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Mars Astronomical symbol of Mars
The planet Mars
A composite image of Mars.
Orbital characteristics (Epoch J2000)
Semi-major axis 227,936,637 km
1.523 662 31 AU
Orbital circumference 1.429 Tm
9.553 AU
Eccentricity 0.093 412 33
Perihelion 206,644,545 km
1.381 333 46 AU
Aphelion 249,228,730 km
1.665 991 16 AU
Revolution period 686.9600 d
(1.8808 a)
Synodic period 779.96 d
(2.135 a)
Avg. Orbital Speed 24.077 km/s
Max. Orbital Speed 26.499 km/s
Min. Orbital Speed 21.972 km/s
Inclination 1.850 61°
(5.65° to Sun's equator)
Longitude of the
ascending node
49.578 54°
Argument of the
286.462 30°
Number of satellites 2
Physical characteristics
Equatorial diameter 6,804.9 km
(0.533 Earths)
Polar diameter 6,754.8 km
(0.531 Earths)
Oblateness 0.007 36
Surface area 1.448×108 km2
(0.284 Earths)
Volume 1.638×1011 km3
(0.151 Earths)
Mass 6.4185×1023 kg
(0.107 Earths)
Mean density 3.934 g/cm3
Equatorial gravity 3.69 m/s2
Escape velocity 5.027 km/s
Rotation period 1.025 957 d
(24.622 962 h)
Rotation velocity 868.22 km/h
(at the equator)
Axial tilt 25.19°
Right ascension
of North pole
317.681 43°
(21 h 10 min 44 s)
Declination 52.886 50°
Albedo 0.15
Surface temp.
- min
- mean
- max

133 K
210 K
293 K
Adjective Martian
Atmospheric characteristics
Atmospheric pressure 0.7-0.9 kPa
Carbon dioxide 95.32%
Nitrogen 2.7%
Argon 1.6%
Oxygen 0.13%
Carbon monoxide 0.07%
Water vapor 0.03%
Nitric oxide 0.01%
Neon 2.5 ppm
Krypton 300 ppb
Xenon 80 ppb
Ozone 30 ppb
Methane 10.5 ppb
Mars from Hubble Space Telescope October 28, 2005 with sandstorm visible.
Mars from Hubble Space Telescope October 28, 2005 with sandstorm visible.
Mars, with polar ice caps visible.
Mars, with polar ice caps visible.
North Polar region with icecap. (Courtesy NASA/JPL-Caltech.)
North Polar region with icecap. (Courtesy NASA/JPL-Caltech.)

Mars, the fourth planet from the Sun in our solar system, is named after the Roman god of war Mars (Ares in Greek mythology), because of its apparent red color. This feature also earned it the nickname "The Red Planet". Mars has two moons, Phobos and Deimos, which are small and oddly-shaped, possibly being captured asteroids. The prefix areo- refers to Mars in the same way geo- refers to Earth—for example, areology versus geology. (However, areology is also used to refer to the study of Mars as a whole rather than just the geological processes of the planet.)

The astronomical symbol for Mars is a circle with an arrow pointing northeast (Unicode: ♂). This symbol is a stylized representation of the shield and spear of the god Mars, and in biology it is used as a sign for the male sex.

The Chinese, Korean, and Japanese cultures refer to the planet as the Fire Star, based on the Five Elements.



Main article: Mars (god)

Mars has been obvious to skygazers since prehistoric times. It was known by the Egyptians as "Her Deschel" or "the Red One". Among the Babylonians Mars was known as "Nirgal" or "the Star of Death". The Romans were the ones to give Mars its modern name, after their god of war.

Physical characteristics

The red, fiery appearance of Mars is caused by iron oxide (rust) on its surface. Mars has only a quarter the surface area of the Earth and only one-tenth the mass, though its surface area is approximately equal to that of the Earth's dry land because Mars lacks oceans. The solar day (or sol) on Mars is very close to Earth's day: 24 hours, 39 minutes, and 35.244 seconds.


