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Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance. HP 586006-321 Battery

Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the volcanoes, valleys, deserts, and polar ice caps of Earth. The rotational period and seasonal cycles of Mars are likewise similar to those of Earth, as is the tilt that produces the seasons. HP 586006-361 Battery

Mars is the site of Olympus Mons, the highest known mountain within the Solar System, and of Valles Marineris, the largest canyon. The smooth Borealis basin in the northern hemisphere covers 40% of the planet and may be a giant impact feature.HP 586028-341 Battery

Until the first flyby of Mars occurred in 1965, by Mariner 4, many speculated about the presence of liquid water on the planet's surface. This was based on observed periodic variations in light and dark patches, particularly in the polar latitudes, which appeared to be seas and continents; HP h588178-141 Battery

long, darkstriations were interpreted by some as irrigation channels for liquid water. These straight line features were later explained as optical illusions, though geological evidence gathered by unmanned missions suggest that Mars once had large-scale water coverage on its surface.HP 593553-001 Battery

In 2005, radar data revealed the presence of large quantities of water ice at the poles,  and at mid-latitudes.  The Mars rover Spirit sampled chemical compounds containing water molecules in March 2007. The Phoenix lander directly sampled water ice in shallow Martian soil on July 31, 2008.HP 593554-001 Battery

Mars has two moons, Phobos and Deimos, which are small and irregularly shaped. These may be captured asteroids, similar to 5261 Eureka, a Martian trojan asteroid. Mars is currently host to three functional orbiting spacecraft: Mars Odyssey, Mars Express, and the Mars Reconnaissance Orbiter. HP HSTNN-CB0W Battery

On the surface are the Mars Exploration Rover Opportunity and its recently decommissioned twin, Spirit, along with several other inert landers and rovers, both successful and unsuccessful. The Phoenix lander completed its mission on the surface in 2008. HP HSTNN-CB0X Battery

Observations by NASA's now-defunct Mars Global Surveyor show evidence that parts of the southern polar ice cap have been receding.

Mars can easily be seen from Earth with the naked eye. Its apparent magnitude reaches ?3.0[7] a brightness surpassed only by Venus, Jupiter, the Moon, and the Sun.HP HSTNN-I79C Battery

Physical characteristics

Mars has approximately half the radius of Earth. It is less dense than Earth, having about 15% of Earth's volume and 11% of the mass. Its surface area is only slightly less than the total area of Earth's dry land.[6]While Mars is larger and more massive than Mercury, Mercury has a higher density. HP HSTNN-I81C Battery

This results in the two planets having a nearly identical gravitational pull at the surface—that of Mars is stronger by less than 1%. Mars is also roughly intermediate in size, mass, and surface gravity between Earth and Earth's Moon (the Moon is about half the diameter of Mars, whereas Earth is twice;HP HSTNN-IB0N Battery

the Earth is about nine times more massive than Mars, and the Moon one-ninth as massive). The red-orange appearance of the Martian surface is caused by iron(III) oxide, more commonly known as hematite, or rust.HP HSTNN-IB0X Battery

Geology

Based on orbital observations and the examination of the Martian meteorite collection, the surface of Mars appears to be composed primarily of basalt. Some evidence suggests that a portion of the Martian surface is more silica-rich than typical basalt, and may be similar to andesitic rocks on Earth;HP HSTNN-LB0W Battery

however, these observations may also be explained by silica glass. Much of the surface is deeply covered by finely grained iron(III) oxide dust.

Although Mars has no evidence of a current structured global magnetic field,observations show that parts of the planet's crust have been magnetized, HP HSTNN-OB0X Battery

and that alternating polarity reversals of its dipole field have occurred in the past. This paleomagnetism of magnetically susceptible minerals has properties that are very similar to the alternating bands found on the ocean floors of Earth. One theory, published in 1999 and re-examined in October 2005 HP HSTNN-OB0Y Battery

(with the help of the Mars Global Surveyor), is that these bands demonstrate plate tectonics on Mars four billion years ago, before the planetarydynamo ceased to function and caused the planet's magnetic field to fade away.

Current models of the planet's interior imply a core region about 1,480 km in radius, consisting primarily of iron with about 14–17% sulfur.HP HSTNN-Q61C Battery

This iron sulfidecore is partially fluid, and has twice the concentration of the lighter elements than exist at Earth's core. The core is surrounded by a silicate mantle that formed many of the tectonic and volcanic features on the planet, but now appears to be inactive.HP HSTNN-Q62C Battery

The average thickness of the planet's crust is about 50 km, with a maximum thickness of 125 km.[ Earth's crust, averaging 40 km, is only one third as thick as Mars’ crust, relative to the sizes of the two planets.HP HSTNN-YB0X Battery

During the Solar System's formation, Mars was created out of the protoplanetary disk that orbited the Sun as the result of a stochastic process of run-away accretion. Mars has many distinctive chemical features caused by its position in the Solar System.HP NBP6A174B1 Battery

Elements with comparatively low boiling points such as chlorine, phosphorus and sulphur are much more common on Mars than Earth; these elements were probably removed from areas closer to the Sun by the young Sun's powerful solar wind.HP HSTNN-YB0X Battery

After the formation of the planets, all were subjected to the "Late Heavy Bombardment". About 60% of the surface of Mars shows an impact record from that era.  Much of the rest of the surface of Mars is probably underlain by immense impact basins that date from this time—HP NBP6A174 Battery

there is evidence of an enormous impact basin in the northern hemisphere of Mars, spanning 10,600 km by 8,500 km, or roughly four times larger than the Moon's South Pole-Aitken basin, the largest impact basin yet discovered.  This theory suggests that Mars was struck by a Pluto-sized body about four billion years ago.HP NBP6A174B1 Battery

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

The geological history of Mars can be split into many periods, but the following are the three primary periods: HP NBP6A175 Battery

  • Noachian period (named after Noachis Terra): Formation of the oldest extant surfaces of Mars, 4.5 billion years ago 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.HP NBP6A175B1 Battery
  • Hesperian period (named after Hesperia Planum): 3.5 billion years ago to 2.9–3.3 billion years ago. The Hesperian period is marked by the formation of extensive lava plains.
  • Amazonian period (named after Amazonis Planitia): 2.9–3.3 Gyr ago billion years ago to present. Amazonian regions have few meteorite impact craters, but are otherwise quite varied. Olympus Mons formed during this period, along with lava flows elsewhere on Mars.HP WD548AA Battery

Some geological activity is still taking place on Mars. The Athabasca Valles is home to sheet-like lava flows up to about 200 Mya. Water flows in the grabens called the Cerberus Fossae occurred less than 20 Mya, indicating equally recent volcanic intrusions.HP WD549AA Battery

On February 19, 2008, images from the Mars Reconnaissance Orbiter showed evidence of an avalanche from a 700 m high cliff.

Soil

The Phoenix lander returned data showing Martian soil to be slightly alkaline and containing elements such as magnesium, sodium, potassium and chloride. HP Envy 17 Notebook PC Battery

These nutrients are found in gardens on Earth, and are necessary for growth of plants.[38] Experiments performed by the Lander showed that the Martian soil has a basic pH of 8.3, and may contain traces of the salt perchlorate.

Streaks are common across Mars and new ones appear frequently on steep slopes of craters, troughs, and valleys. HP Envy 17T Battery

The streaks are dark at first and get lighter with age. Sometimes the streaks start in a tiny area which then spreads out for hundreds of metres. They have also 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 dust devils.HP HSTNN-Q61C Battery

However, several explanations have been put forward, some of which involve water or even the growth of organisms.

