   #copyright

Mars

2007 Schools Wikipedia Selection. Related subjects: The Planets

   CAPTION: Mars Astronomical symbol of Mars

   The planet Mars
   Mars as seen by the Hubble Space Telescope
   Orbital characteristics ( Epoch J2000)
   Semi-major axis 227,936,637 km (141,632,976 mi)
   1.523 662 31 AU
   Orbital circumference 1,429,000,000 km (887,900,000 mi)
   9.553 AU
   Eccentricity 0.093 412 33
   Perihelion 206,644,545 km (128,402,967 mi)
   1.381 333 46 AU
   Aphelion 249,228,730 km (154.863,553 mi)
   1.665 991 16 AU
   Orbital period 686.9600 d
   (1.8808 a)
   Synodic period 779.96 d
   (2.135 a)
   Avg. Orbital Speed 24.077 km/ s (53,859 mi/h)
   Max. Orbital Speed 26.499 km/s (59,277 mi/h)
   Min. Orbital Speed 21.972 km/s (49,150 mi/h)
   Inclination 1.850 61 °
   (5.65° to Sun's equator)
   Longitude of the
   ascending node 49.578 54°
   Argument of the
   perihelion 286.462 30°
   Number of natural satellites 2

   Physical characteristics
   Equatorial diameter 6,804.9 km (4228.4 mi)
   (0.533 Earths)
   Polar diameter 6,754.8 km (4197.2 mi)
   (0.531 Earths)
   Oblateness 0.007 36
   Surface area 1.448×10^8 km² 55,907,000 square miles (144 798 465 square
   kilometers)
   (0.284 Earths)
   Volume 1.6318×10^11 km³
   (0.151 Earths)
   Mass 6.4185×10^23 kg
   (0.107 Earths)
   Mean density 3.934 g/cm³
   Equatorial gravity 3.69 m/s^2
   (0.376 g)
   Escape velocity 5.027 km/s (11,245 mi/h)
   Rotation period 1.025 957 d
   ( 24.622 962 h)
   Rotation velocity 868.22 km/h (539.49 mi/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
   −140 °C (133 K)
   −63 °C ( 210 K)
   20 °C (293 K)
   Adjective Martian

   Atmospheric characteristics
   Atmospheric pressure 0.7–0.9 kPa
   Carbon dioxide 95.72%
   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

          Note: This article contains special characters.

   Mars ( IPA: /ˈmɑɹz/ ( GenAm); /ˈmɑːz/ ( RP)) is the fourth planet from
   the Sun in our solar system and is named after Mars, the Roman god of
   war. Mars is also known as the "Red Planet" due to its reddish
   appearance when seen from Earth. The prefix areo-, from the Greek god
   of war, Ares, refers to Mars in the same way geo- refers to Earth.

   Mars has two moons, Phobos and Deimos, which are small and
   oddly-shaped. These may be captured asteroids similar to 5261 Eureka, a
   Mars Trojan asteroid. Mars can be seen from Earth with the naked eye.
   Its apparent magnitude reaches -2.9, a brightness surpassed only by
   Venus, the Moon, and the Sun. For much of the year, Jupiter may appear
   brighter to the naked eye than Mars.

   Until the first flyby of Mars by Mariner 4 in 1965, it was hoped, both
   within and especially perhaps outside scientific circles, especially in
   the popular media and literary circles, that Mars had ample liquid
   water. This was based on observations of periodic variations in light
   and dark patches, particularly in the polar latitudes, and long dark
   striations that could perhaps even be irrigation channels of liquid
   water.

   These straight line features were shown in fact not to exist when they
   were subsequently analyzed and explained as optical illusions. Still,
   of all the planets in our solar system other than Earth, Mars is the
   most likely to harbour liquid water, and perhaps life, so the myth has
   had enough influence that even now probes carry packages to attempt to
   find microscopic life. Mars' rotational period and seasonal cycles are
   also similar to those of the Earth. It has the highest mountain in the
   solar system, Olympus Mons, the largest canyon in the solar system,
   Valles Marineris, and polar ice caps.

