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Line 1: − + − A terrestrial planet, Mars has a thin atmosphere and surface features reminiscent both of the impact craters of the Moon and the volcanoes, valleys, deserts and polar ice caps of Earth. It is the site of Olympus Mons, the highest known mountain in the solar system, and of Valles Marineris, the largest canyon. In addition to its geographical features, Mars’ rotational period and seasonal cycles are likewise similar to those of the Earth.+ − Until the first flyby of Mars by Mariner 4 in 1965, it was speculated that there might be liquid water on the planet. This was based on observations of periodic variations in light and dark patches, particularly in the polar latitudes, which looked like seas and continents, while long, dark striations were interpreted by some observers as irrigation channels for liquid water. These straight line features were later proven not to exist and were instead explained as optical illusions. Still, of all the planets in our solar system, Mars is the most likely, other than Earth, to harbor liquid water, and perhaps life.+ − Mars is currently host to three functional orbiting spacecraft: Mars Odyssey, Mars Express, and Mars Reconnaissance Orbiter. This is more than any planet except Earth. The surface is also home to the two Mars Exploration Rovers (Spirit and Opportunity). Geological evidence gathered by these and preceding missions suggests that Mars previously had large-scale water coverage, while observations also indicate that small geyser-like water flows have occurred in recent years.[3] Observations by NASA's Mars Global Surveyor show evidence that parts of the southern polar ice cap have been receding.[4]+ − + − ==Physical characteristics== − Mars has half the radius of 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.[5] While Mars is larger and more massive than Mercury, Mercury has a higher density. This results in a slightly stronger gravitational force at Mercury's surface. The red-orange appearance of the Martian surface is caused by iron(III) oxide, more commonly known as hematite, or rust. − '''Geology''' − Based on orbital observations and the examination of the Martian meteorite collection, the surface of Mars appears to be composed primarily of basalt. Some evidence suggests that a portion of the Martian surface is more silica-rich than typical basalt, and may be similar to andesitic stones on Earth; however, these observations may also be explained by silica glass. Much of the surface is deeply covered by a fine iron(III) oxide dust that has the consistency of talcum powder. − − Although Mars has no intrinsic magnetic field, observations show that parts of the planet's crust have been magnetized. This paleomagnetism of magnetically-susceptible minerals has properties that are very similar to the alternating bands found on the ocean floors of Earth. − One theory, published in 1999 and re-examined in October 2005 (with the help of the Mars Global Surveyor), is that these bands demonstrate plate tectonics on Mars 4 billion years ago, before the planetary dynamo ceased to function (and, thus, the magnetic field).Current models of the planet's interior imply a core region approximately 1,480 kilometres (920 mi) in radius, consisting primarily of iron with about 15–17% sulfur. This iron sulfide core is partially fluid, and has twice the concentration of the lighter elements than exist 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 (31 mi), with a maximum thickness of 125 km (78 mi). Earth's crust, averaging 40 km (25 mi), is only a third as thick as Mars’ crust relative to the sizes of the two planets.
Reverted edits by Lordration (Talk); changed back to last version by Fox
[[Image:Mars Viking.jpg|left|thumb|250px|Mars photographed by [[Viking Orbiter]]s]]
[[Image:Mars Viking.jpg|left|thumb|250px|Mars photographed by [[Viking Orbiter]]s]]
{{Solarsystem}}
{{Solarsystem}}
Mars is the fourth planet from the Sun in the Solar System. The planet is named after Mars, the Roman god of war. It is also referred to as the "Red Planet" because of its reddish appearance as seen 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.
Mars was known to the antiquities; the Romans even named one of their gods — [[Ares|Mars, the god of war]] — after it. The Romans also knew about Jupiter and Saturn, but it was not until the 17th century that [[William Herschel]] discovered [[Uranus]], and [[Neptune]] and [[Pluto]] took even longer.
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.
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.
Mars has two moons, Phobos and Deimos, which are small and irregularly shaped. These may be captured asteroids, similar to 5261 Eureka, a Martian 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, though for much of the year Jupiter may appear brighter to the naked eye than Mars.
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:MarsTopoMap-PIA02031 modest.jpg|left|thumb|300px|Topographic map of Mars.]]
[[Image:MarsTopoMap-PIA02031 modest.jpg|left|thumb|300px|Topographic map of Mars.]]
[[Category:Planets]][[Category:Astrology]]
[[Category:Planets]][[Category:Astrology]]