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1、第二章第二章 地球的起源地球的起源 The Formation of the Earth 地地球球起起源源的的问问题题，不不仅仅是是地地球球科科学学，而而且是自然科学中的一个基本理论问题。且是自然科学中的一个基本理论问题。因因为为地地球球是是太太阳阳系系的的成成员员之之一一，所所以以地地球球的的起起源源和和太太阳阳系系的的起起源源基基本本上上是是一一个个问题。问题。2.1 太阳系与地球太阳系与地球The Solar System and the Earth 地球只是太阳系中的普通一员。而太阳地球只是太阳系中的普通一员。而太阳只是银河系中亿万颗恒星中的一名小卒。只是银河系中亿万颗恒星中的一名小卒
2、。2.1.1 2.1.1 太阳系的成员太阳系的成员太阳系有九大行星。太阳系有九大行星。水星（水星（Mercury)、金星（金星（Venus）、）、地球（地球（Earth）、）、火星（火星（Mars）、）、木星（木星（Jupiter）、）、土星（土星（SaturnSaturn）、）、天王星天王星(Uranus)、海王星海王星(Neptune)、冥王星冥王星(Pluto ）九大行星位置排列示意图九大行星位置排列示意图太阳、水星、金星、地球、火星、木星、土星、天王星、海王星、冥王星。太阳系约有30000多个小行星，最大的小行星叫谷神（Ceres）,直径约730km。除除此此之之外外，现现已已发发现现
3、在在火火星星和和木木星星轨轨道道间间至至少少存存在在30000颗颗小小行行星星，其其中中最最大大的的一一叫叫谷谷神神星星（Ceres），是是1801年年发发现现的的，直径约直径约730km。九九大大行行星星中中。大大多多数数都都有有自自己己的的卫卫星星，最最多多的的是是木木星星，已已发发现现有有12个个卫卫星星。卫卫星也是太阳系的组成部分。星也是太阳系的组成部分。慧慧星星也也是是太太阳阳系系的的成成员员。到到目目前前为为止止，已观测到的慧星有已观测到的慧星有1500多颗。多颗。当慧星从太阳身边路过时，壮丽的慧尾，当慧星从太阳身边路过时，壮丽的慧尾，耀眼夺目，给人以难忘的印象。慧星的耀眼夺目，给
4、人以难忘的印象。慧星的出现，并不表明灾难的降临，而是一种出现，并不表明灾难的降临，而是一种天体的自然现象。它非但不是不吉祥的天体的自然现象。它非但不是不吉祥的预兆，而且为人类提供了研究太阳系的预兆，而且为人类提供了研究太阳系的起源和演化的难得的良机。起源和演化的难得的良机。1 太阳（太阳（The Sun）太阳是太阳系的中心，是太阳系中质量和太阳是太阳系的中心，是太阳系中质量和体积最大的天体。体积最大的天体。This image was acquired from NASAs Skylab space station on December 19,1973.质量质量 Mass(kg):1.989
5、e+30 (330,000 Earths)赤道半径赤道半径Equatorial radius(km)695,000 平均密度平均密度Mean density(gm/cm3)1.410 转动周期转动周期 Rotational period(days)25.36 平均表面温度平均表面温度 Mean surface temperature 6,000C 注：把地球质量记为注：把地球质量记为1.10123单位。单位。主要化学成份主要化学成份 Principal chemistry 氢氢 Hydrogen 92.1%氦氦 Helium 7.8%氧氧 Oxygen 0.061%碳碳 Carbon 0.03
6、0%2 水星（Mercury)质量质量 Mass(kg):0.0556 Earths)平均半径平均半径 Mean radius(km)2,434 平均密度平均密度Mean density(gm/cm3)6.03 转动周期转动周期 Rotational period(days)59.7平均距太阳距离平均距太阳距离 Mean distance from the Sun(Earth=1)：0.3871See the press release of May 28,1998(http:/oposite.stsci.edu/pubinfo/pr/1998/19/pr.html)for more info
7、rmation.However,the spot in the lower left hand region of the above Hubble image is very likely a large(about 2-3 times the size of Jupiter)planet ejected from a set of young(3%其它：其它：二氧化硫二氧化硫Sulfur dioxide,水汽水汽water vapor,一氧化碳一氧化碳carbon monoxide,氩氩argon,氦氦 helium,氖氖neon,氯化氢氯化氢hydrogen chloride,and 氟
8、化氢氟化氢hydrogen fluoride.4、地球（The Earth）Mass(kg)1.0000e+00 赤道半径赤道半径Equatorial radius(km)6,378.14 Mean density(gm/cm3)5.515 Mean distance from the Sun(km)149,600,000 Rotational period(days)0.99727 Rotational period(hours)23.9345 Image of earth taken from the Galileo probe enroute to Jupiter in 1990 Pro
9、duced by USGS Flagstaff轨道周期轨道周期 Orbital period(days)365.256 Mean surface temperature 15C Atmospheric pressure(bars)1.013 大气成份大气成份 Atmospheric composition：氮氮 Nitrogen 77%氧氧 Oxygen 21%其它其它 Other 2%其它观测资料其它观测资料 Other Observations:Has Plate Tectonics 板块构造板块构造Has Volcanism 火山作用火山作用Mostly Covered with Wat