Hydrology

Liquid water cannot exist on the surface of Mars due to low atmospheric pressure, except at the lowest elevations for short periods. However, the two polar ice caps appear to be made largely of water.HP GSTNN-Q62C Battery

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. Apermafrost mantle stretches from the pole to latitudes of about 60°.[46]

Large quantities of water ice are thought to be trapped underneath the thick cryosphere of Mars.HP HSTNN-IB1E Battery

Radar data from Mars Express and the Mars Reconnaissance Orbiter show large quantities of water ice both at the poles (July 2005)  and at mid-latitudes (November 2008).[18] The Phoenix lander directly sampled water ice in shallow Martian soil on July 31, 2008.[20]HP HSTNN-IB0X Battery

Landforms visible on Mars strongly suggest that liquid water has at least at times existed on the planet's surface. Huge linear swathes of scoured ground, known as outflow channels, cut across the surface in around 25 places. These are thought to record erosion which occurred during the catastrophic release of water from subsurface aquifers, HP HSTNN-OB0X Battery

though some of these structures have also been hypothesised to result from the action of glaciers or lava.  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, HP HSTNN-YB0X Battery

dendritic networks of valleys are spread across significant proportions of the landscape. Features of these valleys and their distribution very strongly imply that they were carved by runoff resulting from rain or snow fall in early Mars history. HP 586006-361 Battery

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

There are also thousands of features along crater and canyon walls that appear similar to terrestrial gullies. HP NBP6A174 Battery

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 demands the involvement of liquid water, probably from melting ice, although others have argued for formation mechanisms involving carbon dioxide frost or the movement of dry dust. HP NBP6A174B1 Battery

No partially degraded gullies have formed by weathering and no superimposed impact craters have been observed, indicating that these are very young features, possibly even active today.

Other geological features, such as deltas and alluvial fans preserved in craters, also argue very strongly for warmer, wetter conditions at some interval or intervals in earlier Mars history.HP 588178-141 Battery

Such conditions necessarily require the widespread presence of crater lakes across a large proportion of the surface, for which there is also independent mineralogical, sedimentological and geomorphological evidence. Some authors have even gone so far as to argue that at times in the martian past, HP Pavilion dv5 Adapter

much of the low northern plains of the planet were covered with a true ocean hundreds of meters deep, though this remains controversial

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.Sony NP-F330 Battery

Some of the evidence believed to indicate ancient water basins and flows has been negated by higher resolution studies by the Mars Reconnaissance Orbiter.[62] However, in 2004,Opportunity detected the mineral jarosite. This forms only in the presence of acidic water, which demonstrates that water once existed on Mars.Asus Eee PC 904HA Adapter

Polar caps

Mars has two permanent polar ice caps. During a pole's winter, it lies in continuous darkness, chilling the surface and causing 25–30% of the atmosphere to condense out into thick slabs of CO2 ice (dry ice). When the poles are again exposed to sunlight, the frozen CO2sublimes, creating enormous winds that sweep off the poles as fast as 400 km/h. Nikon D80  Battery

These seasonal actions transport large amounts of dust and water vapor, giving rise to Earth-like frost and largecirrus clouds. Clouds of water-ice were photographed by the Opportunity rover in 2004.

The polar caps at both poles consist primarily of water ice.Sony PCGA-AC19V9 Adapter

Frozen carbon dioxide accumulates as a thin layer about one metre thick on the north cap in the northern winter only, while the south cap has a permanent dry ice cover about eight metres thick. The northern polar cap has a diameter of about 1,000 kilometres during the northern Mars summer, Dell T555C Battery

and contains about 1.6 million cubic km of ice, which if spread evenly on the cap would be 2 km thick.[68](This compares to a volume of 2.85 million cubic km (km3) for the Greenland ice sheet.) The southern polar cap has a diameter of 350 km and a thickness of 3 km.HP Pavilion DV6-3013SL Battery

The total volume of ice in the south polar cap plus the adjacent layered deposits has also been estimated at 1.6 million cubic km.[70]Both polar caps show spiral troughs, which are believed to form as a result of differential solar heating, coupled with the sublimation of ice and condensation of water vapor.HP Pavilion DV7-2085EL Battery

The seasonal frosting and defrosting of the southern ice cap results in the formation of spider-like radial channels carved on 1 metre thick ice by sunlight. Then, sublimed CO2—and probably water—increase pressure in their interior producing geyser-like eruptions of cold fluids often mixed with dark basaltic sand or mud.HP Pavilion DV9700 Battery

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

Geography

Although better remembered for mapping the Moon, Johann Heinrich Mädler and Wilhelm Beer were the first "areographers". HP Mini 702EA Battery

They began by establishing that most of Mars’ surface features were permanent, and more precisely determining the planet's rotation period. In 1840, Mädler combined ten years of observations and drew the first map of Mars. Rather than giving names to the various markings, Beer and Mädler simply designated them with letters; Meridian Bay (Sinus Meridiani) was thus feature "a."HP Pavilion DV7-1120EO Battery

Today, features on Mars are named from a number of sources. Large albedo features retain many of the older names, but are often updated to reflect new knowledge of the nature of the features. For example, Nix Olympica (the snows of Olympus) has become Olympus Mons (Mount Olympus).HP Compaq 491278-001 Battery

The surface of Mars as seen from Earth is divided into two kinds of areas, with differing albedo. The paler plains covered with dust and sand rich in reddish iron oxides were once thought of as Martian 'continents' and given names like Arabia Terra (land of Arabia) or Amazonis Planitia (Amazonian plain). HP Pavilion DV6-1030US Battery

The dark features were thought to be seas, hence their names Mare Erythraeum, Mare Sirenum and Aurorae Sinus. The largest dark feature seen from Earth is Syrtis Major Planum.  The permanent northern polar ice cap is named Planum Boreum, while the southern cap is called Planum Australe.HP Compaq 490306-001 Battery

Mars’ 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 in 1830 for their first maps of Mars. After the spacecraft Mariner 9 provided extensive imagery of Mars in 1972, a small crater (later called Airy-0), HP Pavilion DV5-1211EM Battery

located in the Sinus Meridiani ("Middle Bay" or "Meridian Bay"), was chosen for the definition of 0.0° longitude to coincide with the original selection.

Since Mars has no oceans and hence no 'sea level', a zero-elevation surface also had to be selected as a reference level; this is also called the areoid of Mars, analogous to the terrestrial geoid. HP EliteBook 2530P Battery

Zero altitude is defined by the height at which there is 610.5 Pa (6.105 mbar) of atmospheric pressure. This pressure corresponds to the triple point of water, and is about 0.6% of the sea level surface pressure on Earth (0.006 atm). In practice however, today this surface is defined directly from satellite gravity measurements.HP Pavilion DV4385EA Battery

Impact topography

The dichotomy 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,Compaq PP2100 Battery

four billion years ago, the northern hemisphere of Mars was struck by an object one-tenth to two-thirds the size of the Moon. If validated, this would make the northern hemisphere of Mars the site of an impact crater 10,600 km long by 8,500 km wide, or roughly the area of Europe, HP Compaq KU532AA Battery

Asia, and Australia combined, surpassing the South Pole-Aitken basin as the largest impact crater in the Solar System.

