Mars

For other uses, see Mars (disambiguation).

Template:Planet Infobox/Mars Mars is the fourth planet from the Sun in our solar system. It is named after Mars, the Roman god of war. Mars is also known as "The Red Planet" due to its reddish night time 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 — for example, areology versus geology.

Until the first flyby of Mars by Mariner 4 in 1965, it was thought that Mars had channels of liquid water. Observations later showed that these channels do not exist. Still, of any planet in our solar system after the Earth, Mars is the most likely to harbor liquid water, and perhaps life. It also has seasonal cycles that are similar to the ones on Earth. It also has a rotational period nearly the same as our own. 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 has two moons, Phobos and Deimos, which are small and oddly-shaped. These may be captured asteroids such as 5261 Eureka. Mars can be seen from Earth by the naked eye with a brightness of up to -2.9 magnitude, only surpassed by Venus, the Moon and the Sun.

Mars is currently host to four orbiting spacecraft and the two Mars Exploration Rovers, many more than any planet, other than Earth.

Physical characteristics

The fiery appearance of Mars is caused by iron(III) oxide (rust) on its surface. 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.

Atmosphere

Main article: Atmosphere of Mars

The atmosphere of Mars is relatively thin; the atmospheric pressure on the surface is only 0.7–0.9 kPa, compared to Earth's 101.3 kPa. The scale height of the atmosphere is about 11 km, somewhat 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 color when seen from the surface; with dust particles about 1.5 µm across.

Mars from Hubble Space Telescope October 28, 2005 with sandstorm visible.

Methane exists 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 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 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.

Climate

Mars has seasons, which of all of the planets are the most Earth-like due to the similar tilts in their rotational axes. However, the length of its seasons are about twice that of Earth's, as its increased distance from the sun leads to the Martian year being approximately two earth years in length. Martian temperatures reach from lows of –140 °C (−220 °F) to highs of 20 °C (68 °F). Recent evidence has suggested that Mars may be warming in the short term. It appears, however, that this may be unrelated to global warming on Earth.

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.

Size comparison of terrestrial planets (left to right): Mercury, Venus, Earth, and Mars.

Geology (Areology)

Main article: Geology of Mars

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 rocks on Earth, though these observations may also be explained by silica glass. Much of the surface is deeply covered by dust as fine as talcum powder.

Observations of the magnetic fields on Mars 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.

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.

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 as exist at the Earth's core. This 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.

Geography (Areography)

Main pages: Areography, Category:Surface features of Mars, List of mountains on Mars, and List of craters on Mars

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 the 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.

Mars, 2001, with polar ice caps visible.

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), is the highest known mountain in the solar system, at 26 km. It is in the vast upland region Tharsis, which contains several large volcanos. The Tharsis region of 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.

Moons

Main article: Mars' natural satellites

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. It will either crash into Mars' surface or break up into a ring in about 50 million years.

Orbital characteristics

Mars has an eccentricity higher than most of the other planets in the solar system, and has an average distance from the Sun of roughly 230 million km (1.5 AU). Its orbital period is 687 (Earth) days, but the solar day (or sol) on Mars is only slightly more than an Earth day: 24 hours, 39 minutes, and 35.244 seconds. See Timekeeping on Mars.

Approximately every 780 days opposition occurs, which is when Mars is nearest to Earth. This 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) without Light-time correction. 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. Detailed analysis of the solar system's gravitational landscape forecasts an even closer approach 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.

Life

Main article: Life on Mars

Some evidence suggests that the planet was once significantly more habitable than it is today, but whether living organisms ever actually 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. In the Johnson space center lab organic compounds have been found in the asteroid ALH84001, which is supposed to come from Mars. They said that they were deposited by primitive life forms before the meteorite was blasted into space and sent on a 15 million-year voyage to Earth. The small quantity of methane in martian atmospher is allso claimed to be a hint for life.

Exploration

Main article: Exploration of Mars

File:Vikinglander-view.jpg

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 areography. 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 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 many years.

Current missions

Following the 1992 failure of NASA's Mars Observer orbiter, they 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

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 meter 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.

