Mars ♂

Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin atmosphere (less than 1% that of Earth’s), and has a crust primarily composed of elements similar to Earth’s crust, as well as a core made of iron and nickel. Mars has surface features such as impact craters, valleys, dunes and polar ice caps. It has two small and irregularly shaped moons, Phobos and Deimos.

Some of the most notable surface features on Mars include Olympus Mons, the largest volcano and highest known mountain in the Solar System and Valles Marineris, one of the largest canyons in the Solar System. The Borealis basin in the Northern Hemisphere covers approximately 40% of the planet and may be a large impact feature.

Days and seasons on Mars are comparable to those of Earth, as the planets have a similar rotation period and tilt of the rotational axis relative to the ecliptic plane. Liquid water on the surface of Mars cannot exist due to low atmospheric pressure, which is less than 1% of the atmospheric pressure on Earth. Both of Mars’s polar ice caps appear to be made largely of water. In the distant past, Mars was likely wetter, and thus possibly more suited for life. It is not known whether life has ever existed on Mars.

The atmosphere of Mars consists of about 96% carbon dioxide, 1.93% argon and 1.89% nitrogen along with traces of oxygen and water. The atmosphere is quite dusty, containing particulates about 1.5 µm in diameter which give the Martian sky a tawny color when seen from the surface. It may take on a pink hue due to iron oxide particles suspended in it.

The concentration of methane in the Martian atmosphere fluctuates from about 0.24 ppb during the northern winter to about 0.65 ppb during the summer. Estimates of its lifetime range from 0.6 to 4 years, so its presence indicates that an active source of the gas must be present. Methane could be produced by non-biological process such as serpentinization involving water, carbon dioxide, and the mineral olivine, which is known to be common on Mars, or by Martian life.

火星(拉丁語:Mars;天文符號:♂),古称荧惑,为太陽系里四顆類地行星之一。火星又稱為瑪爾斯,是羅馬神話中的戰神,所以在英语中,火星是罗马战神的意思,通常被称为“红色星球”;古漢語中則因为它荧荧如火,位置、亮度時常變動讓人無法捉摸而稱之為熒惑。火星是太陽系的八大行星中第二小的行星,其質量、體積仅比水星略大。火星的直徑約為地球的一半,自轉軸傾角、自轉週期則與地球相當,但繞太陽公轉周期是接近地球的兩倍。在地球上,火星肉眼可見,亮度可達-2.91,只比金星、月球和太陽暗,但在大部分時間裡比木星暗。火星距離地球最近在5400万公里(最遠達4億公里,探測器需飛行約7個月抵達火星)。火星大氣以二氧化碳為主,既稀薄又寒冷,其表面特徵讓人聯想起月球上的撞擊坑,以及地球上的山谷、沙漠和極地冰蓋。英語中,通常被稱為紅色星球(英語:Red Planet)。火星在視覺上呈現為橘紅色是因為地表廣泛普遍的分佈著氧化鐵,它使火星呈現出一种红色的外觀,在肉眼可見的天體中獨具一格。火星地表沙丘、礫石遍布且沒有穩定的液態水,火星南半球是古老、充滿隕石坑的高地,北半球則是較年輕的平原。