   Mars is currently host to four orbiting spacecraft: Mars Global
   Surveyor, Mars Odyssey, Mars Express, and Mars Reconnaissance Orbiter.
   This is more than any planet other than Earth has. It is also home to
   the two Mars Exploration Rovers ( Spirit and Opportunity).

Physical characteristics

   The red/orange appearance of Mars' surface is caused by iron(III) oxide
   (rust). Mars has half the radius of the Earth and only one-tenth the
   mass, being less dense, but its surface area is only slightly less than
   the total area of Earth's dry land. While Mars is larger and more
   massive than Mercury, Mercury has slightly stronger gravity at the
   surface, due to its much higher density.
   Size comparison of terrestrial planets (left to right): Mercury, Venus,
   Earth, and Mars
   Enlarge
   Size comparison of terrestrial planets (left to right): Mercury, Venus,
   Earth, and Mars

Geology

   The surface of Mars is thought to be primarily composed of basalt,
   based upon the Martian meteorite collection and orbital observations.
   There is some evidence that a portion of the Martian surface might be
   more silica-rich than typical basalt, perhaps similar to andesitic
   stones on Earth, though these observations may also be explained by
   silica glass. Much of the surface is deeply covered by iron(III) oxide
   dust as fine as talcum powder.
   Photo of microscopic rock forms indicating past signs of water, taken
   by Opportunity
   Enlarge
   Photo of microscopic rock forms indicating past signs of water, taken
   by Opportunity

   There is conclusive evidence that liquid water existed at one time on
   the surface of Mars. Key discoveries leading to this conclusion include
   the detection of various minerals such as hematite and goethite which
   usually only form in the presence of water.

   Although Mars has no intrinsic magnetic field, observations have
   revealed that parts of the planet's crust have been magnetized. This
   magnetization has been compared to alternating bands found on the ocean
   floors of Earth. One theory, published in 1999 and reexamined in
   October 2005 with the help of the Mars Global Surveyor, is that these
   bands are evidence of the past operation of plate tectonics on Mars.
   Polar wandering could also explain this paleomagnetism.

   Current models of the planet's interior infer a core region
   approximately 1,480 km in radius, consisting primarily of iron with
   about 15-17% sulfur. This iron sulfide core is partially fluid, with
   twice the concentration of light elements that exists at the 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. The average thickness of the planet's crust is about 50 km,
   and it is no thicker than 125 km.

   The geological history of Mars is split into three broad epochs:
     * Noachian epoch (named after Noachis Terra): Formation of Mars to
       between 3800 and 3500 million years ago. Noachian age surfaces are
       scarred by many large impact craters. The Tharsis bulge is thought
       to have formed during this period, with extensive flooding by
       liquid water late in the epoch.
     * Hesperian epoch (named after Hesperia Planum): 3500 million years
       ago to 1800 million years ago. The Hesperian epoch is marked by the
       formation of extensive lava plains.
     * Amazonian epoch (named after Amazonis Planitia): 1800 million 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.

   An alternative series of classifications, based on data from OMEGA
   Visible and Infrared Mineralogical Mapping Spectrometer on board the
   Mars Express orbiter has also been put forward.

Geography of Mars (Areography)

   Topographic map of Mars. 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.
   Enlarge
   Topographic map of Mars. 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.

   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 Mars'
   surface features were permanent, and pinned down Mars' rotation period.
   In 1840, Mädler combined ten years of observations and drew the first
   ever map of Mars. 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".

   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).

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

   Since Mars has no oceans and hence no 'sea level', a zero-elevation
   surface or mean gravity surface must be selected. The zero altitude is
   defined by the height at which there is 610.5 Pa (6.105 mbar) of
   atmospheric pressure (approximately 0.6% of Earth's). This pressure
   corresponds to the triple point of water.

   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 thus 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.

   The shield volcano, Olympus Mons (Mount Olympus), at 26 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. It is over three times the height of Mt. Everest which in
   comparison only stands at 8848 m.

