecraft landed on Mars and on 5 July released its rover, Sojourner, the first robotic rover to operate on Mars. Mars_sentence_17

The Mars Express orbiter, the first European Space Agency (ESA) spacecraft to visit Mars, arrived in orbit on 25 December 2003. Mars_sentence_18

In January 2004, the Mars Exploration Rovers, named Spirit and Opportunity, both landed on Mars. Mars_sentence_19

Spirit operated until 22 March 2010 and Opportunity lasted until 10 June 2018. Mars_sentence_20

On 24 September 2014, the Indian Space Research Organisation (ISRO) became the fourth space agency to visit Mars when its maiden interplanetary mission, the Mars Orbiter Mission spacecraft, arrived in orbit. Mars_sentence_21

There are investigations assessing the past habitability of Mars, as well as the possibility of extant life. Mars_sentence_22

Astrobiology missions are planned, including the Perseverance and Rosalind Franklin rovers. Mars_sentence_23

Liquid water on the surface of Mars cannot exist due to low atmospheric pressure, which is less than 1% of the atmospheric pressure on Earth, except at the lowest elevations for short periods. Mars_sentence_24

The two polar ice caps appear to be made largely of water. Mars_sentence_25

The volume of water ice in the south polar ice cap, if melted, would be sufficient to cover the planetary surface to a depth of 11 metres (36 ft). Mars_sentence_26

In November 2016, NASA reported finding a large amount of underground ice in the Utopia Planitia region. Mars_sentence_27

The volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior. Mars_sentence_28

Mars can easily be seen from Earth with the naked eye, as can its reddish coloring. Mars_sentence_29

Its apparent magnitude reaches −2.94, which is surpassed only by Venus, the Moon and the Sun. Mars_sentence_30

Optical ground-based telescopes are typically limited to resolving features about 300 kilometres (190 mi) across when Earth and Mars are closest because of Earth's atmosphere. Mars_sentence_31

Names Mars_section_0

In English, the planet is named for the Roman god of war, an association made because of its red color, which suggests blood. Mars_sentence_32

The adjectival form of Latin Mars is Martius, which provides the English words Martian, used as an adjective or for a putative inhabitant of Mars, and Martial, used as an adjective corresponding to Terrestrial for Earth. Mars_sentence_33

In Greek, the planet is known as Ἄρης Arēs, with the inflectional stem Ἄρε- Are-. Mars_sentence_34

From this come technical terms such as areology, as well as the adjective Arean and the star name Antares. Mars_sentence_35

'Mars' is also the basis of the name of the month of March (from Latin Martius mēnsis 'month of Mars'), as well as (through loan-translation) of Tuesday (Latin dies Martis 'day of Mars'), where the old Anglo-Saxon god Tíw was identified with Roman Mars. Mars_sentence_36

The archaic Latin form Māvors (/ˈmeɪvɔːrz/) is very occasionally seen in English, though the adjectives Mavortial and Mavortian mean 'martial' in the military rather than planetary sense. Mars_sentence_37

Due to the global influence of European languages, a word like Mars or Marte for the planet is common around the world, though it may be used alongside older, native words. Mars_sentence_38

A number of other languages have provided words with international usage. Mars_sentence_39

For example, Arabic مريخ mirrīkh – which has connotations of fire – is used as the (or a) name for the planet in Persian, Urdu, Malay and Swahili, among others, while Chinese 火星 [Mandarin Huǒxīng] 'fire star' (for in Chinese the five classical planets are identified with the five elements) is used in Korean, Japanese and Vietnamese. Mars_sentence_40

India uses the Sanskrit term Mangal derived from the Hindu goddess Mangala. Mars_sentence_41

A long-standing nickname for Mars is the "Red Planet". Mars_sentence_42

That is also the planet's name in Hebrew, מאדים ma'adim, which is derived from אדום adom, meaning 'red'. Mars_sentence_43

Physical characteristics Mars_section_1

Mars is approximately half the diameter of Earth, with a surface area only slightly less than the total area of Earth's dry land. Mars_sentence_44

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_sentence_45

The red-orange appearance of the Martian surface is caused by iron(III) oxide, or rust. Mars_sentence_46

It can look like butterscotch; other common surface colors include golden, brown, tan, and greenish, depending on the minerals present. Mars_sentence_47

Internal structure Mars_section_2

Like Earth, Mars has differentiated into a dense metallic core overlaid by less dense materials. Mars_sentence_48

Current models of its interior imply a core with a radius of about 1,794 ± 65 kilometres (1,115 ± 40 mi), consisting primarily of iron and nickel with about 16–17% sulfur. Mars_sentence_49

This iron(II) sulfide core is thought to be twice as rich in lighter elements as Earth's. Mars_sentence_50

The core is surrounded by a silicate mantle that formed many of the tectonic and volcanic features on the planet, but it appears to be dormant. Mars_sentence_51

Besides silicon and oxygen, the most abundant elements in the Martian crust are iron, magnesium, aluminium, calcium, and potassium. Mars_sentence_52

The average thickness of the planet's crust is about 50 kilometres (31 mi), with a maximum thickness of 125 kilometres (78 mi). Mars_sentence_53

Earth's crust averages 40 kilometres (25 mi). Mars_sentence_54

Mars is seismically active, with InSight recording over 450 marsquakes and related events in 2019. Mars_sentence_55

Surface geology Mars_section_3

Main article: Geology of Mars Mars_sentence_56

Mars is a terrestrial planet that consists of minerals containing silicon and oxygen, metals, and other elements that typically make up rock. Mars_sentence_57

The surface of Mars 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. Mars_sentence_58

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. Mars_sentence_59

Parts of the southern highlands include detectable amounts of high-calcium pyroxenes. Mars_sentence_60

Localized concentrations of hematite and olivine have been found. Mars_sentence_61

Much of the surface is deeply covered by finely grained iron(III) oxide dust. Mars_sentence_62

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 the past. Mars_sentence_63

This paleomagnetism of magnetically susceptible minerals is similar to the alternating bands found on Earth's ocean floors. Mars_sentence_64

One theory, 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. Mars_sentence_65

It is thought that, during the Solar System's formation, Mars was created as the result of a stochastic process of run-away accretion of material from the protoplanetary disk that orbited the Sun. Mars_sentence_66

Mars has many distinctive chemical features caused by its position in the Solar System. Mars_sentence_67

Elements with comparatively low boiling points, such as chlorine, phosphorus, and sulphur, are much more common on Mars than Earth; these elements were probably pushed outward by the young Sun's energetic solar wind. Mars_sentence_68

After the formation of the planets, all were subjected to the so-called "Late Heavy Bombardment". Mars_sentence_69

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. Mars_sentence_70

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, the largest impact basin yet discovered. Mars_sentence_71

This theory suggests that Mars was struck by a Pluto-sized body about four billion years ago. Mars_sentence_72

The event, thought to be the cause of the Martian hemispheric dichotomy, created the smooth Borealis basin that covers 40% of the planet. Mars_sentence_73

The geological history of Mars can be split into many periods, but the following are the three primary periods: Mars_sentence_74