Mars is scarred by a number of impact craters: a total of 43,000 craters with a diameter of 5 km or greater have been found.HP Pavilion DV6-1270EQ Battery

The largest confirmed of these is the Hellas impact basin, a light albedo feature 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 the Earth. However, Mars is located closer to the asteroid belt, so it has an increased chance of being struck by materials from that source. HP Pavilion DV4385EA Battery

Mars is also more likely to be struck by short-period comets, i.e., those that lie within the orbit of Jupiter. 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. Some craters have a morphology that suggests the ground became wet after the meteor impacted.HP Compaq Business  NC4400 Battery

Tectonic sites

The shield volcano, Olympus Mons (Mount Olympus), at 27 km is the highest known mountain in the Solar System. It is an extinct volcano in the vast upland region Tharsis, which contains several other large volcanoes. Olympus Mons is over three times the height of Mount Everest, which in comparison stands at just over 8.8 km.HP Pavilion ZD8227 Battery

The large canyon, Valles Marineris (Latin for Mariner Valleys, also known as Agathadaemon in the old canal maps), has a length of 4,000 km and a depth of up to 7 km. The length of Valles Marineris is equivalent to the length of Europe and extends across one-fifth the circumference of Mars.Nikon D200 Battery

By comparison, theGrand Canyon on Earth is only 446 km long and nearly 2 km deep. Valles Marineris was formed due to the swelling of the Tharsis area which caused the crust in the area of Valles Marineris to collapse. Another large canyon is Ma'adim Vallis (Ma'adim is Hebrew for Mars). Acer PA-1650-02 Adapter

It is 700 km long and again much bigger than the Grand Canyon with a width of 20 km and a depth of 2 km in some places. It is possible that Ma'adim Vallis was flooded with liquid water in the past.

Caves

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 Arsia Mons volcano.Sony CYBER-SHOT DSC-T10  Battery

The caves, named after loved ones of their discoverers, are collectively known as the "seven sisters.“Cave entrances measure from 100 m to 252 m wide and they are believed to be at least 73 m to 96 m deep. Because light does not reach the floor of most of the caves,HP Compaq Business 6715b Battery

it is likely that they extend much deeper than these lower estimates and widen below the surface. "Dena" is the only exception; its floor is visible and was measured to be 130 m deep. The interiors of these caverns may be protected from micrometeoroids, UV radiation, solar flares and high energy particles that bombard the planet's surface.Kodak KLIC-7004 Battery

Atmosphere

Mars lost its magnetosphere 4 billion years ago, so the solar wind interacts directly with the Martian ionosphere, lowering the atmospheric density by stripping away atoms from the outer layer. Both Mars Global Surveyor and Mars Express have detected these ionised atmospheric particles trailing off into space behind Mars.Acer Aspire 5920G Adapter

Compared to Earth, the atmosphere of Mars is quite rarefied. Atmospheric pressure on the surface ranges from a low of 30 Pa(0.030 kPa) on Olympus Mons to over 1,155 Pa (1.155 kPa) in the Hellas Planitia, with a mean pressure at the surface level of 600 Pa (0.60 kPa).Canon Digital IXUS 90 IS Battery

The surface pressure of Mars is equal to the pressure found 35 km[97] above the Earth's surface. This is less than 1% of the Earth's surface pressure (101.3 kPa). The scale height of the atmosphere is about 10.8 km,[98] which is higher than Earth's (6 km) because the surface gravity of Mars is only about 38% of Earth's,HP 2133 Mini-Note PC Adapter

an effect offset by both the lower temperature and 50% higher average molecular weight of the atmosphere of Mars.

The atmosphere on Mars consists of 95% carbon dioxide, 3% nitrogen, 1.6% argon and contains traces of oxygen and water.Toshiba PA3536U-1BRS Battery

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.

Methane has been detected in the Martian atmosphere with a mole fraction of about 30 ppb; it occurs in extended plumes, and the profiles imply that the methane was released from discrete regions.HP Compaq Business NX6110 Battery

In northern midsummer, the principal plume contained 19,000 metric tons of methane, with an estimated source strength of 0.6 kilogram per second. The profiles suggest that there may be two local source regions, the first centered near 30° N, 260° W and the second near 0°, 310° W.HP Pavilion DV9000 Adapter

It is estimated that Mars must produce 270 ton/year of methane.

The implied methane destruction lifetime may be as long as about 4 Earth years and as short as about 0.6 Earth years.  This rapid turnover would indicate an active source of the gas on the planet. Dell Studio 1537 Battery

Volcanic activity, cometary impacts, and the presence of methanogenic microbial life forms are among possible sources. Methane could also be produced by a non-biological process called serpentinization[b] involving water, carbon dioxide, and the mineralolivine, which is known to be common on Mars.HP PPP009H Adapter

Climate

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. However, the lengths of the Martian seasons are about twice those of Earth's, as Mars’ greater distance from the Sun leads to the Martian year being about two Earth years long.Sony VGP-BPS8 Battery

Martian surface temperatures vary from lows of about ?87 °C (?125 °F) during the polar winters to highs of up to ?5 °C (23 °F) in summers.[44] 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.Dell PA-12 Adapter

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

If Mars had an Earth-like orbit, its seasons would be similar to Earth's because its axial tilt is similar to Earth's. However, the comparatively large eccentricity of the Martian orbit has a significant effect. Sony Cyber-shot DSC-T7/B  Battery

Mars is near perihelion when it is summer in the southern hemisphere and winter in the north, and near aphelionwhen 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. Dell LATITUDE M65 Battery

The summer temperatures in the south can reach up to 30 °C (54.0 °F) warmer than the equivalent summer temperatures in the north.

Mars also has the largest dust storms in our Solar System. HP Compaq 6720s Adapter

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.

Orbit and rotation

Mars’ average distance from the Sun is roughly 230 million km (1.5 AU) and its orbital period is 687 (Earth) days. Acer AS07B41 Battery

The solar day (or sol) on Mars is only slightly longer than an Earth day: 24 hours, 39 minutes, and 35.244 seconds. A Martian year is equal to 1.8809 Earth years, or 1 year, 320 days, and 18.2 hours.

The axial tilt of Mars is 25.19 degrees, which is similar to the axial tilt of the Earth.Dell Vostro 1310 Battery

As a result, Mars has seasons like the Earth, though on Mars they are nearly twice as long given its longer year. Currently the orientation of the north pole of Mars is close to the star Deneb. Mars passed its perihelion in April 2009  and its aphelion in March 2010.Sony VGP-BPL13 Battery

The next perihelion comes in March 2011 and the next aphelion in February 2012.

Mars has a relatively pronounced orbital eccentricity of about 0.09; of the seven other planets in the Solar System, only Mercury shows greater eccentricity. Sony VGP-BPS13 Battery

However, it is known that in the past Mars has had a much more circular orbit than it does currently. At one point 1.35 million Earth years ago, Mars had an eccentricity of roughly 0.002, much less than that of Earth today.[111] The Mars cycle of eccentricity is 96,000 Earth years compared to the Earth's cycle of 100,000 years.Sony VGP-BPS13/B Battery

However, Mars also 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. 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. Sony VGP-BPS13/S Battery

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

Moons

Mars has two relatively small natural moons, Phobos and Deimos, which orbit close to the planet. Sony VGP-BPS13A/B Battery

Asteroid capture is a long-favored theory but their origin remains uncertain.  Both satellites were discovered in 1877 by Asaph Hall, and 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. Ares was known as Mars to the Romans.Sony VGP-BPS13A/S Battery

From the surface of Mars, the motions of Phobos and Deimos appear very different from that of our own moon. Phobos rises in the west, sets in the east, and rises again in just 11 hours. 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 very slowly.Sony VGP-BPS13AS Battery

Despite the 30 hour orbit of Deimos, it takes 2.7 days to set in the west as it slowly falls behind the rotation of Mars, then just as long again to rise.

