【太陽(yáng)系小常識(shí)】八大行星的前世今生

水星：Mercury

Mercury,?first?planet?in?distance from the Sun in the solar system. The smallest of the rocky or terrestrial planets that include Venus, Earth, and Mars, Mercury has a global magnetic field, but only a trace of an atmosphere and no moons of its own. It is the second hottest planet after Venus. Mercury circles the Sun every 88 Earth days at an average distance of 58 million km (36 million mi) and takes 59 days to turns on its axis. It retains an ancient cratered surface that has changed little since the formation of the solar system, making the planet of special interest to planetary scientists. Mercury was named for the fleet-footed messenger of the gods in Roman mythology.

水星（Mercury），中國(guó)古代稱(chēng)為辰星。是太陽(yáng)系中的類(lèi)地行星，其主要由石質(zhì)和鐵質(zhì)構(gòu)成，密度較高。自轉(zhuǎn)周期很長(zhǎng)為58.65天，自轉(zhuǎn)方向和公轉(zhuǎn)方向相同。水星在88個(gè)地球日里就能繞太陽(yáng)一周，平均速度47.89千米，是太陽(yáng)系中運(yùn)動(dòng)最快的行星。無(wú)衛(wèi)星環(huán)繞。它是八大行星中是最小的行星，也是離太陽(yáng)最近的行星。

金星：Venus

Venus,?second?planet?in?distance from the Sun, but the hottest planet in the solar system (hotter than Mercury). Its hellish surface has broiling temperatures that make rocks glow red under a crushing atmosphere that shrouds the planet in thick layers of clouds. Venus is nearly the same size as Earth, but takes 243 days to rotate on its axis in the opposite direction. It also lacks a magnetic field and a moon. Why conditions on Venus and Earth are so different remains a major puzzle for planetary scientists. Venus circles the Sun at a distance of 108 million km (67 million mi) in a little over seven months (about 225 days). The planet was named for Venus, the Roman goddess of beauty.

金星（Venus）是太陽(yáng)系中八大行星之一，按離太陽(yáng)由近及遠(yuǎn)的次序是第二顆。它是離地球最近的行星。中國(guó)古代稱(chēng)之為長(zhǎng)庚、啟明、太白或太白金星。公轉(zhuǎn)周期是224.71地球日。夜空中亮度僅次于月球，排第二，金星要在日出稍前或者日落稍后才能達(dá)到亮度最大。它有時(shí)黎明前出現(xiàn)在東方天空，被稱(chēng)為“啟明”；有時(shí)黃昏后出現(xiàn)在西方天空，被稱(chēng)為“長(zhǎng)庚”。

地球：Earth

Earth,?third?planet?in?distance from the Sun in the solar system, the only planet known to harbor life, and the “home” of human beings. From space Earth resembles a big blue marble with swirling white clouds floating above blue oceans. About 71 percent of Earth’s surface is covered by water, which is essential to life. The rest is land, mostly in the form of continents that rise above the oceans. Earth’s?surface?is?surrounded by a layer of gases known as the atmosphere, which extends upward from the surface, slowly thinning out into space. Below the surface is a hot interior of rocky material and two core layers composed of the metals nickel and iron in solid and liquid form.

地球是上百萬(wàn)種生物的家園， 包括人類(lèi)。地球是目前人類(lèi)所知宇宙中唯一存在生命的天體。地球誕生于45.4億年前， 而生命誕生于地球誕生后的10億年內(nèi)。

火星：Mars

Mars,?fourth?planet?in?distance from the Sun in the solar system. Mars is of special scientific interest because of its similarities to Earth. It has an atmosphere with seasons and changing weather, and its surface shows evidence of ancient water and volcanoes. The length of its day and the tilt of its axis are similar to those of Earth. Mars takes about two years to circle the Sun at an average distance of 228 million km (141.7 million mi). The possibility of life on Mars, now or in the distant past, is one of the major questions in astronomy. More space probes have been sent to Mars than to any other planet. Mars is named for the Roman god of war. It is sometimes called the red planet because it appears fiery red in Earth’s night sky, the result of rusty, iron-oxide mineral dust that covers its surface.

火星（Mars）是太陽(yáng)系由內(nèi)往外數(shù)的第四顆行星，屬于類(lèi)地行星，直徑為地球的一半，自轉(zhuǎn)軸傾角、自轉(zhuǎn)周期相近，公轉(zhuǎn)一周則花兩倍時(shí)間。在西方稱(chēng)為戰(zhàn)神瑪爾斯，中國(guó)則稱(chēng)為“熒惑”。橘紅色外表是因?yàn)榈乇淼某噼F礦（氧化鐵）?；鹦腔旧鲜巧衬行?，地表沙丘、礫石遍布，沒(méi)有穩(wěn)定的液態(tài)水體。二氧化碳為主的大氣既稀薄又寒冷，沙塵懸浮其中，每年常有塵暴發(fā)生。火星兩極皆有水冰與干冰組成的極冠，會(huì)隨著季節(jié)消長(zhǎng)。

木星：Jupiter

Jupiter,?fifth?planet?from?the Sun and the largest planet in the solar system. The fourth brightest object in Earth’s sky, after the Sun, the Moon, and Venus, Jupiter is more than three times brighter than Sirius, the brightest star. Due to its prominence in the sky, the Romans named the planet for their chief god, Jupiter. Jupiter?orbits?the?Sun at an average distance of 778 million km (484 million mi), which is about five times the distance from Earth to the Sun. Jupiter’s year, or the time it takes to complete an orbit about the Sun, is 11.9 Earth years, and its day, or the time it takes to rotate on its axis, is about 9.9 hours, less than half an Earth day.

