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Line 45: − The planet has been known since Antiquity. Because of this, the planet was named after the Roman equivalent of [[Ares]], the Greek god of [[war]].+ + − + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + − − [[Image:MarsTopoMap-PIA02031 modest.jpg|left|thumb|300px|Topographic map of Mars.]] + + + + + + + + + − + − +
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'''Mars''' is the fourth planet from the [[Sun]], after [[Mercury]], [[Venus]], and [[Earth]]. It is called "The Red Planet" because it looks red from Earth.
'''Mars''' is the fourth planet from the [[Sun]], after [[Mercury]], [[Venus]], and [[Earth]]. It is called "The Red Planet" because it looks red from Earth.
== Ancient knowledge and naming ==
Mars has the [[Rome|Roman]] name of the classical god of war. This name in turn derives from the [[Greece|Greek]] name ''Ares'' for this god. The ancient [[Egypt]]ians simply called Mars ''Her Descher'', or "the red one."<ref name=Hamilton>Hamilton, Calvin J. "[http://www.solarviews.com/eng/mars.htm Entry for Mars]." ''Views on the Solar System'', 2008. Accessed May 27, 2008.</ref> The [[Hindu]]s call Mars Mangala, one of the Navagraha.<ref name=ucar>"[http://www.windows.ucar.edu/tour/link=/mythology/mangala.html&edu=high Mangala]." ''Windows to the Universe'', University Corporation for Atmospheric Research, University of Michigan, September, 200. Accessed May 27, 2008.</ref> The [[Maya]] people also tracked Mars regularly.
==Physical and surface features==
== Orbital characteristics ==
Mars is in a highly elliptical orbit around the Sun and maintains an average distance slightly more than 1.5 AU. The synodic period of Mars is roughly 26 months. This fact makes Mars a particularly difficult object to explore, because opportunities to launch a rocket probe to Mars occur so far apart in time.
== Rotational characteristics ==
Mars' sidereal and solar days are only slightly longer than the days of earth. This fact has led long-term Mars mission planners to adopt a permanent system for keeping time "local" to Mars. The first mission to use this "Mars solar clock" was [[Viking 1]] in 1976.<ref name=Allison>Allison, Michael, and Schmunk, Robert. "[http://www.giss.nasa.gov/tools/mars24/help/notes.html Technical Notes on Mars Solar Time as Adopted by the Mars24 Sunclock]." Goddard Institute for Space Studies, [[National Aeronautics and Space Administration|NASA]], May 20, 2008. Accessed May 27, 2008.</ref>
== Physical characteristics ==
Mars is half the size of Earth and has about 11% of earth's mass. The large proportion of [[iron]] in Mars's clay-like topsoil gives Mars its distinctive color.
The weather on Mars is seasonal, on account of Mars's axial inclination. Yet because Mars's orbit is so eccentric, "summer" and "winter" on the northern and southern hemispheres can vary greatly. Temperatures vary from 140 K to 300 K, with an average temperature of 210 K. (The freezing point of [[water]] is 273.15 K.)
=== Atmosphere ===
Mars' atmosphere is quite thin and has an average pressure of 6.36 mb or 0.636% of that of earth. Its chief components are 95.32% [[carbon dioxide]], 2.7% [[nitrogen]], 1.6% [[argon]], 0.13% [[oxygen]], and 0.08% [[carbon monoxide]]. In addition it has trace amounts of [[water]] (210 ppm), [[nitrogen oxide]] (100 ppm), [[neon]] (2.5 ppm), hydrogen-deuterium oxide (HDO) (0.85 ppm), [[krypton]] (0.3 ppm), and [[xenon]] (0.08 ppm). Winds on Mars vary in speed from 2-7 m/s in summer to 5-10 m/s in fall, though the [[Project Viking]] landers have recorded winds varying from 17-30 m/s during dust storms that have swept past the landing sites.<ref name=marsfact/>
Recent warming trends on Mars, including an apparent partial melt of the polar ice caps, have led at least one scientist to question the widely circulating theories of [[global warming]] on earth. Specifically, Habibullo Abdussamatov, head of space research at St. Petersburg's Pulkovo Astronomical Observatory in Russia, asserts that the sun, and not any activity specific to the earth, must be responsible for any warming observed on either planet.<ref name=ngs>Ravilious, Kate. "[http://news.nationalgeographic.com/news/2007/02/070228-mars-warming.html Mars Melt Hints at Solar, Not Human, Cause for Warming, Scientist Says]." ''National Geographic News'', National Geographic Society, February 28, 2007. Accessed May 27, 2008.</ref>
=== Magnetosphere ===
Mars has a very weak magnetic field. Data from various missions has established an upper limit of 2.1 * 10<sup>18</sup> N-m/T on the [[magnetic dipole moment]] of Mars. According to [[Russell Humphreys]]'s model of the creation of magnetic fields, Mars probably had a magnetic dipole moment ''at creation'' of 1.51 * 10<sup>23</sup> N-m/T. Thus Mars's magnetic field has been decaying very rapidly. This tremendous decay, and the presence on [[Mercury (planet)|Mercury]] of a magnetic field of significant strength, baffles [[astronomy|astronomers]] who have assumed that magnetic fields form on rapidly moving planets that have conductive and liquid cores that can act as dynamos. In fact, Humphreys asserts that the characteristic that determines which of the terrestrial planets will have a persistent magnetic field is the core radius, and that the cores of all four of these planets have similar conductivities. Mercury and Earth have larger cores than do Mars and Venus. The lengths of the sidereal days on those worlds do not matter.<ref name=Humphreys/>
=== Geology ===
[[Image:MarsTopoMap-PIA02031 modest.jpg|left|thumb|300px|Topographic map of Mars.]]
