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The commonly accepted theories include that they are dark underlying layers of soil revealed after avalanches of bright dust or. This leads to of CO 2 gas mixed with dark basaltic sand or dust. The 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. Planetary astronomer wrote: Mars has become a kind of mythic arena onto which we have projected our Earthly hopes and fears.

More recent evidence for liquid water comes from the finding of the mineral on the surface by NASA's Mars rover Opportunity in December 2011. Ancient and medieval observations The ancient believed that Mars was , the god of war and plague. In November 2016, reported finding a large amount of in the region of Mars. These seasonal actions transport large amounts of dust and water vapor, giving rise to Earth-like frost and large.

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Mars is the fourth from the and the second-smallest planet in the after. Mars is a with a thin , having surface features reminiscent both of the of the and the valleys, deserts, and of. The and seasonal cycles of Mars are likewise similar to those of Earth, as is the tilt that produces the seasons. Mars is the site of , the largest and , and of , one of the largest canyons in the Solar System. The smooth in the northern hemisphere covers 40% of the planet and may be a giant impact feature. Mars has two , and , which are small and irregularly shaped. These may be captured , similar to , a. There are ongoing investigations assessing the past potential of Mars, as well as. Future astrobiology missions are planned, including the and rovers. Liquid cannot exist on the surface of Mars due to low atmospheric pressure, which is less than 1% of the Earth's, except at the lowest elevations for short periods. The two polar ice caps appear to be made largely of water. 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 meters 36 ft. In November 2016, reported finding a large amount of in the region of Mars. The volume of water detected has been estimated to be equivalent to the volume of water in. Mars can easily be seen from Earth with the naked eye, as can its reddish coloring. Optical ground-based telescopes are typically limited to resolving features about 300 kilometers 190 mi across when Earth and Mars are closest because of Earth's atmosphere. 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 is less dense than Earth, having about 15% of Earth's volume and 11% of Earth's , resulting in about 38% of Earth's surface gravity. The red-orange appearance of the Martian surface is caused by , or rust. It can look like butterscotch; other common surface colors include golden, brown, tan, and greenish, depending on the present. Internal structure Like Earth, Mars has into a dense metallic overlaid by less dense materials. Current models of its interior imply a core with a radius of about 1,794 ± 65 kilometers 1,115 ± 40 mi , consisting primarily of with about 16—17%. This core is thought to be twice as rich in lighter elements as Earth's. The core is surrounded by a silicate that formed many of the and volcanic features on the planet, but it appears to be dormant. Besides silicon and oxygen, the most abundant elements in the Martian are iron, , , , and. The average thickness of the planet's crust is about 50 km 31 mi , with a maximum thickness of 125 km 78 mi. Earth's crust averages 40 km 25 mi. Surface geology Main article: Mars is a that consists of minerals containing and , , and other elements that typically make up. The surface of Mars is primarily composed of , although parts are more -rich than typical basalt and may be similar to rocks on Earth or silica glass. Regions of low suggest concentrations of , with northern low albedo regions displaying higher than normal concentrations of sheet silicates and high-silicon glass. Parts of the southern highlands include detectable amounts of high-calcium. Localized concentrations of and have been found. Much of the surface is deeply covered by finely grained dust. This of magnetically susceptible minerals is similar to the. One theory, published in 1999 and re-examined in October 2005 with the help of the , is that these bands suggest on Mars four years ago, before the planetary ceased to function and the planet's magnetic field faded. It is thought that, during the , Mars was created as the result of a of run-away accretion of material from the 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 , , and , are much more common on Mars than Earth; these elements were probably pushed outward by the young Sun's energetic. 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. There is evidence of an enormous impact basin in the northern hemisphere of Mars, spanning 10,600 by 8,500 km 6,600 by 5,300 mi , or roughly four times the size of the Moon's , the largest impact basin yet discovered. This theory suggests that Mars was struck by a -sized body about four billion years ago. The event, thought to be the cause of the , created the smooth that covers 40% of the planet. Noachian age surfaces are scarred by many large impact craters. The bulge, a volcanic upland, is thought to have formed during this period, with extensive flooding by liquid water late in the period. The Hesperian period is marked by the formation of extensive lava plains. Amazonian regions have few craters, but are otherwise quite varied. Geological activity is still taking place on Mars. The is home to sheet-like lava flows created about 200. Water flows in the called the occurred less than 20 Mya, indicating equally recent volcanic intrusions. On February 19, 2008, images from the showed evidence of an avalanche from a 700-metre-high 2,300 ft cliff. Soil Exposure of silica-rich dust uncovered by the rover The lander returned data showing Martian soil to be slightly alkaline and containing elements such as , , and. These nutrients are found in soils on Earth, and they are necessary for growth of plants. Experiments performed by the lander showed that the Martian soil has a of 7. 