Mars_unordered_list_0

  • Noachian period (named after Noachis Terra): Formation of the oldest extant surfaces of Mars, 4.5 to 3.5 billion years ago. Noachian age surfaces are scarred by many large impact craters. The Tharsis bulge, a volcanic upland, is thought to have formed during this period, with extensive flooding by liquid water late in the period.Mars_item_0_0
  • Hesperian period (named after Hesperia Planum): 3.5 to between 3.3 and 2.9 billion years ago. The Hesperian period is marked by the formation of extensive lava plains.Mars_item_0_1
  • Amazonian period (named after Amazonis Planitia): between 3.3 and 2.9 billion years ago to the present. Amazonian regions have few meteorite impact craters, but are otherwise quite varied. Olympus Mons formed during this period, with lava flows elsewhere on Mars.Mars_item_0_2

Geological activity is still taking place on Mars. Mars_sentence_75

The Athabasca Valles is home to sheet-like lava flows created about 200 Mya. Mars_sentence_76

Water flows in the grabens called the Cerberus Fossae occurred less than 20 Mya, indicating equally recent volcanic intrusions. Mars_sentence_77

On 19 February 2008, images from the Mars Reconnaissance Orbiter showed evidence of an avalanche from a 700-metre-high (2,300 ft) cliff. Mars_sentence_78

Soil Mars_section_4

Main article: Martian soil Mars_sentence_79

The Phoenix lander returned data showing Martian soil to be slightly alkaline and containing elements such as magnesium, sodium, potassium and chlorine. Mars_sentence_80

These nutrients are found in soils on Earth, and they are necessary for growth of plants. Mars_sentence_81

Experiments performed by the lander showed that the Martian soil has a basic pH of 7.7, and contains 0.6% of the salt perchlorate. Mars_sentence_82

This is a very high concentration and makes the Martian soil toxic (see also Martian soil toxicity). Mars_sentence_83

Streaks are common across Mars and new ones appear frequently on steep slopes of craters, troughs, and valleys. Mars_sentence_84

The streaks are dark at first and get lighter with age. Mars_sentence_85

The streaks can start in a tiny area, then spread out for hundreds of metres. Mars_sentence_86

They have been seen to follow the edges of boulders and other obstacles in their path. Mars_sentence_87

The commonly accepted theories include that they are dark underlying layers of soil revealed after avalanches of bright dust or dust devils. Mars_sentence_88

Several other explanations have been put forward, including those that involve water or even the growth of organisms. Mars_sentence_89

Hydrology Mars_section_5

Main article: Water on Mars Mars_sentence_90

Liquid water cannot exist on the surface of Mars due to low atmospheric pressure, which is less than 1% that of Earth's, except at the lowest elevations for short periods. Mars_sentence_91

The two polar ice caps appear to be made largely of water. Mars_sentence_92

The volume of water ice in the south polar ice cap, if melted, would be sufficient to cover the entire planetary surface to a depth of 11 metres (36 ft). Mars_sentence_93

A permafrost mantle stretches from the pole to latitudes of about 60°. Mars_sentence_94

Large quantities of ice are thought to be trapped within the thick cryosphere of Mars. Mars_sentence_95

Radar data from Mars Express and the Mars Reconnaissance Orbiter (MRO) show large quantities of ice at both poles (July 2005) and at middle latitudes (November 2008). Mars_sentence_96

The Phoenix lander directly sampled water ice in shallow Martian soil on 31 July 2008. Mars_sentence_97

Landforms visible on Mars strongly suggest that liquid water has existed on the planet's surface. Mars_sentence_98

Huge linear swathes of scoured ground, known as outflow channels, cut across the surface in about 25 places. Mars_sentence_99

These are thought to be 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. Mars_sentence_100

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. Mars_sentence_101

It is thought to have been carved by flowing water early in Mars's history. Mars_sentence_102

The youngest of these channels are thought to have formed as recently as only a few million years ago. Mars_sentence_103

Elsewhere, particularly on the oldest areas of the Martian surface, finer-scale, dendritic networks of valleys are spread across significant proportions of the landscape. Mars_sentence_104

Features of these valleys and their distribution strongly imply that they were carved by runoff resulting from precipitation in early Mars history. Mars_sentence_105

Subsurface water flow and groundwater sapping may play important subsidiary roles in some networks, but precipitation was probably the root cause of the incision in almost all cases. Mars_sentence_106

Along crater and canyon walls, there are thousands of features that appear similar to terrestrial gullies. Mars_sentence_107

The gullies tend to be in the highlands of the southern hemisphere and to face the Equator; all are poleward of 30° latitude. Mars_sentence_108

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 the movement of dry dust. Mars_sentence_109

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. Mars_sentence_110

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. Mars_sentence_111

Such conditions necessarily require the widespread presence of crater lakes across a large proportion of the surface, for which there is independent mineralogical, sedimentological and geomorphological evidence. Mars_sentence_112

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. Mars_sentence_113

In 2004, Opportunity detected the mineral jarosite. Mars_sentence_114

This forms only in the presence of acidic water, which demonstrates that water once existed on Mars. Mars_sentence_115

More recent evidence for liquid water comes from the finding of the mineral gypsum on the surface by NASA's Mars rover Opportunity in December 2011. Mars_sentence_116

It is estimated that the amount of water in the upper mantle of Mars, represented by hydroxyl ions contained within the minerals of Mars's geology, 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). Mars_sentence_117

In 2005, radar data revealed the presence of large quantities of water ice at the poles and at mid-latitudes. Mars_sentence_118

The Mars rover Spirit sampled chemical compounds containing water molecules in March 2007. Mars_sentence_119

The Phoenix lander directly sampled water ice in shallow Martian soil on 31 July 2008. Mars_sentence_120

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 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. Mars_sentence_121

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 the Yellowknife Bay area in the Glenelg terrain. Mars_sentence_122

In September 2015, NASA announced that they had found conclusive evidence of hydrated brine flows on recurring slope lineae, based on spectrometer readings of the darkened areas of slopes. Mars_sentence_123

These observations provided confirmation of earlier hypotheses based on timing of formation and their rate of growth, that these dark streaks resulted from water flowing in the very shallow subsurface. Mars_sentence_124

The streaks contain hydrated salts, perchlorates, which have water molecules in their crystal structure. Mars_sentence_125

The streaks flow downhill in Martian summer, when the temperature is above −23° Celsius, and freeze at lower temperatures. Mars_sentence_126

Researchers suspect that much of the low northern plains of the planet were covered with an ocean hundreds of meters deep, though this remains controversial. Mars_sentence_127

In March 2015, scientists stated that such an ocean might have been the size of Earth's Arctic Ocean. Mars_sentence_128

This finding was derived from the ratio of water to deuterium in the modern Martian atmosphere compared to that ratio on Earth. Mars_sentence_129

The amount of Martian deuterium is eight times the amount that exists on Earth, suggesting that ancient Mars had significantly higher levels of water. Mars_sentence_130

Results from the Curiosity rover had previously found a high ratio of deuterium in Gale Crater, though not significantly high enough to suggest the former presence of an ocean. Mars_sentence_131

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. Mars_sentence_132

Near the northern polar cap is the 81.4 kilometres (50.6 mi) wide Korolev Crater, where the Mars Express orbiter found it to be filled with approximately 2,200 cubic kilometres (530 cu mi) of water ice. Mars_sentence_133

The crater floor lies about 2 kilometres (1.2 mi) below the rim, and is covered by a 1.8 kilometres (1.1 mi) deep central mound of permanent water ice, up to 60 kilometres (37 mi) in diameter. Mars_sentence_134

In February 2020, it was found that dark streaks called recurring slope lineae (RSL), which appear seasonably, are caused by briny water flowing for a few days annually. Mars_sentence_135

