空间科学与探测技术概论.ppt

1、空间科学与探测技术概论Introduction for Space Science and explore technologyInstitute of Fusion Theory and Simulation马志为,第一章：空间(太空)物理学概论 Introduction of space physics,空间物理学的研究对象、特点、方法、以及重要性(1957)。 研究对象: 一、日地空间物理(Solar-terrestrial physics) 日地空间的范围 太阳上层大气、日地行星际空间、地球磁层、电离层及中高层大气(geospace),2.日地空间物理的分支学科 太阳上层大气物理、日地

2、行星际空间物理、地球磁层物理、电离层物理及中高层大气物理(geospace) 3. 主要研究内容 1) 研究太阳内部的结构和动力学及其对驱动太阳活动的作间,日冕加热 (corona heating) 太阳耀斑 (solar flare) 日冕物质抛射 (CME),2)研究太阳事件在行星际空间的和演化过程 3)研究太阳事件及行星际扰动对地球空间环境的影响 (see movie recon),4)研究太阳事件、行星际扰动、及磁层扰动和低层大气对电离层的影响 See movie (Aurora) 5)日地环境模型及预报方法研究 6)研究日地空间环境变化和人类活动对天、地基技术系统和人类生存环境的影响

3、,第二章：空间物理学的发展史 Many in Europe/US were unaware of observations reported in China. Some elements* of a time-line from the perspective of China: 2,500 BC - Development of Chinese characters 2,357 BC - Chinese records mention the Pleiades昴宿星(团)star cluster. 2,134 BC - Chinese astrologers占星家beheaded beca

4、use they failed to predict a solar eclipse. 2,000 BC - Chinese report sightings of aurora极光,1,500 BC - Sighting of first supernova超新星 by ancient Chinese,1,111 BC - First naked-eye solar flares possibly sighted by Chinese 800 BC - First sunspots太阳的黑点sighted by Chinese 239 BC - Chinese first to record

5、 Halleys Comet 500 AD - First report of naked-eye sunspot by Chinese 1006 AD - Supernova SN1006 1054 AD - Crab巨蟹座Supernova seen by Chinese,超新星SN1006,历史记载中最亮的超新星，中国对其有非常详细的记载，宋代的天文学家称其为周伯星。宋史第五十六卷天文志上详细记载：“景德三年四月戊寅，周伯星见，出氐南，骑官西一度，状如半月，有芒角，煌煌然可以鉴物，历库楼东。八月，随天轮入浊。十一月复见在氐。自是，常以十一月辰见东方，八月西南入浊。”现代天文学家将它编为S

6、N1006。,超新星在天体物理研究中扮演着非常独特和重要的角色，对它的认识极大推动了宇宙学、高能天体物理及恒星物理的发展。近年来，具有标志意义的研究包括：通过对局部Ia型超新星的定标得到哈勃常数的精确测量，通过对高红移Ia型超新星的观测推断出宇宙整体处于加速膨胀阶段。这些概念对现代物理基础提出严峻的挑战，并有可能导致人类对物质世界认识的一场革命。 在这颗超新星爆发的千年纪念日，2006年全世界60多名科学家齐聚西子湖畔举行科学盛会,A bit of history: Gilbert, Halley, Celsius and Hiorter, Birkeland Earths aurora Th

7、e mechanisms that produce it. Aurorae at Jupiter, Saturn, and other solar system bodies. Differences from aurorae at Earth. Moons of Jupiter, their auroral signatures and an aurora on Ganymede! In each case currents flow along the planetary magnetic field from distant space into the upper atmosphere

8、. Electrons must be accelerated to carry the current. The accelerated electrons excite atmospheric neutrals that emit light to create the aurora.,The magnetic field is critical to the process that produces the aurora.The concept that the earths magnetic field resembles that of a uniformly magnetized