Mars' atmosphere is thin: The air pressure on the surface is only 750 pascals, about 0.75% of the average on Earth. However, the scale height of the atmosphere is about 11 km, somewhat higher than Earth's 6 km. The atmosphere on Mars is 95% carbon dioxide, 3% nitrogen, 1.6% argon, and contains traces of oxygen and water. In 2003, methane was apparently discovered in the atmosphere by Earth-based telescopes and possibly confirmed in March 2004 by the Mars Express Orbiter; present measurements state an average methane concentration of about 11±4 ppb by volume (see reference). The thin atmosphere cannot hold heat and is the cause of the lower temperatures on Mars. The maximum temperature is roughly 20 °C (68 °F).

The presence of methane on Mars would be very intriguing, since as an unstable gas it indicates that there must be (or have been within the last few hundred years) a source of the gas on the planet. Volcanic activity, comet impacts, and the existence of life in the form of microorganisms such as methanogens are among possible but as yet unproven sources. The methane appears to occur in patches, which suggests that it is being rapidly broken down before it has time to become uniformly distributed in the atmosphere, and so it is presumably also continually being released to the atmosphere. Plans are now being made to look for other companion gases that may suggest which sources are most likely; in the Earth's oceans biological methane production tends to be accompanied by ethane, while volcanic methane is accompanied by sulfur dioxide.

Other aspects of the Martian atmosphere vary significantly. In the winter months when the poles are in continual darkness, the surface gets so cold that as much as 25% of the entire atmosphere condenses out into meters thick slabs of CO2 ice (dry ice). When the poles are again exposed to sunlight the CO2 ice sublimates, creating enormous winds that sweep off the poles as fast as 250 mph. These seasonal actions transport large amounts of dust and water vapor giving rise to Earth-like frost and large cirrus clouds. These clouds of water-ice were photographed by the Opportunity rover in 2004.[1]

Recently, evidence has been discovered suggesting that Mars may be warming in the short term[2]; however, it is now cooler than it was in the 1970s.[3]


The surface of Mars is primarily composed of basalt and andesite rock, covered in many places by meters-thick layers of dust as fine as talcum powder.

Observations of the magnetic fields on Mars by the Mars Global Surveyor spacecraft have revealed that parts of the planet's crust has been magnetized in alternating bands, typically measuring 100 miles wide by 600 miles long (160 km by 1000 km), in a similar pattern to those found on the ocean floors of Earth. One interesting theory, published in 1999 is that these bands could be evidence of the past operation of plate tectonics on Mars, although this has yet to be proven [4]. New findings, published in October 2005 support this theory, and seem to indicate an early era of tectonic activity similar to that found on Earth due to sea-floor spreading [5]. If true, the processes involved may have helped to sustain an Earth-like atmosphere by transporting carbon rich rocks to the surface, while the presence of a magnetic field would have helped to protect the planet from cosmic radiation. Other explanations have also been proposed.

Microscopic rock forms indicating past signs of water taken by Opportunity
Microscopic rock forms indicating past signs of water taken by Opportunity

Amongst the findings from the Opportunity rover is the presence of hematite on Mars in the form of small spheres on the Meridiani Planum. The spheres are only a few millimeters in diameter and are believed to have formed as rock deposits under watery conditions billions of years ago. Other minerals have also been found containing forms of sulfur, iron or bromine such as jarosite. This and other evidence led a group of 50 scientists to conclude in the December 9, 2004 edition of the journal Science that "Liquid water was once intermittently present at the Martian surface at Meridiani, and at times it saturated the subsurface. Because liquid water is a key prerequisite for life, we infer conditions at Meridiani may have been habitable for some period of time in Martian history". On the opposite side of the planet the mineral goethite, which (unlike hematite) forms only in the presence of water, along with other evidence of water, has also been found by the Spirit rover in the "Columbia Hills".

