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The composition of Mars covers the branch of the geology of Mars that describes the make-up of the planet Mars. == Elemental composition == Mars is a terrestrial planet, which means that its bulk composition, like Earth's, consists of silicates (minerals containing silicon and oxygen), metals, and other elements that typically make up rock. Also like Earth, Mars is a differentiated planet, meaning that it has a central core made up of metallic iron and nickel surrounded by a less dense, silicate mantle and crust. The planet's distinctive red colour is due to the oxidation of iron on its surface. Much of what we know about the elemental composition of Mars comes from orbiting spacecraft and landers. (See Exploration of Mars for list.) Most of these spacecraft carry spectrometers and other instruments to measure the surface composition of Mars by either remote sensing from orbit or ''in situ'' analyses on the surface. We also have many actual samples of Mars in the form of meteorites that have made their way to Earth. Martian meteorites (often called SNC's, for Shergottites, Nakhlites, and Chassignites—the groups of meteorites first shown to have a martian origin) provide data on the chemical composition of Mars' crust and interior that would not otherwise be available except through a sample return mission. Based on these data sources, scientists think that the most abundant chemical elements in the martian crust, besides silicon and oxygen, are iron, magnesium, aluminum, calcium, and potassium. These elements are major components of the minerals comprising igneous rocks.〔Press, F.; Siever, R. (1978). ''Earth,'' 2nd ed.; W.H. Freeman: San Francisco, p. 343.〕 The elements titanium, chromium, manganese, sulfur, phosphorus, sodium, and chlorine are less abundant〔Foley, C.N. et al. (2008). Martian Surface Chemistry: APXS Results from the Pathfinder Landing Site, in ''The Martian Surface: Composition, Mineralogy, and Physical Properties,'' J.F. Bell III, Ed. Cambridge University Press: Cambridge, UK, pp. 42-43, Table 3.1.〕 but are still important components of many accessory minerals〔See http://www.britannica.com/EBchecked/topic/2917/accessory-mineral for definition.〕 in rocks and of secondary minerals (weathering products) in the dust and soils (the regolith). Hydrogen is present as water (H2O) ice and in hydrated minerals. Carbon occurs as carbon dioxide (CO2) in the atmosphere and sometimes as dry ice at the poles. An unknown amount of carbon is also stored in carbonates. Molecular nitrogen (N2) makes up 2.7 percent of the atmosphere. As far as we know, organic compounds are absent except for a trace of methane detected in the atmosphere. On 16 December 2014, NASA reported the ''Curiosity'' rover detected a "tenfold spike", likely localized, in the amount of methane in the Martian atmosphere. Sample measurements taken "a dozen times over 20 months" showed increases in late 2013 and early 2014, averaging "7 parts of methane per billion in the atmosphere." Before and after that, readings averaged around one-tenth that level. The elemental composition of Mars is different from Earth′s in several significant ways. First, Martian meteorite analysis suggests that the planet's mantle is about twice as rich in iron as the Earth's mantle.〔Halliday, A.N. et al. (2001). The Accretion, Composition and Early Differentiation of Mars. In Chronology and Evolution of Mars, Kallenbach, R. et al. Eds., ''Space Science Reviews,'' 96: pp. 197–230.〕 Second, its core is more rich in sulphur. Third, the Martian mantle is richer in potassium and phosphorus than Earth's, and fourth, the Martian crust contains a higher percentage of volatile elements such as sulphur and chlorine than the Earth's crust does. Many of these conclusions are supported by ''in situ'' analyses of rocks and soils on the Martian surface.〔See Bruckner, J. et al. (2008) Mars Exploration Rovers: Chemical Composition by the APX, in ''The Martian Surface: Composition, Mineralogy, and Physical Properties,'' J.F. Bell III, Ed.; Cambridge University Press: Cambridge, UK, p. 58 for example.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Composition of Mars」の詳細全文を読む スポンサード リンク
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