There is a dichotomy on the surface of Mars; the northern hemisphere consists of low-lying volcanic plains, with the southern hemisphere consists of ancient, heavily-cratered highland plains. Mars also has two volcanic regions: Tharsis and Elysium. Within the Tharsis region is the largest volcano in the solar system, [[Olympus Mons]]. Olympus Mons is approximately 500 km across and is about the same size as the state of Arizona. Its peak is 24 km above the surrounding plains and it is surrounded by a vertical scarp 6 km high. A large canyon system, Valles Marineris, is located along the Martian equator east of the Tharsis region. Valles Marineris is 2-6km deep and 200-600km wide and approximately 4,500 km long (approximately the distance from San Francisco to Boston). The eastern part of Valles Marineris appears to have a tectonic origin, but the western part is characterized by features such as teardrop islands and longitudinal grooves, indicating it may have been formed by catastrophic flooding in the past. Such flooding may be possible under current climate conditions. Run-off channels in the cratered highland indicate a thicker atmosphere or warmer climate in the past that would have allowed water to be stable on the surface.
There is a dichotomy on the surface of Mars; the northern hemisphere consists of low-lying volcanic plains, with the southern hemisphere consists of ancient, heavily-cratered highland plains. Mars also has two volcanic regions: Tharsis and Elysium. Within the Tharsis region is the largest volcano in the solar system, [[Olympus Mons]]. Olympus Mons is approximately 500 km across and is about the same size as the state of Arizona. Its peak is 24 km above the surrounding plains and it is surrounded by a vertical scarp 6 km high. A large canyon system, Valles Marineris, is located along the Martian equator east of the Tharsis region. Valles Marineris is 2-6km deep and 200-600km wide and approximately 4,500 km long (approximately the distance from San Francisco to Boston). The eastern part of Valles Marineris appears to have a tectonic origin, but the western part is characterized by features such as teardrop islands and longitudinal grooves, indicating it may have been formed by catastrophic flooding in the past. Such flooding may be possible under current climate conditions. Run-off channels in the cratered highland indicate a thicker atmosphere or warmer climate in the past that would have allowed water to be stable on the surface.
Recent satellite imagery has shown that Mars has a 3 kilometer deep ice cap around its polar regions. The northern polar region is surrounded by dune fields. During the Martian winter, a layer of carbon dioxide condenses at the poles and sublimates in the summer, leaving the water-ice and dust polar caps exposed. The ratio of dust to water-ice contained in the polar caps remains unknown.
Recent satellite imagery has shown that Mars has a 3 kilometer deep ice cap around its polar regions. The northern polar region is surrounded by dune fields. During the Martian winter, a layer of carbon dioxide condenses at the poles and sublimates in the summer, leaving the water-ice and dust polar caps exposed. The ratio of dust to water-ice contained in the polar caps remains unknown.
[[Image:F035a72_processed.jpg|thumb|100px|left|Cydonia Mensae, home of the alleged "face on Mars."]]