In 1996, researchers studying a meteorite (ALH84001) believed to have originated from Mars reported features which they attributed to microfossils left by life on Mars. As of 2005, this interpretation remains controversial with no consensus having emerged.


The dichotomy of Martian topography is striking: northern plains flattened by lava flows contrast with the southern highlands, pitted and cratered by ancient impacts. The surface of Mars as seen from Earth is consequently divided into two kinds of areas, with differing albedo. The paler plains covered with dust and sand rich in reddish iron oxides were once thought of as Martian 'continents' and given names like Arabia Terra (land of Arabia) or Amazonis Planitia (Amazonian plain). The dark features were thought to be seas, hence their names Mare Erythraeum, Mare Sirenum and Aurorae Sinus. The largest dark feature seen from Earth is Syrtis Major.

Mars has polar ice caps that contain frozen water and carbon dioxide that change with the Martian seasons — the carbon dioxide ice sublimates in summer, uncovering a surface of layered rocks, and forms again in winter. An extinct shield volcano, Olympus Mons (Mount Olympus), is at 26 km the highest mountain in the solar system. It is in a vast upland region called Tharsis, containing several large volcanos. See list of mountains on Mars. Mars also has the solar system's largest canyon system, Valles Marineris or the Mariner Valley, which is 4000 km long and 7 km deep. Mars is also scarred by a number of impact craters. The largest of these is the Hellas impact basin, covered with light red sand. See list of craters on Mars.

The difference between Mars' highest and lowest points is nearly 31 km (from the top of Olympus Mons at an altitude of 26 km to the bottom of the Hellas impact basin at an altitude of 4 km below the datum). In comparison, the difference between Earth's highest and lowest points (Mount Everest and the Mariana Trench) is only 19.7 km. Combined with the planets' different radii, this means Mars is nearly three times "rougher" than Earth.

The International Astronomical Union's Working Group for Planetary System Nomenclature is responsible for naming Martian surface features.

Topographic map of Mars, courtesy NASA/JPL-Caltech. Notable features include the Tharsis volcanoes in the west (including Olympus Mons), Valles Marineris to the east of Tharsis, and Hellas Basin in the southern hemisphere.
Topographic map of Mars, courtesy NASA/JPL-Caltech. Notable features include the Tharsis volcanoes in the west (including Olympus Mons), Valles Marineris to the east of Tharsis, and Hellas Basin in the southern hemisphere.

Other notes:

Zero elevation: Since Mars has no oceans and hence no 'sea level', a zero-elevation surface or mean gravity surface must be selected. The datum for Mars is defined by the fourth-degree and fourth-order spherical harmonic gravity field, with the zero altitude defined by the 610.5 Pa (6.105 mbar) atmospheric pressure surface (approximately 0.6% of Earth's) at a temperature of 273.16 K. This pressure and temperature correspond to the triple point of water.

Zero meridian: Mars' equator is defined by its rotation, but the location of its Prime Meridian was specified, as was Earth's, by choice of an arbitrary point which was accepted by later observers. The German astronomers Wilhelm Beer and Johann Heinrich Mädler selected a small circular feature as a reference point when they produced the first systematic chart of Mars features in 1830-32. In 1877, their choice was adopted as the prime meridian by the Italian astronomer Giovanni Schiaparelli when he began work on his notable maps of Mars. After the spacecraft Mariner 9 provided extensive imagery of Mars in 1972, a small crater (later called Airy-0), located in the Sinus Meridiani ('Middle Bay' or 'Meridian Bay') along the line of Beer and Mädler, was chosen by Merton Davies of the RAND Corporation to provide a more precise definition of 0.0° longitude when he established a planetographic control point network.


