| Mars (English) |
| 1 | Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance. Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the volcanoes, valleys, deserts, and polar ice caps of Earth. |
| 2 | The rotational period and seasonal cycles of Mars are likewise similar to those of Earth, as is the tilt that produces the seasons. Mars is the site of Olympus Mons, the highest known mountain within the Solar System, and of Valles Marineris, the largest canyon. The smooth Borealis basin in the northern hemisphere covers 40% of the planet and may be a giant impact feature. Until the first flyby of Mars occurred in 1965, by Mariner 4, many speculated about the presence of liquid water on the planet's surface. |
| 3 | This was based on observed periodic variations in light and dark patches, particularly in the polar latitudes, which appeared to be seas and continents; long, dark striations were interpreted by some as irrigation channels for liquid water. These straight line features were later explained as optical illusions, though geological evidence gathered by unmanned missions suggest that Mars once had large-scale water coverage on its surface. |
| 4 | In 2005, radar data revealed the presence of large quantities of water ice at the poles, and at mid-latitudes. The Mars rover Spirit sampled chemical compounds containing water molecules in March 2007. The Phoenix lander directly sampled water ice in shallow Martian soil on July 31, 2008. 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. |
| 5 | Mars is currently host to three functional orbiting spacecraft: Mars Odyssey, Mars Express, and the Mars Reconnaissance Orbiter. On the surface are the Mars Exploration Rover Opportunity and its recently decommissioned twin, Spirit, along with several other inert landers and rovers, both successful and unsuccessful. The Phoenix lander completed its mission on the surface in 2008. Observations by NASA's now-defunct Mars Global Surveyor show evidence that parts of the southern polar ice cap have been receding. |
| 6 | Observations by NASA's Mars Reconnaissance Orbiter have revealed possible flowing water during the warmest months on Mars. Mars can easily be seen from Earth with the naked eye. Its apparent magnitude reaches ?3.0 a brightness surpassed only by Venus, Jupiter, the Moon, and the Sun. Physical characteristics Mars has approximately half the radius of Earth. It is less dense than Earth, having about 15% of Earth's volume and 11% of themass. |
| 7 | Its surface area is only slightly less than the total area of Earth's dry land. While Mars is larger and more massive thanMercury, Mercury has a higher density. This results in the two planets having a nearly identical gravitational pull at the surface—that of Mars is stronger by less than 1%. Mars is also roughly intermediate in size, mass, and surface gravity between Earth and Earth's Moon (the Moon is about half the diameter of Mars, whereas Earth is twice; the Earth is about nine times more massive than Mars, and the Moon one-ninth as massive). |
| 8 | 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 rocks on Earth; these observations may also be explained by silica glass. |
| 9 | Much of the surface is deeply covered by finely grained iron(III) oxidedust. Although Mars has no evidence of a current structured global magnetic field, observations show that parts of the planet's crust have been magnetized, and that alternating polarity reversals of its dipole field have occurred in the past. This paleomagnetism of magnetically susceptible minerals has properties that are very similar to the alternating bands found on the ocean floors of Earth. |
| 10 | 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 four billion years ago, before the planetary dynamo ceased to function and caused the planet's magnetic field to fade away. Current models of the planet's interior imply a core region about 1,480 km in radius, consisting primarily of iron with about 14–17% sulfur. |
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