   Mars is also scarred by a number of impact craters. The largest of
   these is the Hellas impact basin, covered with light red sand.Despite
   being closer to the asteroid belt, there are far fewer craters on Mars
   compared with the Moon because Mars' atmosphere provides protection
   against small meteors. Some craters have a morphology that suggests
   that the ground was wet when the meteor impacted.

   The large canyon, Valles Marineris (Latin for Mariner Valleys, also
   known as Agathadaemon in the old canal maps), has a length of 4000 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. By comparison, the Grand Canyon on Earth is only 446 km long
   and nearly 2 km deep. Valles Marineris was formed due to the swelling
   of the Tharis 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). 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.

   Mars has two permanent polar ice caps, the northern one located at
   Planum Boreum and the southern one at Planum Australe.
   Mars, 2001, with polar ice caps visible.
   Enlarge
   Mars, 2001, with polar ice caps visible.

Atmosphere

   The atmosphere of Mars is relatively thin; the atmospheric pressure on
   the surface varies from around 30 Pa (0.03 kPa) on Olympus Mons to over
   1155 Pa (1.155 kPa) in the depths of Hellas Planitia, with a mean
   surface level pressure of 600 Pa (0.6 kPa), compared to Earth's
   101.3 kPa. The equivalent pressure of Mars' atmosphere can be found at
   a height of 35 km above the Earth's surface. The scale height of the
   atmosphere is about 11 km, higher than Earth's 6 km. The atmosphere on
   Mars consists of 95% carbon dioxide, 3% nitrogen, 1.6% argon, and
   contains traces of oxygen and water. The atmosphere is quite dusty,
   giving the Martian sky a tawny colour when seen from the surface; the
   particulates responsible are about 1.5 µm across.

   Several researchers claim to have detected methane in the Martian
   atmosphere with a concentration of about 10 ppb by volume. Methane is
   an unstable gas that is broken down by ultraviolet radiation, typically
   lasting in the atmosphere for about 340 years, and its possible
   presence on Mars could indicate that there is (or has 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 sources. It was
   recently shown that methane could also be produced by a non-biological
   process involving water, carbon dioxide, and the mineral olivine, which
   is known to be common on Mars.

   In the winter months when the poles are in continuous darkness, the
   surface gets so cold that as much as 25–30% of the entire atmosphere
   condenses out into thick slabs of CO[2] ice (dry ice).

   When the poles are again exposed to sunlight, the CO[2] ice sublimes,
   creating enormous winds that sweep off the poles as fast as 400 km/h
   (250 mph). These seasonal actions transport large amounts of dust and
   water vapor, giving rise to Earth-like frost and large cirrus clouds.
   Clouds of water-ice were photographed by the Opportunity rover in 2004.
   Strength of Mars' magnetic field. (Red and Blue show stronger than
   average areas)
   Enlarge
   Strength of Mars' magnetic field. (Red and Blue show stronger than
   average areas)

Magnetosphere

   Evidence indicates that in Mars' distant past, it may have had a strong
   enough magnetosphere to deflect the solar wind coming from the Sun.
   However, about 4 billion years ago Mars' planetary dynamo ceased,
   leaving only remnants of the planetary magnetic field to be frozen into
   magnetically susceptible minerals. Over time, most of this material was
   reprocessed through various geological events leaving only sections of
   the ancient southern highlands with remnant magnetic fields. Because of
   this, the solar wind interacts directly with the Martian ionosphere and
   thus the Martian atmosphere has been slowly stripped off into space,
   although the exact amount lost remains uncertain. Both Mars Global
   Surveyor and Mars Express have detected ionised atmospheric particles
   trailing off into space behind Mars.
   Mars from Hubble Space Telescope October 28, 2005 with duststorm
   visible.
   Enlarge
   Mars from Hubble Space Telescope October 28, 2005 with duststorm
   visible.