Mars has an important place in human imagination due to the belief by some that life existed on Mars. These beliefs are due mainly to observations by many in the 19th century popularized by Percival Lowell and Giovanni Schiaparelli. Schiaparelli called these observed features canali, meaning channels in Italian. This was popularly mistranslated as 'canals', and the myth of the Martian canals began. They were apparently artificial linear features on the surface that were asserted to be canals, and due to seasonal changes in the brightness of some areas that were thought to be caused by vegetation growth. This gave rise to many stories concerning Martians. The linear features are now known to be mostly non-existent or, in some cases, dry ancient watercourses. The color changes have been ascribed to dust storms.

The moons of Mars

See also Mars' natural satellites

Orbits of Phobos and Deimos (to scale), seen from above Mars' north pole
Orbits of Phobos and Deimos (to scale), seen from above Mars' north pole

From the surface of Mars, the motions of Phobos and Deimos are very different from our own. Speedy Phobos would be seen rising in the west and setting in the east and back again over 11 hours, while Deimos, being only just outside of synchronous orbit, rises as expected in the east but very slowly. Despite its 30 hour orbit, it takes 2.7 days to set in the west as it slowly falls behind the rotation of Mars and come around to rise again on average after 5.4 days.

Both moons are tidally locked with Mars, always pointing the same face towards it. Since Phobos orbits around Mars faster than the planet itself rotates, tidal forces are slowly but steadily decreasing its orbital radius. At some point in the future Phobos will be broken up by gravitational forces (see Roche limit). Deimos, on the other hand, is far enough away that its orbit is being slowly boosted instead. Several strings of craters on the Martian surface, inclined further from the equator the older they are, suggest that there may have been other small moons that suffered the fate expected of Phobos, and also that the Martian crust as a whole shifted between these events.

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 the Greek god Ares into battle. Ares was known to the Romans as Mars, the god of war.

Mars' natural satellites
Names and pronunciation
Mass (kg) Mean orbital
Orbital period (h) Average moonrise period
Mars I Phobos /ˈfoʊbəs/ 22.2 km (27×21.6×18.8)
13.79 mi (16.7×13.4×11.6)
1.08×1016 9377 km
5827 mi
7.66 11.12 hours
Mars II Deimos /ˈdaɪməs/ 12.6 km (10×12×16)
7.8 mi (6.2×7.4×9.9)
2×1015 23,460 km
14,540 mi
30.35 5.44 days

As seen from Mars, Phobos has an angular diameter of between 8' (rising) and 12' (overhead), while Deimos has an angular diameter of about 2'. The Sun's angular diameter, by contrast, is about 21'.

Phobos transits the Sun, as seen by Mars Rover Opportunity on March 10, 2004.  See Transit of Phobos from Mars
Phobos transits the Sun, as seen by Mars Rover Opportunity on March 10, 2004. See Transit of Phobos from Mars
Deimos transits the Sun, as seen by Mars Rover Opportunity on March 4, 2004.  See Transit of Deimos from Mars
Deimos transits the Sun, as seen by Mars Rover Opportunity on March 4, 2004. See Transit of Deimos from Mars

The existence of two moons of Mars was described in Jonathan Swift's satirical novel Gulliver's Travels, published in 1726, 150 years before their discovery.

They [the Laputan astronomers] have likewise discovered two lesser stars, or 'satellites', which revolve about Mars, whereof the innermost is distant from the centre of the primary planet exactly three of his diameters, and the outermost five; the former revolves in the space of ten hours, and the latter in twenty-one and an half; so that the squares of their periodical times are very near in the same proportion with the cubes of their distance from the centre of Mars, which evidently shows them to be governed by the same law of gravitation, that influences the other heavenly bodies...

A similar discovery was described by Voltaire in his interplanetary romance Micromegas, published in 1752.

The exploration of Mars

Main article: Exploration of Mars

Viking Lander 1 site (click for detailed description).
Viking Lander 1 site (click for detailed description).

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 geography. Roughly two-thirds of all spacecraft destined for Mars have failed in one manner or another before completing or even beginning their missions. Part of this high failure rate can be ascribed to technical problems, but enough have either failed or lost communications for no apparent reason that some researchers half-jokingly speak of an Earth-Mars "Bermuda Triangle" or of a Great Galactic Ghoul which subsists on a diet of Mars probes, or of a Mars Curse.