9、 sphere goes back to William Gilbert, Physician to Queen Elizabeth I of England.,1600,Halley (1716), ultimately the Astronomer Royal, found that aurora was too widespread to arise from volcanic activity! Noted that auroral intensity is greatest near magnetic (not geographic) pole and that auroral ra

10、ys align with field lines, but failed to propose a valid mechanism for the light emitted.,From E. Halley, An account of the late surprising appearance of lights seen in the air on the sixth of March last, with an attempt to explain the principal phenomena thereof. As it was laid before the Royal Soc

11、iety by Edmund Halley, J.V.D., Savilian Professor of Geometry, Oxon. and Reg. Soc. Secr, Phil. Trans. R. Soc. Lond. 29, 406-429 (1716).,His diagram shows that he realized that earths magnetic field must extend into space.,But that is not enough. Even at earth, it took centuries to understand what dr

12、ives the aurora,Ideas, now known to be wrong, were plentiful: Gas was invoked in several ways: one idea: aurora is glowing gas thought to be linked to earthquakes. When the gas leaked out, it created aurora and concurrently reduced the intensity of earthquakes. Burning gas this idea goes back to the

13、 Greeks and keeps coming back. Volcanoes maybe? Reflection of light from ice crystals present in the polar atmosphere.,A link between magnetic fluctuations and the aurora,1733: Celsius (familiar from our temperature scale) published 316 observations of the aurora. 1741 April 5 with his assistant Hio

14、rter observed magnetic fluctuations in Uppsala. At the same time, George Graham recorded similar fluctuations in London. This demonstrated that the motion of the magnetic needles was not produced by local sources. At the same time, Hiorter observed an aurora. International collaboration has long bee

15、n central to advances in environmental sciences!,Sources of magnetic fluctuations,In 1820, Danish scientist Hans Christian Oersted discovered that an electric current produces an magnetic field. (Oersted, H. C., Experiments on the effect of a current of electricity on the magnetic needle, printed by

16、 C. Baldwin, London, 1820). (Dotted line below shows direction of magnetic field at points in space surrounding the current.) This discovery helps establish a link between magnetic fluctuations and the aurora. If currents produce magnetic fluctuations and if aurora are also present, maybe the curren

17、ts produce the aurora.,Aurora appears in an “oval” around the magnetic pole,Here a map published in 1869 by Elias Loomis, Professor at Yale University. He also prepared the first synoptic weather map (1846), a new way of representing data that influenced theories of storms and weather prediction. Ne

18、ither seems to have had broad impact.,E. Loomis, Aurora Borealis or Polar Light, Harpers New Monthly Magazine, V 39, Issue 229, June 1869.,This is roughly the context in which the Nowegian scientist, Birkeland, started his research with some of these questions about aurora in mind:,Driven from the g

19、round or from above? Local to the earth or from space? How high above the ground is the radiating layer? What causes the auroral glow? Connection to the fluctuations of the magnetic field? Does it have anything to do with the weather?,Birkeland adopted a unique approach to attacking scientific probl

20、ems through expeditions, observations, theory, and lab experiment, with work largely self-funded.,Expeditions and observations: Confirmed connection between aurora and particularly active magnetic fluctuations that he christened “polar elementary storms” - now referred to as substorms. Confirmed tha

21、t the auroras occur at altitudes of order 100 km. . . not near the ground. . . widely distributed in auroral regions. The observations ruled out such pictures as a connection with earthquakes or weather. Theory Showed that the horizontal currents that create the magnetic disturbances flow overhead i

22、n an ionized region of the upper atmosphere, now called the ionosphere.,Birkeland,Experiments Developed terrella experiments demonstrated that streams of charged particles from the sun can move along the field into the polar regions, causing auroral glows. The currents flowing vertically along the m

23、agnetic field (field-aligned currents) flow into the ionosphere and move across field lines, causing field fluctuations in the regions below.,Birkelands key discoveries,were disputed by experts. Many thought that there are no field-aligned currents, that those observed are confined to the lower atmo