Because the orbit of Phobos is below synchronous altitude, the tidal forces from the planet Mars are gradually lowering its orbit.Sony VGP-BPS13B/B Battery

In about 50 million years it will either crash into Mars’ 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 carbonaceous chondrite composition have been regarded as similar to asteroids, supporting the capture theory.Sony VGP-BPS13B/Q Battery

The unstable orbit of Phobos would seem to point towards a relatively recent capture. But both have circular orbits, very near the equator, which is very unusual for captured objects and the required capture dynamics are complex. Sony VGP-BPS13B/S Battery

Accretion early in the history of Mars is also 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 some kind of impact disruption.Sony VGP-BPS13Q Battery

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 theoryfor the origin of Earth's moon. Sony VGP-BPS13S Battery

While 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.

Life

The current understanding of planetary habitability—the ability of a world to develop and sustain life—favors planets that have liquid water on their surface.Sony VGP-BPL21 Battery

This most often requires that the orbit of a planet lie within the habitable zone, which for the Sun currently extends from just beyond Venus to about the semi-major axis of Mars. During perihelion Mars dips inside this region, but the planet's thin (low-pressure) atmosphere prevents liquid water from existing over large regions for extended periods.Sony VGP-BPS21 Battery

The past flow of liquid water, however, demonstrates the planet's potential for habitability. Some recent evidence has suggested that any water on the Martian surface may have been too salty and acidic to support regular terrestrial life.

The lack of a magnetosphere and extremely thin atmosphere of Mars are a challenge:Sony VGP-BPS21/S Battery

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 sublimates to a gaseous state). Mars is also nearly, or perhaps totally, geologically dead;Sony VGP-BPS21A Battery

the end of volcanic activity has apparently stopped the recycling of chemicals and minerals between the surface and interior of the planet.

Evidence suggests that the planet was once significantly more habitable than it is today, but whether living organisms ever existed there remains unknown. Sony VGP-BPS21A/B Battery

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 CO2 production on exposure to water and nutrients.Sony VGP-BPS21B Battery

However, this sign of life was later disputed by some scientists, resulting in a continuing debate, with NASA scientist Gilbert Levin asserting that Viking may have found life. 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. Sony VGP-BPL8 Battery

The tests could even have killed a (hypothetical) life form. Tests conducted by the Phoenix Mars lander have shown that the soil has a very alkaline pH 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.Sony VGP-BPL8A Battery

At the Johnson space center lab, some fascinating shapes have been found in the Martian meteorite ALH84001. Some scientists propose that these geometric shapes could be fossilized microbes extant on Mars before the meteorite was blasted into space by a meteor strike and sent on a 15 million-year voyage to Earth. Sony VGP-BPL8B Battery

However, an exclusively inorganic origin for the shapes has also been proposed.

Small quantities of methane and formaldehyde recently detected by Mars orbiters are both claimed to be hints for life, as these chemical compounds would quickly break down in the Martian atmosphere.Sony VGP-BPS8 Battery

It is remotely possible that these compounds may instead be replenished by volcanic or geological means such as serpentinization.

Exploration

Dozens of spacecraft, including orbiters, landers, and rovers, have been sent to Mars by the Soviet Union, the United States, Europe, and Japan to study the planet's surface, climate, and geology. Sony VGP-BPS8A Battery

As of 2008, the price of transporting material from the surface of Earth to the surface of Mars is approximatelyUS$309,000 per kilogram.

Active probes at the Martian system as of 2011 include the Mars Reconnaissance Orbiter (since 2006), Mars Express (since 2003), 2001 Mars Odyssey(since 2001), and on the surface, Opportunity Rover (since 2004). More recently concluded missions include Mars Global Surveyor (1997–2006) and Spirit Rover (2004–2010).Sony VGP-BPS8B Battery

Roughly two-thirds of all spacecraft destined for Mars have failed in one manner or another before completing or even beginning their missions, including the difficult late 20th century period of early pioneers and first-timers. In the 21st century failures are much less common.HP Compaq Business 6910p Battery

Mission failures are typically ascribed to technical problems, such as failed or lost communications or design errors, often due to inadequate funding or incompetence for a given mission. Such failures have given rise to a satirical counter-culture blaming the failures on an Earth-Mars "Bermuda Triangle", Panasonic LUMIX DMC-TZ4S Battery

a Mars "Curse", or the "Great Galactic Ghoul" that feeds on Martian spacecraft.Some of the latest failures include Beagle 2 (2003), Mars Climate Orbiter (1999), and Mars 96(1996).

Past missions

The first successful fly-by of Mars was on July 14–15, 1965, by NASA's Mariner 4. On November 14, 1971 Mariner 9 became the first space probe to orbit another planet when it entered into orbit around Mars.Sony NP-FH100 Battery

The first objects to successfully land on the surface were two Soviet probes: Mars 2 on November 27 and Mars 3 on December 2, 1971, but both ceased communicating within seconds of landing. The 1975 NASA launches of the Viking program consisted of two orbiters, each having a lander; both landers successfully touched down in 1976. Toshiba Equium M50-192 Battery

Viking 1 remained operational for six years, Viking 2 for three. The Viking landers relayed color panoramas of Mars  and the orbiters mapped the surface so well that the images remain in use.

The Soviet probes Phobos 1 and 2 were sent to Mars in 1988 to study Mars and its two moons. Apple MacBook Pro Battery

Phobos 1 lost contact on the way to Mars. Phobos 2, while successfully photographing Mars and Phobos, failed just before it was set to release two landers to the surface of Phobos.

Following the 1992 failure of the Mars Observer orbiter, the NASA Mars Global Surveyor achieved Mars orbit in 1997. Apple PowerBook G4 Battery

This mission was a complete success, having finished its primary mapping mission in early 2001. Contact was lost with the probe in November 2006 during its third extended program, spending exactly 10 operational years in space. The NASA Mars Pathfinder, carrying a robotic exploration vehicle Sojourner, Acer BATBL50L6 Battery

landed in the Ares Vallis on Mars in the summer of 1997, returning many images.

The NASA Phoenix Mars lander arrived on the north polar region of Mars on May 25, 2008. Its robotic arm was used to dig into the Martian soil and the presence of water ice was confirmed on June 20. The mission concluded on November 10, 2008 after contact was lost.Canon EOS 450D Battery

Current missions

The NASA Mars Odyssey orbiter entered Mars orbit in 2001.[141] Odyssey's Gamma Ray Spectrometer detected significant amounts of hydrogen in the upper metre or so of regolith on Mars. This hydrogen is thought to be contained in large deposits of water ice.Acer Travelmate 2400 Battery

The Mars Express mission of the European Space Agency (ESA) reached Mars in 2003. It carried the Beagle 2 lander, which failed during descent and was declared lost in February, 2004.In early 2004 the Planetary Fourier Spectrometer team announced the orbiter had detected methane in the Martian atmosphere.Dell 451-10617 battery

ESA announced in June 2006 the discovery of aurorae on Mars.

In January 2004, the NASA twin Mars Exploration Rovers named Spirit (MER-A) and Opportunity (MER-B) landed on the surface of Mars. Both have met or exceeded all their targets. Among the most significant scientific returns has been conclusive evidence that liquid water existed at some time in the past at both landing sites. Dell Inspiron 1525 Adapter

Martian dust devils and windstorms have occasionally cleaned both rovers' solar panels, and thus increased their lifespan.