Among the most successful missions are the Mars probe program, the Mariner and Viking programs, Mars Global Surveyor, Mars Pathfinder, and Mars Odyssey. Global Surveyor has taken pictures of gullies and debris flow features that suggest there may be current sources of liquid water, similar to an aquifer, at or near the surface of the planet. Mars Odyssey determined that there are vast deposits of water ice in the upper three meters of Mars' regolith within 60° latitude of the south pole.

In 2003, the ESA launched the Mars Express craft consisting of the Mars Express Orbiter and the lander Beagle 2. Mars Express Orbiter confirmed the presence of water ice and carbon dioxide ice at the planet's south pole. NASA had previously confirmed their presence at the north pole of Mars. Attempts to contact the Beagle 2 failed and it was declared lost in early February 2004.

Cahokia Paronama.
Cahokia Paronama.

Also in 2003, NASA launched the twin Mars Exploration Rovers named Spirit (MER-A) and Opportunity (MER-B). Both missions landed successfully in January 2004 and have met or exceeded all their targets; while a 90-day nominal mission was planned, as of February 2005, their missions have been extended twice and they continue to return science, although some mechanical faults have occurred. Among the most significant science return has been evidence of liquid water some time in the past at both landing sites. In addition, dust devils imaged from ground-level have been detected moving across the surface of Mars by Spirit (MER-A). (See picture below). Dust devils were first imaged on Mars from the surface by Mars Pathfinder.

Dust devil on Mars, photographed by the Mars rover Spirit
Dust devil on Mars, photographed by the Mars rover Spirit

Early nomenclature

Although better remembered for mapping the Moon starting in 1830, Johann Heinrich Mädler and Wilhelm Beer were the first "areographers". They started off by establishing once and for all that most of the surface features were permanent, and pinned down Mars' rotation period. In 1840, Mädler combined ten years of observations and drew the first map of Mars ever made. Rather than giving names to the various markings they mapped, Beer and Mädler simply designated them with letters; Meridian Bay (Sinus Meridiani) was thus feature "a".

Over the next twenty years or so, as instruments improved and the number of observers also increased, various Martian features acquired a hodge-podge of names. To give a couple of examples, Solis Lacus was known as the "Oculus" (the Eye), and Syrtis Major was usually known as the "Hourglass Sea" or the "Scorpion". In 1858, it was also dubbed the "Atlantic Canale" by the Jesuit astronomer Angelo Secchi. Secchi commented that it "seems to play the role of the Atlantic which, on Earth, separates the Old Continent from the New" —this was the first time the fateful canale, which in Italian can mean either "channel" or "canal", had been applied to Mars.

In 1867, Richard Anthony Proctor drew up a map of Mars based, somewhat crudely, on the Rev. William Rutter Dawes' earlier drawings of 1865, then the best ones available. Proctor explained his system of nomenclature by saying, "I have applied to the different features the names of those observers who have studied the physical peculiarities presented by Mars." Here are some of his names, paired with those later proposed by Schiaparelli:

  • Kaiser Sea = Syrtis Major
  • Lockyer Land = Hellas
  • Main Sea = Lacus Moeris
  • Herschel II Strait = Sinus Sabaeus
  • Dawes Continent = Aeria and Arabia
  • De La Rue Ocean = Mare Erythraeum
  • Lockyer Sea = Solis Lacus
  • Dawes Sea = Tithonius Lacus
  • Madler Continent = Chryse, Ophir, Tharsis
  • Maraldi Sea = Mares Sirenum and Cimmerium
  • Secchi Continent = Memnonia
  • Hooke Sea = Mare Tyrrhenum
  • Cassini Land = Ausonia
  • Herschel I Continent = Zephyria, Aeolis, Aethiopis
  • Hind Land = Libya

Proctor's nomenclature has often been criticized, mainly because so many of his names honored English astronomers, but also because he used many names more than once. In particular, Dawes appeared no fewer than six times (Dawes Ocean, Dawes Continent, Dawes Sea, Dawes Strait, Dawes Isle, and Dawes Forked Bay). Even so, Proctor's names are not without charm, and for all their shortcomings they were a foundation on which later astronomers would improve.