24、sphere and do not reach into space. (Actually from ground-based observations alone, one cannot be sure which picture is true.) Some details were wrong. but critical elements of the concepts have been fully confirmed in the era of spacecraft measurements. Birkelands conflicts with scientists elsewher

25、e, especially in England, held up widespread acceptance of his ideas. today, many (not all) of Birkelands ideas have been confirmed and fit into the framework of accepted interpretation of aurora and substorms at earth What do we think we know today?,Yes, there are streams of charged particles comin

26、g from the outer part of the sun, the solar corona.,The story starts at the sun. A HOT gas (2 million degrees) blows into interplanetary space at a speed of more than a million km/hour. It is referred to as the solar wind. The gas is fully ionized, electrically neutral, and very low density.This spe

27、cial form of gas is called a plasma.,第三章：太阳及行星际物理学,太阳 The life cycle of the stars,A gas cloud, if big enough, starts to shrink. The density and temperature increase so nuclear fusion can start. This is when Hydrogen is converted into Helium. The burning of Hydrogen stops the gas cloud from shrinking

28、. At this point, the gas cloud becomes a star. This is the present state of our Sun.,After billions of years, most of the Hydrogen fuel has been burned, and the star begins to shrink again. The star has to turn to another source of fuel, Helium. The next stage in the life of a star is called a red g

29、iant. The star here is much bigger than it was initially. When the red giant star runs out of fuel, the star begins to shrink again. This contraction heats up the core of the star enough so that the heavier elements can be made. When the star runs out of this type of fuel, it has neared the end of i

30、ts life.,The star begins to throw off layers because it cant support them anymore. This is called a planetary nebula星云. The core of the star becomes a white dwarf. This is an extremely dense star the size of a planet. Finally, when the white dwarf has used all its energy, it stops shining and become

31、s a black dwarf, a dead star. This is expected to be the final state of our Sun.,For stars with higher masses than the Sun (up to about 40 times greater), the outer layers of the star may be thrown off with much more force. This is a supernova超新星. This type of star collapses down to a very compact s

32、ize. This is what is called a neutron star. Stars bigger then 40 times the Sun may collapse into a black hole.,The Fate of the Sun,In about 5 billion years, the hydrogen in the center of the Sun will start to run out. The helium will get squeezed. This will speed up the hydrogen burning. Our star wi

33、ll slowly puff into a red giant. It will eat all of the inner planets, even the Earth. As the helium gets squeezed, it will soon get hot enough to burn into carbon. At the same time, the carbon can also join helium to form oxygen. The Sun is not very big compared to some stars. It will never get hot

34、 enough in the center to burn carbon and oxygen. These elements will collect in the center of the star. Later it will shed most of its outer layers, creating a planetary nebula, and reveal a hot white dwarf star. Nearly 99 percent of all stars in the galaxy will end their lives as white dwarfs. By s

35、tudying the stars that have already changed, we can learn about the fate of our own Sun.,太阳是小质量恒星 已有50亿年的历史，再过50亿年，随着核反应的进行，核心区的H元素丰度逐渐减小，直至枯竭，全部转变成He。 氦核聚变要求更高的温度，由于温度不够，热核反应暂时停止，由于没有辐射，辐射压大大降低，导致引力大于向外的压力。 3.恒星将会因抗衡不住引力而收缩。收缩的结果导致中心部分温度大增，使氦能发生聚变反应（生成碳和氧），加热中心区的外围大气，使恒星外层向外膨胀。 4.恒星中心部分以外的区域由于温度的增高

36、又开始氢核聚变反应，并且核反应迅速向外层转移，推动外层膨胀，使得恒星体积很快增大上千倍上。,太阳基本物理参数,半径: 696295 千米.比地球大109倍 体积是地球的130万倍 质量: 1.9891030 千克,是地球的33万倍, 温度: 5800 (表面)，1560万 (核心)总辐射功率: 3.831026 焦耳/秒平均密度: 1.409 克/立方厘米日地平均距离: 1亿5千万 千米年龄: 约50亿年 太阳是个气体球，其中氢约占71, 氦约占27, 其它元素占2。但这些物质均处在物质的第四态等离子态。,1. 太阳的能源 L3.81033 erg/s, 5109 year 可能的能源： (1