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 the edges of boulders and other obstacles in their path. The commonly accepted theories include that they are dark underlying layers of soil revealed after avalanches of bright dust or. Several other explanations have been put forward, including those that involve water or even the growth of organisms. Hydrology Main article: 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. The two polar ice caps appear to be made largely of water. 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 meters 36 ft. A mantle stretches from the pole to latitudes of about 60°. Radar data from and the show large quantities of water ice at both poles July 2005 and at middle latitudes November 2008. The Phoenix lander directly sampled water ice in shallow Martian soil on July 31, 2008. Huge linear swathes of scoured ground, known as , cut across the surface in about 25 places. 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. One of the larger examples, is 700 km 430 mi long, much greater than the Grand Canyon, with a width of 20 km 12 mi and a depth of 2 km 1. It is thought to have been carved by flowing water early in Mars's history. The youngest of these channels are thought to have formed as recently as only a few million years ago. Elsewhere, particularly on the oldest areas of the Martian surface, finer-scale, dendritic are spread across significant proportions of the landscape. Features of these valleys and their distribution strongly imply that they were carved by resulting from precipitation in early Mars history. Subsurface water flow and may play important subsidiary roles in some networks, but precipitation was probably the root cause of the incision in almost all cases. Along crater and canyon walls, there are thousands of features that appear similar to terrestrial. The gullies tend to be in the highlands of the southern hemisphere and to 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 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 and preserved in craters, are further evidence for warmer, wetter conditions at an interval or intervals in earlier Mars history. Such conditions necessarily require the widespread presence of 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 and , both of which sometimes form in the presence of water. In 2004, Opportunity detected the mineral. This forms only in the presence of acidic water, which demonstrates that water once existed on Mars. More recent evidence for liquid water comes from the finding of the mineral on the surface by NASA's Mars rover Opportunity in December 2011. It is believed that the amount of water in the upper mantle of Mars, represented by 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 m 660—3,280 ft. In 2005, radar data revealed the presence of large quantities of water ice at the poles and at mid-latitudes. The Mars rover sampled chemical compounds containing water molecules in March 2007. The lander directly sampled water ice in shallow Martian soil on July 31, 2008. On March 18, 2013, reported evidence from instruments on the of , likely hydrated , in several including the broken fragments of and as well as in and in other rocks like and. Analysis using the rover's provided evidence of subsurface water, amounting to as much as 4% water content, down to a depth of 60 cm 24 in , during the rover's traverse from the site to the Yellowknife Bay area in the terrain. In September 2015, NASA announced that they had found conclusive evidence of hydrated flows on , based on spectrometer readings of the darkened areas of slopes. 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. The streaks contain hydrated salts, perchlorates, which have water molecules in their crystal structure. On September 28, 2015, NASA briny flowing on the Martian surface. Researchers believe that much of the low northern plains of the planet were hundreds of meters deep, though this remains controversial. In March 2015, scientists stated that such an ocean might have been the size of Earth's. This finding was derived from the ratio of water to in the modern Martian atmosphere compared to that ratio on Earth. The amount of Martian deuterium is eight times the amount that exists on Earth, suggesting that ancient Mars had significantly higher levels of water. Results from the Curiosity rover had previously found a high ratio of deuterium in , 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. Polar caps South polar midsummer ice cap 2000 Mars has two permanent polar ice caps. During a pole's winter, it lies in continuous darkness, chilling the surface and causing the of 25—30% of the atmosphere into slabs of ice. When the poles are again exposed to sunlight, the frozen CO 2. These seasonal actions transport large amounts of dust and water vapor, giving rise to Earth-like frost and large. Clouds of water-ice were photographed by the rover in 2004. The caps at both poles consist primarily 70% of water ice. 