Polar caps Mars_section_6

Main article: Martian polar ice caps Mars_sentence_136

Mars has two permanent polar ice caps. Mars_sentence_137

During a pole's winter, it lies in continuous darkness, chilling the surface and causing the deposition of 25–30% of the atmosphere into slabs of CO2 ice (dry ice). Mars_sentence_138

When the poles are again exposed to sunlight, the frozen CO2 sublimes. Mars_sentence_139

These seasonal actions transport large amounts of dust and water vapor, giving rise to Earth-like frost and large cirrus clouds. Mars_sentence_140

Clouds of water-ice were photographed by the Opportunity rover in 2004. Mars_sentence_141

The caps at both poles consist primarily (70%) of water ice. Mars_sentence_142

Frozen carbon dioxide accumulates as a comparatively thin layer about one metre thick on the north cap in the northern winter only, whereas the south cap has a permanent dry ice cover about eight metres thick. Mars_sentence_143

This permanent dry ice cover at the south pole is peppered by flat floored, shallow, roughly circular pits, which repeat imaging shows are expanding by meters per year; this suggests that the permanent CO2 cover over the south pole water ice is degrading over time. Mars_sentence_144

The northern polar cap has a diameter of about 1,000 kilometres (620 mi) during the northern Mars summer, and contains about 1.6 million cubic kilometres (5.7×10 cu ft) of ice, which, if spread evenly on the cap, would be 2 kilometres (1.2 mi) thick. Mars_sentence_145

(This compares to a volume of 2.85 million cubic kilometres (1.01×10 cu ft) for the Greenland ice sheet.) Mars_sentence_146

The southern polar cap has a diameter of 350 kilometres (220 mi) and a thickness of 3 kilometres (1.9 mi). Mars_sentence_147

The total volume of ice in the south polar cap plus the adjacent layered deposits has been estimated at 1.6 million cubic km. Mars_sentence_148

Both polar caps show spiral troughs, which recent analysis of SHARAD ice penetrating radar has shown are a result of katabatic winds that spiral due to the Coriolis Effect. Mars_sentence_149

The seasonal frosting of areas near the southern ice cap results in the formation of transparent 1-metre-thick slabs of dry ice above the ground. Mars_sentence_150

With the arrival of spring, sunlight warms the subsurface and pressure from subliming CO2 builds up under a slab, elevating and ultimately rupturing it. Mars_sentence_151

This leads to geyser-like eruptions of CO2 gas mixed with dark basaltic sand or dust. Mars_sentence_152

This process is rapid, observed happening in the space of a few days, weeks or months, a rate of change rather unusual in geology – especially for Mars. Mars_sentence_153

The gas rushing underneath a slab to the site of a geyser carves a spiderweb-like pattern of radial channels under the ice, the process being the inverted equivalent of an erosion network formed by water draining through a single plughole. Mars_sentence_154

Geography and naming of surface features Mars_section_7

Main article: Geography of Mars Mars_sentence_155

Further information: Areoid Mars_sentence_156

See also: :Category:Surface features of Mars Mars_sentence_157

Although better remembered for mapping the Moon, Johann Heinrich Mädler and Wilhelm Beer were the first areographers. Mars_sentence_158

They began by establishing that most of Mars's surface features were permanent and by more precisely determining the planet's rotation period. Mars_sentence_159

In 1840, Mädler combined ten years of observations and drew the first map of Mars. Mars_sentence_160

Rather than giving names to the various markings, Beer and Mädler simply designated them with letters; Meridian Bay (Sinus Meridiani) was thus feature "a". Mars_sentence_161

Today, features on Mars are named from a variety of sources. Mars_sentence_162

Albedo features are named for classical mythology. Mars_sentence_163

Craters larger than 60 km are named for deceased scientists and writers and others who have contributed to the study of Mars. Mars_sentence_164

Craters smaller than 60 km are named for towns and villages of the world with populations of less than 100,000. Mars_sentence_165

Large valleys are named for the word "Mars" or "star" in various languages; small valleys are named for rivers. Mars_sentence_166

Large albedo features retain many of the older names, but are often updated to reflect new knowledge of the nature of the features. Mars_sentence_167

For example, Nix Olympica (the snows of Olympus) has become Olympus Mons (Mount Olympus). Mars_sentence_168

The surface of Mars as seen from Earth is divided into two kinds of areas, with differing albedo. Mars_sentence_169

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). Mars_sentence_170

The dark features were thought to be seas, hence their names Mare Erythraeum, Mare Sirenum and Aurorae Sinus. Mars_sentence_171

The largest dark feature seen from Earth is Syrtis Major Planum. Mars_sentence_172

The permanent northern polar ice cap is named Planum Boreum, whereas the southern cap is called Planum Australe. Mars_sentence_173

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. Mars_sentence_174

After the spacecraft Mariner 9 provided extensive imagery of Mars in 1972, a small crater (later called Airy-0), located in the Sinus Meridiani ("Middle Bay" or "Meridian Bay"), was chosen by Merton Davies of the Rand Corporation for the definition of 0.0° longitude to coincide with the original selection. Mars_sentence_175

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 the areoid of Mars, analogous to the terrestrial geoid. Mars_sentence_176

Zero altitude was defined by the height at which there is 610.5 Pa (6.105 mbar) of atmospheric pressure. Mars_sentence_177

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). Mars_sentence_178

Map of quadrangles Mars_section_8

Main article: List of quadrangles on Mars Mars_sentence_179

For mapping purposes, the United States Geological Survey divides the surface of Mars into thirty cartographic quadrangles, each named for a classical albedo feature it contains. Mars_sentence_180

The quadrangles can be seen and explored via the interactive image map below. Mars_sentence_181

Impact topography Mars_section_9

The dichotomy of Martian topography is striking: northern plains flattened by lava flows contrast with the southern highlands, pitted and cratered by ancient impacts. Mars_sentence_182

Research in 2008 has presented evidence regarding a theory proposed in 1980 postulating 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. Mars_sentence_183

If validated, this would make the northern hemisphere of Mars the site of an impact crater 10,600 by 8,500 kilometres (6,600 by 5,300 mi) in size, or roughly the area of Europe, Asia, and Australia combined, surpassing the South Pole–Aitken basin as the largest impact crater in the Solar System. Mars_sentence_184

Mars is scarred by a number of impact craters: a total of 43,000 craters with a diameter of 5 kilometres (3.1 mi) or greater have been found. Mars_sentence_185

The largest confirmed of these is the Hellas impact basin, a light albedo feature clearly visible from Earth. Mars_sentence_186

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_sentence_187

Mars is located closer to the asteroid belt, so it has an increased chance of being struck by materials from that source. Mars_sentence_188

Mars is more likely to be struck by short-period comets, i.e., those that lie within the orbit of Jupiter. Mars_sentence_189

In spite of this, there are far fewer craters on Mars compared with the Moon, because the atmosphere of Mars provides protection against small meteors and surface modifying processes have erased some craters. Mars_sentence_190

Martian craters can have a morphology that suggests the ground became wet after the meteor impacted. Mars_sentence_191

Volcanoes Mars_section_10

Main article: Volcanology of Mars Mars_sentence_192

The shield volcano Olympus Mons (Mount Olympus) is an extinct volcano in the vast upland region Tharsis, which contains several other large volcanoes. Mars_sentence_193