Observation of Mars

The "Ares Vallis" area as photographed by Mars Pathfinder (click for detailed description).
The "Ares Vallis" area as photographed by Mars Pathfinder (click for detailed description).

Earth passes Mars every 780 days (or two years plus seven weeks and one day) at a distance of about 80,000,000 km. However, this varies because the orbits are elliptical. To a naked-eye observer, Mars usually shows a distinct yellow, orange or reddish colour, and varies in brightness more than any other planet as seen from Earth over the course of its orbit, due to the fact that when furthest away from the Earth it is more than seven times as far from the latter as when it is closest (and can be lost in the Sun's glare for months at a time when least favourably positioned). At its most favourable times — which occur twice every 32 years, alternately at 15 and 17-year intervals, and always between late July and late September — Mars shows a wealth of surface detail to a telescope. Especially noticeable, even at low magnification, are the polar ice caps.

On August 27, 2003, at 9:51:13 UT, Mars made its closest approach to Earth in nearly 60,000 years: 55,758,006 km (approximately 35 million miles) without Light-time correction. This close approach came about because Mars was one day from opposition and about three days from its perihelion, making Mars particularly easy to see from Earth. The last time it came so close is estimated to have been on September 12, 57,617 BC. Detailed analysis of the solar system's gravitational landscape forecasts an even closer approach in 2287. However, to keep this in perspective, this record approach was only an imperceptibly tiny fraction less than other recent close approaches that occur four times every 284 years. For instance, the minimum distance on August 22, 1924 was 0.37284 AU, compared to 0.37271 AU on August 27, 2003, and the minimum distance on August 24, 2208 will be 0.37278 AU.

A transit of the Earth as seen from Mars will occur on November 10, 2084. At that time the Sun, the Earth and Mars will be exactly in a line. There are also transits of Mercury and transits of Venus, and the moon Deimos is of sufficiently small angular diameter that its partial "eclipses" of the Sun are best considered transits (see Transit of Deimos from Mars).

The only occultation of Mars by Venus to be observed was that of October 3, 1590, seen by M. Möstlin at Heidelberg.

Photograph of a Martian sunset taken by Spirit at Gusev crater, May 19th, 2005.
Photograph of a Martian sunset taken by Spirit at Gusev crater, May 19th, 2005.


Stationary, retrograde Opposition Minimum distance to Earth (AU) Maximum
brightness (mag)
Stationary, prograde Conjunction to Sun
July 30, 2003 August 28, 2003 0.37271 -2.9 25.11" September 29, 2003 September 15, 2004
October 1, 2005 November 7, 2005 0.46407 -2.3 20.17" December 10, 2005 October 23, 2006
November 15, 2007 December 24, 2007 0.58936 -1.6 15.88" January 30, 2008 December 5, 2008
December 21, 2009 January 29, 2010 0.66399 -1.3 14.10" March 11, 2010 February 4, 2011
January 25, 2012 March 3, 2012 0.67368 -1.2 13.89" April 15, 2012 April 18, 2013
March 1, 2014 April 8, 2014 0.61756 -1.5 15.16" May 21, 2014 June 14, 2015
April 17, 2016 May 22, 2016 0.50321 -2.1 18.60" June 30, 2016 July 27, 2017
June 28, 2018 July 27, 2018 0.38495 -2.8 24.31" August 28, 2018 September 2, 2019
September 9, 2020 October 13, 2020 0.41491 -2.6 22.56" November 15, 2020 October 8, 2021
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Martian meteorites

Main article: Martian meteorites

A handful of objects are known that are surely meteorites and may be of Martian origin. Two of them may show signs of ancient bacterial activity. On August 6, 1996 NASA announced that analysis of the ALH 84001 meteorite thought to have come from Mars, shows some features that may be fossils of single-celled organisms, although this idea is controversial.