Persistent rumors tell of a "face on Mars," allegedly located in the Cydonia Mensae region at coordinates 40.9°N and 9.45°W. This alleged "face" is located in the midst of several pyramids and other mountains. Prevailing opinion at NASA is that the "face" is a trick of the eye due to the unusual lighting conditions.<ref name=faq>Williams, David R. "[http://nssdc.gsfc.nasa.gov/planetary/planetaryfaq.html#Mars Frequently Asked Questions - Planetary - Mars]." National Space Science Data Center, [[National Aeronautics and Space Administration|NASA]], January 2, 2008. Accessed May 27, 2008.</ref>
=== Water on Mars ===
[[Image:Weeping_100.jpg|thumb|100px|right|Multiple gullies in a south-facing wall in the Gorgonum Chaos region on Mars]]
Mars cannot have liquid water on its surface. The thin atmosphere does not permit this, even during high summer on Mars. Yet the [[Mars Global Surveyor]] mission in June 2000 took photographs of gully-like formations on several precipices and crater walls on Mars. These formations tend to occur between 30° and 70° north and south latitude. Mission analysts further suggest that these formations are relatively fresh and estimate that liquid water might be found less than 500 meters beneath the surface.<ref name=msss>"[http://www.msss.com/mars_images/moc/june2000/ MOC Images Suggest Recent Sources of Liquid Water on Mars]." Malin Space Science Systems, June 22, 2000. Accessed May 27, 2008.</ref>
== Life on Mars ==
Speculation on whether [[extraterrestrial life]] exists on Mars has been the subject of persistent scientific speculation for decades. The earliest speculation concerned a possible civilization on Mars,<ref name=Hamilton/> this after Percival Lowell theorized that the straight lines that several astronomers had seen on Mars were in fact artificial constructs, and specifically canals.<ref name=canals>"[http://ssed.gsfc.nasa.gov/tharsis/canals.html The canals of Mars--historical note]." Goddard Space Flight Center, [[National Aeronautics and Space Administration|NASA]], n.d. Accessed May 27, 2008.</ref> Lovell popularized his theory as early as 1906, and for a long time the suspicion of a non-human civilization native to Mars would find repeated expression in novels and dramatic presentations. Only with the first successful explorations of Mars would the scientific community, and the public, abandon that theory.
Current speculation concerns the possible finding of [[microbe]]s. These would be [[extremophile]]s, or microbes that survive and even grow in environments lethal to other forms of life. Direct attempts to find such life began in 1976 with the [[Viking 1]] and [[Viking 2]] landers. To date no positive sign of life on Mars has been found. The Viking landers found evidence of unexplained chemical activity, but no clear evidence of microbes. Whether the Viking landers would have been able to detect extremophiles, a concept unknown to the Viking mission planners, is unclear.<ref name=Hamilton/>
The [[astrobiology|astrobiologists]] involved with [[Project Viking]] suspect that Mars might be an inherently inhospitable environment for life. Ultraviolet light from the sun shines unchecked on Mars, on account of Mars' thin atmosphere and weak magnetic field. The soil of Mars is also very dry, and the soil has a high proportion of oxidizing agents.<ref name=Hamilton/>
== Problem for uniformitarian theories ==
The most formidable current problem that Mars poses for uniformitarians today is that its magnetic field is weak and inconsequential, while a planet (Mercury) of little more than half its weight does have a significant magnetic field. According to current theory, planets derive their magnetic fields by dynamo action. This requires fast rotation and liquid cores. Mars and Earth have comparable sidereal days, but Earth's magnetic field is strong enough to protect Earth from the [[solar wind]], while that of Mars is not. Mercury has a far longer sidereal day than Mars has, and yet Mercury has a significant magnetic field while Mars has none.
== Mars in popular culture ==
Mars has figured prominently in [[science fiction]] in the Western world for more than a century.
=== The War of the Worlds ===
The first novel speculating on a civilization on Mars was ''The War of the Worlds'' by [[H. G. Wells]], in 1897. Wells' Martians had a military strength that human civilization could not match, but ultimately perished after contracting various [[infectious disease]]s caused by microbes native to Earth to which the Martians effectively had no defense.
In 1938, actor/director [[Orson Welles]] and his Mercury Theater produced a [[radio]] drama based on this novel. Welles updated the novel to his own period but otherwise remained faithful to the source material. The broadcast created such a panic in the [[United States]] that Welles was compelled to order a broadcast disclaimer in mid-show and, at the end of the show, personally assure his listeners that no such thing as an extraterrestrial invasion had taken place.<ref name=Hamilton/>
H. G. Wells' novel would inspire two [[motion picture]] projects and one [[television]] series.
=== Other speculations on civilizations ===
Author [[Edgar Rice Burroughs]] published several novels speculating on an elaborate civilization on Mars to which humans traveled, but which was not bent on invading the earth. Author [[C. S. Lewis]], in his novel ''Out of the Silent Planet'', envisioned Mars as the home of three races of non-fallen beings that were instructed to regard the earth as off-limits on account of man's [[fall of man|fallen nature]].
With the abandonment of the Lowell canal theory, science fiction authors and dramatists envisioned Mars as home to a human colony. But at least one motion-picture producer saw Mars as a place that very ancient [[astronaut]]s had once visited. These astronauts, according to this scenario, left behind some advanced equipment that a human rebel was subsequently able to use to give Mars a breathable atmosphere and thus facilitate the Martian colony's liberation from the venal and tyrannical civilization on earth.
=== Speculation on microbes ===
At least two science-fiction authors have recently speculated about the finding of microbes on Mars, and the implications that such a discovery would hold for the [[Christianity|Christian]] faith and the possible "back-contamination" of the earth when the crew that found the microbes returned to earth.