On March 10, 2006, the NASA Mars Reconnaissance Orbiter (MRO) probe arriv

ed in orbit to conduct a two-year science survey.Compaq Presario 2100 Adapter

The orbiter will map the Martian terrain and weather to find suitable landing sites for upcoming lander missions. The MRO snapped the first image of a series of active avalanches near the planet's north pole, scientists said March 3, 2008.

The Dawn spacecraft flew by Mars in February 2009 for a gravity assist on its way to investigate Vesta and then Ceres. Acer Aspire 1362 Battery

Future missions

The Mars Science Laboratory, named Curiosity, will be launched in 2011. It is a larger and more advanced version of the Mars Exploration Rovers, with a movement rate of 90 m/h. Experiments include a laser chemical sampler that can deduce the make-up of rocks at a distance of 13 m.Toshiba Equium M50-192 Battery

The joint Russian and Chinese Phobos-Grunt mission to return samples of the Martian moon, Phobos, is scheduled for launch in 2011. In 2008, NASA announced MAVEN, a robotic mission in 2013 to provide information about the atmosphere of Mars. In 2018 the ESA plans to launch its first Rover to Mars;Dell XPS M1330 Battery

the ExoMars rover will be capable of drilling 2 m into the soil in search of organic molecules.

The Finnish-Russian MetNet mission will land multiple small vehicles on Mars to establish a widespread observation network to investigate the planet's atmospheric structure, physics and meteorology.Acer Travelmate 2200 Adapter

A precursor mission using one or a few landers is scheduled for launch in 2009 or 2011.[152] One possibility is a piggyback launch on the Russian Phobos-Grunt mission.[152]

Manned mission plans

The ESA hopes to land humans on Mars between 2030 and 2035.HP Compaq 6735b Adapter

This will be preceded by successively larger probes, starting with the launch of the ExoMars probe[154] and a joint NASA-ESAMars sample return mission.

Manned exploration by the United States was identified as a long-term goal in the Vision for Space Exploration announced in 2004 by then US President George W. Bush.Dell Vostro 1000 Battery

The planned Orionspacecraft would be used to send a human expedition to Earth's moon by 2020 as a stepping stone to a Mars expedition. On September 28, 2007, NASA administrator Michael D. Griffin stated that NASA aims to put a man on Mars by 2037.HP Compaq nx7300 Adapter

Mars Direct, a low-cost human mission proposed by Robert Zubrin, founder of the Mars Society, would use heavy-lift Saturn V class rockets, such as the Space X Falcon X, or, the Ares V, to skip orbital construction, LEO rendezvous, and lunar fuel depots. Asus f82 Battery

A modified proposal, called "Mars to Stay", involves not returning the first immigrant explorers immediately, if ever (see Colonization of Mars).

Astronomy on Mars

With the existence of various orbiters, landers, and rovers, it is now possible to study astronomy from the Martian skies.Dell XPS M1330 Battery

While Mars’ moon Phobos appears about one third the angular diameter of the full Moon as it appears from Earth, Deimos appears more or less star-like, and appears only slightly brighter than Venus does from Earth.

There are also various phenomena well-known on Earth that have now been observed on Mars, such as meteors and auroras.HP Compaq Business 6910p Battery

A transit of the Earth as seen from Mars will occur on November 10, 2084. There are also transits of Mercury and transits of Venus, and the moons Phobos and Deimos are of sufficiently smallangular diameter that their partial "eclipses" of the Sun are best considered transits (see Transit of Deimos from Mars). Compaq PRESARIO R3000 Battery

Viewing

Because the orbit of Mars is eccentric its apparent magnitude at opposition from the Sun can range from ?3.0 to ?1.4. The minimum brightness is magnitude +1.6 when the planet is in conjunction with the Sun. Mars usually appears a distinct yellow, orange, or reddish color, HP Compaq Business NX6110 Battery

however the actual color of Mars is closer to butterscotch, and the redness seen is actually just dust in the planet's atmosphere; considering this NASA's Spirit rover has taken pictures of a greenish-brown, mud-colored landscape with blue-grey rocks and patches of light red colored sand.Dell Latitude D610 Adapter

When farthest away from the Earth, it is more than seven times as far from the latter as 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—Mars shows a wealth of surface detail to a telescope. Asus Eee PC 701 Adapter

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

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. The duration of this retrograde motion lasts for about 72 days, and Mars reaches its peak luminosity in the middle of this motion.HP Compaq Business NX6325 Battery

Closest approaches

Relative

The point Mars’ geocentric longitude is 180° different from the Sun's is known as opposition, which is near the time of closest approach to the Earth. The time of opposition can occur as much as 8½ days away from the closest approach.Dell Studio XPS 16 Battery

The distance at close approach varies between about 54  and about 103 million km due to the planets' elliptical orbits, which causes comparable variation in angular size. The last Mars opposition occurred on January 29, 2010. The next one will occur on March 3, 2012 at a distance of about 100 million km.Acer Aspire 5520 Battery

The average time between the successive oppositions of Mars, itssynodic period, 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 retrograde motion, 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.Acer TravelMate 5720 Adapter

Absolute, around the present time

Mars made its closest approach to Earth and maximum apparent brightness in nearly 60,000 years, 55,758,006 km (0.372719 AU), magnitude?2.88, on 27 August 2003 at 9:51:13 UT. This occurred when Mars was one day from opposition and about three days from its perihelion, making Mars particularly easy to see from Earth. HP Compaq 6735s Adapter

The last time it came so close is estimated to have been on September 12, 57 617 BC, the next time being in 2287.  However, this record approach was only very slightly closer than other recent close approaches. For instance, the minimum distance on August 22, 1924 was 0.37285 AU, and the minimum distance on August 24, 2208 will be 0.37279 AU.Dell XPS M1330 Battery

An email sent during the close approach in 2003 has, in succeeding years, repeatedly spawned hoax emails saying that Mars will make its closest approach for thousands of years, and will look as big as the Moon.

Historical observations

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.HP Compaq nc6230 Adapter

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.

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.Dell T117C Battery

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. For Mars, they knew that the planet made 37synodic periods, or 42 circuits of the zodiac, every 79 years. Asus x5dij-sx039c Battery

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

In the fourth century BCE, Aristotle noted that Mars disappeared behind the Moon during an occultation, indicating the planet was farther away.Dell Inspiron 1464 Battery

Ptolemy, a Greek living in Alexandria, attempted to address the problem of the orbital motion of Mars. 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.HP Compaq 6720s Adapter

Literature from ancient China confirms that Mars was known by Chinese astronomers by no later than the fourth century BCE.In the fifth century CE, the Indian astronomical text Surya Siddhanta estimated the diameter of Mars.