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. This permanent dry ice cover at the south pole is peppered by , which repeat imaging shows are expanding by meters per year; this suggests that the permanent CO 2 cover over the south pole water ice is degrading over time. The northern polar cap has a diameter of about 1,000 km 620 mi during the northern Mars summer, and contains about 1. This compares to a volume of 2. The southern polar cap has a diameter of 350 km 220 mi and a thickness of 3 km 1. The total volume of ice in the south polar cap plus the adjacent layered deposits has been estimated at 1. Both polar caps show spiral troughs, which recent analysis of ice penetrating radar has shown are a result of that spiral due to the. 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. With the arrival of spring, sunlight warms the subsurface and pressure from subliming CO 2 builds up under a slab, elevating and ultimately rupturing it. This leads to of CO 2 gas mixed with dark basaltic sand or dust. 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. 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. 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. Today, features on Mars are named from a variety of sources. Craters larger than 60 km are named for deceased scientists and writers and others who have contributed to the study of Mars. Craters smaller than 60 km are named for towns and villages of the world with populations of less than 100,000. Large 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 Mount Olympus. The surface of Mars as seen from Earth is divided into two kinds of areas, with differing albedo. The dark features were thought to be seas, hence their names , Mare Sirenum and. The largest dark feature seen from Earth is. The permanent northern polar ice cap is named , whereas the southern cap is called. Mars's equator is defined by its rotation, but the location of its was specified, as was Earth's at , by choice of an arbitrary point; Mädler and Beer selected a line for their first maps of Mars in 1830. Zero altitude was defined by the height at which there is 610. This pressure corresponds to the of water, and it is about 0. In practice, today this surface is defined directly from satellite gravity measurements. The quadrangles can be seen and explored via the interactive image map below. Bonneville crater and Spirit rover's lander The of Martian topography is striking: northern plains flattened by lava flows contrast with the southern highlands, pitted and cratered by ancient impacts. 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. If validated, this would make the northern hemisphere of Mars the site of an 10,600 by 8,500 km 6,600 by 5,300 mi in size, or roughly the area of Europe, Asia, and Australia combined, surpassing the as the largest impact crater in the Solar System. Fresh impact on Mars at. These before and after images of the same site were taken on the Martian afternoons of March 27 and 28, 2012 respectively Mars is scarred by a number of impact craters: a total of 43,000 craters with a diameter of 5 km 3. The largest confirmed of these is the , a light clearly visible from Earth. Due to the smaller mass of Mars, the probability of an object colliding with the planet is about half that of Earth. Mars is located closer to the , so it has an increased chance of being struck by materials from that source. Mars is more likely to be struck by short-period , i. 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. Martian craters can have a morphology that suggests the ground became wet after the meteor impacted. Volcanoes Main article: The Mount Olympus is an extinct volcano in the vast upland region , which contains several other large volcanoes. Olympus Mons is roughly three times the height of , which in comparison stands at just over 8. 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 km 13 to 17 mi high. The length of Valles Marineris is equivalent to the length of Europe and extends across one-fifth the circumference of Mars. By comparison, the on Earth is only 446 km 277 mi long and nearly 2 km 1. Valles Marineris was formed due to the swelling of the 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 , but a plate boundary where 150 km 93 mi of has occurred, making Mars a planet with possibly a two- arrangement. Holes Images from the THEMIS aboard NASA's have revealed seven possible entrances on the flanks of the volcano. Cave entrances measure from 100 to 252 m 328 to 827 ft wide and they are estimated to be at least 73 to 96 m 240 to 315 ft deep. 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. The interiors of these caverns may be protected from micrometeoroids, UV radiation, and high energy particles that bombard the planet's surface. Atmosphere The tenuous visible on the horizon Mars lost its 4 billion years ago, possibly because of numerous asteroid strikes, so the interacts directly with the Martian , lowering the atmospheric density by stripping away atoms from the outer layer. Both and have detected ionised atmospheric particles trailing off into space behind Mars, and this atmospheric loss is being studied by the orbiter. Compared to Earth, the of Mars is quite rarefied. The highest atmospheric density on Mars is equal to that found 35 km 22 mi above Earth's surface. The resulting mean surface pressure is only 0. The of the atmosphere is about 10. The atmosphere of Mars consists of about 96% , 1. The atmosphere is quite dusty, containing particulates about 1. It may take on a hue due to particles suspended in it. Potential sources and sinks of CH 4 on Mars has been detected in the ; it occurs in extended plumes, and the profiles imply that the methane is released from discrete regions. The concentration of methane fluctuates