Climate

   Of all the planets, Mars' seasons 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
   approximately two Earth years in length. Martian surface temperatures
   vary from lows of approximately –140 °C (−220 °F) during the polar
   winters to highs of up to 20 °C (70 °F) in summers. The wide range in
   temperatures is due to the thin atmosphere which cannot store much
   solar heat. Recent evidence has suggested that Mars is subject to short
   term regional climate changes.

   If Mars had an Earthlike 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. Mars is near perihelion when it is summer in the southern
   hemisphere and winter in the north, and near aphelion when it is winter
   in the southern hemisphere and summer in the north. As a result, the
   seasons in the southern hemisphere are more extreme and the seasons in
   the northern are milder than would otherwise be the case.
   Mars' northern ice cap.
   Enlarge
   Mars' northern ice cap.

   Mars also has the largest dust storms in the Solar System. 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,
   which increases the global temperature.

   Mars possesses polar caps at both poles, which mainly consist of water
   ice. Frozen carbon dioxide (dry ice) 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 approximately 1,000 kilometres
   during the northern Mars summer, and contains about 1.6 million cubic
   kilometres of ice, which if spread evenly on the cap would be 2
   kilometres thick The southern polar cap has a diameter of 350 km, and a
   thickness of 3 km. Both polar caps show spiral cuts, which remain
   unexplained. Both polar caps shrink and regrow following the
   temperature fluctuation of the Martian seasons.

Orbit and rotation

     Orbit of Mars (red) and Ceres (yellow). Orbit of Mars (red) and Ceres
                                                                 (yellow).

   Mars has a relatively pronounced orbital eccentricity of about 9%; of
   the other planets in the solar system, only Mercury shows greater
   eccentricity. Mars' average distance from the Sun is roughly 230
   million km (1.5 AU) and its orbital period is 687 (Earth) days. The
   solar day (or sol) on Mars is only slightly longer than an Earth day:
   24 hours, 39 minutes, and 35.244 seconds.

   Mars' axial tilt is 25.19 degrees, which is similar to the axial tilt
   of the Earth. As a result, Mars has seasons like the Earth, though
   Mars' are about twice as long given its longer year.

   The image to the right shows a comparison between Mars and Ceres, a
   dwarf planet in the Asteroid Belt as seen from the ecliptic pole (top)
   and from the ascending node (below). The segments of orbits below the
   ecliptic are plotted in darker colours. The perihelia (q) and aphelia
   (Q) are labelled with the date of the nearest passage. Mars passed its
   aphelion in June 2006 and is now heading for its perihelion in June
   2007.

Moons

   Phobos (top) and Deimos (bottom)
   Enlarge
   Phobos (top) and Deimos (bottom)

   Mars has two tiny natural moons, Phobos and Deimos, which orbit very
   close to the planet and are thought to be captured asteroids.

   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.

   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, while Deimos, being only
   just outside 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 as long again to
   rise.

   Because Phobos' orbit is below synchronous altitude, the tidal forces
   are lowering its orbit and in about 50 million years, it will either
   crash into Mars' surface or break up into a ring structure around Mars.

   Famous literary author Jonathan Swift made reference to these moons of
   Mars, approximately 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.

Life

   Some evidence suggests that the planet was once significantly more
   habitable than it is today, but whether living organisms ever existed
   there is still an open question. The Viking probes of the mid-1970s
   carried experiments designed to detect microorganisms in Martian soil
   at their respective landing sites, and had some positive results, later
   disputed by many scientists, resulting in a continuing fight. At the
   Johnson space centre lab organic compounds have been found in the
   meteorite ALH84001, which is supposed to have come from Mars. They
   concluded that these were deposited by primitive life forms extant on
   Mars before the meteorite was blasted into space by a meteor strike and
   sent on a 15 million-year voyage to Earth. Small quantities of methane,
   and formaldehyde are both claimed to be hints for life, as these
   particles would quickly break down in the Martian atmosphere. It is
   possible that these compounds may be replenished by volcanic or
   geological means such as serpentinization.

