Mars

Mars is the fourth planet from the Sun in our solar system. It is named after Mars, the god of war in Roman mythology (the counterpart to Ares in Greek mythology), because of its red color as viewed in the night sky. This feature also earned it the name "The Red Planet." Mars has two moons (Phobos and Deimos) which are both small and oddly-shaped, possibly being captured asteroids. The prefix areo- refers to Mars in the same way geo- refers to Earth—e.g. areology versus geology.

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 almost the same length as it is on Earth: 24 hours, 39 minutes, and 35.244 seconds.

Related Topics:
Earth - Mass - Ocean - Solar day

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Atmosphere

Mars' atmosphere is thin: the air pressure on the surface is only 750 pascals, about 0.75 percent 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 percent carbon dioxide, 3 percent nitrogen, 1.6 percent argon, and 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 (20 degrees Celsius or 68 degrees Fahrenheit is about as hot as it gets).

Related Topics:
Atmosphere - Air pressure - Pascal - Scale height - Carbon dioxide - Nitrogen - Argon - Oxygen - Water - 2003 - Methane - Telescope - March 2004 - Mars Express Orbiter - Ppb - Reference

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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 (and so is presumably also continually being released to the atmosphere) before it has time to become uniformly distributed in 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.

Related Topics:
Volcanic - Comet - Microorganism - Methanogen - Ethane - Sulfur dioxide

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Other aspects of the Martian atmosphere are also very dynamic. 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. 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 http://marsrovers.jpl.nasa.gov/gallery/press/opportunity/20041213a/merb_sol290_clouds-B313R1_br.jpg of water-ice were photographed by the Opportunity rover in 2004.

Related Topics:
Frost - Cirrus cloud

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Recently, evidence has been discovered suggesting that Mars may be warming on the short term http://news.bbc.co.uk/2/hi/science/nature/4266474.stm; however, it is now cooler than it was in the 1970's http://catdynamics.blogspot.com/2005/09/climate-science-mars-and-politics.html.

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Geology

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

Related Topics:
Basalt - Andesite

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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 http://photojournal.jpl.nasa.gov/catalog/PIA02008. 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.

Related Topics:
Magnetic field - Mars Global Surveyor - Crust - 1999 - Plate tectonics - Cosmic radiation

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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".

Related Topics:
Hematite - Meridiani Planum - Jarosite - December 9 - 2004 - Science - Goethite

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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.

Related Topics:
1996 - ALH84001 - As of 2005

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Topography

The dichotomy of Martian topography is striking: northern plains flattened by lava flows contrast with the southern highlands, pitted and cratered by ancient impacts. 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.

Related Topics:
Albedo - Arabia Terra - Amazonis Planitia - Mare Erythraeum - Mare Sirenum - Aurorae Sinus - Syrtis Major

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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 27 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.

Related Topics:
Carbon dioxide - Shield - Volcano - Olympus Mons (''Mount Olympus'') - Tharsis - List of mountains on Mars - Valles Marineris - Mariner - Impact crater - Hellas impact basin - List of craters on Mars

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The difference between Mars' highest and lowest points is nearly 31 km (from the top of Olympus Mons at an altitude of 27 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.

Related Topics:
Mount Everest - Mariana Trench

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

Related Topics:
International Astronomical Union - Working Group for Planetary System Nomenclature

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Other notes:

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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.

Related Topics:
Mean gravity surface - Datum - Triple point

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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.

Related Topics:
Prime Meridian - Wilhelm Beer - Johann Heinrich Mädler - 1877 - Giovanni Schiaparelli - Mariner 9 - 1972 - Airy-0 - Sinus Meridiani - Merton Davies - RAND Corporation

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Canals

Mars has an important place in human imagination due to the belief by some that life existed on Mars, 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.

Related Topics:
Percival Lowell - Giovanni Schiaparelli - Martian canal - Many stories

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