37、) 化学反应：2H + O H2O + E 30 year (2) 引力收缩(Kelvin and Helmholtz) ： 辐射压力收缩温度辐射 (GM2/RL) 107 year,1926年，爱丁顿首先提出恒星的能源只能是来自核反应。研究核反应的物理学家认为不可能. 当时的物理学研究知道，只有当温度达到几百亿度时，才能发生聚变。而恒星中心区域的温度达不到这样的高温，所以他们认为在恒星内部不可能发生核反应。 最后还是爱丁顿胜利了，物理学家终于发现，由于量子力学的隧道效应，在恒星内部温度的条件下是可以发生核反应的。但并不是爱丁顿解决的这个难题，他提出的看法和他的名气促进物理学家研究这个问题。,

38、Sir Arthur S. Eddington (1882 - 1944),结合能较小的原子核聚变成结合能较大的原子核会释放能量。,Energy Released by NuclearFusion and Fission,Fusion reactions release much higher energies than Fission reactions,氢核聚变为氦核,4 1H 4He + Energy Energy(4mHmHe)c2 (41.67-6.644) 10-24 c2 410-5 erg 燃烧效率 0.7% 这是最简单的聚变反应 但是4个质子2个电子同时碰在一起太困难了。质子

39、之间的静电斥力和它们之间的距离的平方成反比。它们越接近，斥力越大。分几次完成是可行的。,H + H D + positron + neutrino D + H He3 + gamma ray He3 + He3 2H + He4 共6个质子参与，形成两个质子、一个氦核、两个中微子、两个正电子和两个光子。同时释放24.158电子伏特的能量。 条件：8106 K T 2107 K, M 1.5M 在太阳内部，99的能源来自于质子质子反应。太阳内部H核聚变释放能量的5%被中微子携带向外传输,neutrino(中微子),The neutrino is an extremely light partic

40、le. It has no electric charge. The neutrino interactions with matter are extremely rare. Fusion reactions in the Sun produce neutrinos. By detecting these neutrinos, scientists can learn about the solar interior. The Sun is estimated to produce some 1038 neutrinos per second (thats a lot!). Billions

41、 of these neutrinos pass through the Earth without a single interaction (每秒大约有1015个中微子穿过我们的身体). Large and very sensitive detectors are actually able to detect neutrinos.,The Suns energy, which is produced in the core, travels outwards. The energy travels first through the radiative zone, where parti

42、cles of light (photons光子) carry the energy. It actually takes millions of years for a photon to move to the next layer, the convection zone. At the convection zone, energy is transferred more rapidly. This time it is the motion of the gases in the Sun that transfers the energy outwards. The gas at t

43、his layer mixes and bubbles, like the motion in a pot of boiling water.This bubbling effect is seen on the surface of the Sun, and is called granulation太阳米粒组织. We cant see inside the Sun. So scientists use other diagnostics. These diagnostics help us know what is inside the Sun.,The convection zone

44、The convection zone in the Sun occurs above the radiative zone, at about .7 to .8 solar radii from the center of the Sun. At this point the temperature gradient (the change in temperature with depth) becomes so large that turbulent convective motions occur, similar to a pot of boiling water. The ove

45、rturning motions inside the Sun are responsible for the granulation pattern seen on the Suns surface.,Sun surface or Atmosphere,The visible solar atmosphere consists of three regions: the photosphere (光球), the chromosphere (色球), and the solar corona(日冕). Most of the visible (white) light comes from

46、the photosphere, this is the part of the Sun we actually see. The chromosphere and corona also emit white light, and can be seen when the light from the photosphere is blocked out, as occurs in a solar eclipse日食. The sun emits electromagnetic radiation at many other wavelengths as well. Different ty