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 are known to be passing over the Rovers, cleaning their solar panels, and thus extending 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 do more studies and prepare 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

Further information: Exploration of Mars § Manned missions

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 2011 or more likely 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. Initially, the ESA had planned a joint venture with the USA, but obstacles, such as American technology law (ITAR) that prohibits the sharing of classified space technology information, has led to the EU 'going it alone', in competition with the USA.

New information recently relased shows that there is intelligent life on Mars. In response to this new find, wealthy entrepeneurs have decided to open a themepark on Mars. The Martians are to be enslaved and work at concesion stands until death. At which point the Disney Corporation will claim the bodies and sell them to scientists all over the world. Upon the extinction of all life on Mars, the planet is to be renamed "The Stephan Colbert Planet."

Astronomical observations

Earth and Moon from Mars, imaged by Mars Global Surveyor on May 8 2003 13:00 UTC. South America is visible.

Main article: Astronomy on Mars

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.

Observations

To a naked-eye observer, Mars usually shows a distinct yellow, orange or reddish color, 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.

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, 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.

Name and symbolism

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 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.

Fictional Works

Main article: Mars in fiction

The depiction of Mars in fiction has been stimulated by its dramatic red color 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 released in the form of a news release, and many people mistook it for the truth.

The first Space Trilogy book Out of the Silent Planet created by C.S. Lewis also told the story of a man who gets sent to Malacandra which is C.S. Lewis' scientific term meaning Mars.

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

See also

• Areography
• Astrobiology
• Astronomy on Mars
• Colonization of Mars
• Darian calendar
• Face on Mars photo article
• Flag of Mars
• Timekeeping on Mars
• Exploration of Mars
• List of artificial objects on Mars
• List of craters on Mars
• List of mountains on Mars
• Extraterrestrial life
• Terraforming
• Mars Direct
• Mars in astrology

External links

• The Planet Mars: A History of Observation and Discovery,William Sheehan, The University of Arizona Press, Tucson, 1996
• Detection of methane in the Martian atmosphere: evidence for life?,Vladimir A. Krasnopolsky, Jean-Pierre Maillard, Tobias C. Owen, Icarus, 172 (2), 537-547.
• NASA's Mars fact sheet
• 3D maps of Mars in NASA World Wind
• Google Mars Interactive image of Mars
• Flight Into Mariner Valley NASA/JPL/Arizona State University 3D flythrough of Valles Marineris
• Marsgeo.com Mars Rover photos, videos & surface geology
• Nine Planets Mars page
• Introduction to Martian topography, with Hubble Space Telescope photos
• FU Berlin: HRSC (camera) experiment at Mars Express (eng. & ger.; press releases and high resolution images)
• Technical Notes about Time on Mars
• On Mars: Exploration of the Red Planet 1958-1978 from the NASA History Office.
• A Trip Into Space Photos and descriptions of Mars
• Martian Law - a CATO white paper
• Computer Simulation of a flyby through Mariner Valley
• Mars Unearthed - Comparisons of terrains between Earth and Mars
• 3D VRML Mars globe
• Ralph Aeschliman's Online Atlas of Mars
• Planets - Mars A kid's guide to Mars.
• Is there Global Warming on Mars?
• BBC: Wheels on Mars
• Space.com: All About Mars
• Geody Mars World's search engine that supports NASA World Wind, Celestia, and other applications.

Water

• Highly visible ice lake found on Mars - BBC
• Dr. Tony Phillips: "Making a Splash on Mars", Science@NASA article, June 29, 2000. Phillips describes the Martian "gullies" and explains the conditions under which liquid water can exist on the surface of Mars.
• BBC News story on subsurface ice deposits on Mars
• BBC News update on Mars Express' findings of polar water ice and water-eroded features on the surface
• Mars Rover Scientists Wring Water Story from Rocks This image taken by Mars Rover Opportunity shows microscopic rock forms indicating past signs of water. Courtesy: NASA
• BBC News Mars pictures reveal frozen sea

Exploration

• The Political Economy of Very Large Space Projects (Journal Of Evolution and Technology)
• exploreMarsnow Interactive Mars base simulation. Winner of 2003 Webby Award for Science.
• NASA Mars Exploration Rover Home Page
• Be on Mars Anaglyphs from the Mars Rovers (3D)
• Martian Travel Guide Student's project for Catch a Star
• Google Mars View some of the most detailed maps of Mars created by NASA scientists