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.Dell Latitude D630 Adapter

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 Giovanni Domenico Cassini in 1672. However, the early parallax measurements were hampered by the quality of the instruments.HP Pavilion dm4 Battery

The only occultation of Mars by Venus observed was that of October 13, 1590, seen by Michael Maestlin atHeidelberg. In 1610, Mars was viewed by Galileo Galilei, 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 Christiaan Huygens. Sony NP-FS11 Battery

Martian 'canals'

By the 19th century, the resolution of telescopes reached a level sufficient for surface features to be identified. In September 1877, a perihelic opposition of Mars occurred on September 5. In that year, Italian astronomer Giovanni Schiaparelli used a 22 cm telescope in Milan to help produce the first detailed map of Mars. Dell Inspiron 1520 Adapter

These maps notably contained features he called canali, which were later shown to be an optical illusion. These canali were supposedly long straight lines on the surface of Mars to which he gave names of famous rivers on Earth. His term, which means 'channels' or 'grooves', was popularly mistranslated in English ascanals.Toshiba PA3399U-1BRS Battery

Influenced by the observations, the orientalist Percival Lowell founded an observatory which had a 300 and 450 mm telescope. The observatory was used for the exploration of Mars during the last good opportunity in 1894 and the following less favorable oppositions. Acer Aspire 5920G Adapter

He published several books on Mars and life on the planet, which had a great influence on the public. The canali were also found by other astronomers, like Henri Joseph Perrotin and Louis Thollon in Nice, using one of the largest telescopes of that time.Acer Aspire 5920 Battery

The seasonal changes (consisting of the diminishing of the polar caps and the dark areas formed during Martian summer) in combination with the canals lead 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. IBM Thinkpad T40 Adapter

However, as bigger telescopes were used, fewer long, straight canali were observed. During an observation in 1909 by Flammarionwith a 840 mm 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.Nikon COOLPIX 4300 Battery

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

It was not until spacecraft visited the planet during NASA's Mariner missions in the 1960s that these myths were dispelled. The results of the Viking life-detection experiments started an intermission in which the hypothesis of a hostile, dead planet was generally accepted.Apple MB771 Battery

Some maps of Mars were made using the data from these missions, but it was not until the Mars Global Surveyor mission, launched in 1996 and operated until late 2006, that complete, extremely detailed maps of the martian topography, magnetic field and surface minerals were obtained. These maps are now available online, for example, at Google Mars.Sony DSC-P5 Battery

In culture

Mars is named after the Roman god of war. In different cultures, Mars represents masculinity and youth. Its symbol, a circle with an arrow pointing out to the upper right, is also used as a symbol for the male gender.Dell Inspiron 6400 Adapter

Intelligent "Martians"

The popular idea that Mars was populated by intelligent Martians exploded in the late 19th century. 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.Toshiba PA3534U-1BRS Battery

Many other observations and proclamations by notable personalities added to what has been termed "Mars Fever". 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. Sony NP-FP50 Battery

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.HP Compaq nx7300 Adapter

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.Dell Latitude D820 Adapter

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. However, Kelvin "emphatically" denied this report shortly before departing America: Toshiba PA3399U-1BRS Battery

"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."

In a New York Times article in 1901, Edward Charles Pickering, director of the Harvard College Observatory,Dell Studio XPS 1640 Battery

said that they had received a telegram fromLowell Observatory in Arizona that seemed to confirm that Mars was trying to communicate with the Earth.

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. Dell Latitude D830 Battery

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. That was all. Now the story has gone the world over.Dell Inspiron E1505 Adapter

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.Asus Eee PC 1201PN Battery

Pickering later proposed creating a set of mirrors in Texas with the intention of signaling Martians.

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,Asus Eee PC 701 Adapter

but pseudoscientific speculation about intelligent life on Mars continues from commentators such as Richard C. Hoagland. Reminiscent of the canali controversy, some speculations are based on small scale features perceived in the spacecraft images, such as 'pyramids' and the 'Face on Mars'. Planetary astronomer Carl Sagan wrote:Dell XPS M1330 Battery

The depiction of Mars in fiction has been stimulated by its dramatic red color and by nineteenth century scientific speculations that its surface conditions not only might support life, but intelligent life.Thus originated a large number of science fiction scenarios, among which is H. G.fujifilm np95 Battery

Wells' The War of the Worlds, published in 1898, in which Martians seek to escape their dying planet by invading Earth. A subsequent US radio adaptation of The War of the Worlds on October 30, 1938 byOrson Welles was presented as a live news broadcast, and became notorious for causing a public panic when many listeners mistook it for the truth.Asus Eee PC 900 Adapter

Influential works included Ray Bradbury's The Martian Chronicles, in which human explorers accidentally destroy a Martian civilization, Edgar Rice Burroughs'Barsoom series, C. S. Lewis' novel Out of the Silent Planet (1938),  the Mars trilogy of Kim Stanley Robinson and a number of Robert A. Heinlein stories before the mid-sixties.Sony VAIO PCG-713 Battery

Author 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.

A comic figure of an intelligent Martian, Marvin the Martian, appeared on television in 1948 as a character in the Looney Tunes animated cartoons of Warner Brothers, and has continued as part of popular culture to the present.Dell Latitude D830 Adapter

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. Dell Studio XPS 1640 Battery

However, 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. Panasonic LUMIX DMC-TZ4S  Battery

The theme of a Martian colony that fights for independence from Earth is a major plot element in the novels of Greg Bear and Kim Stanley Robinson, as well as the movie Total Recall (based on a short story by Philip K. Dick) and the television series Babylon 5. Some video games also use this element, including Red Faction and the Zone of the Enders series. HP Compaq Business NX6320 Battery

Mars (and its moons) were also the setting for the popular Doom video game franchise and the later Martian Gothic.

The colonization of Mars by humans is the focus of speculation and serious study because the surface conditions and availability of water on Mars make it arguably the most hospitable planet in the solar system other than Earth.Canon POWERSHOT G2 Battery

The Moon has been proposed as the first location for human colonization but Mars has an atmosphere, giving it the potential capacity to host human and other organic life.

Relative similarity to Earth

The Earth is very like its "sister planet" Venus in bulk composition, size and surface gravity but Mars' similarities to Earth are more compelling when considering colonization. These include:Dell Latitude E6500 Battery

  • The Martian day (or sol) is very close to Earth's. A Mars solar day is 24 hours 39 minutes 35.244 seconds. (See timekeeping on Mars.)
  • Mars has a surface area that is 28.4% of Earth's, only slightly less than the amount of dry land on Earth (which is 29.2% of Earth's surface). Mars has half the radius of Earth and only one-tenth the mass.Dell LATITUDE D630 Battery
  • This means that it has a smaller volume (~15%) and lower average density than Earth.
  • Mars has an axial tilt of 25.19°, compared with Earth's 23.44°. As a result, Mars has seasons much like Earth, though they last nearly twice as long because the Martian year is about 1.88 Earth years.Asus R33030 Adapter
  • The Martian north pole currently points at Cygnus, not Ursa Minor.
  • Mars has an atmosphere. Although it is very thin (about 0.7% of Earth's atmosphere) it provides some protection from solar and cosmic radiation and has been used successfully for aerobraking of spacecraft.Dell Mini 1011 Battery
  • Recent observations by NASA's Mars Exploration Rovers, ESA's Mars Express and NASA's Phoenix Lander confirm the presence of water ice on Mars. Mars appears to have significant quantities of all the elements necessary to support Earth-based life.toshiba pa3332u-1brs Battery

Differences from Earth

  • The surface gravity on Mars is 38% of that on Earth. It is not known if this is enough to prevent the health problems associated with weightlessness.HP Compaq 6710b Adapter
  • Mars is much colder than Earth, with a mean surface temperature of ?63 °C and a low of ?140 °C. The lowest temperature ever recorded on Earth was ?89.2 °C, inAntarctica.
  • Because Mars is further from the Sun, the amount of solar energy reaching the upper atmosphere (the solar constant) is less than half of what reaches the Earth's upper atmosphere or the Moon's surface. However, the solar energy that reaches the surface of Mars is not impeded by a thick atmosphere like on Earth.Acer Aspire 5720 Adapter
  • Mars' orbit is more eccentric than Earth's, exacerbating temperature and solar constant variations.
  • The atmospheric pressure on Mars is ~6 mbar, far below the Armstrong Limit (61.8 mbar) at which people can survive without pressure suits. Toshiba Equium A110-252 Battery
  • Since terraformingcannot be expected as a near-term solution, habitable structures on Mars would need to be constructed with pressure vessels similar to spacecraft, capable of containing a pressure between a third and a whole bar.Acer Aspire 5052ANWXMi Battery
  • The Martian atmosphere consists mainly of carbon dioxide. Because of this, even with the reduced atmospheric pressure, the partial pressure of CO2 at the surface of Mars is some 52 times higher than on Earth. It also has significant levels of carbon monoxide.Dell Mini 1011v Battery
  • Mars has a very weak magnetosphere, so it deflects solar winds poorly.