10、er 大部分由水大部分由水覆盖覆盖Strong Magnetic Field 强磁场强磁场月亮（Moon）Mass(kg)7.349e+22 (1.2%earth)赤道半径赤道半径Equatorial radius(km)1,737.4 (27%earth)Mean density(gm/cm3)3.34 (Light!)Mean distance from Earth(km)384,400 Rotational period(days)27.32166 Orbital period(days)27.32166 5、火星（Mars）Mass(kg)6.421e+23 (11%of earth)
11、Equatorial radius(km)3,397.2 (50%of earth)Mean density(gm/cm3)3.94 Mean distance from the Sun(km)227,940,000 Rotational period(hours)24.6229 Rotational period(days)1.025957 Orbital period(days)686.98Mean surface temperature-63C Maximum surface temperature 20C Atmospheric pressure(bars)0.007 (0.0068
12、to 0.009)大大 气成份气成份 Atmospheric composition：二氧化碳二氧化碳 Carbon Dioxide(C02)95.32%氮氮 Nitrogen(N2)2%氩氩 Argon(Ar)1.6%氧氧 Oxygen(O2)0.13%水水 Water 0.03%Other Observations Has seasons 季节季节-atmosphere but weakVolcanism 火山火山Weather-water clouds,wind storms,evidence for floods,polar ice caps(CO2 and H20)Appears t
13、o have a crust,mantle,and core Extreme topographic variations(-4 to 27 km)Two small moons Martian South Pole about 400 km wide(smallest extent)6、木星（Jupiter）Mass(kg)1.900e+27 (320%earth)Equatorial radius(km)71,492 (11.2 earths)Mean density(gm/cm3)1.33 Mean distance from the Sun(km)778,330,000 (5.3 ti
14、mes earth)Rotational period(days)0.41354 Orbital period(days)4332.71 Juipiter as seen by the Hubble Space Telescope in 1995Mean cloud temperature -121C Atmospheric pressure(bars)0.7 Atmospheric composition 氢氢 Hydrogen 90%氦氦 Helium 10%Other Observations Extremely strong magnetic field,maybe produced
15、by a metallic hydrogen dynamo Has a ring complex of small dust particles High winds(400 km/hour)observed by probe 16 known moons(4 of which you can see with binoculars)7、土星（、土星（Saturn）Mass(kg)5.688e+26 (95 earths)Equatorial radius(km)60,268 (9.5 earths)Mean density(gm/cm3)0.69 (Low!)Mean distance fr
16、om the Sun(km)1,429,400,000 (9.5 earth)Rotational period(hours)10.233 (fast!planet visibly flattened)Orbital period(years)29.458 Mean cloud temperature -125C Atmospheric pressure(bars)1.4 Atmospheric composition 氢氢 Hydrogen 97%氦氦 Helium 3%发现甲烷发现甲烷 Methane detected Other Observations Rings of unknown
17、 composition(but some kind of ice)18 confirmed plus 4 maybe moons Also gives off more energy than receives 12000K at center due to Kelvin-Helmholtz mechanism but may also need another source to make it this hot(raining our of He?)Probably has a metallic hydrogen core like Jupiter.Titan-largest moon