Olympus Mons is roughly three times the height of Mount Everest, which in comparison stands at just over 8.8 kilometres (5.5 mi). Mars_sentence_194

It is either the tallest or second-tallest mountain in the Solar System, depending on how it is measured, with various sources giving figures ranging from about 21 to 27 kilometres (13 to 17 mi) high. Mars_sentence_195

Tectonic sites Mars_section_11

The large canyon, Valles Marineris (Latin for "Mariner Valleys", also known as Agathadaemon in 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). Mars_sentence_196

The length of Valles Marineris is equivalent to the length of Europe and extends across one-fifth the circumference of Mars. Mars_sentence_197

By comparison, the Grand Canyon on Earth is only 446 kilometres (277 mi) long and nearly 2 kilometres (1.2 mi) deep. Mars_sentence_198

Valles Marineris was formed due to the swelling of the Tharsis area, which caused the crust in the area of Valles Marineris to collapse. Mars_sentence_199

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. Mars_sentence_200

Holes Mars_section_12

Images from the Thermal Emission Imaging System (THEMIS) aboard NASA's Mars Odyssey orbiter have revealed seven possible cave entrances on the flanks of the volcano Arsia Mons. Mars_sentence_201

The caves, named after loved ones of their discoverers, are collectively known as the "seven sisters". Mars_sentence_202

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. Mars_sentence_203

Because light does not reach the floor of most of the caves, it is possible that they extend much deeper than these lower estimates and widen below the surface. Mars_sentence_204

"Dena" is the only exception; its floor is visible and was measured to be 130 metres (430 ft) deep. Mars_sentence_205

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_sentence_206

Atmosphere Mars_section_13

Main article: Atmosphere of Mars Mars_sentence_207

Mars lost its magnetosphere 4 billion years ago, possibly because of numerous asteroid strikes, so the solar wind interacts directly with the Martian ionosphere, lowering the atmospheric density by stripping away atoms from the outer layer. Mars_sentence_208

Both Mars Global Surveyor and Mars Express have detected ionised atmospheric particles trailing off into space behind Mars, and this atmospheric loss is being studied by the MAVEN orbiter. Mars_sentence_209

Compared to Earth, the atmosphere of Mars is quite rarefied. Mars_sentence_210

Atmospheric pressure on the surface today ranges from 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). Mars_sentence_211

The highest atmospheric density on Mars is equal to that found 35 kilometres (22 mi) above Earth's surface. Mars_sentence_212

The resulting mean surface pressure is only 0.6% of that of Earth 101.3 kPa (14.69 psi). Mars_sentence_213

The scale height of 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, an effect offset by both the lower temperature and 50% higher average molecular weight of the atmosphere of Mars. Mars_sentence_214

The atmosphere of Mars consists of about 96% carbon dioxide, 1.93% argon and 1.89% nitrogen along with traces of oxygen and water. Mars_sentence_215

The atmosphere is quite dusty, containing particulates about 1.5 µm in diameter which give the Martian sky a tawny color when seen from the surface. Mars_sentence_216

It may take on a pink hue due to iron oxide particles suspended in it. Mars_sentence_217

Methane Mars_section_14

Main article: Methane on Mars Mars_sentence_218

Methane has been detected in the Martian atmosphere; it occurs in extended plumes, and the profiles imply that the methane is released from discrete regions. Mars_sentence_219

The concentration of methane fluctuates from about 0.24 ppb during the northern winter to about 0.65 ppb during the summer. Mars_sentence_220

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. Mars_sentence_221

Methane could be produced by non-biological process such as serpentinization involving water, carbon dioxide, and the mineral olivine, which is known to be common on Mars. Mars_sentence_222

Methanogenic microbial life forms in the subsurface are among possible sources. Mars_sentence_223

But even if rover missions determine that microscopic Martian life is the source of the methane, the life forms likely reside far below the surface, outside of the rover's reach. Mars_sentence_224

Aurora Mars_section_15

In 1994, the European Space Agency's Mars Express found an ultraviolet glow coming from "magnetic umbrellas" in the southern hemisphere. Mars_sentence_225

Mars does not have a global magnetic field which guides charged particles entering the atmosphere. Mars_sentence_226

Mars has multiple umbrella-shaped magnetic fields mainly in the southern hemisphere, which are remnants of a global field that decayed billions of years ago. Mars_sentence_227

In late December 2014, NASA's MAVEN spacecraft detected evidence of widespread auroras in Mars's northern hemisphere and descended to approximately 20–30° North latitude of Mars's equator. Mars_sentence_228

The particles causing the aurora penetrated into the Martian atmosphere, creating auroras below 100 km above the surface, Earth's auroras range from 100 km to 500 km above the surface. Mars_sentence_229

Magnetic fields in the solar wind drape over Mars, into the atmosphere, and the charged particles follow the solar wind magnetic field lines into the atmosphere, causing auroras to occur outside the magnetic umbrellas. Mars_sentence_230

On 18 March 2015, NASA reported the detection of an aurora that is not fully understood and an unexplained dust cloud in the atmosphere of Mars. Mars_sentence_231

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 a massive, and unexpected, solar storm in the middle of the month. Mars_sentence_232

Climate Mars_section_16

Main article: Climate of Mars Mars_sentence_233

Of all the planets in the Solar System, the seasons of Mars are the most Earth-like, due to the similar tilts of the two planets' rotational axes. Mars_sentence_234

The lengths of the Martian seasons are about twice those of Earth's because Mars's greater distance from the Sun leads to the Martian year being about two Earth years long. Mars_sentence_235

Martian surface temperatures vary from lows of about −143 °C (−225 °F) at the winter polar caps to highs of up to 35 °C (95 °F) in equatorial summer. Mars_sentence_236

The wide range in temperatures is due to the thin atmosphere which cannot store much solar heat, the low atmospheric pressure, and the low thermal inertia of Martian soil. Mars_sentence_237

The planet is 1.52 times as far from the Sun as Earth, resulting in just 43% of the amount of sunlight. Mars_sentence_238

If Mars had an Earth-like orbit, its seasons would be similar to Earth's because its axial tilt is similar to Earth's. Mars_sentence_239

The comparatively large eccentricity of the Martian orbit has a significant effect. Mars_sentence_240

Mars is near perihelion when it is summer in the southern hemisphere and winter in the north, and near aphelion when it is winter in the southern hemisphere and summer in the north. Mars_sentence_241

As a result, the seasons in the southern hemisphere are more extreme and the seasons in the northern are milder than would otherwise be the case. Mars_sentence_242

The summer temperatures in the south can be warmer than the equivalent summer temperatures in the north by up to 30 °C (54 °F). Mars_sentence_243

Mars has the largest dust storms in the Solar System, reaching speeds of over 160 km/h (100 mph). Mars_sentence_244

These can vary from a storm over a small area, to gigantic storms that cover the entire planet. Mars_sentence_245

They tend to occur when Mars is closest to the Sun, and have been shown to increase the global temperature. Mars_sentence_246

Orbit and rotation Mars_section_17

Main article: Orbit of Mars Mars_sentence_247

Mars's average distance from the Sun is roughly 230 million km (143 million mi), and its orbital period is 687 (Earth) days. Mars_sentence_248

The solar day (or sol) on Mars is only slightly longer than an Earth day: 24 hours, 39 minutes, and 35.244 seconds. Mars_sentence_249

A Martian year is equal to 1.8809 Earth years, or 1 year, 320 days, and 18.2 hours. Mars_sentence_250