47、pes of radiation (such as radio, ultraviolet, X-rays, and gamma rays) originate from different parts of the sun. Scientists use special instruments to detect this radiation and study different parts of the solar atmosphere. The solar atmosphere is so hot that the gas is primarily in a plasma state:

48、electrons are no longer bound to atomic nuclei, and the gas is made up of charged particles (mostly protons and electrons). In this charged state, the solar atmosphere is greatly influenced by the strong solar magnetic fields that thread through it. These magnetic fields, and the outer solar atmosph

49、ere (the corona) extend out into interplanetary space as part of the solar wind.,Photosphere,Most of the energy we receive from the Sun is the visible (white) light emitted from the photosphere. The photosphere is one of the coolest regions of the Sun (6000 K), so only a small fraction (0.1% ) of th

50、e gas is ionized (in the plasma state). The photosphere is the densest part of the solar atmosphere, but is still tenuous compared to Earths atmosphere (0.01% of the mass density of air at sea level). The photosphere looks somewhat boring at first glance: a disk with some dark spots(sun spots). Howe

51、ver, these sunspots are the site of strong magnetic fields. The solar magnetic field is believed to drive the complex activity seen on the Sun. Magnetographs measure the solar magnetic field at the photosphere. Because of the tremendous heat coming from the solar core, the solar interior below the p

52、hotosphere (the convection zone) bubbles like a pot of boiling water. The bubbles of hot material welling up from below are seen at the photosphere, as slightly brighter regions. Darker regions occur where cooler plasma is sinking to the interior. This constantly churning pattern of convection is ca

53、lled the solar granulation pattern.,光球 可见光辐射区， 光球厚度约500 km， 温度约6000 K， 利用吸收光谱确定了67种元素的化学组成。,Sunspots,Sunspots are dark, planet-sized regions that appear on the surface of the Sun. Sunspots are dark because they are colder than the areas around them. A large sunspot might have a temperature of about

54、4,000 K. This is much lower than the 5,800 K temperature of the bright photosphere that surrounds the sunspots. Sunspots are only dark in contrast to the bright face of the Sun. If you could cut an average sunspot out of the Sun and place it in the night sky, it would be about as bright as a full mo

55、on. Sunspots have a lighter outer section called the penumbra(半影), and a darker middle region named the umbra(本影).,利用黑子在日面的运动可以确定太阳的较差转动。,2D Dynamics in Rotating Fluids,Navier-Stokes Eqn for Rotating Fluid:,See movie of Jupiter Cloud Movie,Sunspots are caused by the Suns magnetic field welling up to

56、 the photosphere, the Suns visible surface.,sunspot cycle,The number of sunspots seen on the surface of the Sun changes from year to year. This rise and fall in sunspot counts is a cycle. The length of the cycle is about eleven years on average. The Sunspot Cycle was discovered in 1843 by the amateu

57、r German astronomer Samuel Heinrich Schwabe. A peak in the sunspot count is called solar maximum (or solar max). The time when few sunspots appear is called a solar minimum (or solar min). An example of a recent sunspot cycle spans the years from the solar min in 1986, when 13 sunspots were seen, th

58、rough the solar max in 1989 when more than 157 sunspots appeared, on to the next solar min in 1996 (ten years after the 1986 solar min) when the sunspot count had fallen back down to fewer than 9.,The length of the sunspot cycle is, on average, around eleven years. But the length of the cycle does v

59、ary. Between 1700 and today, the sunspot cycle (from one solar min to the next solar min) has varied in length from as short as nine years to as long as fourteen years. Sometimes it is hard to get an exact count of number of sunspots on the Sun. Some spots are much bigger than others, some sunspots cross together at their edges, and many spots appear in groups. In 1848, a Swiss astronomer named Rudolf Wolf came up with the best way to count sunspots. The sunspot count using Wolfs formula, now known as the Wolf sunspot number, is still in use today. Wo