from about 0. In northern midsummer 2003, the principal plume contained 19,000 metric tons of methane, with an estimated source strength of 0. The profiles suggest that there may be two local source regions, the first centered near and the second near. It is estimated that Mars must produce 270 tonnes per year of methane. Methane can exist in the Martian atmosphere for only a limited period before it is destroyed—estimates of its lifetime range from 0. Its presence despite this short lifetime indicates that an active source of the gas must be present. Methane could be produced by a non-biological process called involving water, carbon dioxide, and the mineral , which is known to be common on Mars. The first measurements with the indicated that there is less than 5 ppb of methane at the landing site at the point of the measurement. The by is searching for methane in the atmosphere, while the , launched in 2016, would further study the methane as well as its decomposition products, such as and. Ammonia was tentatively detected on Mars by the Mars Express satellite, but with its relatively short lifetime, it is not clear what produced it. Ammonia is not stable in the Martian atmosphere and breaks down after a few hours. One possible source is volcanic activity. In September 2017, NASA reported on the surface of the planet Mars were temporarily , and were associated with an 25 times brighter than any observed earlier, due to a massive, and unexpected, in the middle of the month. Mars does not have a global magnetic field which guides charged particles entering the atmosphere. 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. In late December 2014, NASA's MAVEN spacecraft detected evidence of widespread auroras in Mars's northern hemisphere and descended to approximately 20—30 degrees North latitude of Mars's equator. 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. 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. On March 18, 2015, NASA reported the detection of an that is not fully understood and an unexplained dust cloud in the. Climate Main article: 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. 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. The wide range in temperatures is due to the thin atmosphere which cannot store much solar heat, the low atmospheric pressure, and the low of Martian soil. The planet is 1. If Mars had an Earth-like orbit, its seasons would be similar to Earth's because its is similar to Earth's. The comparatively large of the Martian orbit has a significant effect. Mars is near when it is summer in the southern hemisphere and winter in the north, and near when it is winter in the southern hemisphere and summer in the north. 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. The summer temperatures in the south can be warmer than the equivalent summer temperatures in the north by up to 30 °C 54 °F. These can vary from 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 the global temperature. Mars is about 230 million kilometres 143,000,000 mi from the Sun; its orbital period is 687 Earth days, depicted in red. Earth's orbit is in blue. Mars's average distance from the Sun is roughly 230 million kilometres 143,000,000 mi , and its orbital period is 687 Earth days. The solar day or on Mars is only slightly longer than an Earth day: 24 hours, 39 minutes, and 35. A Martian year is equal to 1. The axial tilt of Mars is 25. 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. In the present day epoch, the orientation of the of Mars is close to the star. Mars has a relatively pronounced of about 0. It is known that in the past, Mars has had a much more circular orbit. At one point, 1. Mars's cycle of eccentricity is 96,000 Earth years compared to Earth's cycle of 100,000 years. Mars has a much longer cycle of eccentricity, with a period of 2. 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. The closest distance between Earth and Mars will continue to mildly decrease for the next 25,000 years. Viking 1 lander's sampling arm scooped up soil samples for tests The current understanding of —the ability of a world to develop environmental conditions favorable to the emergence of life—favors planets that have liquid water on their surface. Most often this requires the orbit of a planet to lie within the , which for the Sun extends from just beyond Venus to about the of Mars. 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. The past flow of liquid water demonstrates the planet's potential for habitability. Recent evidence has suggested that any water on the Martian surface may have been too salty and acidic to support regular terrestrial life. This image from Gale crater in 2018 prompted speculation that some shapes were worm-like fossils, but they were geological formations probably formed under water. The lack of a magnetosphere and the extremely thin atmosphere of Mars are a challenge: the planet has little across its surface, poor insulation against bombardment of the and insufficient atmospheric pressure to retain water in a liquid form water instead to a gaseous state. 