The axial tilt of Mars is 25.19° relative to its orbital plane, which is similar to the axial tilt of Earth. Mars_sentence_251

As a result, Mars has seasons like Earth, though on Mars they are nearly twice as long because its orbital period is that much longer. Mars_sentence_252

In the present day epoch, the orientation of the north pole of Mars is close to the star Deneb. Mars_sentence_253

Mars has a relatively pronounced orbital eccentricity of about 0.09; of the seven other planets in the Solar System, only Mercury has a larger orbital eccentricity. Mars_sentence_254

It is known that in the past, Mars has had a much more circular orbit. Mars_sentence_255

At one point, 1.35 million Earth years ago, Mars had an eccentricity of roughly 0.002, much less than that of Earth today. Mars_sentence_256

Mars's cycle of eccentricity is 96,000 Earth years compared to Earth's cycle of 100,000 years. Mars_sentence_257

Mars has a much longer cycle of eccentricity, with a period of 2.2 million Earth years, and this overshadows the 96,000-year cycle in the eccentricity graphs. Mars_sentence_258

For the last 35,000 years, the orbit of Mars has been getting slightly more eccentric because of the gravitational effects of the other planets. Mars_sentence_259

The closest distance between Earth and Mars will continue to mildly decrease for the next 25,000 years. Mars_sentence_260

Habitability and search for life Mars_section_18

Main article: Life on Mars Mars_sentence_261

The current understanding of planetary habitability — the ability of a world to develop environmental conditions favorable to the emergence of life — favors planets that have liquid water on their surface. Mars_sentence_262

Most often this requires the orbit of a planet to lie within the habitable zone, which for the Sun extends from just beyond Venus to about the semi-major axis of Mars. Mars_sentence_263

During perihelion, Mars dips inside this region, but Mars's thin (low-pressure) atmosphere prevents liquid water from existing over large regions for extended periods. Mars_sentence_264

The past flow of liquid water demonstrates the planet's potential for habitability. Mars_sentence_265

Recent evidence has suggested that any water on the Martian surface may have been too salty and acidic to support regular terrestrial life. Mars_sentence_266

The lack of a magnetosphere and the extremely thin atmosphere of Mars are a challenge: the planet has little heat transfer across its surface, poor insulation against bombardment of the solar wind and insufficient atmospheric pressure to retain water in a liquid form (water instead sublimes to a gaseous state). Mars_sentence_267

Mars is nearly, or perhaps totally, geologically dead; the end of volcanic activity has apparently stopped the recycling of chemicals and minerals between the surface and interior of the planet. Mars_sentence_268

In situ investigations have been performed on Mars by the Viking landers, Spirit and Opportunity rovers, Phoenix lander, and Curiosity rover. Mars_sentence_269

Evidence suggests that the planet was once significantly more habitable than it is today, but whether living organisms ever existed there remains unknown. Mars_sentence_270

The Viking probes of the mid-1970s carried experiments designed to detect microorganisms in Martian soil at their respective landing sites and had positive results, including a temporary increase of CO 2 production on exposure to water and nutrients. Mars_sentence_271

This sign of life was later disputed by scientists, resulting in a continuing debate, with NASA scientist Gilbert Levin asserting that Viking may have found life. Mars_sentence_272

A re-analysis of the Viking data, in light of modern knowledge of extremophile forms of life, has suggested that the Viking tests were not sophisticated enough to detect these forms of life. Mars_sentence_273

The tests could even have killed a (hypothetical) life form. Mars_sentence_274

Tests conducted by the Phoenix Mars lander have shown that the soil has an alkaline pH and it contains magnesium, sodium, potassium and chloride. Mars_sentence_275

The soil nutrients may be able to support life, but life would still have to be shielded from the intense ultraviolet light. Mars_sentence_276

A recent analysis of martian meteorite EETA79001 found 0.6 ppm ClO− 4, 1.4 ppm ClO− 3, and 16 ppm NO− 3, most likely of Martian origin. Mars_sentence_277

The ClO− 3 suggests the presence of other highly oxidizing oxychlorines, such as ClO− 2 or ClO, produced both by UV oxidation of Cl and X-ray radiolysis of ClO− 4. Mars_sentence_278

Thus, only highly refractory and/or well-protected (sub-surface) organics or life forms are likely to survive. Mars_sentence_279

A 2014 analysis of the Phoenix WCL showed that the Ca(ClO 4) 2 in the Phoenix soil has not interacted with liquid water of any form, perhaps for as long as 600 million years. Mars_sentence_280

If it had, the highly soluble Ca(ClO 4) 2 in contact with liquid water would have formed only CaSO 4. Mars_sentence_281

This suggests a severely arid environment, with minimal or no liquid water interaction. Mars_sentence_282

Scientists have proposed that carbonate globules found in meteorite ALH84001, which is thought to have originated from Mars, could be fossilized microbes extant on Mars when the meteorite was blasted from the Martian surface by a meteor strike some 15 million years ago. Mars_sentence_283

This proposal has been met with skepticism, and an exclusively inorganic origin for the shapes has been proposed. Mars_sentence_284

Small quantities of methane and formaldehyde detected by Mars orbiters are both claimed to be possible evidence for life, as these chemical compounds would quickly break down in the Martian atmosphere. Mars_sentence_285

Alternatively, these compounds may instead be replenished by volcanic or other geological means, such as serpentinite. Mars_sentence_286

Impact glass, formed by the impact of meteors, which on Earth can preserve signs of life, has been found on the surface of the impact craters on Mars. Mars_sentence_287

Likewise, the glass in impact craters on Mars could have preserved signs of life if life existed at the site. Mars_sentence_288

In May 2017, evidence of the earliest known life on land on Earth may have been found in 3.48-billion-year-old geyserite and other related mineral deposits (often found around hot springs and geysers) uncovered in the Pilbara Craton of Western Australia. Mars_sentence_289

These findings may be helpful in deciding where best to search for early signs of life on the planet Mars. Mars_sentence_290

In early 2018, media reports speculated that certain rock features at a site called Jura looked like a type of fossil, but project scientists say the formations likely resulted from a geological process at the bottom of an ancient drying lakebed, and are related to mineral veins in the area similar to gypsum crystals. Mars_sentence_291

On 7 June 2018, NASA announced that the Curiosity rover had discovered organic compounds in sedimentary rocks dating to three billion years old, indicating that some of the building blocks for life were present. Mars_sentence_292

In July 2018, scientists reported the discovery of a subglacial lake on Mars, the first known stable body of water on the planet. Mars_sentence_293

It sits 1.5 km (0.9 mi) below the surface at the base of the southern polar ice cap and is about 20 kilometres (12 mi) wide. Mars_sentence_294

The lake was discovered using the MARSIS radar on board the Mars Express orbiter, and the profiles were collected between May 2012 and December 2015. Mars_sentence_295

The lake is centered at 193° East, 81° South, a flat area that does not exhibit any peculiar topographic characteristics. Mars_sentence_296

It is mostly surrounded by higher ground except on its eastern side, where there is a depression. Mars_sentence_297

Moons Mars_section_19

Main articles: Moons of Mars, Phobos (moon), and Deimos (moon) Mars_sentence_298

Mars has two relatively small (compared to Earth's) natural moons, Phobos (about 22 kilometres (14 mi) in diameter) and Deimos (about 12 kilometres (7.5 mi) in diameter), which orbit close to the planet. Mars_sentence_299