木星（Jupiter），為太陽(yáng)系八大行星之一，距太陽(yáng)（由近及遠(yuǎn)）順序?yàn)榈谖?，亦為太?yáng)系體積最大、自轉(zhuǎn)最快的行星。木星主要由氫和氦組成，中心溫度估計(jì)高達(dá)30,500℃。古代中國(guó)稱(chēng)之歲星，取其繞行天球一周為12年，與地支相同之故。西方語(yǔ)言一般稱(chēng)之朱比特，源自羅馬神話中的眾神之王、相當(dāng)于希臘神話中的宙斯。

天王星：Saturn

Saturn, sixth planet in order of distance from the Sun, and the second largest in our solar system. Saturn’s most distinctive feature is a giant system of rings that surrounds the planet at its equator, stretching over twice the width of the planet itself. The first person to see the rings was the Italian scientist Galileo in 1610, using one of the earliest telescopes. Space probes have greatly increased our knowledge of Saturn, its rings, and its many moons. Flybys by the Pioneer and the Voyager probes led to the Cassini orbiter that began studying Saturn in detail in 2004. As seen from Earth, Saturn appears as a yellowish object—one of the brightest in the night sky. The planet is named for Saturn, the Roman god of agriculture. Saturn takes about 29.5 years to orbit the Sun at an average distance of 1,435 billion km (891.5 million mi), or about 9.59 astronomical unit (AU). An AU is equal to the average distance between the Earth and the Sun, or 150 million km (93 million mi). Saturn rotates on its axis in about 10.5 hours and is tilted at about 27°, giving the planet distinct seasons.

土星（Saturn）古稱(chēng)鎮(zhèn)星或填星，是太陽(yáng)系八大行星之一。赤道直徑約120660公里（為地球的9.46倍），兩極直徑大約108000公里，扁率很大，是最扁平的行星，也是太陽(yáng)系第二大行星。它與鄰居木星十分相像，表面也是液態(tài)氫和氦的海洋，上方同樣覆蓋著厚厚的云層。土星上狂風(fēng)肆虐，沿東西方向的風(fēng)速可超過(guò)每小時(shí)1600公里，是木星的4倍。土星上空的云層就是這些狂風(fēng)造成的，云層中含有大量的結(jié)晶氨。

海王星：Uranus

Uranus, seventh planet in distance from the Sun, third largest planet in diameter, and fourth largest in mass in the solar system. Unlike other major planets, Uranus is tipped sideways on its axis of rotation. It experiences extreme seasons, and its 13 rings and 27 known moons revolve around its equator nearly vertically to the plane of its orbit around the Sun. Because of its great size and mass, scientists classify Uranus as one of the giant or Jovian (Jupiter-like) planets—along with Jupiter, Saturn, and Neptune. Like more distant Neptune, Uranus is also classified as an ice giant planet, mainly made of the ice-forming molecules water, ammonia, and methane as a liquid mixture above what is thought to be a rocky core. Its atmosphere is mainly hydrogen and helium, along with methane gas that gives the planet a blue-green color.

天王星（Uranus）是太陽(yáng)向外的第七顆行星，在太陽(yáng)系的體積是第三大（比海王星大），質(zhì)量排名第四（比海王星輕）。他的名稱(chēng)來(lái)自古希臘神話中的天空之神烏拉諾斯，是克洛諾斯（農(nóng)神）的父親，宙斯（朱比特）的祖父。天王星是第一顆在現(xiàn)代發(fā)現(xiàn)的行星，雖然它的光度與五顆傳統(tǒng)行星一樣，亮度是肉眼可見(jiàn)的，但由于較為黯淡而未被古代的觀測(cè)者發(fā)現(xiàn)。威廉·赫歇耳爵士在1781年3月13日宣布他的發(fā)現(xiàn)，在太陽(yáng)系的現(xiàn)代史上首度擴(kuò)展了已知的界限。這也是第一顆使用望遠(yuǎn)鏡發(fā)現(xiàn)的行星。

冥王星：Neptune

Neptune, eighth planet in distance from the Sun, fourth largest planet in diameter, and third largest in mass in the solar system. Neptune’s gravity has a major influence on the Kuiper Belt, a region of icy bodies in the outer solar system that is a source of comets and includes the dwarf planet Pluto, formerly counted as the ninth planet. Because of its great size and mass, scientists classify Neptune as one of the giant or Jovian (Jupiter-like) planets—along with Jupiter, Saturn, and Uranus. Like Uranus, Neptune is also classified as an ice giant planet, mainly made of the ice-forming molecules water, ammonia, and methane as a liquid mixture above what is thought to be a rocky core. Its atmosphere is mainly hydrogen and helium, along with methane gas that gives the planet a blue-green color.