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. In situ investigations have been performed on Mars by the , and Opportunity rovers, lander, and Curiosity rover. Evidence suggests that the planet was once significantly more habitable than it is today, but whether living ever existed there remains unknown. The 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. This sign of life was later disputed by scientists, resulting in a continuing debate, with NASA scientist asserting that Viking may have found life. A re-analysis of the Viking data, in light of modern knowledge of forms of life, has suggested that the Viking tests were not sophisticated enough to detect these forms of life. The tests could even have killed a hypothetical life form. Tests conducted by the Phoenix Mars lander have shown that the soil has a and it contains magnesium, sodium, potassium and chloride. The soil nutrients may be able to support life, but life would still have to be shielded from the intense ultraviolet light. A recent analysis of martian meteorite EETA79001 found 0. 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 Myr. If it had, the highly soluble Ca ClO 4 2 in contact with liquid water would have formed only CaSO 4. This suggests a severely arid environment, with minimal or no liquid water interaction. Scientists have proposed that carbonate globules found in , 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. This proposal has been met with skepticism, and an exclusively inorganic origin for the shapes has been proposed. Small quantities of and detected by Mars orbiters are both claimed to be possible evidence for life, as these would quickly break down in the Martian atmosphere. Alternatively, these compounds may instead be replenished by volcanic or other geological means, such as. Likewise, the glass in impact craters on Mars could have preserved signs of life if life existed at the site. In May 2017, evidence of the on Earth may have been found in 3. These findings may be helpful in deciding where best to search for early signs of. 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 crystals. On June 7, 2018, NASA announced that the Curiosity rover had discovered in sedimentary rocks dating to three billion years old, indicating that some of the building blocks for life were present. Mars has two relatively small compared to Earth's natural moons, about 22 km 14 mi in diameter and about 12 km 7. Asteroid capture is a long-favored theory, but their origin remains uncertain. Mars was the Roman counterpart of Ares. In modern , though, the planet retains its ancient name Ares Aris: †Á·Â. From the surface of Mars, the motions of Phobos and Deimos appear different from that of the. Phobos rises in the west, sets in the east, and rises again in just 11 hours. Deimos, being only just outside — where the orbital period would match the planet's period of rotation — rises as expected in the east but slowly. Despite the 30-hour orbit of Deimos, 2. Orbits of Phobos and Deimos to scale Because the orbit of Phobos is below synchronous altitude, the from the planet Mars are gradually lowering its orbit. In about 50 million years, it could either crash into Mars's surface or break up into a ring structure around the planet. The origin of the two moons is not well understood. Their low albedo and composition have been regarded as similar to asteroids, supporting the capture theory. The unstable orbit of Phobos would seem to point towards a relatively recent capture. But both have , near the equator, which is unusual for captured objects and the required capture dynamics are complex. 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. A third possibility is the involvement of a third body or a type of impact disruption. More-recent lines of evidence for Phobos having a highly porous interior, and suggesting a composition containing mainly 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 for the origin of Earth's moon. Although the spectra of the moons of Mars resemble those of outer-belt asteroids, the spectra of Phobos are reported to be inconsistent with of any class. 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 Science Laboratory under parachute during its atmospheric entry at Mars Dozens of crewless , including , , and , have been sent to Mars by the , the , , and to study the planet's surface, climate, and geology. As of 2018 , Mars is host to eight functioning : six in orbit— , , , , and —and two on the surface— and the. Observations by the have revealed possible flowing water during the warmest months on Mars. In 2013, NASA's Curiosity rover discovered that Mars's soil contains between 1. The public can request images of Mars via the Mars Reconnaissance Orbiter 's. The , named Curiosity, launched on November 26, 2011, and reached Mars on August 6, 2012. It is larger and more advanced than the Mars Exploration Rovers, with a movement rate up to 90 m 300 ft per hour. Experiments include a laser chemical sampler that can deduce the make-up of rocks at a distance of 7 m 23 ft. On February 10, 2013, the obtained the first deep rock samples ever taken from another planetary body, using its on-board drill. On September 24, 2014, MOM , launched by the , reached Mars orbit. ISRO launched MOM on November 5, 2013, with the aim of analyzing the Martian atmosphere and topography. The Mars Orbiter Mission used a to escape Earth's gravitational influence and catapult into a nine-month-long voyage to Mars. The mission is the first successful Asian interplanetary mission. The , in collaboration with , launched the and on March 14, 2016. While the Trace Gas Orbiter successfully entered Mars orbit on October 19, 2016, Schiaparelli crashed during its landing attempt. Future Concept for a Bimodal Nuclear Thermal Transfer Vehicle in low Earth orbit In May 2018 NASA's lander was launched, along with the twin that will fly by Mars and provide a relay for the landing. The mission is expected to arrive at Mars in November 2018. NASA plans to launch its rover in July or August 2020. The will launch the and in July 2020. The United Arab Emirates' orbiter