Asteroid capture is a long-favored theory, but their origin remains uncertain. Mars_sentence_300

Both satellites were discovered in 1877 by Asaph Hall; they are named after the characters Phobos (panic/fear) and Deimos (terror/dread), who, in Greek mythology, accompanied their father Ares, god of war, into battle. Mars_sentence_301

Mars was the Roman counterpart of Ares. Mars_sentence_302

In modern Greek, the planet retains its ancient name Ares (Aris: Άρης). Mars_sentence_303

From the surface of Mars, the motions of Phobos and Deimos appear different from that of the Moon. Mars_sentence_304

Phobos rises in the west, sets in the east, and rises again in just 11 hours. Mars_sentence_305

Deimos, being only just outside synchronous orbit – where the orbital period would match the planet's period of rotation – rises as expected in the east but slowly. Mars_sentence_306

Despite the 30-hour orbit of Deimos, 2.7 days elapse between its rise and set for an equatorial observer, as it slowly falls behind the rotation of Mars. Mars_sentence_307

Because the orbit of Phobos is below synchronous altitude, the tidal forces from the planet Mars are gradually lowering its orbit. Mars_sentence_308

In about 50 million years, it could either crash into Mars's surface or break up into a ring structure around the planet. Mars_sentence_309

The origin of the two moons is not well understood. Mars_sentence_310

Their low albedo and carbonaceous chondrite composition have been regarded as similar to asteroids, supporting the capture theory. Mars_sentence_311

The unstable orbit of Phobos would seem to point towards a relatively recent capture. Mars_sentence_312

But both have circular orbits, near the equator, which is unusual for captured objects and the required capture dynamics are complex. Mars_sentence_313

Accretion early in the history of Mars is plausible, but would not account for a composition resembling asteroids rather than Mars itself, if that is confirmed. Mars_sentence_314

A third possibility is the involvement of a third body or a type of impact disruption. Mars_sentence_315

More-recent lines of evidence for Phobos having a highly porous interior, and suggesting a composition containing mainly phyllosilicates and other minerals known from Mars, point toward an origin of Phobos from material ejected by an impact on Mars that reaccreted in Martian orbit, similar to the prevailing theory for the origin of Earth's moon. Mars_sentence_316

Although the VNIR spectra of the moons of Mars resemble those of outer-belt asteroids, the thermal infrared spectra of Phobos are reported to be inconsistent with chondrites of any class. Mars_sentence_317

Mars may have moons smaller than 50 to 100 metres (160 to 330 ft) in diameter, and a dust ring is predicted to exist between Phobos and Deimos. Mars_sentence_318

Exploration Mars_section_20

Main article: Exploration of Mars Mars_sentence_319

Dozens of crewless spacecraft, including orbiters, landers, and rovers, have been sent to Mars by the Soviet Union, the United States, Europe, and India to study the planet's surface, climate, and geology. Mars_sentence_320

As of 2018, Mars is host to eight functioning spacecraft: six in orbit — 2001 Mars Odyssey, Mars Express, Mars Reconnaissance Orbiter, MAVEN, Mars Orbiter Mission and ExoMars Trace Gas Orbiter — and two on the surface — Mars Science Laboratory Curiosity (rover) and InSight (lander). Mars_sentence_321

The public can request images of Mars via the Mars Reconnaissance Orbiter's HiWish program. Mars_sentence_322

The Mars Science Laboratory, named Curiosity, launched on 26 November 2011, and reached Mars on 6 August 2012 UTC. Mars_sentence_323

It is larger and more advanced than the Mars Exploration Rovers, with a movement rate up to 90 metres (300 ft) per hour. Mars_sentence_324

Experiments include a laser chemical sampler that can deduce the make-up of rocks at a distance of 7 metres (23 ft). Mars_sentence_325

On 10 February 2013, the Curiosity rover obtained the first deep rock samples ever taken from another planetary body, using its on-board drill. Mars_sentence_326

The same year, it discovered that Mars's soil contains between 1.5% and 3% water by mass (albeit attached to other compounds and thus not freely accessible). Mars_sentence_327

Observations by the Mars Reconnaissance Orbiter had previously revealed the possibility of flowing water during the warmest months on Mars. Mars_sentence_328

On 24 September 2014, Mars Orbiter Mission (MOM), launched by the Indian Space Research Organisation (ISRO), reached Mars orbit. Mars_sentence_329

ISRO launched MOM on 5 November 2013, with the aim of analyzing the Martian atmosphere and topography. Mars_sentence_330

The Mars Orbiter Mission used a Hohmann transfer orbit to escape Earth's gravitational influence and catapult into a nine-month-long voyage to Mars. Mars_sentence_331

The mission is the first successful Asian interplanetary mission. Mars_sentence_332

The European Space Agency, in collaboration with Roscosmos, launched the ExoMars Trace Gas Orbiter and Schiaparelli lander on 14 March 2016. Mars_sentence_333

While the Trace Gas Orbiter successfully entered Mars orbit on 19 October 2016, Schiaparelli crashed during its landing attempt. Mars_sentence_334

In May 2018, NASA's InSight lander was launched, along with the twin MarCO CubeSats that flew by Mars and acted as telemetry relays during the landing. Mars_sentence_335

The mission arrived at Mars in November 2018. Mars_sentence_336

InSight detected potential seismic activity (a "marsquake") in April 2019. Mars_sentence_337

In 2019, MAVEN spacecraft mapped high-altitude global wind patterns at Mars for the first time. Mars_sentence_338

It was discovered that the winds which are miles above the surface retained information about the land forms below. Mars_sentence_339

Future Mars_section_21

Main article: Exploration of Mars § Timeline of Mars exploration Mars_sentence_340

NASA launched the Mars 2020 mission on 30 July 2020. Mars_sentence_341

The mission will cache samples for future retrieval and return to Earth. Mars_sentence_342

The current concept for the Mars sample-return mission would launch in 2026 and feature hardware built by NASA and ESA. Mars_sentence_343

The European Space Agency will launch the ExoMars rover and surface platform sometime between August and October 2022. Mars_sentence_344

The United Arab Emirates' Mars Hope orbiter was launched on 19 July 2020, and is scheduled to reach Mars in 2021. Mars_sentence_345

The probe will conduct a global study of the Martian atmosphere. Mars_sentence_346

Several plans for a human mission to Mars have been proposed throughout the 20th and 21st centuries, but no human mission has yet launched. Mars_sentence_347

SpaceX founder Elon Musk presented a plan in September 2016 to, optimistically, launch a crewed mission to Mars in 2024 at an estimated development cost of US$10 billion, but this mission is not expected to take place before 2027. Mars_sentence_348

In October 2016, President Barack Obama renewed United States policy to pursue the goal of sending humans to Mars in the 2030s, and to continue using the International Space Station as a technology incubator in that pursuit. Mars_sentence_349

The NASA Authorization Act of 2017 directed NASA to get humans near or on the surface of Mars by the early 2030s. Mars_sentence_350

Astronomy on Mars Mars_section_22

Main article: Astronomy on Mars Mars_sentence_351

See also: Solar eclipses on Mars Mars_sentence_352

With the presence of various orbiters, landers, and rovers, it is possible to practice astronomy from Mars. Mars_sentence_353

Although Mars's moon Phobos appears about one-third the angular diameter of the full moon on Earth, Deimos appears more or less star-like, looking only slightly brighter than Venus does from Earth. Mars_sentence_354