18、in the solar system.8、天王星（Uranus）Mass(kg)8.686e+25 (14 earths)Equatorial radius(km)25,559 (4 earths)Mean density(gm/cm3)1.29 Mean distance from the Sun(km)2,870,990,000 (20 earths)Rotational period(hours)-17.9 Orbital period(years)84.01 Tilt of axis(degrees)97.86 Mean temperature-193C Atmospheric pr
19、essure(bars)1.2 Atmospheric composition:氢氢 Hydrogen 83%氦氦 Helium 15%甲烷甲烷 Methane 2%but:Uranus is composed primarily of rock and various ices,with only about 15%hydrogen and a little helium(in contrast to Jupiter and Saturn which are mostly hydrogen).Other observations Very few features visible on pl
20、anet,blue from absorption of red by the methane.Also has rings(found before Jupiters)Planets axis of rotation is nearly 90 degrees from the plane of its rotation about the sun!It is rolling like a ball.Has magnetic field(but origin unknown as metallic hydrogen unlikely-not enough pressure).The axis
21、of this is tilted at 60 degrees from its axis of rotation.Appears to be cold inside,is not giving off extensive radiation.9、海王星（Neptune）Mass(kg)1.024e+26 (17 earths)Equatorial radius(km)24,746 (3.9 earths)Mean density(gm/cm3)1.64 Mean distance from the Sun(km)4,504,300,000 (30 earths)Rotational peri
22、od(hours)16.11 Orbital period(years)164.79 Mean cloud temperature-193 to-153C Atmospheric pressure(bars)1-3 Atmospheric composition 氢氢 Hydrogen 85%氦氦 Helium 13%甲烷甲烷 Methane 2%Other observations The first two thirds of Neptune is composed of a mixture of molten rock,water,liquid ammonia and prised of
23、 hydrogen,helium,water and methane.Methane gives Neptune its blue cloud color.Cirrus type clouds seen(see figure)Winds of 2000 km/hour observed Four sets of weak rings Magnetic field tilted at 47 degrees from rotation axis and offset 0.55 the planets diameter from its center!10、冥王星（Pluto）Mass(kg)1.2
24、7e+22 (0.002 earths)Equatorial radius(km)1,137 (17%earth)Mean density(gm/cm3)2.05 Mean distance from the Sun(km)5,913,520,000 (40 earths)Rotational period(days)-6.3872 Orbital period(years)248.54 Tilt of axis(degrees)122.52 Orbital inclination(degrees)17.148 Surface temperature-230 degrees Atmospher
25、ic composition 甲烷甲烷 Methane 0.3%氮氮 Nitrogen Plutos composition is unknown,but its density(about 2 gm/cm3)indicates that it is probably a mixture of 70%rock and 30%water ice much like Triton.The bright areas of the surface seem to be covered with ices of nitrogen with smaller amounts of(solid)methane
26、 and carbon monoxide.The composition of the darker areas of Plutos surface is unknown but may be due to primordial organic material or photochemical reactions driven by cosmic rays.Other observations Rotational plane highly tilted(122 degrees)with respect to its ecliptic.Really a double planet with Charon.流星和小行星（Meteors and asteroids）慧星（Comets）