   In general, Mars shows some promise in terms of habitablity but also
   several handicaps. It is half of an astronomical unit beyond the Sun's
   habitable zone and water is thus frozen on its surface, though liquid
   water flows in the past underscore the planet's potential. Its lack of
   a magnetosphere and extremely thin atmosphere are a greater challenge:
   the planet has little heat transfer across its surface, poor insulation
   against bombardment and the solar wind, and insufficient atmospheric
   pressure to keep water in liquid form (instead it sublimates to a
   gaseous state). Mars is also nearly, or perhaps totally, geologically
   dead; the end of volcanic activity has stopped the recycling of
   chemicals and minerals between the surface and interior of the planet.

Exploration

   Viking Lander 1 site
   Enlarge
   Viking Lander 1 site

   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.

   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 a Mars Curse, or even a reference
   made to a "Great Galactic Ghoul" that feeds on Martian spacecraft.

Past missions

   The first successful fly-by mission to Mars was NASA's Mariner 4
   launched in 1964. The first successful objects to land on the surface
   were two Soviet probes, Mars 2 and Mars 3 from the Mars probe program,
   launched in 1971, but both lost contact within seconds of landing. Then
   came the 1975 NASA launches of the Viking program, which consisted of
   two orbiters, each having a lander. Both landers successfully touched
   down in 1976 and remained operational for 6 and 3 years, for Viking 1
   and Viking 2 respectively. The Viking landers also relayed the first
   colour pictures of Mars. They also mapped the surface of Mars so well
   that the images are still sometimes used to this day. The Soviet probes
   Phobos 1 and 2 were also sent to Mars in 1988 to study Mars and its two
   moons, unfortunately Phobos 1 lost contact on the way to Mars, and
   Phobos 2, while successfully photographing Mars and Phobos, failed just
   before it was set to release two landers on Phobos' surface.

Current missions

   Following the 1992 failure of Mars Observer orbiter, NASA launched the
   Mars Global Surveyor in 1996. This mission was a complete success,
   having finished its primary mapping mission in early 2001. Only a month
   after the launch of the Surveyor, NASA launched the Mars Pathfinder,
   carrying a robotic exploration vehicle, which landed in the Ares Vallis
   on Mars. This mission was another big success, and received much
   publicity, partially due to the many spectacular images that were sent
   back to Earth.
   Artist's concept of the 2001 Mars Odyssey
   Enlarge
   Artist's concept of the 2001 Mars Odyssey

   In 2001 NASA launched the successful Mars Odyssey orbiter, which is
   still in orbit as of August 2006. Odyssey's Gamma Ray Spectrometer
   detected significant amounts of elemental hydrogen in the upper metre
   or so of Mars' regolith. This hydrogen is thought to be contained in
   large deposits of water ice.

   In 2003, the ESA launched the Mars Express craft consisting of the Mars
   Express Orbiter and the lander Beagle 2. Beagle 2 apparently failed
   during descent and was declared lost in early February 2004. In early
   2004 the Planetary Fourier Spectrometer team announced it had detected
   methane in the Martian atmosphere. ESA announced in June 2006 the
   discovery of aurorae on Mars.

   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. Among the most significant science returns has been the
   conclusive evidence that liquid water existed at some time in the past
   at both landing sites. Martian dust devils and windstorms have
   occasionally cleaned both rovers' solar panels, and thus increased
   their lifespan.

   On August 12, 2005 the NASA Mars Reconnaissance Orbiter probe was
   launched toward the planet, to conduct a two-year science survey. The
   purpose of the mission is to map the Martian terrain and find suitable
   landing sites for the upcoming lander missions. It arrived in orbit on
   March 10, 2006. The next scheduled mission to Mars is the NASA Phoenix
   Mars lander, expected to launch in 2007.

Future plans

   Future plans for unmanned Mars Exploration include the sending of the
   Phoenix Lander in 2007, followed by the Mars Science Laboratory in
   2009, the Phobos-Grunt sample-return mission, to return samples of
   Phobos, a Martian moon. Other missions have been proposed, although not
   yet confirmed.