Various phenomena seen from Earth have also been observed from Mars, such as meteors and auroras. Mars_sentence_355

The apparent sizes of the moons Phobos and Deimos are sufficiently smaller than that of the Sun; thus, their partial "eclipses" of the Sun are best considered transits (see transit of Deimos and Phobos from Mars). Mars_sentence_356

Transits of Mercury and Venus have been observed from Mars. Mars_sentence_357

A transit of Earth will be seen from Mars on 10 November 2084. Mars_sentence_358

On 19 October 2014, comet Siding Spring passed extremely close to Mars, so close that the coma may have enveloped Mars. Mars_sentence_359

Viewing Mars_section_23

The mean apparent magnitude of Mars is +0.71 with a standard deviation of 1.05. Mars_sentence_360

Because the orbit of Mars is eccentric, the magnitude at opposition from the Sun can range from about −3.0 to −1.4. Mars_sentence_361

The minimum brightness is magnitude +1.86 when the planet is in conjunction with the Sun. Mars_sentence_362

At its brightest, Mars (along with Jupiter) are second only to Venus in luminosity. Mars_sentence_363

Mars usually appears distinctly yellow, orange, or red. Mars_sentence_364

NASA's Spirit rover has taken pictures of a greenish-brown, mud-colored landscape with blue-grey rocks and patches of light red sand. Mars_sentence_365

When farthest away from Earth, it is more than seven times farther away than when it is closest. Mars_sentence_366

When least favorably positioned, it can be lost in the Sun's glare for months at a time. Mars_sentence_367

At its most favorable times — at 15-year or 17-year intervals, and always between late July and late September — a lot of surface detail can be seen with a telescope. Mars_sentence_368

Especially noticeable, even at low magnification, are the polar ice caps. Mars_sentence_369

As Mars approaches opposition, it begins a period of retrograde motion, which means it will appear to move backwards in a looping motion with respect to the background stars. Mars_sentence_370

The duration of this retrograde motion lasts for about 72 days, and Mars reaches its peak luminosity in the middle of this motion. Mars_sentence_371

Closest approaches Mars_section_24

Relative Mars_section_25

The point at which Mars's geocentric longitude is 180° different from the Sun's is known as opposition, which is near the time of closest approach to Earth. Mars_sentence_372

The time of opposition can occur as much as 8.5 days away from the closest approach. Mars_sentence_373

The distance at close approach varies between about 54 and 103 million km (34 and 64 million mi) due to the planets' elliptical orbits, which causes comparable variation in angular size. Mars_sentence_374

The last Mars opposition occurred on 27 July 2018, at a distance of about 58 million km (36 million mi). Mars_sentence_375

The next Mars opposition occurs on 13 October 2020, at a distance of about 63 million km (39 million mi). Mars_sentence_376

The average time between the successive oppositions of Mars, its synodic period, is 780 days; but the number of days between the dates of successive oppositions can range from 764 to 812. Mars_sentence_377

As Mars approaches opposition it begins a period of retrograde motion, which makes it appear to move backwards in a looping motion relative to the background stars. Mars_sentence_378

The duration of this retrograde motion is about 72 days. Mars_sentence_379

Absolute, around the present time Mars_section_26

Mars made its closest approach to Earth and maximum apparent brightness in nearly 60,000 years, 55,758,006 km (0.37271925 AU; 34,646,419 mi), magnitude −2.88, on 27 August 2003, at 09:51:13 UTC. Mars_sentence_380

This occurred when Mars was one day from opposition and about three days from its perihelion, making it particularly easy to see from Earth. Mars_sentence_381

The last time it came so close is estimated to have been on 12 September 57,617 BC, the next time being in 2287. Mars_sentence_382

This record approach was only slightly closer than other recent close approaches. Mars_sentence_383

For instance, the minimum distance on 22 August 1924, was 0.37285 AU, and the minimum distance on 24 August 2208, will be 0.37279 AU. Mars_sentence_384

Every 15 to 17 years, Mars comes into opposition near its perihelion. Mars_sentence_385

These perihelic oppositions make a closer approach to earth than other oppositions which occur every 2.1 years. Mars_sentence_386

Mars comes into perihelic opposition in 2003, 2018 and 2035, with 2020 and 2033 being close to perihelic opposition. Mars_sentence_387

Historical observations Mars_section_27

Main article: History of Mars observation Mars_sentence_388

The history of observations of Mars is marked by the oppositions of Mars, when the planet is closest to Earth and hence is most easily visible, which occur every couple of years. Mars_sentence_389

Even more notable are the perihelic oppositions of Mars, which occur every 15 or 17 years and are distinguished because Mars is close to perihelion, making it even closer to Earth. Mars_sentence_390

Ancient and medieval observations Mars_section_28

The ancient Sumerians believed that Mars was Nergal, the god of war and plague. Mars_sentence_391

During Sumerian times, Nergal was a minor deity of little significance, but, during later times, his main cult center was the city of Nineveh. Mars_sentence_392

In Mesopotamian texts, Mars is referred to as the "star of judgement of the fate of the dead". Mars_sentence_393

The existence of Mars as a wandering object in the night sky was recorded by the ancient Egyptian astronomers and, by 1534 BCE, they were familiar with the retrograde motion of the planet. Mars_sentence_394

By the period of the Neo-Babylonian Empire, the Babylonian astronomers were making regular records of the positions of the planets and systematic observations of their behavior. Mars_sentence_395

For Mars, they knew that the planet made 37 synodic periods, or 42 circuits of the zodiac, every 79 years. Mars_sentence_396

They invented arithmetic methods for making minor corrections to the predicted positions of the planets. Mars_sentence_397

In Ancient Greece, the planet was known as Πυρόεις. Mars_sentence_398

In the fourth century BCE, Aristotle noted that Mars disappeared behind the Moon during an occultation, indicating that the planet was farther away. Mars_sentence_399

Ptolemy, a Greek living in Alexandria, attempted to address the problem of the orbital motion of Mars. Mars_sentence_400

Ptolemy's model and his collective work on astronomy was presented in the multi-volume collection Almagest, which became the authoritative treatise on Western astronomy for the next fourteen centuries. Mars_sentence_401

Literature from ancient China confirms that Mars was known by Chinese astronomers by no later than the fourth century BCE. Mars_sentence_402

In the East Asian cultures, Mars is traditionally referred to as the "fire star" (Chinese: 火星), based on the Five elements. Mars_sentence_403

During the seventeenth century, Tycho Brahe measured the diurnal parallax of Mars that Johannes Kepler used to make a preliminary calculation of the relative distance to the planet. Mars_sentence_404

When the telescope became available, the diurnal parallax of Mars was again measured in an effort to determine the Sun-Earth distance. Mars_sentence_405

This was first performed by Giovanni Domenico Cassini in 1672. Mars_sentence_406

The early parallax measurements were hampered by the quality of the instruments. Mars_sentence_407

The only occultation of Mars by Venus observed was that of 13 October 1590, seen by Michael Maestlin at Heidelberg. Mars_sentence_408

In 1610, Mars was viewed by Italian astronomer Galileo Galilei, who was first to see it via telescope. Mars_sentence_409

The first person to draw a map of Mars that displayed any terrain features was the Dutch astronomer Christiaan Huygens. Mars_sentence_410

Martian "canals" Mars_section_29

Main article: Martian canal Mars_sentence_411

By the 19th century, the resolution of telescopes reached a level sufficient for surface features to be identified. Mars_sentence_412