is planned for launch in 2020, reaching Mars orbit in 2021. The probe will make a global study of the Martian atmosphere. Several plans for a have been proposed throughout the 20th century and into the 21st century, but no active plan has an arrival date sooner than the 2020s. In October 2016, President renewed U. The NASA Authorization Act of 2017 directed NASA to get humans near or on the surface of Mars by the early 2030s. See also: With the presence of various orbiters, landers, and rovers, it is possible to practice from Mars. Although Mars's moon appears about one-third the of the on Earth, appears more or less star-like, looking only slightly brighter than Venus does from Earth. Various phenomena seen from Earth have also been observed from Mars, such as and. A will be seen from Mars on November 10, 2084. On October 19, 2014, passed extremely close to Mars, so close that the may have enveloped Mars. The minimum brightness is magnitude +1. Mars usually appears distinctly yellow, orange, or red; the actual color of Mars is closer to , and the redness seen is just dust in the planet's atmosphere. When farthest away from Earth, it is more than seven times farther away than when it is closest. When least favorably positioned, it can be lost in the Sun's glare for months at a time. At its most favorable times—at 15- or 17-year intervals, and always between late July and late September—a lot of surface detail can be seen with a. Especially noticeable, even at low magnification, are the. As Mars approaches opposition, it begins a period of , which means it will appear to move backwards in a looping motion with respect to the background stars. The duration of this retrograde motion lasts for about 72 days, and Mars reaches its peak luminosity in the middle of this motion. Closest approaches Relative The point at which Mars's geocentric longitude is 180° different from the Sun's is known as , which is near the time of closest approach to Earth. The time of opposition can occur as much as 8. The distance at close approach varies between about 54 and about 103 million km due to the planets' orbits, which causes comparable variation in. The last Mars opposition occurred on May 22, 2016 at a distance of about 76 million km. The next Mars opposition occurs on July 27, 2018 at a distance of about 58 million km. The average time between the successive oppositions of Mars, its , is 780 days; but the number of days between the dates of successive oppositions can range from 764 to 812. As Mars approaches opposition it begins a period of , which makes it appear to move backwards in a looping motion relative to the background stars. The duration of this retrograde motion is about 72 days. Absolute, around the present time Mars oppositions from 2003—2018, viewed from above the ecliptic with Earth centered Mars made its closest approach to Earth and maximum apparent brightness in nearly 60,000 years, 55,758,006 km 0. This occurred when Mars was one day from opposition and about three days from its , making it particularly easy to see from Earth. The last time it came so close is estimated to have been on September 12, , the next time being in 2287. This record approach was only slightly closer than other recent close approaches. Main article: 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. 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. Ancient and medieval observations The ancient believed that Mars was , the god of war and plague. During Sumerian times, Nergal was a minor deity of little significance, but, during later times, his main cult center was the city of. The existence of Mars as a wandering object in the night sky was recorded by the ancient and, by 1534 BCE, they were familiar with the of the planet. By the period of the , the were making regular records of the positions of the planets and systematic observations of their behavior. For Mars, they knew that the planet made 37 , or 42 circuits of the zodiac, every 79 years. They invented arithmetic methods for making minor corrections to the predicted positions of the planets. In the fourth century BCE, noted that Mars disappeared behind the Moon during an , indicating that the planet was farther away. Ptolemy's model and his collective work on astronomy was presented in the multi-volume collection , which became the authoritative treatise on for the next fourteen centuries. Literature from ancient China confirms that Mars was known by by no later than the fourth century BCE. In the fifth century CE, the text estimated the diameter of Mars. During the seventeenth century, measured the of Mars that used to make a preliminary calculation of the relative distance to the planet. When the telescope became available, the diurnal parallax of Mars was again measured in an effort to determine the Sun-Earth distance. This was first performed by in 1672. The early parallax measurements were hampered by the quality of the instruments. The only of Mars by Venus observed was that of October 13, 1590, seen by at. In 1610, Mars was viewed by , who was first to see it via telescope. The first person to draw a map of Mars that displayed any terrain features was the Dutch astronomer. A perihelic opposition of Mars occurred on September 5, 1877. In that year, the Italian astronomer used a 22 cm 8. These maps notably contained features he called canali, which were later shown to be an. These canali were supposedly long, straight lines on the surface of Mars, to which he gave names of famous rivers on Earth. Influenced by the observations, the orientalist founded an which had 30 and 45 cm 12 and 18 in telescopes. The observatory was used for the exploration of Mars during the last good opportunity in 1894 and the following less favorable oppositions. He published several books on Mars and life on the planet, which had a great influence on the public. The canali were independently found by other astronomers, like and in Nice, using one of the largest telescopes of that time. 