   Manned Mars exploration by the United States has been explicitly
   identified as a long-term goal in the Vision for Space Exploration
   announced in 2004 by US President George W. Bush.

   The European Space Agency hopes to land the first humans on Mars
   between 2030 and 2035. This will be preceded by successively larger
   probes, starting with the launch of the ExoMars probe in 2013, followed
   by the 'Mars Sample Return Mission'. Likewise, astronauts will be sent
   to the moon between 2020 and 2025 in preparation for this mission.

Astronomical observations from Mars

   Earth and Moon from Mars, imaged by Mars Global Surveyor. South America
   is visible.
   Enlarge
   Earth and Moon from Mars, imaged by Mars Global Surveyor. South America
   is visible.

   It is now possible, with the existence of various orbiters, landers,
   and rovers to study astronomy from the Martian skies. In particular,
   the Earth and the Moon would easily be visible to the naked eye. Also,
   one could observe the two moons of Mars. The moon Phobos appears about
   one third the angular diameter that the full Moon appears from Earth,
   and when it is full it is bright enough to cast shadows. On the other
   hand Deimos appears more or less starlike, 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. The first meteor
   photographed on Mars was on March 7, 2004 by the Spirit rover. Auroras
   occur on Mars, but they do not occur at the poles as on Earth, because
   Mars has no planetwide magnetic field. Rather, they occur near magnetic
   anomalies in Mars's crust, which are remnants from earlier days when
   Mars did have a magnetic field. They would probably be invisible to the
   naked eye, being largely ultraviolet phenomena.
   Photograph of a Martian sunset taken by Spirit at Gusev crater, May
   19th, 2005.
   Enlarge
   Photograph of a Martian sunset taken by Spirit at Gusev crater, May
   19th, 2005.

   A transit of the Earth as seen from Mars will occur on November 10,
   2084. At that time, the Sun, Earth and Mars will be exactly collinear.
   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 observed was that of October 3,
   1590, seen by M. Möstlin at Heidelberg.

Viewing Mars

   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. When farthest away
   from the Earth, it is more than seven times as far from the latter as
   when it is closest (when least favourably positioned, it can be lost in
   the Sun's glare for months at a time). 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.

   Approximately every 780 days opposition occurs, which is about when
   Mars is nearest to Earth. (Because of the eccentricities of the orbits,
   the times of opposition and minimum distance can differ by up to 8.5
   days.) The minimum distance varies between about 55 and 100 million km
   due to the planets' elliptical orbits. The next Mars opposition will
   occur on December 24, 2007.

   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). This occurred when 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., 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
   0.37284 AU, compared to 0.37271 AU on August 27, 2003, and the minimum
   distance on August 24, 2208 will be 0.37278 AU.

   The orbital changes of Earth and Mars are making the approaches nearer:
   the 2003 record will be bettered 22 times by the year 4000.

Historical observations of Mars

   Map of Mars by Giovanni Schiaparelli.
   Enlarge
   Map of Mars by Giovanni Schiaparelli.

   The history of observations of Mars is marked by the oppositions of
   Mars, when the planet is closest to Earth and hence is most easily
   visible, which occur every couple of years. Even more notable are the
   perihelic oppositions of Mars which occur approximately every 16 years,
   and are distiguished because Mars is close to perihelion making it even
   closer to Earth.

   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, while in Milan, used a 22cm
   telescope to help produce the first detailed map of Mars. 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 was popularly mistranslated as canals.

   Influenced by the observations the orientalist Percival Lowell founded
   an observatory which had a 12 and 18 inch telescope. The observatory
   was used for the exploration of Mars during the last good opportunity
   in 1894 and the following less favorable oppositions. He published
   several books on Mars and life on Mars which had a great influence on
   the public. The canali were also found by other astronomers, like
   Perrotin and Thollon in Nice, using one of the largest telescopes of
   that time.