A perihelic opposition of Mars occurred on 5 September 1877. Mars_sentence_413

In that year, the Italian astronomer Giovanni Schiaparelli used a 22 centimetres (8.7 in) telescope in Milan to help produce the first detailed map of Mars. Mars_sentence_414

These maps notably contained features he called canali, which were later shown to be an optical illusion. Mars_sentence_415

These canali were supposedly long, straight lines on the surface of Mars, to which he gave names of famous rivers on Earth. Mars_sentence_416

His term, which means "channels" or "grooves", was popularly mistranslated in English as "canals". Mars_sentence_417

Influenced by the observations, the orientalist Percival Lowell founded an observatory which had 30 and 45 centimetres (12 and 18 in) telescopes. Mars_sentence_418

The observatory was used for the exploration of Mars during the last good opportunity in 1894 and the following less favorable oppositions. Mars_sentence_419

He published several books on Mars and life on the planet, which had a great influence on the public. Mars_sentence_420

The canali were independently found by other astronomers, like Henri Joseph Perrotin and Louis Thollon in Nice, using one of the largest telescopes of that time. Mars_sentence_421

The seasonal changes (consisting of the diminishing of the polar caps and the dark areas formed during Martian summer) in combination with the canals led to speculation about life on Mars, and it was a long-held belief that Mars contained vast seas and vegetation. Mars_sentence_422

The telescope never reached the resolution required to give proof to any speculations. Mars_sentence_423

As bigger telescopes were used, fewer long, straight canali were observed. Mars_sentence_424

During an observation in 1909 by Camille Flammarion with an 84 centimetres (33 in) telescope, irregular patterns were observed, but no canali were seen. Mars_sentence_425

Even in the 1960s, articles were published on Martian biology, putting aside explanations other than life for the seasonal changes on Mars. Mars_sentence_426

Detailed scenarios for the metabolism and chemical cycles for a functional ecosystem have been published. Mars_sentence_427

Spacecraft visitation Mars_section_30

Main article: Exploration of Mars Mars_sentence_428

Once spacecraft visited the planet during NASA's Mariner missions in the 1960s and 1970s, these concepts were radically broken. Mars_sentence_429

The results of the Viking life-detection experiments aided an intermission in which the hypothesis of a hostile, dead planet was generally accepted. Mars_sentence_430

Mariner 9 and Viking allowed better maps of Mars to be made using the data from these missions, and another major leap forward was the Mars Global Surveyor mission, launched in 1996 and operated until late 2006, that allowed complete, extremely detailed maps of the Martian topography, magnetic field and surface minerals to be obtained. Mars_sentence_431

These maps are available online; for example, at Google Mars. Mars_sentence_432

Mars Reconnaissance Orbiter and Mars Express continued exploring with new instruments, and supporting lander missions. Mars_sentence_433

NASA provides two online tools: Mars Trek, which provides visualizations of the planet using data from 50 years of exploration, and Experience Curiosity, which simulates traveling on Mars in 3-D with Curiosity. Mars_sentence_434

In culture Mars_section_31

Main articles: Mars in culture and Mars in fiction Mars_sentence_435

Mars is named after the Roman god of war. Mars_sentence_436

In different cultures, Mars represents masculinity and youth. Mars_sentence_437

Its symbol, a circle with an arrow pointing out to the upper right, is used as a symbol for the male gender. Mars_sentence_438

The many failures in Mars exploration probes resulted in a satirical counter-culture blaming the failures on an Earth-Mars "Bermuda Triangle", a "Mars Curse", or a "Great Galactic Ghoul" that feeds on Martian spacecraft. Mars_sentence_439

Intelligent "Martians" Mars_section_32

The fashionable idea that Mars was populated by intelligent Martians exploded in the late 19th century. Mars_sentence_440

Schiaparelli's "canali" observations combined with Percival Lowell's books on the subject put forward the standard notion of a planet that was a drying, cooling, dying world with ancient civilizations constructing irrigation works. Mars_sentence_441

Many other observations and proclamations by notable personalities added to what has been termed "Mars Fever". Mars_sentence_442

In 1899, while investigating atmospheric radio noise using his receivers in his Colorado Springs lab, inventor Nikola Tesla observed repetitive signals that he later surmised might have been radio communications coming from another planet, possibly Mars. Mars_sentence_443

In a 1901 interview, Tesla said: Mars_sentence_444

Tesla's theories gained support from Lord Kelvin who, while visiting the United States in 1902, was reported to have said that he thought Tesla had picked up Martian signals being sent to the United States. Mars_sentence_445

Kelvin "emphatically" denied this report shortly before leaving: "What I really said was that the inhabitants of Mars, if there are any, were doubtless able to see New York, particularly the glare of the electricity". Mars_sentence_446

In a New York Times article in 1901, Edward Charles Pickering, director of the Harvard College Observatory, said that they had received a telegram from Lowell Observatory in Arizona that seemed to confirm that Mars was trying to communicate with Earth. Mars_sentence_447

Pickering later proposed creating a set of mirrors in Texas, intended to signal Martians. Mars_sentence_448

In recent decades, the high-resolution mapping of the surface of Mars, culminating in Mars Global Surveyor, revealed no artifacts of habitation by "intelligent" life, but pseudoscientific speculation about intelligent life on Mars continues from commentators such as Richard C. Hoagland. Mars_sentence_449

Reminiscent of the canali controversy, these speculations are based on small scale features perceived in the spacecraft images, such as "pyramids" and the "Face on Mars". Mars_sentence_450

Planetary astronomer Carl Sagan wrote: Mars_sentence_451

The depiction of Mars in fiction has been stimulated by its dramatic red color and by nineteenth century scientific speculations that its surface conditions might support not just life but intelligent life. Mars_sentence_452

Thus originated a large number of science fiction scenarios, among which is H. Mars_sentence_453 G. Wells' The War of the Worlds, published in 1898, in which Martians seek to escape their dying planet by invading Earth. Mars_sentence_454

Influential works included Ray Bradbury's The Martian Chronicles, in which human explorers accidentally destroy a Martian civilization, Edgar Rice Burroughs' Barsoom series, C. Mars_sentence_455 S. Lewis' novel Out of the Silent Planet (1938), and a number of Robert A. Heinlein stories before the mid-sixties. Mars_sentence_456

Jonathan Swift made reference to the moons of Mars, about 150 years before their actual discovery by Asaph Hall, detailing reasonably accurate descriptions of their orbits, in the 19th chapter of his novel Gulliver's Travels. Mars_sentence_457

A comic figure of an intelligent Martian, Marvin the Martian, appeared in Haredevil Hare (1948) as a character in the Looney Tunes animated cartoons of Warner Brothers, and has continued as part of popular culture to the present. Mars_sentence_458

After the Mariner and Viking spacecraft had returned pictures of Mars as it really is, an apparently lifeless and canal-less world, these ideas about Mars had to be abandoned, and a vogue for accurate, realist depictions of human colonies on Mars developed, the best known of which may be Kim Stanley Robinson's Mars trilogy. Mars_sentence_459

Pseudo-scientific speculations about the Face on Mars and other enigmatic landmarks spotted by space probes have meant that ancient civilizations continue to be a popular theme in science fiction, especially in film. Mars_sentence_460

Interactive Mars map Mars_section_33

See also Mars_section_34

Mars_unordered_list_1


Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Mars.