Habitability

Conditions on the surface of Mars are much closer to habitability than the surface of any other known planet or moon, as seen by the extremely hot and cold temperatures on Mercury, the furnace-hot surface of Venus, or the cryogenic cold of the outer planets and their moons. HP Compaq nx7300 Adapter

Only the cloud tops of Venus are closer in terms of habitability to Earth than Mars is.  There are natural settings on Earth where humans have explored that match most conditions on Mars. The highest altitude reached by a manned balloon ascent, a record set in May 1961, was 34,668 meters (113,740 feet).Dell Vostro 1510 Battery

The pressure at that altitude is about the same as on the surface of Mars. Extreme cold in the Arctic and Antarctic match all but the most extreme temperatures on Mars.

NASA Deputy Administrator Shana Dale said, "We also hope to discover if Mars can provide a second home for humans—an extension of our civilization—40 million miles from Earth."Toshiba PA3534U-1BRS Battery

Terraforming

It may be possible to terraform Mars to allow a wide variety of living things, including humans, to survive unaided on Mars' surface.

Radiation

Mars has no global magnetic field comparable to Earth's geomagnetic field. Asus M50 Battery

Combined with a thin atmosphere, this permits a significant amount of ionizing radiation to reach the Martian surface. The Mars Odyssey spacecraft carried an instrument, the Mars Radiation Environment Experiment (MARIE), to measure the dangers to humans.Asus Eee PC 901 Battery

MARIE found that radiation levels in orbit above Mars are 2.5 times higher than at the International Space Station. Average doses were about 22 millirads per day (220 micrograys per day or 0.08 gray per year.) A three year exposure to such levels would be close to the safety limits currently adopted by NASA. Dell Inspiron 6400 Battery

Levels at the Martian surface would be somewhat lower and might vary significantly at different locations depending on altitude and local magnetic fields.

Occasional solar proton events (SPEs) produce much higher doses.HP Compaq Business NC6220 Battery

Some SPEs were observed by MARIE that were not seen by sensors near Earth due to the fact that SPEs are directional, making it difficult to warn astronauts on Mars early enough.

Much remains to be learned about space radiation. In 2003, NASA's Lyndon B. Johnson Space Center opened a facility,Sony VGP-BPS9 Battery

the NASA Space Radiation Laboratory, at Brookhaven National Laboratory that employs particle accelerators to simulate space radiation. The facility will study its effects on living organisms along with shielding techniques. There is some evidence that this kind of low level, chronic radiation is not quite as dangerous as once thought; and that radiation hormesis occurs.Sony VGP-BPS13 Battery

The consensus among those that have studied the issues is that radiation levels, with the exception of the SPEs, that would be experienced on the surface of Mars, and while journeying there, are certainly a concern, but are not thought to prevent a trip from being made with current technology.HP Compaq nx7300 Adapter

Interplanetary spaceflight

Mars requires less energy per unit mass (delta V) to reach from Earth than any planet except Venus. Using a Hohmann transfer orbit, a trip to Mars requires approximately nine months in space.HP Compaq 2510p Adapter

Modified transfer trajectories that cut the travel time down to seven or six months in space are possible with incrementally higher amounts of energy and fuel compared to a Hohmann transfer orbit, and are in standard use for robotic Mars missions. Dell Studio PP39L Battery

Shortening the travel time below about six months requires higher delta-v and an exponentially increasing amount of fuel, and is not feasible with chemical rockets, but would be perfectly feasible with advanced spacecraft propulsion technologies, some of which have already been tested, such as VASIMR,Nikon COOLPIX 5700  Battery

and nuclear rockets. In the former case, a trip time of forty days could be attainable,  and in the latter, a trip time down to about two weeks. Another possibility is constant-acceleration technologies such as space-proven solar sails and ion drives which permit passage times at close approaches on the order of several weeks. Dell Studio XPS 16 Battery

Both of these propulsion systems have been deployed and could readily obtain a constant acceleration of 0.1 g.

During the journey the astronauts are subject to radiation, which requires a means to protect them. Cosmic radiation and solar wind cause DNA damage, which increases the risk of cancer significantly. HP Compaq nx7400 Adapter

The effect of long term space travel in the interplanetary space is unknown, but scientists estimate up to 1% probability for male persons to die of cancer because of the radiation during the journey to Mars and back to Earth. Together with the base probability of 20% for a male person on Earth to die from cancer this gives a probability of 21%.HP Pavilion DV6500 Adapter

For women the probability is higher due to their larger glandular tissues.

Landing on Mars

Mars has a gravity 0.38 times that of the Earth and the density of its atmosphere is 1% of that on Earth.  The relatively strong gravity and the presence of aerodynamic effects makes it difficult to land heavy, Dell T117C Battery

crewed spacecraft with thrusters only as was done with the Apollo moon landings, yet the atmosphere is too thin for aerodynamic effects to be of much help in braking and landing a large vehicle. Landing piloted missions on Mars will require braking and landing systems different from anything used to land crewed spacecraft on the Moon or robotic missions on Mars.Acer PA-1650-02 Adapter

If one assumes carbon nanotube construction material will be available with a strength of 130 GPa then a space elevator could be built to land men and material on Mars. A space elevator on Phobos has also been proposed.

Communication

Communications with Earth are relatively straightforward during the half-sol when the Earth is above the Martian horizon. Acer Aspire 5920G Adapter

NASA and ESA included communications relay equipment in several of the Mars orbiters, so Mars already has communications satellites. While these will eventually wear out, additional orbiters with communication relay capability are likely to be launched before any colonization expeditions are mounted.Asus S1 Adapter

The one-way communication delay due to the speed of light ranges from about 3 minutes at closest approach (approximated by perihelion of Mars minus aphelion of Earth) to 22 minutes at the largest possible superior conjunction (approximated by aphelion of Mars plus aphelion of Earth).HP Pavilion dv6000 Battery

Telephone conversations or Internet Relay Chat between Earth and Mars would be highly impractical due to the long time lags involved. NASA has found that direct communication can be blocked for about two weeks every synodic period, around the time of superior conjunction when the Sun is directly between Mars and Earth,Ibm Thinkpad T30 Battery

although the actual duration of the communications blackout varies from mission to mission depending on various factors - such as the amount of link margin designed into the communications system, and the minimum data rate that is acceptable from a mission standpoint. In reality most missions at Mars have had communications blackout periods of the order of a month.Dell Studio PP39L Battery

A satellite at either of the Earth-Sun L4/L5 Lagrange points could serve as a relay during this period to solve the problem; even a constellation of communications satellites would be a minor expense in the context of a full colonization program. HP Pavilion dv5 Adapter

However the size and power of the equipment needed for these distances make the L4 and L5 locations unrealistic for relay stations, and the inherent stability of these regions, while beneficial in terms of station-keeping, also attracts asteroids, which could pose a severe risk to any satellite.HP Compaq Business NC6400 Battery

Recent work by the University of Strathclyde's Advanced Space Concepts Laboratory, in collaboration with the European Space Agency, has suggested an alternative relay architecture based on highly non-Keplerian orbits. These are a special kind of orbit produced when continuous low-thrust propulsion, HP Compaq 490306-001 Battery

such as that produced from an ion engine or solar sail, modifies the natural trajectory of a spacecraft. Such an orbit would enable continuous communications during solar conjunction by allowing a relay spacecraft to "hover" above Mars, out of the orbital plane of the two planets.Compaq Presario CQ35-100 Battery

Such a relay avoids the problems of satellites stationed at either L4 or L5 by being significantly closer to the surface of Mars while still maintaining continuous communication between the two planets.