   The seasonal changes (consisting of the diminishing of the polar caps
   and the dark areas formed during Martian summer) in combination with
   the canals 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. However, as bigger telescopes were used, fewer long,
   straight canali were observed. During an observation in 1909 by
   Flammarion with a 33 inch telescope, irregular patterns were observed,
   but no canali were seen.

   Even in the 1960s articles were published on Martian biology, putting
   aside explanations other than life for the seasonal changes on Mars.
   Detailed scenarios for the metabolism and chemical cycles for a
   functional ecosystem have been published.

   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 hostile dead Mars was generally accepted.

   Some maps of Mars were made using the data from these missions, but it
   wasn't until the Mars Global Surveyor mission, launched in 1996 and
   still operational as of 2006, that complete, extremely detailed maps
   were obtained. These maps are now available online at Google Mars.

Mars in human culture

Historic connections

   Mars is named after the Roman god of war. In Babylonian astronomy, the
   planet was named after Nergal, their deity of fire, war, and
   destruction, most likely due to the planet's reddish appearance. When
   the Greeks equated Nergal with their god of war, Ares, they named the
   planet Ἄρεως ἀστἡρ (Areos aster), or "star of Ares". Then, following
   the identification of Ares and Mars, it was translated into Latin as
   stella Martis, or "star of Mars", or simply Mars. The Greeks also
   called the planet Πυρόεις Pyroeis meaning "fiery". In Hindu mythology,
   Mars is known as Mangala (मंगल). The planet is also called Angaraka in
   Sanskrit. He is the god of war and is celibate. He is the owner of the
   Aries and Scorpio signs, and a teacher of the occult sciences. The
   planet was known by the Egyptians as "Ḥr Dšr";;;; or " Horus the Red".
   The Hebrews named it Ma'adim (מאדים) - "the one who blushes"; this is
   where one of the largest canyons on Mars, the Ma'adim Vallis, gets its
   name. It is known as al-Mirrikh in both Arabic and Persian, and Merih
   in Turkish. The etymology of al-Mirrikh is unknown. Ancient Persians
   named it Bahram, the Zoroastrian god of faith. Ancient Turks called it
   Sakit. The Chinese, Japanese, Korean and Vietnamese cultures refer to
   the planet as 火星, or the fire star, a naming based on the ancient
   Chinese mythological cycle of Five Elements.

   Its symbol, derived from the astrological symbol of Mars, a circle with
   a small arrow pointing out from behind it is a stylized representation
   of a shield and spear used by the Roman God Mars. Mars in Roman
   mythology was the God of War and patron of warriors. This symbol is
   also used in biology to describe the male sex. ♂ occupies Unicode
   position U+2642.

In fiction

   The depiction of Mars in fiction has been stimulated by its dramatic
   red colour and by early scientific speculations that its surface
   conditions might be capable of supporting life.

   Until the arrival of planetary probes, the traditional view of Mars
   derived from the astronomers Percival Lowell and Giovanni Schiaparelli,
   whose observation of supposedly linear features on the planet created
   the myth of canals on Mars. For many years, the standard notion of the
   planet was a drying, cooling, dying world with ancient civilizations
   constructing irrigation works. Thus originated a large number of
   science fiction scenarios, the best known of which is H. G. Wells' The
   War of the Worlds, in which Martians seek to escape their dying planet
   by invading Earth. Of considerable note is the release of a radio
   broadcast of War of the Worlds on October 30, 1938. It was broadcasted
   as a news release, and many people mistook it for the truth. Also
   influential was Ray Bradbury's The Martian Chronicles, in which human
   explorers find a dying Martian civilization, as well as Burroughs'
   Barsoom series and a number of Robert A. Heinlein stories prior to the
   mid-sixties.

   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. 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.

   Another popular theme, particularly among American writers, is the
   Martian colony that fights for independence from Earth. This 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. Many video games also use
   this element, such as Red Faction and the Zone of the Enders series.
   Mars (and its moons) were also the setting for the popular Doom video
   game franchise and the later Martian Gothic .

   Retrieved from " http://en.wikipedia.org/wiki/Mars"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