== Observation and exploration ==
Observation of Mars has been ongoing since the ancients noted its existence and its movements. The invention of the telescope provoked the first serious study of Mars as a celestial object, and not a prophetic sign. Yet not all of this observation led to proper inferences. Percival Lowell's canal theory would lead to more than half a century of vain speculation on extraterrestrial civilization before the first successful exploratory missions would return evidence forcing the abandonment of that theory.
Mars has been the subject of more attempt to explore it, and more failures, than any other planet. Of approximately 37 separate missions to Mars, only 13 have had any success. The planetary scientists of the [[Union of Soviet Socialist Republics]], so successful in exploring [[Venus]], experienced ten mission failures before achieving their first success, seven years after the [[United States]] achieved success with its [[Mariner 4]] mission. That Soviet mission, [[Mars 3]] in 1971, succeeded in placing a lander on Mars, but the lander's system transmitted for only 20 seconds before failing.
In 1975, [[Project Viking]] achieved the most notable success by placing two orbiters and two landers on Mars. Neither nation would attempt any further missions to Mars until 1988, when the Soviets lost one craft en route and lost contact with the other ([[Phobos 2]] seconds after its rendezvous with Mars's inner [[moon]] [[Phobos]]. Nor was the United States' program immune to failure; its ''Mars Observer'' vessel was lost prior to arrival after some propulsion systems failed.<ref name=faq/>
In 1996 the [[Mars Global Surveyor]] enjoyed the most success to date, returning more images than all previous missions combined. In that same year, the United States landed the first mobile explorer, or "rover," called the [[Mars Pathfinder]].
The United States would, unfortunately, lose the next two successive craft that it sent to Mars. But its [[Mars Odyssey]] would arrive intact in 2001 and send back the first high-resolution images. Two years later the [[European Space Agency]] would successfully place its [[Mars Express]] orbiter in the Martian system; sadly, its associated landing craft would crash-land. The Mars Express orbiter continues in orbit around Mars.<ref name=esa>"[http://www.esa.int/SPECIALS/Mars_Express/ Mars Express home page]." European Space Agency. Accessed May 27, 2008.</ref>
[[Image:Mcmurdo_pan_spirit.jpg|thumb|left|150px||360 degree panorama from mars rover ''Spirit''.]]
The most successful missions to date have been the Mars Excursion Rover missions. Two of these sophisticated mobile robots, named ''Spirit'' and ''Opportunity'', launched in 2003 and arrived safely on Mars about six months later, on opposite sides of the planet. They have been running for four years now, at least fifteen times longer than they were warranted to run. The Opportunity rover has been taking pictures of the Victoria Crater, and Spirit has been photographing the Esperanza formation which contains "vesicular" basalt (characterized by multiple cavities representing dissolved gas escaping from solution during a volcanic eruption).<ref name=David>David, Leonard. "[http://www.space.com/missionlaunches/061228_rovers_update.html Mars Rovers: On the Roll to New Targets]." ''Space.com'' December 28, 2006. Accessed May 27, 2008.</ref>
On May 26, 2008, NASA placed a polar lander on Mars for the first time: the [[Phoenix lander]]. As of May 28, 2008, the Phoenix lander is functioning well and is about to begin its program to sample the soil and ice where it rests.
At least one non-governmental group, calling itself the Mars Society, has been actively studying technologies appropriate to send a crew of from four to six astronauts to Mars for a roughly two-year stay.<ref name=marssoc>[http://www.marssociety.org/portal The Mars Society] global and USA portal. Accessed May 27, 2008.</ref>
==Satellites==
==Satellites==
Mars has two moons: [[Phobos]] and [[Deimos]] (which respectively mean "Fear and "Panic" in [[Greek]]). Russian scientists in the 1950s posited that Phobos might be hollow, but these claims were discredited in the late 1960s.
Mars has two moons: [[Phobos]] and [[Deimos]] (which respectively mean "Fear and "Panic" in [[Greek]]). Russian scientists in the 1950s posited that Phobos might be hollow, but these claims were discredited in the late 1960s.
== References ==
== References ==
{{reflist|2}}
{{reflist|2}}
{{Astronomy portal}}
== Related Links ==
* [[wikipedia:Mars|Mars]] by Wikipedia
* [http://mars.jpl.nasa.gov/missions/log/ NASA Historical Log: Missions to Mars]
* [http://www.space.com/mars/ Space.com] All About Mars
* [http://www.google.com/mars/ Google Mars], an interactive topographical map
* [http://starchild.gsfc.nasa.gov/docs/StarChild/solar_system_level2/mars.html Mars: the Red Planet] by Starchild, an educational service of NASA.
* [http://www.war-of-the-worlds.org/ War of the Worlds] commemorative site.
{{Solarsystem}}
{{solarsystem}}
[[Category:Astrology]]
[[Category:Mars]]