Robotic precursors

The path to a human colony could be prepared by robotic systems such as the Mars Exploration Rovers Spirit and Opportunity.HP Compaq HSTNN-LB51 Battery

These systems could help locate resources, such as ground water or ice, that would help a colony grow and thrive. The lifetimes of these systems would be measured in years and even decades, and as recent developments in commercial spaceflight have shown, it may be that these systems will involve private as well as government ownership.HP Pavilion ZE4500 Battery

These robotic systems also have a reduced cost compared with early crewed operations, and have less political risk.

Wired systems might lay the groundwork for early crewed landings and bases, by producing various consumables including fuel, oxidizers, water, and construction materials. HP G62-100EB Battery

Establishing power, communications, shelter, heating, and manufacturing basics can begin with robotic systems, if only as a prelude to crewed operations.

Early human missions

Early human missions to Mars, such as those being tentatively planned by NASA, FKA and ESA would not be direct precursors to colonization.HP Pavilion DV6-1211AX Battery

They are intended solely as exploration missions, as the Apollo missions to the Moon were not planned to be sites of a permanent base.

Colonization requires the establishment of permanent bases that have potential for self-expansion. A famous proposal for building such bases is the Mars Direct plan, advocated by Robert Zubrin.HP Pavilion DV6-1220SO Battery

The Mars Society has established the Mars Analogue Research Station Programme at sites Devon Island in Canada and in Utah, United States, to experiment with different plans for human operations on Mars, based on Mars Direct. Modern Martian architecture concepts often include facilities to produce oxygen and propellant on the surface of the planet.HP EliteBook 6930P Battery

Economics

As with early colonies in the New World, economics would be a crucial aspect to a colony's success. The reduced gravity well of Mars and its position in the solar system may facilitate Mars-Earth trade and provide the rationalization for continued settlement of the planet.HP Pavilion DV6-1210SA Battery

Mars' reduced gravity together with its rotation rate makes it possible for the construction of a space elevator with today's materials, although the low orbit ofPhobos could present engineering challenges. If constructed, the elevator could transport minerals and other natural resources extracted from the planet.Compaq Presario CQ71 Battery

A major economic problem is the enormous up-front investment required to establish the colony and perhaps also terraform the planet.

Some early Mars colonies might specialize in developing local resources for Martian consumption, such as water and/or ice. Local resources can also be used in infrastructure construction.HP Pavilion DV7-1290EO Battery

One source of Martian ore currently known to be available is reduced iron in the form of nickel-iron meteorites. Iron in this form is more easily extracted than from the iron oxides that cover the planet.

Another main inter-Martian trade good during early colonization could be manure.HP G6000 Battery

Assuming that life doesn't exist on Mars, the soil is going to be very poor for growing plants, so manure and other fertilizers will be valued highly in any Martian civilization until the planet changes enough chemically to support growing vegetation on its own.HP HDX X18-1005EA Battery

Solar power is a candidate for power for a Martian colony. Solar insolation (the amount of solar radiation that reaches Mars) is about 42% of that on Earth, since Mars is about 52% farther from the Sun and insolation falls off as the square of distance. HP Pavilion DV6-3013SL Battery

But the thin atmosphere would allow almost all of that energy to reach the surface as compared to Earth, where the atmosphere absorbs roughly a quarter of the solar radiation.

Nuclear power is also a good candidate, since the fuel is very dense for cheap transportation from Earth. HP Compaq HSTNN-IB62 Battery

Nuclear power also produces heat, which would be extremely valuable to a Mars colony.

Heating requirements could be lowered if the colonists use domes to trap solar heat, especially for greenhouses.HP Pavilion DV6100 Battery

Advocacy

Making Mars colonization a reality is advocated by several groups with different reasons and proposals. One of the oldest is the Mars Society. They promote a NASA program to accomplish human exploration of Mars and have set up Mars analog research stations in Canada and the United States. HP EliteBook 2730P Battery

Another group is MarsDrive, which is dedicated to private initiatives for the exploration and settlement of Mars.

Concerns

Besides the general criticism of human colonization of space (see space colonization), there are specific concerns about a colony on Mars:HP Pavilion DV9000 Battery

  • Mars has a gravity 0.38 times that of the Earth and a density of the atmosphere of 1% that on Earth. The stronger gravity than the Moon and the presence of aerodynamic effects makes it more difficult to land heavy, crewed spacecraft with thrusters only, HP Pavilion DV7 Battery
  • yet the atmosphere is also too thin to get very much use out of aerodynamic effects for braking and landing. Landing piloted missions on Mars will require a braking and landing system different from anything used to land crewed spacecraft on the Moon or robotic missions on Mars.HP Pavilion DV7-1290EO Battery
  • The question of whether life once existed or exists now on Mars has not been settled, raising concerns about possible contamination of the planet with Earth life. See Life on Mars.
  • Advocates of a return to the Moon say the Moon is a more logical first location for a first planetary colony, perhaps using it as practice for future manned missions to Mars.HP Compaq Business 6735S Battery
  • However, in several ways experience gained on the moon would not be applicable to the task of colonizing Mars. The moon has no atmosphere, no analogous geology and a much greater temperature range and rotational period. These differences make Mars more in common with Earth than the Moon. HP 540 Battery
  • Antarctica or desert areas of Earth provide much better training grounds at vastly lesser cost. Also, the Moon is extremely poor in several of the key elements required for life, most notably hydrogen, nitrogen and carbon (50 – 100 ppm) , and has only 47.2% of the delta-v requirement for launching to orbit that Mars has.HP Compaq Business NW9440 Battery
  • It is unknown whether Martian gravity can support human life in the long term (all experience is at either ~1g or zero gravity). Space medicine researchers have theorized on whether the health benefits of gravity rise slowly or quickly between weightlessness and full Earth gravity. HP Compaq Business  TC4400 Battery
  • One theory is that sleeping chambers built inside centrifuges would minimize the health problems. The Mars Gravity Biosatellite experiment was due to become the first experiment testing the effects of partial gravity, artificially generated at 0.38 g to match Mars gravity, HP Compaq 491278-001 Battery
  • on mammal life, specifically on mice, throughout the life cycle from conception to death.  However, in 2009 the Biosatellite project was cancelled due to lack of funds.
  • Mars' escape velocity is 5 km/s, which, though less than half that for Earth, HP HSTNN-LB31 Battery
  • is reasonably high compared to the Moon's 2.38 km/s or the negligible escape velocity of most asteroids.[31] This could make physical export trade from Mars to other planets and habitats less viable economically.HP Pavilion DV3-4000  Battery
  • There is likely to be little economic return from the colonization of Mars while Lunar and Near Earth Asteroid industry is likely to be exporting to Earth.

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