火星_综合百科_百问中文

火星(Mars)

太阳的第四个行星，根据罗马战神而命名。与太阳的平均距离是2.28亿公里，一天相当於地球的24.6小时，一年相当於地球的687天。它有两个小卫星：火卫一和火卫二。火星的平均直径是6,790公里，约等於地球直径的一半，而密度小於地球。其质量大约等於地球的十分之一，表面引力强度为地球的三分之一左右。火星上没有测出磁场，暗示着它缺乏坚实的金属核心，这也是密度低的原因。和地球一样，它有季节和大气层，但表面平均温度只有-23℃。火星的薄薄大气主要是二氧化碳，内含一些氮和氩，还有少许水蒸气。「水手号」、「海盗号」太空船和後来太空任务所取得的影像显示火星表面多爆裂口，类似月球表面，具有火山、大型熔岩平原、水道和峡谷、山崩的残留，其中许多在地球的标准中是巨大的，例如奥林帕斯火山即是太阳系中已知最大的火山。风是火星上重要的元素，偶尔导致星球尘暴，并造成沙丘、爆裂口条痕等沈积。火星上没有侦测到生命形式。

English version：

Mars

Fourth planet from the sun, named after the Roman god of war. Its mean distance from the sun is 141 million mi (228 million km); its day is 24.6 earth hours and its year about 687 earth days. It has two small moons, Phobos and Deimos. Mars's mean diameter is 4,244 mi (6,790 km), about half that of earth, and it is less dense than earth. Its mass is about one-tenth of earth's and its surface gravity is about one-third as strong as earth's. No magnetic field has been detected on Mars, suggesting, as does its low density, the absence of a substantial metallic core. Like earth, it has seasons and an atmosphere, but its mean surface temperature is only −9°F (−23°C). Mars's thin atmosphere is mainly carbon dioxide, with some nitrogen and argon and traces of water vapor. Images obtained by spacecraft of the Mariner, Viking, and later missions show a cratered surface, similar to the moon's, with volcanoes, extensive lava plains, channels and canyons, and remnants of landslides, many large by earth standards; Olympus Mons, for example, is the largest known volcano in the solar system. Wind is an important element on Mars, occasionally causing global dust storms and forming deposits such as dunes and crater streaks. No life-forms have been detected on the planet.

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