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. The telescope never reached the resolution required to give proof to any speculations. As bigger telescopes were used, fewer long, straight canali were observed. During an observation in 1909 by with an 84 cm 33 in telescope, irregular patterns were observed, but no canali were seen. Even in the 1960s articles were published on Martian biology, putting aside explanations other than life for the seasonal changes on Mars. Detailed scenarios for the metabolism and chemical cycles for a functional ecosystem have been published. Spacecraft visitation Main article: Once visited the planet during NASA's in the 1960s and 70s, these concepts were radically broken. The results of the Viking life-detection experiments aided an intermission in which the hypothesis of a hostile, dead planet was generally accepted. 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 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. These maps are available online; for example, at. NASA provides two online tools: , which provides visualizations of the planet using data from 50 years of exploration, and , which simulates traveling on Mars in 3-D with Curiosity. Mars is named after the. In different cultures, Mars represents masculinity and youth. In 1899, while investigating atmospheric radio noise using his receivers in his Colorado Springs lab, inventor observed repetitive signals that he later surmised might have been radio communications coming from another planet, possibly Mars. In a 1901 interview Tesla said: It was some time afterward when the thought flashed upon my mind that the disturbances I had observed might be due to an intelligent control. Although I could not decipher their meaning, it was impossible for me to think of them as having been entirely accidental. The feeling is constantly growing on me that I had been the first to hear the greeting of one planet to another. Tesla's theories gained support from 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. Early in December 1900, we received from Lowell Observatory in Arizona a telegram that a shaft of light had been seen to project from Mars the Lowell observatory makes a specialty of Mars lasting seventy minutes. I wired these facts to Europe and sent out neostyle copies through this country. The observer there is a careful, reliable man and there is no reason to doubt that the light existed. It was given as from a well-known geographical point on Mars. Now the story has gone the world over. In Europe it is stated that I have been in communication with Mars, and all sorts of exaggerations have spring up. Whatever the light was, we have no means of knowing. Whether it had intelligence or not, no one can say. It is absolutely inexplicable. Pickering later proposed creating a set of mirrors in , intended to signal Martians. Planetary astronomer wrote: Mars has become a kind of mythic arena onto which we have projected our Earthly hopes and fears. Martian tripod illustration from the 1906 French edition of The War of the Worlds by H. Wells 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. Thus originated a large number of scenarios, among which is ' , published in 1898, in which Martians seek to escape their dying planet by invading Earth. Influential works included 's , in which human explorers accidentally destroy a Martian civilization, ' , ' novel 1938 , and a number of stories before the mid-sixties. A comic figure of an intelligent Martian, , appeared in 1948 as a character in the of , and has continued as part of popular culture to the present. After the and 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 's. Pseudo-scientific speculations about the Face on Mars and other enigmatic landmarks spotted by have meant that ancient civilizations continue to be a popular theme in science fiction, especially in film. The view is centered on the , with , the landing site of the , prominently visible just left of center. The darker, more heavily cratered terrain in the south, , is composed of older terrain than the much smoother and brighter to the north. Geologically recent processes, such as the possible existence of a in Mars's past, could have helped lower-elevated areas, such as Elysium Planitia, retain a more youthful look. Archived from on May 14, 2009. Retrieved April 10, 2009. Kenneth; Archinal, Brent A. 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Lunar and Planetary Science XXXVIII. The profiles suggest that there may be two local source regions, the first centered near and the second near. Spacecraft visitation Main article: Once visited the planet during NASA's in the 1960s and 70s, these concepts were radically broken. Retrieved October 11, 2016. Archived from on August 31, 2003. Today, features on Mars are named from a variety of sources. Ancient and medieval observations The ancient believed that Mars was , the god of war and plague. 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. Retrieved March 16, 2007. Aris is the Greek name of the planet Mars, the fourth planet from the sun, also known as the Red planet. 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.

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