In Solar System Research (March 2004, vol 38, page 97) it was suggested that the unique Kaidun meteorite, recovered from Yemen, may have originated on the Martian moon of Phobos.

On April 14, 2004, NASA revealed that a rock known as "Bounce", studied by the Mars Exploration Rover Opportunity, was similar in composition to the meteorite EETA79001-B, discovered in Antarctica in 1979. The rock may have been ejected from the same crater as the meteorite, or from another crater in the same area of the Martian surface.

Ice lakes

On 29 July 2005, the BBC reported that a visible ice lake had been discovered in a crater in the north polar region of Mars[6]. Images of the crater, taken by the High Resolution Stereo Camera on board the European Space Agency's Mars Express spacecraft, clearly show a broad sheet of ice in the bottom of an unnamed crater located on Vastitas Borealis, a broad plain that covers much of Mars' far northern latitudes, at approximately 70.5° North and 103° East. The crater is 35 km (23 mi) wide and about 2 km (1.2 mi) deep.

Water ice-covered dunes at the bottom of a crater
Water ice-covered dunes at the bottom of a crater

The BBC report however, appears to have either intentionally sensationalized or unintentionally mis-interpreted the original HRSC/Mars Express feature[7], which makes no claim or insinuation that this is a "lake". Like many thousands of other places on Mars, this ice sheet is a thin layer of frost that has condensed onto dark, cold sand dunes (about 200 m high) making their way across the bottom of the crater. The only thing remarkable about this feature is that it is far enough north to maintain at least some frost throughout the year. Keep in mind that water cannot exist in the liquid state over most of Mars' surface because of the thinness of the atmosphere; it can only subsist in liquid form in a few places, such as the Hellas basin.

Life on Mars

Main article: Life on Mars

Evidence exists that the planet once was significantly more habitable than today, but the question whether living organisms ever actually existed there is an open one. Some researchers think that a certain rock which is believed to have originated on Mars - specifically, meteorite ALH84001 - does contain evidence of past biologic activity, but no consensus about these claims has been achieved so far and recent research indicates that the rock, since its creation several billion years ago, has never been exposed to temperatures for extended periods of time that would allow for liquid water.

The Viking probes carried experiments designed to detect microorganisms in Martian soil at their respective landing sites, and had some positive results, later denied by many scientists, resulting in ongoing controversy. Also, present biologic activity is one of the explanations that have been suggested for the presence of traces of methane within the Martian atmosphere, but other explanations not involving life are generally considered more likely.

If colonization is going to happen, Mars seems a likely choice due to its rather hospitable conditions (compared with other planets, it is most like Earth).

The Mars flag

The official Mars Society tricolor
The official Mars Society tricolor

In early 2000, a proposed Mars flag flew aboard the space shuttle Discovery. Designed by NASA engineer and Flashline Mars Arctic Research Station task force leader Pascal Lee and carried aboard by astronaut John Mace Grunsfeld, the flag consists of three vertical bars of red, green, and blue, symbolizing the transformation of Mars from a barren planet (red) to one bearing sustainable life (green), and finally to a fully terraformed planet with open bodies of water. This design was suggested by the Kim Stanley Robinson science fiction trilogy Red Mars, Green Mars, and Blue Mars. While other designs have been proposed, the republican tricolor has been adopted by the Mars Society as its own official banner. In a statement released after the launch of the mission, the Society said that the flag "has now been honored by a vessel of the leading spacefaring nation on Earth," and added that "(i)t is fitting that this action occurred when it did: at the dawning of a new millenium."

See also

External links

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Water on Mars

Mars exploration


Mars' natural satellites edit

Phobos | Deimos

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 See also astronomical objects and the solar system's list of objects, sorted by radius or mass

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